JPH11145131A - Manufacture of semiconductor device, semiconductor manufacturing apparatus, and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a silicon oxide film having a high breakdown endurability at a low temperature, by supplying to a silicon layer an oxidizing source gas composed mainly of oxygen atom radicals whose excited state is in a singlet state, and oxidizing the surface of the silicon layer. SOLUTION: A trench formed in the surface of a p-type silicon substrate 101 is buried by filling its inside with a silicon oxide film 102, and an element isolating region is formed. On the surface, n-type impurity diffused layers of high impurity concentrations as a source region 105 and a drain region 106 are formed. Besides, a floating gate electrode 1041 composed of a polysilicon film containing arsenic is formed interposing a tunnel oxide film 1031 , and on it a control electrode 1042 is formed interposing an intergate-electrode insulating film 1032 . It becomes possible to form a tunnel oxide film at a low temperature, by exposing a silicon substrate to an atmosphere (550 deg.C or higher) where the concentration of active species having high oxidizing forces and optimum for oxidation is made higher selectively, in a tunnel-oxide-film forming process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly to a semiconductor manufacturing apparatus and a semiconductor manufacturing method characterized by a method of forming a silicon oxide film.

[0002]

2. Description of the Related Art NAND-type EEPROMs, which are characterized by low cost, high reliability, and high-speed writing characteristics, have attracted attention as an alternative to magnetic memories. NAND type EEPRO
M has two electrodes, an electrode for storing electric charges (floating gate electrode) and an electrode for forming an electric field for putting electric charges in and out of the floating gate electrode (control gate electrode).

In this type of semiconductor memory, a high voltage is applied to a control gate electrode, and electrons are transferred into and out of a floating gate electrode through a gate oxide film from a substrate, thereby performing electrical writing and erasing. I have.

[0004] Since the inflow and outflow of electrons between the substrate and the floating gate electrode are performed using the Fowler-Nordheim tunnel mechanism, the gate oxide film between the substrate and the floating gate electrode is called a tunnel oxide film.

What is important in the tunnel oxide film is that the total amount of electrons (Qbd) that pass until the dielectric breakdown occurs must be larger than that of a normal MOS transistor. The reason is that a high electric field is applied to the tunnel oxide film to take in and out electrons to use the memory.
This is because if bd is small, the reliability is reduced and the life is shortened. At the same time, applying a high electric field to the tunnel oxide film increases the leakage current at a low electric field.
The so-called stress-induced leakage current must be reduced.

As a typical method of forming a tunnel oxide film, which has been conventionally used, there is a thermal oxidation method in which a silicon substrate is exposed to a dry oxygen atmosphere and heated. The quality of the thermal oxide film formed by the thermal oxidation method varies depending on the oxidation process conditions such as the oxide film formation temperature (oxidation temperature), heat treatment (annealing) temperature in a non-oxidizing gas atmosphere, annealing time, and temperature rise / fall rate. Therefore, attempts to improve the dielectric breakdown resistance of the oxide film by devising the process conditions have been continued. However, a thermal oxide film satisfying the dielectric breakdown resistance required in the future has not been obtained.

On the other hand, from the viewpoint of reducing the manufacturing cost of the semiconductor device and simplifying the semiconductor manufacturing device, it is required to lower the oxidation temperature. In the conventional thermal oxidation method, a method of rapidly raising and lowering the substrate temperature to a high temperature (for example, 1000 ° C.) has been developed in order to obtain a required oxidation rate. However, there is a problem that an apparatus that can withstand such a high temperature has a high cost, and a high temperature rise / fall speed causes a large thermal stress on the substrate.

As a candidate for the method of forming an oxide film which satisfies the requirements of improving the dielectric breakdown resistance of the tunnel oxide film and lowering the oxidation temperature as described above, there is an oxidation method in an atmosphere of an oxygen active species such as oxygen radicals and ozone. .

The oxidation method using oxygen radicals has been developed so far from the viewpoint of lowering the oxidation temperature. For example, Kimura, Warabisako, Applied Physics Vol. 56, 64-69
According to page (1987), an oxide film having a dielectric strength equivalent to that of a thermal oxide film is obtained by oxidation in an oxygen radical atmosphere at 580 ° C.

Further, in order to obtain a sufficient oxide film formation rate and a low temperature interface between the silicon substrate and the oxide film having the same characteristics as the thermal oxide film, a thin oxide film is formed on the silicon substrate surface in an oxygen radical atmosphere. Chemical vapor deposition (CVD) on it
G. Lucovsky, Y.
Ma, T. Yasuda, C. Silvestre, JR Hauser, Jpn. J. App
l. Phys. Vol. 31, pp. 4387-4395 (1992).

However, an oxygen radical oxide film having a higher dielectric breakdown resistance than a thermal oxide film has not yet been reported.
It is considered that this is because the oxygen radical atmosphere that has been used for oxidation is a mixture of active species in various excited states.

As the oxygen radical generating means, a microwave discharge, a parallel plate plasma discharge, an electron cyclotron resonance plasma discharge and the like in a reduced-pressure oxygen gas atmosphere have been used. As an alternative to these discharges, a method of irradiating an oxidizing gas with excitation light has been proposed.

However, in any of these methods, active species optimal for the oxidation step are not selectively formed, but various active species (for example, oxygen atoms / oxygen molecules in various electronically excited states, oxygen atoms) Positive and negative ions and positive and negative ions of oxygen molecules) are simultaneously formed in the atmosphere.

Active species unsuitable for the oxidation step react with, for example, active species optimal for oxidation or adsorb on the oxide film surface.
Such an inappropriate reaction or adsorption by the active species causes inhibition of supply of the active species optimal for oxidation to the oxide film, deterioration of the dielectric breakdown resistance of the oxide film, reduction of the oxidation rate, and the like.

As for the method of oxidizing with ozone, it has been reported that as the oxidation temperature is lowered, the dielectric breakdown resistance of the oxide film is improved (for example, Takasaki, Proceedings of the 42nd Seminar on Semiconductor Specialization (1995)).

As a cause of the improvement in insulation resistance due to ozone oxidation, when ozone molecules reach the surface of the oxide film on the oxidizing atmosphere side, active oxygen radicals are supplied into the oxide film, and the active oxygen radicals are generated in the oxide film. It is considered that this reacts with a lattice defect or the like that causes charge trapping (trap sites), whereby the charge trapping is taken into the SiO ₂ network structure and eliminated.

However, it is considered that various kinds of oxygen atoms or oxygen ions in an electronically excited state are generated due to a difference in the microscopic structure of the oxide film surface where the ozone molecules supply the oxide film on the oxide film surface.

In conventional ozone oxidation, active species that are optimal for oxidation and non-optimal active species are both supplied to the substrate surface, which is not preferable for the same reason as the above-described oxygen radical oxidation.

In order to realize a semiconductor device having low cost, high reliability, and high-speed operation characteristics, it is necessary to improve the reliability of an insulating layer and a wiring layer constituting the semiconductor device,
It is essential to improve the flatness at the interface between the insulating layer, the wiring layer, and the semiconductor.

For element isolation and formation of a capacitor having a large capacitance, for example, reactive ion etching (RIE)
When a hole or a groove is selectively formed in the surface of a semiconductor substrate by using the method, the substrate surface including the side wall and the bottom surface of the hole and the groove is damaged by etching species such as ions and plasma, and RIE damage occurs. . Conventionally, after performing thermal oxidation in a dry oxygen atmosphere until an oxide film having a thickness of about 50 nm or more is formed on the substrate surface, the thermal oxide film is peeled off to thereby form an RIE damage layer on the substrate surface. To improve the reliability of the gate oxide film and the buried insulating layer formed thereafter.

However, if thermal oxidation is used to oxidize (buffer oxidize) the substrate for removing the damaged layer, the interface between the substrate and the thermal oxide film is not sufficiently flattened. Large roughness remains. When oxidizing the substrate surface where such roughness remains to form an ultra-thin gate oxide film, or embedding an insulating layer in a hole or groove where large surface roughness remains to form an element isolation or trench capacitor, Insulation breakdown easily occurs due to the interface roughness with the insulating layer, and the drain current response speed of the gate oxide film is reduced. Also, although the depth of the RIE damage layer is only about 10 nm or less,
Performing buffer oxidation of 50 nm or more on the side wall of the hole or groove causes an unnecessary increase in the element area, which hinders miniaturization of the semiconductor element.

In the step of establishing electrical connection between a semiconductor and a wiring layer thereabove, conventionally, a hole (contact hole) is selectively formed in an insulating layer therebetween, and the semiconductor is exposed at the bottom of the hole. Then, a silicidation step or a step of embedding a wiring in a hole has been performed without flattening the exposed surface.

However, if the roughness of the exposed surface of the semiconductor at the bottom of the hole is large, uniform growth of the silicide layer or the buried wiring layer is hindered, resulting in poor electrical connection between the wiring layer and the semiconductor and reduction in the reliability of the wiring layer. Become. Further, when an impurity injection layer is formed on the surface of the semiconductor, a phenomenon that charges flow through the impurity injection layer is also induced. Conventional buffer thermal oxidation requires an oxidation temperature of about 1000 ° C., and thermal deformation occurs around the contact hole, so that buffer oxidation at the bottom of the contact hole is difficult.

On the other hand, as a method of ultra-planarizing the substrate surface at the atomic level, a method of heating a substrate with a natural oxide film at about 1000 ° C. or more in an ultra-high vacuum atmosphere (flushing, for example, M. Niwa, T., et al. Kouzaki, K. Okada, M.U
dagawa, and R. Sinclair, Japanese Journal of Appl
ied Physics, Vol. 33, p. 388 (1994))
And molecular beam epitaxy (for example, A. Ourmaz
d, DW Taylor, JA Rentschler, and J. Bevk,
Physical Review Letter, Vol. 59, 213 pages (1
987)). However, these methods are not practical in terms of processing temperature, processing time, or equipment cost, and cause metal contamination of the insulating layer due to metal on the inner wall of the equipment, which causes dielectric breakdown.

[0025]

As described above, the conventional method for forming an oxide film using oxygen radicals or ozone uses an active species that is optimal for oxidation because an active species that is optimal for oxidation is not used. In this case, the dielectric breakdown resistance of the oxide film is reduced, and the speed of forming the oxide film is also reduced.

As described above, when thermal oxidation in a dry oxygen atmosphere is used for buffer oxidation of a semiconductor substrate, the semiconductor substrate is not formed on the substrate surface due to insufficient flatness after the buffer oxide film is removed. Reliability of the gate oxide film and the buried insulating layer is reduced. Further, the exposed surface of the semiconductor substrate on the bottom surface of the contact hole is not planarized, so that the reliability of the wiring layer is reduced. As described above, conventionally, the reliability and characteristics of the semiconductor device are deteriorated due to the fact that the semiconductor surface is not sufficiently flattened.

An object of the present invention is to provide a method of manufacturing a semiconductor device and a semiconductor manufacturing apparatus capable of forming a silicon oxide film having high dielectric breakdown resistance.

Another object of the present invention is to improve the reliability and characteristics of a semiconductor device by flattening the surface of a semiconductor, thereby flattening the interface between the semiconductor and an insulating layer or a conductive layer formed on the semiconductor surface. It is an object of the present invention to provide a semiconductor device manufacturing method and a semiconductor manufacturing apparatus which can be made to operate.

[0029]

According to the present invention, the following means have been taken in order to solve the above-mentioned problems.

In order to achieve the above object, the first aspect of the present invention is described.
In a method for manufacturing a semiconductor device according to an aspect, an oxidizing gas mainly containing oxygen atom radicals in a singlet excited state is supplied to a silicon layer, and the surface thereof is oxidized to form a silicon oxide film.

In the present invention, the silicon layer means a silicon substrate other than the one formed on the substrate.

As a result of the study by the present inventors, the excited singlet state oxygen atom radical (O ( ¹ D)) is converted into the ground state triplet state oxygen atom radical (O ( ³ P)).
It is clear that the dielectric breakdown resistance is better than that. Further, it has been revealed that when oxygen gas or ozone gas is irradiated with light having a specific wavelength, O ( ¹ D) can be selectively generated more than O ( ³ P).

Here, the following method may be used to generate an oxidizing source gas containing a singlet state oxygen atom radical as a main component.

(1) The oxygen source gas is irradiated with light having a wavelength of 175 nm or less to generate the oxygen atom radical in the singlet state.

(2) Irradiating a plasma atmosphere of a gas containing molecules having oxygen atoms with light having a wavelength of 175 nm or less,
The oxygen atom radical in the singlet state is generated.

(3) The plasma atmosphere is divided into a plasma generation region and an oxidation region.

(4) Irradiating the gas atmosphere containing molecules having oxygen atoms with light having a wavelength at which the generation efficiency of the singlet state oxygen atom radicals is higher than that of the triplet state oxygen atom radicals, The oxygen atom radical in the singlet state is generated.

(5) The oxidizing source gas containing the singlet state oxygen atom radical has a rate constant of a reaction of deactivating the singlet state oxygen atom radical into a triplet state oxygen atom radical at a temperature of 298 K. × 10 ¹¹ cm ³ mo
Including gas molecules that are less than l ^-1 s ^-1 .

(6) The atmosphere containing dinitrogen monoxide gas is irradiated with light having a wavelength of 341 nm or less to generate the oxygen atom radical in the singlet state.

(7) The oxidation is performed under the conditions that the partial pressure of oxygen molecules in the oxidation source gas is 10 Torr or less and the oxidation temperature is 550 ° C. or less.

According to the first aspect of the present invention, since an oxidizing gas source containing a singlet-state oxygen radical as a main component is supplied to the silicon layer, the oxidation proceeds efficiently and the oxidizing gas proceeds at a lower temperature than the conventional one. In addition to the formation of a silicon oxide film at the same time, trap sites such as lattice defects in the silicon oxide film are eliminated, resulting in dense film quality, the interface between the silicon layer and the silicon oxide film is flattened, and the silicon oxide film is formed. Can improve the electrical reliability.

In FIG. 32, the growth rate of the oxide film by the conventional oxygen radical oxidation (O ^* ) and ozone oxidation (O ₃ ) is compared with the dry oxygen oxidation rate. The high oxidizing power of the active species contained in conventional oxygen radical oxidation and ozone oxidation atmospheres means that the oxide film growth rate in these atmospheres is higher than thermal oxidation by dry oxygen oxidation at the same pressure and temperature. Is shown in

In an oxide film formed by a conventional oxygen active species atmosphere (O ^* , O ₃ ) containing these active species having a high oxidizing power, generation of electron traps is suppressed as compared with a thermal oxide film. The fact that the gate voltage shift ΔV _g due to the formation of an electron trap in the injection of a constant current is small (FIG. 33) is reflected in the improvement in the dielectric breakdown resistance of the oxide film. The total amount of electrons Qbd passing through the film is large (see FIG. 3).
This is reflected in 4).

FIG. 35 shows the electron mobility at the substrate side interface of the silicon oxide film formed on the silicon substrate by each oxidation method (oxidation species). Conventional oxygen activated species atmosphere (O
^* , O ₃ ) The electron mobility in the silicon oxide film formed by O ₃ is higher than that in the thermal oxide film because the oxygen active species flattens the interface between the silicon substrate and the silicon oxide film. It is considered that

Further, the densities of the O ^* silicon oxide film and the O ₃ silicon oxide film in which the dielectric breakdown characteristics were improved with respect to the thermal oxide film were measured.
The value was larger than m ³ . It is considered that the improvement in the density of the silicon oxide film reflects the densification of the film quality.

On the other hand, when the density of a silicon oxide film formed in an atmosphere having a low concentration of active species was measured, the density was 2.10 g / cm ³ or less, which is equivalent to that of a thermal oxide film, and the dielectric breakdown characteristic was lower than that of the thermal oxide film. The result was improved.

In this case, the density reflects that the oxide film was formed mainly by thermal oxidation, and the electrical characteristics were improved by the fact that some of the trap sites in the oxide film were improved by the oxygen active species. It is inferred that

As described above, when the oxygen radical oxidation and the ozone oxidation, which are the conventional techniques, are used, the action of the oxygen atom radical O ( ³ P), which is the main oxidizing species supplied to the substrate, causes the dry oxygen oxidation. The effects of improving the oxidation rate, improving the electrical characteristics of the oxide film, flattening the interface between the substrate and the oxide film, and densifying the oxide film quality can be seen.

[0049] Thus, an excited state of ^{O (3 P), O (} 1 a ^{O (3} P) Preferred active species oxidation than
By using D) for oxidation, the oxidation rate is further improved with respect to oxygen radical oxidation and ozone oxidation, which are conventional techniques, the electrical characteristics of the oxide film are improved, the interface between the substrate and the oxide film is flattened, and the quality of the oxide film is densified. Is achieved.

FIG. 37 shows the difference in flatness of the interface between the silicon substrate and the silicon oxide film due to the difference in the oxidizing species. Radical O ( ¹ D), which is optimal for oxidation, compared to conventional oxidation in an atmosphere containing a large amount of oxygen radical O ( ³ P)
In the oxidation of the present invention in an atmosphere in which is mainly active species, an atomically flat substrate-oxide film interface was realized.

FIG. 35 (a) shows the effect of the oxidation method (the present invention) in an atmosphere in which O ( ¹ D) is the main active species.

Since O ( ¹ D) has a valence electron spin of ↑ ↓, it easily enters the Si—Si bond at the interface between the substrate and the oxide film, and oxidation proceeds one layer at a time on the silicon substrate (layer-by-lay).
er) proceeding, forming a flat interface without mixing at the atomic level with the underlying silicon substrate, and forming SiO in the oxide film.
_{The two-} mesh structure becomes strong, and a dense film quality is obtained.

On the other hand, in the conventional method, FIG.
As shown in ( ¹ ), since the inappropriate oxidizing species O (3P) contained in the atmosphere cannot enter the Si-Si bond at the interface between the substrate and the oxide film, the flatness of the interface is deteriorated, and the oxide film is deteriorated. Si atoms and O atoms having unbonded valence electrons are left inside, and dielectric breakdown of the oxide film easily occurs.

Since the optimum active species has a high oxide film formation rate, it is possible to form an oxide film at a lower temperature than before by increasing the concentration of the optimum active species.

According to the first aspect of the present invention, a silicon oxide film having a high dielectric breakdown resistance can be formed at a low temperature by supplying an oxygen gas source mainly containing singlet oxygen radicals to the silicon layer. Can be formed.

A method of manufacturing a semiconductor device according to a second aspect of the present invention includes the steps of: oxidizing a surface of a semiconductor in an atmosphere containing oxygen active species to form an oxide film; and removing the oxide film to form the semiconductor film. Exposing the surface. here,
Preferably, the film thickness exceeds 6.4 nm.

The oxygen active species (corresponding to oxygen radicals) include positive ion (O ⁺ , O ₂ ⁺ ) radicals, negative ion (O ⁻ , O ₂ ⁻ ) radicals, neutral atoms or molecules (O, O ₂ ). O ₂ ) radicals and the like. As a source gas for generating oxygen active species, O ₃ (ozone) gas, a gas of a compound containing oxygen, or the like can be used in addition to O ₂ gas.

As the semiconductor, besides the semiconductor substrate itself, a semiconductor film or the like formed on the semiconductor substrate via an insulating film or the like can be used. As a semiconductor material, silicon can be typically given, but other semiconductor materials can also be used.

As described above, the surface of the semiconductor is oxidized in an atmosphere containing oxygen active species (hereinafter referred to as oxygen radical oxidation).
By forming an oxide film (hereinafter, referred to as a buffer oxide film), the interface between the semiconductor and the buffer oxide film can be extremely flattened, and the surface of the semiconductor after the removal of the buffer oxide film is also flattened. You. Therefore, when a desired film is formed on the surface of the semiconductor exposed after removing the buffer oxide film, the interface between the two is also extremely flattened, and a semiconductor device having excellent reliability, electrical characteristics, and the like can be manufactured. .

After the buffer oxide film formed by the oxygen radical oxidation is removed to expose the surface of the semiconductor, a process for forming a desired film on the exposed surface of the semiconductor includes the following. it can.

(1) The method further comprises the step of oxidizing or nitriding the exposed surface of the semiconductor to form an insulating film. A typical example is a step of forming a buffer oxide film by oxygen radical oxidation on the surface of a semiconductor substrate, removing the buffer oxide film, and then forming a gate oxide film on the planarized semiconductor substrate surface. Since the surface of the semiconductor before the gate oxide film is formed is flattened, an extremely flat semiconductor / gate oxide film interface is obtained. In particular, in the case of an extremely thin gate oxide film, the roughness of the semiconductor surface before oxidation is largely reflected on the flatness of the semiconductor / gate oxide film interface. However, by applying the present invention, an extremely flat semiconductor / gate oxide film interface can be obtained. can get.

Here, the surface of the semiconductor layer planarized using the present invention is also effective as a base to be nitrided. Particularly in the case of an extremely thin gate nitride film, the roughness of the semiconductor surface before oxidation is greatly reflected on the flatness of the gate nitride film / semiconductor interface, similarly to the gate oxide film. By planarizing the surface of the semiconductor before oxidation and nitriding the surface by using the present invention, an extremely flat gate oxide film / semiconductor interface is formed, and the electrical characteristics of the nitride film are improved.

The nitriding gas for the semiconductor layer includes, for example, ammonia (NH ₃ ), nitrogen trifluoride (NF ₃ ), nitric oxide (NO), nitrous oxide (NO ₂ ), nitrous oxide (NO ₂ ) N ₂ O) and nitrogen (N ₂ ) are used. These gases are
It may be used as it is, or may be diluted with an inert gas such as argon or a combination of a plurality of source gases as needed. These gases may be directly introduced into the atmosphere near the heated substrate, or may be used to form nitrogen active species by plasma discharge, light irradiation, metal / metal oxide catalyst, etc., and to be used for nitriding the base surface. Good.

(2) The method further comprises a step of depositing an insulating film on the exposed surface of the semiconductor. Typically, after a groove for forming element isolation is formed in a semiconductor substrate by RIE or the like, a buffer oxide film is formed and removed by oxygen radical oxidation, and then an element is formed in a groove whose inner surface is planarized. A step of embedding an isolation insulating film is given. Irregularities are formed on the inner surface of the groove by RIE or the like, but the inner surface of the groove is extremely flattened by forming and removing a buffer oxide film by oxygen radical oxidation. Therefore, the dielectric breakdown resistance of the element isolation insulating film can be improved as compared with the case where the unevenness is formed on the inner surface of the groove.

(3) The method further comprises a step of depositing a conductive film on the exposed surface of the semiconductor. Typically, the source
After forming a contact hole to the drain region (impurity diffusion layer), a buffer oxide film is formed and removed by oxygen radical oxidation to planarize the semiconductor surface at the bottom of the contact hole, and then a metal serving as a wiring layer is formed in the contact hole. A step of depositing a film or the like. Since the bottom surface of the contact hole is flattened, the wiring layer is uniformly deposited, the contact resistance between the wiring layer and the semiconductor substrate is reduced, the charge is prevented from penetrating into the impurity diffusion layer, and the impurity diffusion layer is formed. It becomes possible to make it shallow.

(4) The method further comprises the step of forming a layer mainly composed of the semiconductor and a desired metal on the exposed surface of the semiconductor. Typically, after forming a contact hole to the source / drain region, a buffer oxide film is formed and removed by oxygen radical oxidation to planarize the semiconductor surface at the bottom of the contact hole, and then the semiconductor surface at the bottom of the contact hole is formed. To form a metal silicide layer by silicidation. Also in this case, since the contact hole bottom surface is flattened, the above (3)
The same effect as described above can be obtained.

(5) A step of oxidizing the surface of the semiconductor with the semiconductor containing the oxygen active species to form a first oxide film, and a step of removing the first oxide film to expose the surface of the semiconductor. In addition, a step of forming a second oxide film by oxidizing the surface of the semiconductor and a step of removing the second oxide film to expose the surface of the semiconductor are performed at least once.

(6) The step of removing the oxide film and exposing the surface of the semiconductor further includes a step of removing the oxide film in a gas phase atmosphere. Here, the gas phase atmosphere is F
A gaseous atmosphere containing molecules or active species having one or more of atoms, Cl atoms, Br atoms, and I atoms is used.

As an atmosphere containing oxygen active species (oxygen radicals), it is effective to use an atmosphere containing oxygen radicals whose excited state is a singlet state as a main component. Oxygen radical whose excited state is a singlet state, that is, O ( ¹ D)
And O ( ¹ S) have s = 0, and the spin directions of the valence electrons form a pair (↑ ↓). Therefore, since an O atom easily enters a Si—Si bond (valence electron:） ↓) (for example, ( ³ P) is s = 1, and both spins of two valence electrons are upward (↑↑) or Downward (↓↓)
O atoms do not easily enter Si-Si bonds (valence electrons: ↑ ↓). ), The reactivity is high and the oxide film formation rate is high, and the flattening action of the semiconductor / buffer oxide film interface is also enhanced.

A buffer oxide film (silicon oxide film)
If the removal rate of the buffer oxide film is too fast when removing the oxide to expose the surface of the semiconductor, the roughness of the semiconductor surface after the oxide film is stripped may be deteriorated, and the flatness of the buffer oxide film / semiconductor interface may be impaired. There is. Therefore, in order to suppress the removal rate and maintain good flatness, it is preferable to remove the buffer oxide film as follows.

(1) The buffer oxide film is etched using an aqueous solution of hydrofluoric acid having a concentration of 1% or less.

(2) The hydrogen ion concentration is 10 ⁻⁴ mol / l
The buffer oxide film is etched using an ammonium fluoride aqueous solution having the following (pH ≧ 4).

(3) The exposed surface of the semiconductor is exposed to a gas atmosphere containing hydrogen fluoride molecules to etch the buffer oxide film.

According to the second aspect of the present invention, the interface between the semiconductor and the buffer oxide film is made extremely flat by oxidizing the surface of the semiconductor in an atmosphere containing oxygen active species to form a buffer oxide film. The surface of the semiconductor after removing the buffer oxide film is also flattened. Therefore, when an insulating layer or a conductive layer is formed on the surface of the semiconductor exposed after removing the buffer oxide film, the interface between the two is extremely flattened, and a semiconductor device having excellent reliability and characteristics can be manufactured.

A method of manufacturing a semiconductor device according to a third aspect of the present invention includes a step of oxidizing a surface of a semiconductor layer in an atmosphere containing oxygen active species at a temperature exceeding 550 ° C. to form an oxide film. Oxidizes the surface of the semiconductor layer in an atmosphere containing oxygen active species at a temperature exceeding 550 ° C. to form an oxide film. A preferred embodiment of the third aspect of the present invention is as follows.

(1) The atmosphere containing the pre-oxygen active species is a plasma atmosphere of a gas containing molecules having oxygen atoms.

(2) The atmosphere containing the oxygen active species has ozone molecules.

(3) The oxygen active species are generated by irradiating a gas containing a molecule having an oxygen atom with light.

(4) The oxygen active species is generated by exposing a metal or metal oxide to a gas containing a molecule having an oxygen atom.

According to the third aspect of the present invention, since the semiconductor substrate can be oxidized at an optimum temperature in an atmosphere containing oxygen active species, the same effect as in the second aspect of the present invention can be obtained.

A semiconductor manufacturing apparatus according to a fourth aspect of the present invention comprises a step of oxidizing a surface of a semiconductor in an atmosphere containing oxygen active species to form an oxide film, and removing the oxide film to remove the surface of the semiconductor. The step of exposing is performed continuously without at least exposing to outside air, and the method of manufacturing a semiconductor includes the steps of: oxidizing a surface of the semiconductor in an atmosphere containing the oxygen active species to form a first oxide film; Removing the oxide film to expose the surface of the semiconductor, oxidizing the surface of the semiconductor to form a second oxide film, and removing the second oxide film to expose the surface of the semiconductor And 1
It is performed continuously at least twice without exposing it to outside air. A preferred embodiment of the fourth aspect is as follows.

(1) The method further comprises a step of oxidizing or nitriding the exposed surface of the semiconductor to form an insulating film while maintaining at least a state not exposed to the outside air.

(2) The method further comprises a step of depositing an insulating film on the exposed surface of the semiconductor while maintaining at least a state of not being exposed to the outside air.

(3) The method further comprises a step of depositing a conductive film on the exposed surface of the semiconductor while maintaining at least a state of not being exposed to the outside air.

(4) A step of forming a layer mainly composed of the semiconductor and a desired metal on the exposed surface of the semiconductor while maintaining at least a state of not being exposed to the outside air.

(5) The step of removing the oxide film and exposing the surface of the semiconductor includes the step of removing the oxide film in a gas phase atmosphere. Here, the gas phase atmosphere is F atom, Cl
A gaseous atmosphere containing a molecule or an active species having one or more of atoms, Br atoms, and I atoms is used.

In the fourth aspect of the present invention, since a series of steps can be performed without exposing to the outside air, deterioration of the insulation breakdown resistance of the insulating film due to contamination of the semiconductor surface, poor contact between the wiring layer and the semiconductor surface, etc. This is extremely effective for improving the performance and the yield of the semiconductor device by preventing the deterioration of the electrical characteristics, and for improving the throughput and the labor saving of the semiconductor device manufacturing.

In a preferred embodiment according to the first and fourth aspects, the step of oxidizing the surface of the semiconductor in an atmosphere containing oxygen active species to form an oxide film is performed at a temperature exceeding 550 ° C.

In a preferred embodiment of the first to fourth aspects, the oxygen active species contains an oxygen atom radical whose excited state is a singlet state as a main component.

[0090]

Embodiments of the present invention (hereinafter, referred to as embodiments) will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
FIG. 4 is a cross-sectional view showing an element structure of a memory cell of an EEPROM according to the embodiment.

In FIG. 1, a trench is formed on the surface of a p-type silicon substrate 101. In the present embodiment, an element isolation region is formed by filling the inside of the trench with a silicon oxide film 102. Note that the element isolation may be performed by another element isolation such as LOCOS.

The source region 1 is formed on the surface of the silicon substrate 101 in the element region defined by the silicon oxide film 102.
A high impurity concentration n-type impurity diffusion layer is formed as the drain region 05 and the drain region 106.

[0094] Further, on the p-type silicon substrate 101 through the tunnel oxide film 103 ₁ according to the present invention, the floating gate electrode 104 ₁ made of a polysilicon film containing arsenic is formed. The floating gate electrode 104 _first gate insulating film 103 ₂ is formed on
The control gate electrode 104 ₂ through is formed.

A silicon oxide film 107 is deposited on the entire surface of the substrate, and a source electrode formed by patterning the same conductive film such as an Al film through a contact hole formed in the silicon oxide film 107. 108, a gate electrode wiring 109, and a drain electrode 110 are provided in the source region 105, the control gate electrode 104 ₂ , and the drain region 106, respectively.

FIGS. 2 and 3 are process sectional views showing a method of manufacturing the memory cell of FIG.

First, as shown in FIG. 2A, after a trench 120 is formed on the surface of a p-type silicon substrate 101, a silicon oxide film 102 is formed by a CVD method such as a liquid phase CVD method. The inside of the trench 120 is buried to perform element isolation.

[0098] Next, as shown in FIG. 2 (b), the p-type silicon substrate 101, for example, in the preferred oxygen-activated species ^{O (1} D) an atmosphere for the oxidation of 550 ° C., for example, exposure for 120 minutes, the film thickness forming a tunnel oxide film 103 ₁ of 5 nm.

The oxidation with the active species O ( ¹ D), which is preferable for the oxidation, is performed using, for example, an oxidation apparatus shown in FIG. Note that this oxidizing apparatus can oxidize without using O ( ¹ D), and has an unnecessary configuration for the oxidizing method of the present embodiment. In FIG. 4, the same reference numerals except for the subscript indicate the same components.

In this embodiment, N ₂ O is used as the oxidizing gas source.
Although a gas is used, the oxidizing apparatus in FIG. 4 has a configuration in which O ₂ gas, NO gas, H ₂ O vapor, and H ₂ O ₂ vapor can be used.

For example, H ₂ O vapor or H ₂ O ₂ vapor is supplied to a heater 214 by putting the liquid in a quartz container 214.
5 generated by heating. The piping system from the outlet of the container 214 to the quartz tube 201 is heated by the heater 213 in order to prevent the generated steam from aggregating.

The active species O ( ¹ D) is, for example, a gas such as dinitrogen monoxide (N ₂ O) gas
Through 2 _2, valve 211 _2, pipe 209, and introduced into the quartz tube 201 is placed a silicon substrate 101, is generated by excitation by light of wavelength 197nm for emitting the oxygen gas from the source 203. O ( ¹ D) generated in this manner is supplied to the silicon substrate 101 by downflow.

Here, the pressure in the quartz tube 201 is controlled by an exhaust system, for example, 0.1 Torr, and the flow rate of nitrous oxide is controlled by the mass flow controller 212.
₂ , for example, 20 sccm.

Preferably, as a purification step, nitrous oxide gas is passed through a gas purifier 210 to remove impurities, such as moisture and carbon dioxide, which are slightly mixed in the nitrous oxide gas.

As the source gas for O ( ¹ D), oxygen gas (O ₂ ) may be used instead of dinitrogen monoxide gas. An oxidation temperature is set to, for example, 550 ° C., an oxidation atmosphere pressure is set to, for example, 0.1 Torr, an oxidation time is set to, for example, 120 minutes, and a silicon oxide film having a thickness of, for example, 5 nm is formed on the surface of the silicon substrate.

The silicon substrate 101 is heated by the heater 207, for example. The temperature of the oxidation treatment with O ( ¹ D) is, for example, 550 ° C.

By using such an oxidizing apparatus,
The plasma generation region and the oxidation region can be separated. The need to separate the plasma generation region from the oxidation region is required for the following reasons.

Considering a conventional oxygen plasma atmosphere, a small amount of O ( ¹ D) may exist because high-frequency energy is applied to the plasma generation region.

However, when the oxidized region is within the plasma generation region, various ion species and active species existing in the high energy region collide with the oxide film, and the oxide film is damaged, and the dielectric breakdown characteristics of the oxide film become extremely high. It is not preferable because it becomes worse.

When the oxidized region is separated from the plasma generation region, ionic species and active species existing only in the high energy state are deactivated before reaching the oxidized region, and damage to the formed oxide film is also prevented. However, O ( ¹ D) generated in the plasma generation region is also deactivated before reaching the oxidation region.

In order to supply O ( ¹ D) to the oxidized region, a gas contained in the down-flow atmosphere of the plasma in which active species such as ions causing damage to the oxide film are deactivated is used. It is preferable to irradiate light for exciting molecules to O ( ¹ D).

[0112] Next, as shown in FIG. 3 (c), a polysilicon film doped with arsenic as the floating gate electrode 104 ₁ is deposited on the entire surface of the substrate at 650 ° C. using a low pressure CVD method, followed by the gate electrode Insulating film 103 ₂
Insulating film as, after sequentially depositing a conductive film serving as a control gate electrode 104 _2, these conductive films, insulating film, a polysilicon film, continuously etched tunnel oxide film 103 ₁ by reactive ion etching method do it,
A gate electrode portion having a predetermined shape is formed.

Next, as shown in FIG. 3D, arsenic ions were implanted into the substrate surface using the gate electrode as a mask under the conditions of an acceleration voltage of 40 keV and a dose of 2 × 10 ¹⁵ cm ^−2. The region 105 and the drain region 106 are formed in a self-aligned manner. Thereafter, as shown in FIG.
A silicon oxide film 107 is formed on the entire surface of the substrate by using a low-pressure CVD method.

[0114] Next, as shown in FIG. 3 (e), a contact hole for making connection source region 105, drain region 106 and the control gate electrode 104 ₂ on the silicon oxide film 107.

Finally, as shown in FIG. 3E, after forming an Al film on the entire surface of the substrate, this Al film is patterned to form a source electrode 108, a gate electrode wiring 109, and a drain electrode 110.

The cross section of the tunnel oxide film of the memory cell manufactured according to the method of the present embodiment is shown by a transmission electron microscope (T
EM) and compared with those formed by conventional methods.

[0117] As a result, as shown in FIG. 5, the method of the present embodiment ^{(O (1} D) oxide) Si substrate in the case of using the - tunnel oxide film (gate oxide film) interface (FIG. 5 (a)) Is
Conventional methods Si substrate in the case of using ^{(O (3} P) oxide, dry oxygen oxidation) a - tunnel oxide film interface (FIG. 5 (b), the 5
It was flatter than (c)). Further, Qbd was also a conventional method tunnel oxide film is greater than value obtained by (O ⁽³ P oxide)).

These results reflect the flattening of the interface and the densification of the oxide film due to the use of an atmosphere in which the active species O ( ¹ D) having a high oxidizing power and preferable for the oxidation is mainly used for the oxidation. It is considered something.

When the oxidation process is considered microscopically, the oxidizing species is adsorbed on the surface of the oxide film on the oxidizing atmosphere side, diffuses inside the oxide film, and oxygen atoms are formed between the Si—Si bonds at the silicon substrate-oxide film interface. Is inserted to grow an oxide film.

As active species preferable for oxidation, the upward spin (↑) and the downward spin (↓) of valence electrons are paired, and therefore, diffusion in an oxide film or Si—Si bond (constituting a bond) Oxygen atoms having an electron spin quantum number s = 0 of the active species as a whole that are easily inserted into valence electron spins: ↑ ↓) are preferable.

Here, the four valence electrons of the 2p orbital bound to the oxygen atom are respectively upward spin (↑: spin quantum number）) or downward spin (↓: spin quantum number -−１). It is considered that the sum of the spin quantum numbers of each valence electron is reflected in s.

When oxygen atoms having various electron configurations are arranged in ascending order of energy, O ( ³ P: triplet-P, s =
1), ^{O (1} D: singlet -D, s = 0), O (1
S: singlet-S, s = 0),.

S, P, and D correspond to the azimuthal quantum numbers 1 = 0, 1, and 2 of the valence electrons as the entire oxygen atom. In the conventional oxygen active species generation technology, these are generated and used without being sorted, and thus O ( ³⁾ having the lowest energy among them is used.
The concentration of P) is the highest, and the effects of O ( ¹ D) and O ( ¹ S) that are more effective due to oxidation are not fully utilized.

O ( ³ P) has s = 1, and the spins of the two valence electrons are both upward (↑↑) or downward (↓).
↓). Therefore, the Si—Si bond (valence electron: ↑
↓) Difficult to penetrate and unsuitable for oxidation.

On the other hand, O ( ¹ D) and O ( ¹ S) are s
= 0, and the spin directions of the valence electrons form a pair (↑ ↓). Therefore, the Si—Si bond (valence electron: ↑
↓) Easy to penetrate and is favorable for oxidation.

In an oxidation method using an oxygen active species,
(1 ^D) and O (1 ^S), such as, s = 0 a is the concentration of effective active species selectively increase it by oxidation, efficiency and good progress oxide, highly reliable tunnel oxide film ( (Gate oxide film).

In the conventional oxidation by oxygen radicals, the oxidizing power is higher than that of dry oxygen but lower than that of O ( ¹ D).
( ³ P) was the main component. Therefore, as shown in FIG. 6B, Si-S at the interface between the silicon substrate and the oxide film is formed.
Insertion of O atoms into the i-bond is unlikely to occur, and the flatness of the interface has not been sufficiently achieved.

In the oxide film after oxidation, most of Si. And -O., Which can serve as charge trap sites,
Although they are dissolved by reacting with other Si atoms or O atoms having dangling bonds, some of them remain unreacted in the oxide film and the oxide film is insufficiently densified.

On the other hand, in the present embodiment, FIG.
As shown in ( ¹ ), by increasing the concentration of O ( ¹ D) (valence electron spin: ↑ ↓), which is preferable for oxidation, O atoms of Si—Si bonds at the substrate-oxide film interface efficiently occur, and Is achieved. Further, by eliminating unbonded Si and -O, the structure of the oxide film becomes more dense, the electrical reliability is improved, and the dielectric constant of the oxide film is reduced.

The flattening of the oxide film-base substrate interface by O ( ¹ D) oxidation is considered as follows.

As shown in FIG. 7A, the surface of the substrate 301 before oxidation is not completely flat, and has, for example, a step 312 of one atomic layer and a step 311 of two atomic layers. During the progress of the oxidation, as shown in FIG. 7B, the oxidizing species (O ( ¹
D)) can diffuse not only in the film thickness direction but also in various directions in the oxide film. When the oxide film thickness is small at the initial stage of oxidation, O (
¹ D) is extensively penetrates into the SiO _2, ^{O (1} D) enters into the Si-Si bonds, it will oxidize the silicon substrate by one atomic layer.

In the steps 311 and 312 at the beginning, since the Si—Si bond is more exposed at the interface than at the other terrace portions, it is preferentially oxidized by O ( ¹ D), and this effect causes the first step. Steps 311 and 3
12 is the interface 3 which disappears at the interface and is flattened at the atomic level.
13 are formed.

On the other hand, after the formation of the flat interface 313, the oxidation of the next Si atomic layer can proceed preferentially in the region 314 due to, for example, a temporary imbalance in the O ( ¹ D) concentration. If the oxidation process is completed at this stage, the end of the region 314 becomes an atomic layer step.

When the oxide film grows to a certain thickness,
The depth reaches the penetration depth of O ( ¹ D), after which the oxide film does not grow. As the ambient temperature is higher, the lattice vibration of the constituent atoms of the oxide film becomes more intense, so that O ( ¹ D) easily advances into the oxide film, and the penetration depth increases.

FIG. 7C conceptually shows a state in which the oxide film has grown to a depth of about O ( ¹ D). Oxide film is O
(1 ^D) is not only grow to the extent that entering. If the oxide film surface 317 has irregularities, O ( ¹ D)
Differs depending on the location, and reflecting this, the interface 315 has, for example, steps 316 ₁ , 316 ₂ ,
316 ₃ is formed.

[0136] However, even irregularities 2 atomic layers or the oxide film surface, step _{316 1,} 316 2, 316 ₃ of the height is less than 1 atomic layer. This is because, for example, considered from step ₃₁₈ 1, 318 ₂ of the surface of the oxide film and the ^{O (1} D) is defined in each range arc ₃₁₉ 1, 319 ₂ to reach, not greater unevenness of surface of the oxide film, the interface In the above, O for an atom adjacent in the interface direction
(1 ^D) of the reaching distance change is because stays below 1 atomic layer.

The O ( ¹ D) oxide film was cut with a cross-sectional electron microscope (TE).
Observation by M) showed that an atomic image was regularly arranged over several layers at the interface on the substrate side, indicating the presence of a crystal structure. It is known that the conventional thermal oxide film has an amorphous structure, and such an arrangement of atoms was not found near the interface of the thermal oxide film on the substrate side.

[0138] O (1 ^D) of the vicinity of the interface oxide film by oxidation becomes crystalline structure, ^{O (1} D) and oxide film and the silicon substrate are strongly bonded by oxidation, ordered atomic arrangement of the silicon substrate It is considered that this was reflected in the vicinity of the interface of the oxide film on the substrate side.

The fact that the vicinity of the interface of the oxide film shows a crystal structure having a regular atomic arrangement corresponds to the fact that the interface is flat at the atomic level. In addition, the oxide film having a crystalline structure is denser in film quality than the amorphous structure, and the dielectric breakdown resistance of the oxide film is improved.

Considering that O ( ¹ D) enters Si—Si bond, Si (100) plane and (111) plane
Easy to understand the interface between the O _2.

That is, as shown in FIGS. 8A and 8B, the silicon substrate side of the interface is a Si atom,
The O atom on the SiO ₂ side bonds to this Si atom.

These figures also show an example of the step structure of the interface, and the steps 316 ₁ and 316 _{1 of} the interface shown in FIG.
16 _2, 316 is an example of a _3.

FIG. 8C shows that the SiO ₂ / Si (110)
Shows the interface. Si ¹ and Si ³ and Si ² and Si ⁴ are each in the same atomic layer. O ¹ , O ² , and O ³ are Si—
This shows a state in which O ( ¹ D) enters Si bonds and is bonded.

There are two types of chemical bonds at the SiO ₂ / Si (110) interface (Si ¹ -Si ² , O ³ -S
i ⁴ ). In each case, the silicon substrate side of the interface is Si atoms. One of the atoms on the SiO ₂ side bonded to Si is a Si atom bonded to three O atoms like Si ¹ , and the other is an oxygen atom like O ³ .

Although the Si ¹ -Si ² bond remains unreacted, the adjacent Si ³ -Si ⁴ bond on the same atomic layer is oxidized by the incorporation of O atoms. This difference is caused by the interface between the substrate and the oxide film. Corresponds to an example of the step.

In the oxidation by O ( ¹ D), O atoms always enter Si—Si bonds at the oxide film-substrate interface, and
Since an O-Si bond is formed, a _Pb defect center (•
SiSi ₃ ) does not appear, and unreacted Si—Si is present in the oxide film.
Bond (oxygen _{vacancies, O 3 Si-Si O 3} ) also does not remain.

[0147] _{P b} defect centers of the electron spin resonance (ESR)
Observed by The _Pb center found in the conventional thermal oxide film or O ( ³ P) oxide film is no longer seen in the O ( ¹ D) oxide film.

Oxygen vacancies are formed at the E′γ center (O ₃ S) by irradiation with high-energy electromagnetic waves such as radiation or strong ultraviolet rays.
_{^{i · + + Si O 3 +}} e -) , and the like the _{P b} center, becomes observable by ESR. In the conventional thermal oxide film and O ( ³ P) oxide film, the E′γ center was observed by irradiation, but was not observed in O ( ¹ D).

[0149] O (1 ^D) did not show a P _b centers and E'γ centered oxide film, ^{O (1} D) no defect in the oxide film, indicating that the film quality becomes dense . (Reference: "silicon thermal oxide film and the interface", Aizawa, ed., Realize Inc., 1991) In the O (1 ^D) oxide, since the silicon substrate and the oxide film strongly bonded, the stress applied to the oxide film It becomes larger than the conventional oxide film. Nevertheless, the reason why the electrical characteristics of the oxide film are not deteriorated as compared with the conventional case is considered to be because the effect of improving the electrical characteristics of the oxide film by flattening the interface between the substrate and the oxide film and densifying the film quality is great.

When the O ( ¹ D) oxide film was used as a gate oxide film of a field effect transistor (MOSFET) and the mobility of charge carriers was measured, the value was larger than that of a conventional thermal oxide film or oxygen radical oxide film. This is presumably because the flatness of the interface between the silicon substrate and the oxide film was improved as compared with the conventional oxide film, so that the carrier mobility was increased.

In O ( ¹ D) oxidation, O atoms efficiently enter between Si—Si bonds at the silicon substrate-oxide film interface, and the generation of unbonded Si atoms and O atoms is suppressed. Position becomes smaller.

O ( ¹ D) oxidation has the effect of penetrating into a small amount of Si—H bonds present in the oxide film to form a Si—O—H bond having a higher binding energy. Improve fracture resistance.

The Si—H bond in the oxide film is
Improving dielectric breakdown resistance by bonding
For example, Satake, Yasuda, Toriumi, Extended Abstracts of th
e 1995 International Conference on Solid State Dev
ices and Materials, 264-266.

The base pressure in the oxidizing apparatus shown in FIG. 4 is preferably low. In addition, it is preferable to minimize the entry of moisture and outside air into the oxidizer.

[0155] O The reaction was quenched with (1 ^D) other than gas species of the silicon substrate, O in order to proceed only (1 ^D) oxidation of the silicon substrate by the substrate temperature, for example 550 ° C. The following low temperature preferable. On the other hand, in order to form a nitrided oxide film by utilizing the nitridation effect of nitrous oxide itself, the substrate temperature may be higher, for example, 800 ° C. or lower.

Active species preferable for oxidation are considered to have a high oxide film formation rate. Therefore, if such an oxide film can be supplied to a substrate at a high concentration, an oxide film can be formed at a lower temperature, which contributes to simplification of an oxidation apparatus and improvement in substrate processing efficiency (throughput).

As in the case of O ( ¹ D) used in this embodiment,
O ⁽¹ S) also, because the electron spin quantum number s = 0, O ⁽¹
As in D), there are effects of flattening the interface and densifying the oxide film.

In this embodiment, O 2 gas is converted from nitrous oxide to O 2 gas.
While using light of wavelength 197nm to form a (1 ^D), it may be light of other wavelengths according to the wavelength of available light generated from the active species and the light source that requires. For example, from oxygen gas to O
When forming the ⁽¹ D), using light of wavelength 138 nm.

The rate of the active species generation reaction by photoexcitation is
It is given by (excitation light intensity) × (light absorption cross section) × (quantum efficiency for generating the active species) × (source gas concentration). In order to selectively form a specific active species, it is preferable to use excitation light having a wavelength range in which the quantum efficiency for generating the active species is higher than the quantum efficiency for generating other active species.

On the other hand, even if the excitation light has a low quantum efficiency for generating a certain active species, if the (excitation light intensity) × (light absorption cross section) is large, the active species may be obtained in a high concentration. There is.

The photoexcitation reaction N ₂ O + hν → N ₂ + O ( ¹ D) in which O ( ¹ D) is generated from dinitrogen monoxide gas proceeds at an excitation light wavelength of 341 nm or less. With the energy of this excitation light, N ₂ O + hν → N ₂ + O ( ³ P) can also travel, and O ( ³ P) can be generated together with O ( ¹ D).

[0162] To increase production efficiency of the ^{O (1} D), as photoexcitation reaction _{N 2 O + hν → N 2} + O (1 D) proceeds in quantum efficiency 1, the excitation light in the wavelength range of 185~230nm Preferably, it is used.

185 generated by O ( ¹ D) with quantum efficiency 1
In the wavelength range of ２３０230 nm, the light absorption cross section of N ₂ O decreases as the wavelength of the excitation light increases. As an excitation light source for obtaining an atmosphere in which oxygen atom radicals are mainly O ( ¹ D), those having a small wavelength and a high light intensity within this range are more preferable.

On the other hand, even if the excitation light generated by O ( ¹ D) outside this wavelength range has a quantum efficiency of <1, even if there is a light source that emits light having a wavelength of (excitation light intensity) × (light absorption cross section) is large. ,
The effect of increasing the concentration of O ( ¹ D) is obtained.

In the present embodiment, the excitation light is irradiated by the light source 203. However, the excitation light may be irradiated by the light source 205 to increase the concentration of active species near the substrate surface. Further, these light sources 203 and 205 may be used in combination.

As a source gas for forming oxygen radicals by discharge, a gas of a molecule having an oxygen atom other than the dinitrogen monoxide gas may be used. For example, ozone (O ₃ ), nitric oxide (NO), nitrogen dioxide (N
O ₂ ), water vapor (H ₂ O), hydrogen peroxide (H ₂ O ₂ ), and the like. These gases and oxygen gas may be used as a pure gas, a mixture of a plurality of gases, helium, neon,
It may be used by mixing with an inert gas such as argon. Ozone gas, for example, opens the valve 211 ₁₄ and 211 ₁₅ by closing the valve 211 ₁₃ in FIG. 4, is generated by introducing oxygen gas into the ozonizer 208.

In the plasma atmosphere of these source gases, O (
To increase the ^{1 D)} and O (1 ^S) concentration may be a light to excite the reaction product oxygen radicals separately illuminated. The wavelength is, for example, an excitation wavelength of an oxygen molecule (O ₂ ) which is considered to be formed as an intermediate of the plasma reaction as shown in FIG. Alternatively, the ground state O ( ³ P) of an oxygen atom, which is considered to be present in a large amount in the atmosphere, is changed to O ( ¹ D).
And the ^{O (1} S) to the excitation to the wavelength range of light (see FIG. 10). Alternatively low active species existing in the atmosphere of the excited-state oxygen molecules _{^{O 2 (a 1 Δ g)}} , O 2 and ^{(b 1} Σ _g ⁺⁾ O
⁽¹ D) and ^O is irradiated with light in the wavelength range with energy to excite the ⁽¹ S) (see FIG. 11, FIG. 12). Alternatively, light having the above wavelengths may be used in combination.

FIG. 9 shows that the wavelength from 138 nm to 17
The excitation light 5 nm, from the _{O 2} mainly the ^{O (3} P) ^O
(1 D) is formed. Wavelength from 110 nm to 138 nm
In the case, O ( ¹ D), O ( ³ P), and O ( ¹ S) are mainly formed. At a wavelength of 110 or less, mainly O ( ¹ D)
^{O (1} S) is formed with. 175 nm to 243 wavelength
The active species formed in nm is mainly O ( ³ P), which is not preferable for oxidation.

The smaller the excitation wavelength, the smaller the spin quantum number s =
At 0, active species having higher energy can be obtained, which is generally preferable for oxidation. On the other hand, in the method in which the excitation wavelength is relatively large, the light energy is not so large, and the light source can be prepared relatively easily.

In order to more selectively obtain the required active species at a high concentration, it is preferable to irradiate a light having a wavelength close to each excitation light shown in FIG. 9 at a high light amount. Further, in order to excite O ( ³ P), which is a ground state of oxygen atoms and considered to be present in a large amount in the atmosphere, into O ( ¹ D) and O ( ¹ S), light having a wavelength of 620 nm or less is emitted from the light source 2, for example.
19 or from the light source 220.

Although the excitation wavelength by one photon is shown in FIGS. 9 to 12, the necessary excitation energy may be given by multiphoton excitation.

Active species (O ( ¹ D), O ( ¹ S)) having a spin quantum number s = 0, which are preferable for oxidation, have a higher energy state than O ( ³ P). For this reason, if the frequency of collision with another gas in the atmosphere is high, the gas is easily deactivated to O ₂ or O ( ³ P). In order to prevent deactivation of these active species due to collision with other gas molecules, it is preferable to set the atmospheric pressure to a low pressure of about 10 Torr or less.

When the atmospheric pressure exceeds 10 Torr, O
⁽¹ D) and ^{O (3} P) the reaction ^{O (1 D, 3 P)} + O 2 +
M → O ₃ + M (M is a third body molecule) changes into ozone, which is not preferable.

Since this reaction is a three-molecule reaction, if the pressure is reduced, the traveling speed becomes extremely low. In particular, in order to suppress the deactivation of O ( ¹ D) into O ( ³ P) in oxygen gas or ozone gas, the pressure is preferably set to about 1 mTorr or less.

The above-described molecular gas having an oxygen atom may be excited only by excitation light without performing discharge. In that case, it is preferable to irradiate light in which O ( ¹ D) or O ( ¹ S) is selectively formed from each molecule. O ( ³
In order to excite P) to O ( ¹ D), light having a wavelength of 620 nm or less may be irradiated.

O ( ¹ D) is an excited state of an oxygen atom radical, and is easily deactivated to a ground-state radical O ( ³ P) by collision with gas molecules in the atmosphere. In order to realize an active species atmosphere in which O ( ¹ D) is the main radical, O
It is preferable to use gas molecules having a small rate constant for the reaction of deactivating ( ¹ D) to O ( ³ P). Further, a gas molecule containing an O atom so as to be an O ( ¹ D) generation source is more preferable.

DL Baulch et al., Journal of Physical and
Chemical Reference Data Vol. 11, No. 2, 327-496 pages (19
According to (1982), oxygen gas (O ₂ ) and ozone gas (O ₃ ) conventionally used for O ( ¹ D) generation include O (
¹ reaction ^O (1 D deactivating D) to ^{O (3 P)) + M} →
The rate constants of O ( ³ P) + products, M = O ₂ or O ₃ , and Products are the excited state of M are 4 × 10 ⁻¹¹ cm ³ molecular ⁻¹ s ⁻¹ and 1.2 × at 298 K, respectively. 10 ^-10 cm ³ molecule ^- a ¹ s ^-1.

Therefore, the rate constant of the reaction for inactivating O ( ¹ D) to O ( ³ P) is 4 × 10 ⁻¹¹ cm ³ mole.
With the cule ^-1 s ^-1 smaller gas molecules in main ambient gas, O (1 ^D) concentration is high oxygen radical atmosphere than conventional O ₂ atmosphere or O ₃ atmosphere can be achieved at higher pressures.

As the gas satisfying the above requirements, for example,
There is nitrous oxide _(N 2 O) gas. The rate constant for the inactivation of O ( ¹ D) to O ( ³ P) by N ₂ O molecules is Ba
According to ulch et al., 1 × 10 ^-12 cm ³ molecular
It is less than e ^-1 s ^-1 .

In oxidizing a silicon substrate, it is necessary that oxidizing species diffuse in the oxide film and reach the interface between the substrate and the oxide film.
The oxidation by O (1 ^D), O toward the rear from the oxidizing atmosphere side surface of the oxide film (1 ^D) is deactivated, seems to radical density decreases.

As described above, in order to suppress the reaction between the substrate and a gas species other than O ( ¹ D), and to enhance the effect of oxidation by O ( ¹ D), the substrate temperature is generally set to 550 ° C. or lower. Is preferably low.

[0182] In view of the penetration depth into the oxide film in the O (1 ^D) in such a low temperature, the substrate according to O (1 ^D) - the large oxidation action of the oxide film interface, the oxide film thickness is generally The range is 5 nm or less.

The density of the oxide film formed by O ( ¹ D) oxidation was higher than that of the conventional thermal oxide film made of dry oxygen because the film quality was higher than that of the conventional thermal oxide film formed by dry oxygen. The density of the conventional thermal oxide film is approximately 2.1 g / cm ³ . On the other hand, the density when the oxide film is in the densest state is 2.6 to 2.7 g / cm ^{3 of} quartz which is the highest density in solid silicon dioxide.
It seems to be. Therefore, the density of the oxide film formed by singlet oxygen radical oxidation is 2.1 g / cm.
^It exceeds ³ and is 2.7 g / cm ³ or less.

The density of the oxide film was determined from the weight difference between the substrate on which the oxide film was formed and the substrate from which the oxide film was removed by hydrofluoric acid etching, and the oxide film thickness. A method of obtaining the density of an oxide film using X-ray reflection is described in, for example, Hasegawa, Jou
rnal of Electrochemical Society Vol. 142 No. 1 273-28
2 Base (1995).

As described above, the memory cell manufactured by the manufacturing method of this embodiment has the following features. That is, the density of the tunnel oxide film 103 _1,
It is higher than 2.1 g / cm ³ and 2.7 g / cm ³ or less. Silicon substrate 101 and there is no interface mixed at the atomic level between the tunnel oxide film 103 _1, the height of the interface of the step is not more than one atom layer. Further, the tunnel oxide 103 ₁ film side of the interface has a crystalline structure.

Oxygen atom radicals form tunnel oxide film 103
_In consideration of the depth at which the tunnel oxide film 10 can penetrate without deactivation, the tunnel oxide film 10 is oxidized by singlet oxygen atom radicals.
3 of ₁ is particularly large improvement in the electrical properties, the film thickness 5n
m or less.

As a method for selecting the excited state of the active species,
It is also possible to use a magnetic field. That is, the active species O ( ¹ D) and O ( ¹ S), which are preferable for oxidation, have an electron spin quantum number s = 0, and the valence electrons form a pair (↑ ↓). Is small.

On the other hand, the active species O which is not
(3 ^P) is s = 1, since neither of the two valence electron spin upward (↑↑) or downward (↓↓), it receives a large external force from the magnetic field.

Therefore, when a magnetic field is applied perpendicularly to the plasma atmosphere flow containing these active species, O
(3 ^P) is traveling direction is changed greatly, the ratio to be removed by colliding with the inner walls of the apparatus is increased, the proportion of not less subjected to directional change by a magnetic field O (1 ^D) and O (1 ^S) becomes higher.

Such a change in direction of a particle having an electron spin due to a magnetic field is caused by Stern-Gerlach.
Gerlach).

The change in the traveling direction of the particles due to the magnetic field is larger for positive and negative ions than for neutral particles. Therefore, applying a magnetic field also has the effect of removing ions contained in the atmosphere of the active species and preventing the formed tunnel oxide film (gate oxide film) from being damaged by the ions.

The magnetic field is generated, for example, by the magnet 204 or the magnet 20.
6 to apply. These magnets 204 and 206 may be permanent magnets or electromagnets.

As described above, according to the present embodiment, in the step of forming a tunnel oxide film using oxygen active species,
By exposing the silicon substrate to an atmosphere having a high oxidizing power and selectively increasing the concentration of active species optimal for oxidation, oxidation proceeds efficiently, and a tunnel oxide film can be formed at a lower temperature than before. At the same time, trap sites such as lattice defects in the tunnel oxide film are eliminated, resulting in dense film quality, and the silicon substrate-tunnel oxide film interface is flattened,
The electrical reliability (for example, stress-induced leak current) of the tunnel oxide film is improved. Also, the method of the present embodiment differs from the conventional method only in the difference of the oxidizing species, and thus there is no problem that the number of processes increases or the processes become complicated.

In the first embodiment, it has been described that the oxidation of O ( ¹ D) is preferably performed at 550 ° C. or lower. However, ordinary oxygen radicals O ( ³ P) and O ( ¹ D) are Temperature dependence of the oxidizing power of the catalyst. The oxidizing power of O ( ³ P)
At a temperature of 550 ° C. or lower, O ( ¹ D) having higher reactivity than conventional O ( ³ P) is used to obtain an effect of improving electrical reliability of an oxide film by using radicals for oxidation. There is a need. Here, the effect of the radical to improve the electrical reliability of the oxide film is an effect that oxygen radicals enter oxygen atom vacancies in the oxide film, repair trap sites in the oxide film, and improve the dielectric breakdown resistance of the oxide film. is there. On the other hand, when the temperature exceeds 550 ° C., the reactivity of O ( ³ P) increases, and the effect of improving the electrical reliability of the oxide film can be sufficiently obtained. In addition, by increasing the oxidation temperature, the speed of forming an oxide film is improved, and the throughput of the semiconductor device is also improved.

(Second Embodiment) Next, a method for manufacturing an EEPROM memory cell according to a second embodiment of the present invention will be described.

The manufacturing method of this embodiment differs from the first embodiment in the method of forming a tunnel oxide film in the first half of the manufacturing method.

The step of FIG. 13A is the same as the step of FIG. 2A. That is, after forming the trench 120 on the surface of the p-type silicon substrate 101, for example, liquid phase CVD is performed.
The inside of the trench 120 is buried with the silicon oxide film 102 using a CVD method such as a CVD method to perform element isolation.

Next, as shown in FIG.
The silicon substrate 101 is exposed to, for example, 30 minutes in an oxygen radical atmosphere at 00 ° C.
Thickness 9nm of the tunnel oxide film 01 is formed on the surface of the (underlying tunnel oxide film) 103 _1a.

Oxidation by oxygen radicals includes, for example,
This is performed using the oxidizing apparatus shown in FIG. The apparatus shown in FIG. 4 can perform oxidation without using oxygen radicals, and has a configuration unnecessary for the oxidation of the present embodiment.

[0200] Oxygen radicals oxygen _{(O 2)} flow rate of gas is controlled by the mass flow controller 212 _7, for example, an oxygen gas flow rate of 800sccm introduced into the quartz tube 201, exciting the oxygen gas by the discharge electrodes 202 And generate it. Oxygen radicals generated in this manner are converted into a p-type silicon substrate 10 by downflow.
1 is supplied.

[0202] Here, the pressure in the quartz tube 201 is controlled by the exhaust system, for example, a 5 Torr, The oxygen flow rate is controlled by mass flow controller 112 _7, for example, 800 sccm.

Preferably, as a purification step, oxygen gas is passed through a gas purifier 210 to remove impurities, such as moisture and carbon dioxide, mixed in a small amount into the oxygen gas.

The p-type silicon substrate 101 is heated by, for example, a heater 207.

Next, as shown in FIG. 13C, the p-type silicon substrate 101 is, for example,
During ⁽¹ D) atmosphere, e.g., by exposure for 60 minutes,
Modify the tunnel oxide film _{103 1a,} a tunnel oxide film _{103 1b} with a thickness of 10 nm. Oxidation in an O ( ¹ D) atmosphere is performed, for example, in the same manner as in the first embodiment.

Finally, FIG. 3 described in the first embodiment
Through the steps similar to those shown in FIGS.
The memory cells of the ROM are completed.

The cross section of the tunnel oxide film of the memory cell manufactured according to the method of the present embodiment is shown by a transmission electron microscope (T
EM) and compared with those formed by conventional methods.

[0207] As a result, as in the first embodiment, the silicon substrate in the case of using the method of this embodiment (O (1 ^D) oxide) - tunnel oxide film interface is conventionally method (O (3 ^P)
(Oxidation, dry oxygen oxidation) was flatter than the interface between the silicon substrate and the tunnel oxide film. Also, Qbd
Was also a conventional method tunnel oxide film is greater than value obtained by (O (3 ^P oxide)).

[0208] These results, preferred active species O to high oxidation oxidizing force (1 ^D), a tunnel oxide film by the conventional method, was used for the reforming of the formed tunnel oxide film 103 _1a by oxygen radicals by, interface is planarized, it is considered that the quality of the tunnel oxide film 103 _1a densified.

In the present embodiment, the active species O (
^When the concentration of 1D) is low and the formation rate of the tunnel oxide film is low, the underlying tunnel oxide film having a thickness close to the required tunnel oxide film thickness is formed by another oxidation method (oxygen radical oxidation) having a higher oxidation rate. formed, as well as modified by this O (1 ^D) atmosphere, a silicon substrate - planarized oxide film interface is a method of forming a desired film thickness of the tunnel oxide film. Therefore, there is a feature that the film forming efficiency is increased as a whole.

In this embodiment, an oxide film by oxygen radicals is used as the underlying tunnel oxide film. Instead, for example, an ozone oxide film, a thermal oxide film by dry oxygen, or a wet oxide film by steam atmosphere is used. May be used.

The underlying ozone oxide film is, for example, O ₃ / O
An ozone-containing gas of _{2 to} 7% is formed by an ozonizer, and the surface of a silicon substrate heated to, for example, 900 ° C., is
It is formed by exposing to this ozone-containing gas atmosphere for 5 minutes.
The ambient pressure is, for example, 10 Torr, and the thickness of the formed silicon oxide film is, for example, 8 nm.

The underlying thermal oxide film is formed by exposing the surface of the silicon substrate heated to, for example, 1000 ° C. to a dry oxygen atmosphere at normal pressure for 3 minutes, for example. The thickness of the formed silicon oxide film is, for example, 8 nm.

The underlying wet oxide film is formed by exposing the surface of a silicon substrate heated to, for example, 900 ° C. to a normal-pressure hydrogen combustion atmosphere for, for example, 5 minutes. The thickness of the formed silicon oxide film is, for example, 8 nm.

A silicon oxide film formed by a CVD method or a spin-on-glass method may be used as a base oxide film to be processed in an O ( ¹ D) atmosphere.

(Third Embodiment) In the second embodiment,
An example has been described in which an oxide film is formed at 800 ° C. using oxygen radicals O ( ³ P) for oxidation, and the oxide film is further modified by O ( ¹ D) oxidation. Here, O ( ³ P) at 800 ° C.
When the oxide film formed by oxidation and before being modified by O ( ¹ D) was examined, the thermal oxide film formed in a dry oxygen atmosphere passed through the oxide film until Qbd (dielectric breakdown occurred). (The total amount of electrons) was increased, the flatness of the oxide film / substrate interface was improved, and the density of the oxide film was also increased. Therefore, oxidation at temperatures above 550 ° C. results in O (
Be used ^{3 P),} it is clear that the effect of improving the dielectric breakdown resistance of the oxide film can be obtained.

In the third embodiment, an embodiment will be described in which O (3P) is oxidized at a temperature exceeding 550 ° C. using O ( ³ P).

Oxidation using O ( ³ P) has a substrate temperature of 55
The temperature is preferably higher than 0 ° C., more preferably O ( ³
In order to increase the reactivity of P) and suppress the growth of an oxide film due to dry oxidation, the substrate temperature exceeds 950 ° C. and reaches 950 ° C.
It should be in the range of ℃ or less.

FIG. 14 is a diagram comparing the oxide film formation rate between radical oxidation (oxidation using O ( ³ P) for oxidation) and conventional dry oxidation (oxidation using O ₂ for oxidation). . FIG. 14 shows the time required for forming an oxide film having a thickness of 6 nm, and indicates that the shorter the time, the higher the oxidation rate. Radical oxidation proceeds faster than dry oxidation in the oxidation temperature range of 700 to 900 ° C., indicating that O ( ³ P) has a higher oxidizing power. The increase in the formation time of the thickness of 6 nm with a decrease in temperature due to radical oxidation indicates a decrease in the oxidizing power of O ( ³ P) with a change in temperature.

FIG. 15 shows the results of radical oxidation (oxidation using O ( ³ P) for oxidation) and conventional dry oxidation (oxidation using O ₂ for oxidation), which results in Qbd (dielectric breakdown) of the oxide film. FIG. 4 is a diagram comparing the total amount of electrons that have passed through the oxide film up to the present. At an oxidation temperature of 700 ° C., Qbd of radical oxidation is about 4 times of dry oxidation.
This is twice as large, indicating that the dielectric oxidation has improved the dielectric breakdown resistance of the oxide film. Even at a temperature of 900 ° C., Qbd of radical oxidation is about twice that of dry oxidation, and radical oxidation is effective for improving the electrical reliability of an oxide film.

Here, the radical oxidation was performed, for example, by applying a microwave discharge at a frequency of 2.45 GHz and an output of 200 W to a low-pressure oxygen gas, and exposing the silicon substrate to this plasma downflow atmosphere. The atmosphere pressure was, for example, 5 Torr. Dry oxidation is, for example, 900 ° C.
The test was performed by exposing the silicon substrate to a dry oxygen atmosphere at normal pressure.

After forming a flat oxide film / silicon layer interface by using oxygen radicals O ( ³ P) for oxidation, flattening the silicon surface as in the present embodiment by removing the oxide film is performed at an oxidation temperature of 550. It is effective even at ℃ or lower. However, when the oxidation temperature exceeds 550 ° C., the reactivity of radicals is increased, so that the flatness of the oxide film / silicon layer interface is improved, and the flatness of the silicon surface after removing the oxide film is further improved.

The density of the oxide film was compared by using an X-ray reflection method between a radical oxide film formed using oxygen radicals O ( ³ P) and a thermal oxide film formed by dry oxidation.
The formation conditions of the oxide film sample used for the density measurement are, for example, 930 ° C. for radical oxidation, 5 Torr for 15 minutes, and 900 ° C. for dry oxidation for 10 minutes at normal pressure.

Since the density of the oxide film changes in the thickness direction, assuming a two-layer model in which the oxide film is divided into the oxide film / substrate interface side and the oxidizing atmosphere side, the following results are obtained.

In the radical oxide film, the density of a region of about 11 nm on the oxide film / substrate interface side is 2.386 g / cm ³ , and the density of about 2 nm on the oxidizing atmosphere side is 2.2.
It was 80 g / cm ³ .

The thermal oxide film has an oxide film of approximately 2.3 g / cm ^3.
In contrast, the density of the radical oxide film is almost 2.4 g / cm ³ , which indicates that the quality of the oxide film is dense. The fact that the radical oxide film is denser than the thermal oxide film reflects the fact that the former oxide film has a larger Qbd than the latter, as shown in FIG.

At a high temperature exceeding 550 ° C., O ( ³ P) oxidation also has an effect of improving the underlying oxide film, similar to the effect of improving the underlying tunnel oxide film by O ( ¹ D) oxidation described in the previous embodiment. .

As a base oxide film, for example, the surface of a silicon substrate heated to 1000 ° C. is exposed to a hydrogen combustion atmosphere at normal pressure for 3 minutes, for example, to form a thermal oxide film having a thickness of 8 nm, for example.

As a base oxide film, the surface of a silicon substrate heated to, for example, 900 ° C. is exposed to a hydrogen combustion atmosphere at normal pressure for 5 minutes, for example, to form a wet oxide film having a thickness of, for example, 8 nm.

As a base oxide film, the surface of a silicon substrate heated to, for example, 900 ° C. is exposed to O ₂ / O ₃ -7% at a pressure of 5 Torr for 15 minutes, for example, to a thickness of 8, for example.
An ozone oxide film having a thickness of nm is formed. The ozone-containing gas is formed using, for example, an ozonizer.

These underlying oxide films are formed, for example, at a temperature of 90.degree.
It is exposed to a microwave plasma downflow atmosphere of oxygen gas at 0 ° C., a pressure of 5 Torr, a discharge frequency of 2.45 GHz, and a discharge output of 200 W, for example, for 10 minutes, and the thickness of the oxide film is set to, for example, 10 nm. Due to the action of active oxygen radicals O ( ³ P), the formed silicon oxide film has improved flatness at the interface between the substrate and the oxide film, and has a finer oxide film quality, thereby improving the dielectric breakdown voltage of the oxide film. . A silicon oxide film formed by a CVD method or a spin-on-glass method may be used as a base oxide film to be treated in an oxygen radical O ( ³ P) atmosphere.

Here, a plasma atmosphere, ozone, light irradiation, or an active metal surface is preferably used as a generation source of oxygen radicals O ( ³ P) used for oxidation at a temperature exceeding 550 ° C.

The source gas for generating O ( ³ P) is preferably a gas containing a molecule having an oxygen atom. For example, as described above, oxygen gas (O ₂ ), ozone (O ₃ ), nitric oxide, nitrous oxide, nitrous oxide, water vapor, and hydrogen peroxide.

A plasma atmosphere for generating O ( ³ P) is
Instead of the microwave discharge plasma described in the present embodiment, a parallel plate plasma, a helicon plasma, an electron cyclotron resonance plasma, or a radical beam source may be used.

As a means for generating O ( ³ P), light having energy for dissociating source gas molecules may be irradiated.
When light irradiation is used, generation of electrons and ions can be suppressed, and O ( ³ P) in a specific excited state can be selectively formed.

Ozone (O ₃ ) may be used as the O ( ³ P) source. Ozone is O ₃ → O ( ³ P) near the substrate surface
Dissociated in the + _{O 2} supply the ^{O (3} P) in the substrate. Ozone may be generated by corona discharge of a source gas using an ozonizer, or O ( ³ P) is generated by plasma discharge or light irradiation of the source gas, and this O ( ³ P) and O and O O ₃ may be generated from the reaction with ₂ .

As a means for generating O ( ³ P), the source gas may be exposed to the surface of a metal or metal oxide having a catalytic action. For example, a tungsten filament of 15
When heated to 00 ° C, oxygen gas can be decomposed into O ( ³ P) (Ikegami, Ohmori, Ikeda, Iwano, Zaima,
and Yasuda, Extended Abstracts Of the 1995 Interna
nation Conference On Solid State Devices and Mater
ials, Osaka, 16-18 pages (1995)). Further, for example, a metal surface such as platinum or gold which is stable in an oxygen atmosphere and has a catalytic action may be used. As a catalyst having these characteristics, for example, a metal oxide such as titanium oxide may be used. These catalysts are optionally heated to a temperature of about 150-1000 ° C., or
It is used by cooling to a temperature of 0 to 0 ° C.

Next, a semiconductor manufacturing apparatus according to the present embodiment will be described. FIG. 16 is a diagram illustrating a schematic configuration of a semiconductor manufacturing apparatus according to the present embodiment. In FIG. 16, for simplicity, details such as control units, wiring, and a cooling water circulation system of each unit are omitted. 16, the same parts as those in FIG. 4 are denoted by the same reference numerals.

The material of the furnace 201 for oxidizing is, for example, quartz, but other materials such as BN (boron nitride), alumina, Teflon, SUS, and aluminum may be used if necessary. The use of quartz is highly effective in preventing metal contamination of an oxide film formed by oxidation.

The furnace 201 is a single tube. However, in order to prevent contamination of the substrate due to inward diffusion of impurities from the outside of the furnace, a multi-tube such as a double tube or a triple tube is used as necessary. A purge gas may flow between the outer tube.

A heater 207 is used to heat the substrate 101 to be processed.
, But an infrared lamp 220 may be used. A heating unit may be provided near the substrate 101. The temperature of the substrate 101 is, for example, approximately 700 ° C. to 900 ° C.

In order to generate oxygen active species, for example, a microwave plasma is set up for a low-pressure oxygen gas using the electrode 202. That is, the mass flow controller 2
12 ₇ , valve 211 ₇ , piping 209, valve 211
Oxygen gas (O ₂ ) at a pressure of 5 Torr is supplied to the quartz furnace 20 via ₁₂ , 211 ₁₃ , 211 ₁₆ and 211 _18.
Introduce into 1. More preferably, the valve 211 ₁₂ is closed, oxygen gas is passed through the valve 211 ₁₀ , the gas purifier 210, and the valve 211 ₁₁ , and moisture in the gas,
Removes impurities such as carbon dioxide and increases the purity of oxygen gas. A microwave having a frequency of 2.45 GHz is applied to the oxygen gas flow from the electrode 202 to generate plasma, and the substrate 101 is exposed to the downflow atmosphere to oxidize the substrate surface.

When using ozone for oxidation, for example,
An ozonizer 208 is used. The ozonizer has a cooling water circulation system (not shown in FIG. 16). The oxygen gas is supplied to the mass flow controller 212 ₇ and the valve 21.
₁₇ , piping 209, valves 211 ₁₂ and 211
₁₄ , the ozone-containing oxygen gas is introduced into the ozonizer 208, and the ozone-containing oxygen gas is supplied to the valves 211 ₁₅ , 211 ₁₆ and 21.
Via 1 ₁₈ is introduced into the quartz furnace 201. The substrate 101 is exposed to the atmosphere of the ozone-containing gas to oxidize the substrate surface.

When light irradiation is used to oxidize a substrate, for example, a light source 205 is used. When using oxygen gas as a raw material,
O ₂ is converted to O ₂ → O by light having a wavelength of 243 nm or less.
Since ⁽³ P) + decomposed as ^{O (3} P), the light source, for example, using a low pressure mercury lamp having an emission line of 184.9 nm. Oxygen gas is introduced into the furnace 201 along the same route as in the case of the microwave plasma,
The oxygen gas in the vicinity of the substrate 101 is decomposed, and the generated oxygen radicals are used for oxidizing silicon. 205 light sources
In this position, high-intensity oxygen radicals are generated in the vicinity of the substrate surface, and oxidation can be performed efficiently at high speed. In order to avoid damage to the surface of the substrate 101 due to light irradiation, the substrate 1
01 in a direction parallel to the gas flow (in FIG.
1 may be changed), or light may be irradiated from the side surface of the substrate 101. On the other hand, if the light source is at the position of 203,
The radicals are uniformly supplied on the substrate 101, and an oxide film having excellent film thickness uniformity is formed.

When a metal or metal oxide having a catalytic action is used as an oxygen radical source, for example, as shown in FIG. 16, a catalyst is provided at a position 221 upstream of the substrate 101 to be processed. The shape of the catalyst is the same as that of the wire shown in this figure.
It may be a foil, a net, a powder, or may be supported by another member such as alumina. When using a catalyst that requires heating, the catalyst 22
Heater 207 may be used by bringing substrate 1 closer to substrate 101, or radiant heating using an infrared lamp or the like may be used. Resistance heating may be performed by passing an electric current directly through the catalyst. In the case of a catalyst requiring cooling, for example, a coolant such as water or liquid nitrogen is passed near the catalyst to be cooled.

For example, a platinum wire heated to about 800 ° C. by energizing heating is placed in an oxygen gas at a pressure of about 0.1 Torr, and the silicon substrate heated to about 800 ° C. is exposed to this atmosphere for about 60 minutes. However, the thickness is about 2n
m silicon oxide films were formed.

The above-described methods for generating several types of oxygen active species are effective for both single-wafer processing (processing of one substrate at a time) and batch processing (processing of a plurality of substrates at once).
More preferably, oxygen plasma and ozone are excellent in batch processing because radicals are supplied substantially uniformly in the furnace. On the other hand, light irradiation and metal / metal oxide catalysts
Since radicals are generated in high concentration in the vicinity of these sources, they are suitable for single-wafer processing of substrates.

(Fourth Embodiment) Next, a method of manufacturing an EEPROM memory cell according to a fourth embodiment of the present invention will be described.

The manufacturing method of this embodiment differs from the first embodiment in the formation of a tunnel oxide film in the first half of the manufacturing method.

The step of FIG. 17A is the same as the step of FIG. 2A. That is, after forming the trench 120 on the surface of the p-type silicon substrate 101, for example, liquid phase CVD is performed.
The inside of the trench 201 is filled with the silicon oxide film 102 by using a CVD method such as a CVD method, and element isolation is performed.

Next, as shown in FIG. 17 (b), a p-type silicon substrate 101 is placed on an oxygen-active species O ( ^{1) at} 550 ° C., for example.
D) Exposure to an atmosphere for, for example, 120 minutes to form a first tunnel oxide film 103 ₁₁ (underlying tunnel oxide film) having a thickness of 5 nm.
To form

Oxidation with active species O ( ¹ D), which is preferable for oxidation, is performed, for example, by the same method as in the first embodiment.

[0252] tunnel oxide film _{130 11} may be formed by using an oxygen radical ^{O (3} P). For example, a microwave discharge at a frequency of 2.45 GHz and an output of 200 W is applied to a low-pressure oxygen gas, and a silicon substrate at a temperature of, for example, 800 ° C. is placed in a down-flow atmosphere of the plasma.
Exposure was performed for 0 minutes to form a silicon oxide film of, for example, 5 nm. The atmosphere pressure was, for example, 5 Torr.

[0253] tunnel oxide film _{130 11} may be formed by using ozone. For example, using an ozonizer,
An ozone-containing gas of ₃ / O ₂ -7% was formed, and the surface of the silicon substrate heated to, for example, 900 ° C. for 10 minutes was exposed to this atmosphere to form a silicon oxide film of, for example, 5 nm. The atmosphere pressure was, for example, 5 Torr.

In an oxidizing atmosphere containing these oxygen active species,
A halogen-containing gas of approximately 1 to 10% is allowed to coexist.
By terminating the O-Si bond and enhancing the quality of the oxide film, the effect of improving dielectric breakdown resistance can be enhanced. The halogen-containing gas preferably includes a gas containing a molecule having a halogen atom, and is, for example, F ₂ or Cl ₂ . It is preferable that the halogen-containing gas does not generate microwave discharge or discharge in the ozonizer in order to prevent etching of the substrate or oxide film by the halogen active species. For example, a halogen-containing gas is introduced into the substrate surface without passing through a discharge electrode or an ozonizer.

[0255] Next, as shown in FIG. 17 (c), the second tunnel oxide film _{103 12} is deposited by low-pressure CVD on the entire surface of the substrate. These stacked tunnel oxide films 103
₁₁ , 103 ₁₂ are the tunnel oxide films 1 of the first embodiment.
Equivalent to 03 _1.

In the low pressure CVD method, for example, a silane gas 50
A mixed gas of sccm and dinitrogen monoxide gas at 450 sccm was introduced near the substrate heated to 750 ° C., and a silicon oxide film having a thickness of 15 nm was deposited, for example, for 5 minutes. The atmosphere pressure was, for example, 1 TorrR.

As a method of depositing an oxide film, for example, silicon difluoride SiF ₂ may react with oxygen radicals near the surface of the silicon substrate. SiF ₂ is, for example, a silicon tetrafluoride gas SiF having a flow rate of about 50 sccm.
₄ is formed by passing through a silicon crystal heated to about 1000 ° C. and supplied to, for example, a substrate heated to 700 ° C. As an oxygen radical source, for example, a flow rate of about 500
Microwave plasma is applied to the flow of oxygen gas of sccm, and this down-flow atmosphere is used. The atmospheric pressure is, for example, 1 Torr. For example, a silicon oxide film having a thickness of 15 nm was deposited in 10 minutes.

These silicon oxide film deposition steps were performed continuously in the same furnace as the above-described silicon oxidation step using oxygen activated species, without exposing the substrate to the outside air, at least.

[0259] The deposition step of the tunnel oxide film _{103 12,}
Tunnel oxide film 103 by radical oxidation of silicon
_In a furnace different from the formation step of the step ₁₁ , the substrate may be subjected to the oxidation step continuously without exposing the substrate to at least the outside air.

For example, a flow rate of 500 sccm and a pressure of about 1
The substrate at 700 ° C. is exposed, for example, to a TEOS (Si (OC ₂ H ₅ ) ₄ ) atmosphere of Torr for 2 minutes to a thickness of 15 nm.
Is formed.

[0261] as a tunnel oxide film _{103 12} may be a silicon nitride film or a silicon nitride oxide film.

For example, a flow rate of approximately 50 sccm of SiH ₂
The substrate heated to 780 ° C. is exposed, for example, to Cl ₂ , a flow rate of about 500 sccm NH ₃ , and a flow rate of about 70 sccm N ₂ atmosphere for, for example, 5 minutes to deposit a silicon nitride film having a thickness of 15 nm. The atmospheric pressure is, for example, 0.5 Torr.

For example, approximately 135 sccm of SiH ₂ C
l ₂ , NH _{3 at} a flow rate of about 90 sccm, and a flow rate of about 4
The substrate heated at 800 ° C. is exposed to an N ₂ O atmosphere of 50 sccm for, for example, 5 minutes to deposit a silicon nitride film having a thickness of 15 nm. The atmospheric pressure is, for example, 1 Torr.

The tunnel oxide films 103 ₁₁ and 103 ₁₂
May be a thickness other than 5 nm and 15 nm, respectively. The total thickness of these may be smaller than 20 nm, for example, may be 10 nm or less.

Finally, FIG. 3 described in the first embodiment
Through the steps similar to those shown in FIGS.
The memory cells of the ROM are completed.

The cross section of the tunnel oxide film of the memory cell manufactured according to the method of the present embodiment is shown by a transmission electron microscope (T
EM) and compared with those formed by conventional methods.

[0267] As a result, as in the first embodiment, Si substrates in the case of using the method of this embodiment ^{(O (1} D) oxide, ^{O (3} P) oxide) - tunnel oxide film interface is conventionally It was flatter than the interface between the silicon substrate and the tunnel oxide film when the method (dry oxygen oxidation) was used. Also, Qbd was larger than the tunnel oxide film obtained by the conventional method (dry oxidation).

These results indicate that the first tunnel oxide film 1
03 ( ₁₁ ), O ( ¹ D) and O ( ³ ) which have high flatness and dense film quality at the interface with the p-type silicon substrate 101.
P) It is considered that this is due to the use of the oxide film.

In this embodiment, the active species O (
^{1 D),} O (small concentration of 3 ^P), if the rate of formation of the tunnel oxide film is slow, the film thickness required to ensure the dense film quality of flattening and near the interface of the interface between the silicon substrate and the tunnel oxide film first tunnel oxide film (underlying tunnel oxide film) _{103 11} ^O (1 D), ^{O (3} P) formed by the atmosphere, the second tunnel oxide film by fast deposition rate low-pressure CVD method on its 103 ₁₂ is deposited. Therefore, there is a feature that the film forming efficiency is increased as a whole.

[0270] Once the dense film quality near the interface between the p-type silicon substrate 101 and the tunnel oxide film 103 _1, electrons from the floating gate electrode 104 ₁ in question by Qbd small to the tunnel oxide film 103 ₁ improved hot electron resistance of the tunnel oxide film 103 ₁ is for injection, thereby improving electrical reliability of the tunnel oxide film 103 _1.

As another factor of the improvement in reliability, O (
By that ¹ D) and ^{O (3} P) formed by the tunnel oxide film _{103 11} and the tunnel oxide film _{103 12} deposited by the CVD method, the film quality of different oxide film are laminated, the current leading to breakdown leak path also be mentioned that the hard connection from the floating gate electrode 104 ₁ to the p-type silicon substrate 101.

[0272] In the present embodiment, to improve the resistance of the tunnel oxide film 103 ₁ for electron injection from the p-type silicon substrate 101 to the tunnel oxide film 103 _1, a tunnel oxide film _{103 12} ^{O (1} D) Ya O
(3 ^P) may be modified by exposure to atmosphere.

Note that the present invention is not limited to the above embodiment. For example, FIG. 4 shows an oxidizing apparatus having a configuration capable of coping with any of the above-described embodiments. For example, a case where only O ( ¹ D) or O ( ³ P) is used as an oxidizing species In the case where only a part of the configuration of the oxidizing apparatus shown in FIG. 4 is used, an oxidizing apparatus having the configuration of only that part may be used.

The substrate heating heater 207 is resistance heating, but may be radiation heating using an infrared lamp.

In FIG. 4, the surface of the substrate 101 is set perpendicular to the gas flow, but it may be installed parallel to the gas flow.

As the oxygen radical generating source, a parallel plate plasma, a helicon plasma, an electron cyclotron resonance plasma, or a radical beam source may be used instead of the microwave discharge.

In addition to those described in the above embodiment, examples of the base oxidized by the active species preferable for oxidation include a silicon oxide film, a silicon nitride film, and a silicon nitride oxide film as an interlayer insulating film.

In each of these, the electron spin quantum number s = 0
In such preferred oxidizing active species O (1 ^D) react readily penetrate into the base film to form an oxide film or a nitride oxide film having a dense film quality. When O ( ¹ D) reaches the interface between the base film and the silicon substrate, the effect of flattening the interface is added, and the reliability of the insulating film is further improved.

As a base to be oxidized by O ( ¹ D),
A conventional thermal oxide film or ozone oxide film may be used.

O ( ¹ D) oxidation is also effective for repairing process damage to a gate oxide film and an interlayer insulating film by a semiconductor manufacturing process such as etching, CVD, and lithography.

[0281] Instead of ^{O (1} D), also with a higher singlet excited state, for example ^{O (1} S), the same effect as ^{O (1} D) is obtained.

The substrate to be oxidized is not limited to a silicon substrate, but may be, for example, a GaAs substrate or an InP substrate. Instead of the substrate, a polycrystalline layer or an amorphous layer of Si, GaAs, InP or the like may be used.

The above is a technique for using an active species that is optimal for an oxidation step which is a part of a semiconductor manufacturing process. In the step of utilizing the active species, each step can be improved by selectively forming an active species optimal for each step at a high concentration.
For example, improvement in processing efficiency (throughput) of a substrate, improvement in film quality of a formed film, suppression of damage to a base film after being removed and washed, and the like can be cited.

The present invention can be applied to a method of forming a silicon oxide film other than an EEPROM, for example, a gate oxide film of a MOSFET.

(Fifth Embodiment) FIGS. 18A1 to 1
FIG. 8 (d1) is a view showing a fifth embodiment of the present invention, wherein the flatness of the interface between the gate oxide film and the silicon substrate is improved by using the present invention in a step before the gate oxide film forming step. It shows the points of improvement. FIG.
1) to FIG. 18 (d1) show steps according to the present invention, and FIGS. 18 (a2) to 18 (d2) show steps using a conventional technique for comparison.

First, as shown in FIG. 18 (a1), a silicon substrate 11 is prepared (the surface of the silicon substrate is formed with irregularities), and as shown in FIG. Buffer oxide film 12 (6.4 nm
Is preferable).

For example, for an oxygen gas flow having a flow rate of approximately 800 sccm, a discharge frequency of 2.45 GHz and a discharge output of 2
A microwave plasma of 00 W is set up, and the silicon substrate heated to, for example, 930 ° C. is exposed to this downflow atmosphere for, for example, 15 minutes to form a silicon oxide film having a thickness of, for example, 10 nm. The ambient pressure is, for example, 5 Torr.

Also, for example, an ozone-containing gas of O ₃ / O ₂ ７7% is formed by an ozonizer, and the silicon substrate surface heated to, for example, 930 ° C. is exposed to this ozone-containing gas atmosphere for, for example, 20 minutes. A silicon oxide film having a thickness of 10 nm is formed. Atmospheric pressure is, for example, 5 Torr
It is.

Here, the substrate temperature is preferably higher than 550 ° C., more preferably, in order to increase the reactivity of O ( ³ P) and suppress the growth of an oxide film due to dry oxidation.
The substrate temperature is set to be in a range of more than 600 ° C. and 950 ° C.

In the prior art, as shown in FIG. 18A2, the buffer oxide film 12 is formed by ordinary thermal oxidation. For example, the silicon substrate is exposed to a dry oxygen atmosphere at a flow rate of approximately 20 l / min and 1000 ° C. for, for example, 20 minutes to form a silicon oxide film having a thickness of, for example, 20 nm.
At this time, when the buffer oxide film 12 is formed using the conventional technique, the interface between the silicon substrate 11 and the buffer oxide film 12 is uneven, whereas the buffer oxide film 12 is formed using the oxygen radical oxidation of the present invention. Is formed, the interface between the silicon substrate 11 and the buffer oxide film 12 is flattened at the atomic level. Hereinafter, this point will be described.

The substrate / oxide film interface is flattened at the atomic level by oxygen radical oxidation, unlike the conventional thermal oxidation, because active oxygen atom radicals are supplied to the silicon substrate. Both thermal oxidation and radical oxidation
The concentration of the oxidized diffusion species decreases from the oxide film surface (oxidizing atmosphere side) to the inside of the oxide film. When the interface flatness is relatively low, the convex portion on the interface side of the substrate (the portion where the substrate protrudes into the oxide film) is closer to the oxide film surface than the concave portion (the portion where the oxide film protrudes from the substrate). The concentration of the supplied oxidizing species increases, and the improvement of the interface flatness proceeds. It is considered that when the flatness of the interface is increased to some extent, the progress of the oxidation reaction is suppressed by the interface stress between the substrate and the oxide film having different interatomic distances. In conventional thermal oxidation, the reactivity of the oxidizing species at the substrate / oxide film interface is not high, so the progress of the oxidation reaction is suppressed by the stress at the interface with increased flatness, and the improvement in interface flatness is saturated with a certain degree of roughness. Resulting in. On the other hand, when oxygen atom radicals are supplied from an oxidizing atmosphere, active oxidizing species reach the substrate / oxide film interface, get over an oxidation reaction barrier due to interfacial stress, and become closer to the oxide film surface. Is presumed to be oxidized preferentially, so that the interface is flattened to the atomic level.

O ( ¹ D) which is more preferable for oxidation than O ( ³ P)
When is used for oxidation, the oxide film / substrate interface can be planarized at a lower temperature than O ( ³ P) and with a smaller oxide film thickness. Further, the flatness of the interface is further improved.

After forming the buffer oxide film 12, the buffer oxide film 12 is peeled off as shown in FIG. 18 (c1). Actually, a silicon substrate (p-type (10
0)), a buffer oxide film was formed thereon by oxygen radical oxidation (930 ° C., 15 minutes, film thickness 10 nm), and the buffer oxide film was peeled off (0.25% HF, 12 minutes). When the flatness was evaluated by a microscope (TEM), the interface between the substrate and the buffer oxide film was flat at the atomic level, and the substrate surface after the oxide film was stripped was also flat at the atomic level. On the other hand, in the sample manufactured by using the conventional technique (thermal oxidation using dry oxygen at 1000 ° C. for 20 minutes, film thickness: 20 nm), irregularities of several atomic layers are observed at the interface between the substrate and the buffer oxide film. The substrate surface after peeling the film was also uneven.

After the buffer oxide film 12 is peeled off, FIG.
As shown in (d1), when the gate oxide film 13 is formed by oxygen radical oxidation, even if the thickness of the gate oxide film 13 is as thin as less than 8 nm, for example,
A gate oxide interface is obtained.

In a range where the thickness of the oxide film is as small as about 5 nm or less, even in the conventional dry oxidation or wet oxidation, the surface of the silicon substrate before oxidation is flattened, so that a flat oxide film / substrate interface is obtained after oxidation. Been formed. This is because when the oxide film pressure is small, the roughness of the silicon surface before oxidation is largely reflected on the flatness of the oxide film / substrate interface after oxidation.

Here, the oxygen radical oxidation is carried out at a flow rate of about 8
A frequency of 2.45 G for an oxygen gas flow of 00 sccm
A silicon plasma heated to 900 ° C., for example, was heated to 900 ° C. in this downflow atmosphere for 1 minute, for example. The ambient pressure was, for example, 5 Torr, and the thickness of the formed silicon oxide film was, for example, 3 nm.

In the dry oxidation, for example, the silicon substrate was exposed to a dry oxygen atmosphere at 900 ° C. and normal pressure for 2 minutes, for example, to form a silicon oxide film having a thickness of 3 nm, for example.

In the wet oxidation, for example, 50%
The silicon substrate was exposed to, for example, a hydrogen combustion atmosphere at normal pressure diluted for 2 minutes to form a silicon oxide film having a thickness of, for example, 3 nm.

Also, a thin oxide film may be formed in an ozone atmosphere. For example, an ozone-containing gas of O ₃ / O ₂ ７7% is formed by an ozonizer, and the surface of a silicon substrate heated to, for example, 900 ° C. is exposed to this ozone-containing gas atmosphere for, for example, 5 minutes to form a silicon oxide having a thickness of, for example, 3 nm. A film was formed. The atmosphere pressure was, for example, 5 Torr.

On the other hand, when the buffer oxide film 12 is formed by using the conventional technique based on thermal oxidation, the surface of the substrate 11 before the gate oxide film 13 is formed is insufficiently flat. Even if oxygen radical oxidation having a high planarizing effect on the film interface is used, a flat substrate / gate oxide film interface cannot be obtained.

(Sixth Embodiment) FIGS. 19 (a1) to 1
9 (c1) is a view showing a sixth embodiment of the present invention, and shows a case where the present invention is used in a pre-process of a process of embedding a hole or a groove formed in a substrate surface. 19 (a1) to 19 (c1) show steps according to the present invention, and FIGS. 19 (a2) to 19 (c2) show steps using a conventional technique for comparison.

First, FIGS. 19 (a1) and 19 (a2)
As shown in FIG. 5, a groove or hole 23 is formed in the silicon substrate 21 by RIE. At this time, the RIE damage layer 22 is formed on the substrate surface. Subsequently, as shown in FIG. 19 (b1), the buffer oxide film 2 is formed by oxygen radical oxidation.
4 (preferably 8 nm or more in thickness) is formed. For example,
A microwave plasma having a frequency of 2.45 GHz and an output of 200 W is set up with respect to an oxygen gas flow having a flow rate of approximately 800 sccm.
The silicon substrate heated to ° C. was exposed, for example, for 15 minutes to form a silicon oxide film of, eg, 10 nm. The atmosphere pressure was, for example, 5 Torr.

In the prior art, as shown in FIG. 19B2, the buffer oxide film 24 is formed by ordinary thermal oxidation. For example, the silicon substrate was exposed to a dry oxygen atmosphere at a flow rate of approximately 20 l / min and 1000 ° C. for, for example, 20 minutes to form a silicon oxide film having a thickness of, for example, 20 nm. afterwards,
As shown in FIGS. 19C1 and 19C2, the buffer oxide film 24 is peeled off. For example, the substrate was immersed in an approximately 0.25% aqueous hydrogen fluoride solution for, for example, 12 minutes.

When the buffer oxide film 24 is formed by the conventional technique, not only the RIE damaged layer (above the broken line) but also the non-damaged layer (below the broken line) are taken into the buffer oxide film 24 with a considerable thickness. It has gone. Therefore, after the buffer oxide film is peeled off, not only the flatness of the substrate surface is poor, but also the width and depth of the grooves and holes are unnecessarily widened, which is a great obstacle to miniaturization of semiconductor elements. In addition, since the bottom and side walls have large irregularities, dielectric breakdown of an insulating layer embedded in a later step is likely to occur. On the other hand, when the buffer oxide film 24 is formed with a thickness slightly larger than the RIE damage layer by oxygen radical oxidation, the loss of the substrate surface layer due to the buffer oxidation is required to be a minimum.
In addition to miniaturization of the semiconductor element, the surface of the substrate and the bottom and side walls of the holes and grooves become extremely flat, and the corners of the upper ends of the holes and grooves become rounded, thereby improving the dielectric breakdown resistance of an insulating layer embedded in a later step. .

According to the present invention, the inner wall and the bottom surface of the element isolation groove having a thickness of, for example, 0.5 μm and a depth of 0.4 μm are formed on the above-mentioned oxide film having a thickness of 10 nm by radical oxidation. Is flattened by a procedure called oxide film stripping by TEOS (Si (OC (OC
_A silicon oxide film was embedded by a CVD method using ₂ H ₅ ) ₄ ). For example, the flow rate of TEOS is 500 scc
m, the pressure was approximately 1 Torr, and the substrate heated to 700 ° C. was exposed, for example, for 30 minutes to fill the groove with a silicon oxide film.

Also, for example, a width of 0.4 μm and a depth of 4 μm
The inner wall and bottom surface of the trench capacitor of the above,
After forming an oxide film of 10 nm by radical oxidation, the oxide film was planarized by the procedure of peeling the oxide film with hydrofluoric acid.

In oxidizing the inside of the flattened or processed trench, for example, the silicon substrate is exposed to a dry oxygen atmosphere at a flow rate of approximately 20 l / min, normal pressure and 1000 ° C. for 20 minutes, for example, a silicon oxide film having a thickness of 20 nm. Was formed.
For this oxidation, other oxidation methods such as a wet oxidation atmosphere, an oxygen radical atmosphere, and an ozone atmosphere may be used.

A polysilicon layer was deposited in the trench in which the oxide film was formed on the inner wall surface by using, for example, a low pressure CVD method. For example, a silane gas of 100 sccm was introduced near the substrate, and the pressure was set to, for example, 0.1 Torr. The substrate temperature was set to, for example, 620 ° C., and the trench inner wall was buried with polysilicon for approximately 40 minutes. Instead of the polysilicon layer, for example, a ferroelectric material such as RZT (Pb-Zn-Ti oxide) or BSTO (Ba-Sr-Ti oxide) may be embedded.

In any of these, the flatness of holes and grooves was improved as compared with the conventional method in which an oxide film was peeled off after dry oxidation.
The dielectric breakdown resistance of the trench for element isolation and the trench capacitor after being buried in the hole or the groove has been improved as compared with the related art.

In the present embodiment, the oxide film thickness of the buffer oxidation necessary for flattening the surface of the silicon layer is 6.
Although a thickness exceeding 4 nm is preferred, this value will be supplemented.

FIG. 20 shows the dependency of the SiO ₂ / Si (100) interface roughness on the oxide film thickness of a silicon oxide film formed by radical oxidation (oxidation using oxygen active species). Here, the interface roughness is SiO ₂ / Si
(100) The height between the highest point and the lowest point of the SiO ₂ / Si interface on a cross-sectional TEM (transmission electron microscope) photograph of the interface. The visual field in the interface direction of the TEM photograph is about 70 nm. In FIG. 20, the lower the SiO ₂ / Si interface roughness, the higher the flatness of the silicon surface after removing the oxide film.

[0312] As shown in FIG.
The (100) surface has a roughness of a height of 2 to 3 atomic layers. When this surface is oxidized, the oxidation proceeds and the Si
The height of the O ₂ / Si (100) interface roughness is reduced. When an oxide film having a thickness exceeding 6.4 nm is formed by oxidation with oxygen radicals, the height of the SiO ₂ / Si (100) interface roughness becomes one atomic layer or less, and the SiO ₂ / Si (100 ) An interface is formed. On the other hand, in the conventional dry oxidation, even if an oxide film having a thickness of 10 nm is formed, an interface roughness of a height of 1 to 2 atomic layers remains, and a flat SiO ₂ / Si (100) interface cannot be obtained. Therefore,
In order to form a flat silicon surface at the atomic level, an oxide film having a thickness exceeding 6.4 nm is formed by radical oxidation.
This oxide film may be removed.

(Seventh Embodiment) An embodiment in which the unevenness of the semiconductor surface before oxidation is large will be described.

If the unevenness of the semiconductor surface before the buffer oxidation is large, the thickness becomes approximately 8 by the buffer oxidation using the oxygen active species.
Even if an oxide film having a thickness of 10 to 10 nm is formed, unevenness before oxidation cannot be completely eliminated. Although the thickness of the buffer oxide film formed of oxygen active species may be increased, as shown in FIG. 21, oxidation by oxygen radicals tends to saturate the growth of the oxide film. Increasing the oxidation thickness is not very efficient. More preferably, FIG.
As shown in FIG. 2, it is effective to form and remove the oxide film a plurality of times.

An oxide film is formed by oxidation using oxygen active species.
The reason that the silicon substrate interface is flattened at the atomic level is
The following can be considered when comparing the oxide film growth rate by this oxidation.

FIG. 21 shows the dependence of the thickness of an oxide film formed using oxygen active species on the oxidation time. An oxide film grows rapidly in the early stage of oxidation, and an increase in the film thickness is suppressed as the oxide film grows. For this reason, oxidation by oxygen active species has a feature that oxidation of silicon by oxygen radicals proceeds rapidly, while diffusion of oxygen radicals in the oxide film is suppressed. The fact that the growth rate of the oxide film is fitted by a logarithmic function as shown in this figure indicates that oxygen radicals are deactivated during oxidation. The oxygen radical concentration in the oxide film is 1 / e (e:
The depth at which the natural logarithm is reached is represented by the relaxation distance d * = 3 nm.

From FIG. 20, the effect of flattening the oxide film / substrate interface is found in a range exceeding the film thickness of 6.4 nm. Since this film thickness is considerably larger than the relaxation distance d * shown in FIG. 21, the oxygen radical concentration near the oxide film / substrate interface is:
It is considered that the size has been extremely reduced due to the deactivation of radicals in the oxide film. Therefore, oxygen radicals are
In the vicinity of the substrate interface, it is possible to easily move in the interface direction, the radical senses the unevenness at the level of one atomic layer at the interface, and oxygen radicals oxidize the unoxidized Si atoms at the interface protrusions, Is estimated to be flattened to the atomic level.

According to FIG. 20, the surface of the silicon substrate before oxidation has irregularities of approximately three atomic layers, and the height of the roughness is approximately 0.8 to 1 nm. In order to eliminate this roughness, the thickness exceeds 6.4 nm by radical oxidation and is approximately 10 n.
It is necessary to form an oxide film to a thickness of m. For this reason, in order to eliminate the roughness of the silicon surface using the oxygen active species, it is preferable to form the silicon oxide film up to a thickness approximately 10 times the height of the roughness and remove the formed oxide film. .

FIG. 22 shows an example of a process of forming and removing an oxide film a plurality of times to planarize a semiconductor surface having large irregularities, taking planarization of an inner wall of a trench as an example.

FIG. 22A shows a trench immediately after being formed by, for example, an RIE (reactive ion etching) process.

The first buffer oxidation is performed on the trench immediately after the RIE step to obtain the shape shown in FIG.
When O ₂ is removed, a trench having improved inner wall surface roughness is obtained as shown in FIG. This first buffer oxidation includes conventional oxidation such as dry oxidation, wet oxidation in a steam atmosphere, oxidation in a hydrochloric acid atmosphere, and oxidation in a liquid phase containing ozone or strong hydrogen oxide, as well as oxidation using active oxygen species. Oxidation by a method may be used.

Here, the trench has a width of, for example, 0.4 μm,
The one having a depth of 4 μm was used. For the first buffer oxidation, for example, an oxygen radical atmosphere was used. That is,
For example, for an oxygen gas flow at a flow rate of approximately 800 sccm,
After increasing the flatness of the inner wall of the trench to some extent by the first buffer oxidation, the second buffer oxidation was performed to
22 (d), and when SiO ₂ is removed, FIG.
As shown in (e), a trench with further improved roughness on the inner wall surface is obtained. In order to enhance the flatness of the inner wall of the trench after removing the oxide film, it is preferable to use an oxidizing active species for the second buffer oxidation.

In the second buffer oxidation, for example, an oxidized radical atmosphere was used. That is, for example, for an oxygen gas flow having a flow rate of approximately 800 sccm, a frequency of 2.45
A microwave plasma of GHz and output of 200 W was set up, and a silicon substrate heated to, for example, 900 ° C. was exposed to the downflow atmosphere for, for example, 1 minute. The ambient pressure was, for example, 5 Torr, and the thickness of the formed silicon oxide film was, for example, 10 nm. After the formation of the oxide film, the substrate was immersed in, for example, an approximately 0.25% aqueous hydrogen fluoride solution for, for example, 12 minutes to peel off the formed oxide film.

In order to improve the flatness of the semiconductor surface,
The second buffer oxidation may be performed a plurality of times. Further, after the second buffer oxidation, for example, as a pretreatment of the next step, oxidation may be performed again by any method so as not to deteriorate the roughness of the planarized semiconductor surface to remove the oxide film. .

(Eighth Embodiment) FIGS. 23A1 to 23A2
FIG. 3 (d1) is a diagram showing an eighth embodiment of the present invention, and shows a case where the present invention is used for flattening a substrate surface exposed at the bottom of a contact hole. FIG.
3 (a1) to FIG. 23 (d1) show steps according to the present invention, and FIGS. 24 (a2) and 24 (b2) show steps using a conventional technique for comparison. Note that FIG.
Step 4 (b2) corresponds to the step of FIG. 23 (d1).

First, FIGS. 23 (a1) and 24 (a2)
As shown in FIG. 3, an impurity diffusion layer 32 serving as a source / drain and an interlayer insulating film 33 are formed on a silicon substrate 31.
A contact hole 34 is formed by RIE or the like. At this time, irregularities are formed on the exposed surface of the impurity diffusion layer 32. Thereafter, in the present invention, after the contact hole is opened, the buffer oxide film 3 is formed on the bottom surface of the contact hole by oxygen radical oxidation as shown in FIG.
5 (preferably with a film thickness exceeding 6.4 nm).
Subsequently, as shown in FIG. 23 (c1), after the buffer oxide film 35 is peeled off, a metal wiring layer 36 is formed as shown in FIG. 23 (d1).

The width of the contact hole is, for example, 0.3 μm.
m and a depth of, for example, 500 nm. For example, oxygen radicals were used to form the buffer oxide film 35 on the bottom surface.
That is, for example, a microwave plasma having a frequency of 2.45 GHz and an output of 200 W is set up against an oxygen gas flow having a flow rate of approximately 800 sccm, and a silicon substrate heated to, for example, a temperature of 700 ° C. is exposed to the downflow atmosphere for, for example, 90 minutes. I went. The ambient pressure is, for example, 5
Torr, and the thickness of the formed silicon oxide film was, for example, 10 nm.

For the removal of the buffer oxide film, for example, a mixed gas atmosphere of hydrogen fluoride and methanol was used. The mixing ratio of hydrogen fluoride and methanol was, for example, 38.5% and 61.5%, which are the azeotropic compositions thereof, but the ratio of hydrogen fluoride was reduced to adjust the etching rate of the oxide film. May be. The substrate was exposed to this vapor phase atmosphere at room temperature and normal thickness for 1 minute, for example, to remove the buffer oxide film. This step was continuously performed without exposing the substrate to at least the outside air after the buffer oxide film forming step was completed.

In the step of removing the buffer oxide film in the gas phase, in addition to the above-mentioned atmosphere of the empress of hydrogen fluoride and methanol, for example, the above-mentioned atmosphere of anhydrous hydrogen fluoride, F ₂ /
CDE (chemical dry etching) or RIE (reactive ion etching) with an F-containing gas such as H ₂ gas or CF ₄ , hydrogen radical treatment, or sputtering with Ar plasma or N ₂ plasma may be used.

On the entire substrate including the inside of the contact hole from which the buffer oxide film was removed, aluminum having a thickness of, for example, 200 nm was deposited by magnetron sputtering.
A wiring layer was formed.

As described above, according to the present invention, since the buffer oxide film is formed on the bottom surface of the contact hole and then removed, an extremely flat bottom surface of the contact hole can be obtained. Therefore, since the wiring layer grows uniformly on the bottom surface, the contact resistance between the wiring layer and the substrate is reduced, the reliability of the wiring layer is improved, and charge penetration in the impurity diffusion layer is prevented, and the impurity implantation is performed. The depth of the layer can be reduced. Note that the same effect can be obtained when the metal silicide layer is formed by silicidizing the flattened silicon substrate on the bottom surface of the contact hole instead of depositing the metal wiring layer.

The silicide layer was formed by depositing, for example, a titanium layer having a thickness of 20 nm on the substrate by magnetron sputtering, and subsequently performing a heat treatment at, for example, 700 ° C. for 30 seconds. An aluminum layer having a thickness of, for example, 200 nm was formed on the entire substrate including the silicide layer by a sputtering method. A titanium nitride layer having a thickness of, for example, 70 nm is formed on the substrate by a sputtering method.
Silicide may be formed by a heat treatment at 0 ° C. for 30 seconds, and then, for example, copper having a thickness of 200 nm may be deposited.

(Ninth Embodiment) Next, as a ninth embodiment of the present invention, a case where the present invention is used in a manufacturing process of a MOS transistor will be described. In the present embodiment, E
The same applies to a nonvolatile memory such as an EPROM.

FIG. 24 is a sectional view showing an element structure of an n-channel MOS transistor according to the ninth embodiment.

On the surface of the p-type silicon substrate 41, an element isolation region 44 in which a silicon oxide film is buried in a trench to which the present invention is applied is formed. Note that element isolation may be performed by LOCOS or the like. On the surface of the silicon substrate 41 in the element region, a high concentration n-type impurity diffusion layer is formed as a source / drain region 48. On the surface of the silicon substrate 41, a gate oxide film 46 to which the present invention is applied is formed. On this gate oxide film 46, a polysilicon film containing arsenic is formed as a gate electrode 47. A silicon oxide film 49 is formed on the entire surface of the substrate, and a wiring layer 50 and a wiring layer 50 formed by patterning the same conductive layer (such as Al) through connection holes formed in the silicon oxide film 49 are formed. 51 are provided.

FIGS. 25 to 27 show n channel M of FIG.
FIG. 7 is a process cross-sectional view illustrating the method for manufacturing the OS transistor.
Hereinafter, the manufacturing process will be described with reference to FIGS.

First, as shown in FIG. 25A, a trench 42 is formed on the surface of a p-type silicon substrate 41 by using, for example, a reactive ion etching (RIE) method. Irregularities are formed on the bottom and side walls of the groove depending on the type of etching.

Next, as shown in FIG. 25B, the p-type silicon substrate 41 is exposed to, for example, an oxygen radical atmosphere at 800 ° C. for 60 minutes to form a buffer oxide film 43 having a thickness of, for example, 10 nm. As a result, the flatness of the bottom surface and side surfaces of the trench groove is improved by the flattening action of the oxygen radical oxide film at the substrate / oxide film interface. In the example of FIG. 25B,
Although the surface of the substrate other than the trench groove is also oxidized at the same time to improve the flatness, a mask layer such as a silicon oxide film may be provided in a region other than the trench groove to oxidize only the trench groove.

Buffer oxide film 43 using oxygen radicals
Is formed using, for example, the manufacturing apparatus shown in FIG.

As the oxygen radical, for example, oxygen gas (O ₂ ) is supplied to the mass flow controller 212 and the valve 21.
1. The oxygen gas is introduced into the quartz tube 201 on which the silicon substrate 101 is installed through a pipe 209 or the like, and this oxygen gas is generated by plasma discharge. The oxygen radicals generated in this manner are supplied to the silicon substrate 101 by downflow. Preferably, the oxygen gas is purified by passing it through a gas purifier 210 to remove impurities such as water and carbon dioxide mixed in a small amount into the oxygen gas.

The pressure in the quartz tube 201 is controlled by an exhaust system, for example, 5 Torr. The oxygen gas flow rate is controlled by the mass flow controller 212, and is, for example, 800 sccm. The plasma discharge is performed using, for example, a cavity (discharge electrode for generating microwave plasma) provided outside the quartz tube 201. The plasma frequency is, for example, 2.45 GHz, and the discharge output is, for example, 200 W.
The silicon substrate 101 is heated by, for example, the heater 206, and the oxidation treatment temperature by plasma discharge of oxygen gas is, for example, 800 ° C. In this example, the substrate heating heater 206 is of resistance heating, but radiation heating by an infrared lamp may be used. In this example, the substrate 101
Is set to be perpendicular to the gas flow, but it is also possible to set the surface of the substrate 101 at an arbitrary angle to the gas flow.

Returning to the description of the manufacturing process shown in FIGS. 25 to 27, after forming the buffer oxide film 43 using the apparatus of FIG. 4, the buffer oxide film 4 is formed as shown in FIG.
3 is peeled off. As a result, a trench having high flatness of the bottom surface and the side wall can be obtained. In the oxide film stripping process, the substrate 4
1 is immersed in, for example, a 0.25% aqueous solution of hydrofluoric acid, for example, for 12 minutes. If the oxide film etching rate is too high,
The roughness of the substrate surface after the oxide film is stripped is deteriorated. In order to suppress the stripping rate of the oxide film and expose the substrate surface without deteriorating the flatness of the oxygen radical oxide film at the substrate / oxide film interface, the concentration of the hydrofluoric acid aqueous solution is set to 1% or less, or The hydrogen ion concentration of the aqueous solution of ammonium
It is preferably ^-4 mol / l or less (pH ≧ 4).
Note that the buffer oxide film may be peeled off in a gas atmosphere containing hydrogen fluoride molecules.

Next, as shown in FIG.
Using a CVD method such as a VD method, the trench is filled with the silicon oxide film 44 to perform element isolation.

Next, as shown in FIG. 26 (e), the silicon oxide film 4 is formed using, for example, a 5% aqueous solution of hydrofluoric acid.
4 is removed to expose the surface of the silicon substrate 41 in the element region. The exposed surface of the substrate is made flat by, for example, reactive plasma in the deposition process of the silicon oxide film 41 or a high-concentration aqueous solution of hydrofluoric acid used for high-speed etching of the relatively thick silicon oxide film 41. become worse.

Next, as shown in FIG.
1 is exposed to an oxygen radical atmosphere to form a buffer oxide film 45. The oxidation conditions are, for example, the same as those in the above-described step of FIG. As a result, the surface of the substrate as an element region is flattened at an atomic level by the flattening action of the oxide radical oxide film at the substrate / oxide film interface.

Next, as shown in FIG. 26 (g), by peeling off the buffer oxide film 45, a substrate surface with extremely high flatness can be obtained. The conditions for removing the oxide film are, for example, the same as those in the step of FIG.

Next, as shown in FIG. 26H, the surface of the silicon substrate 41 is oxidized to form a gate oxide film 46 having a thickness of, for example, 3 nm. In such an ultrathin oxide film, the roughness of the substrate surface before oxidation is largely reflected on the flatness of the substrate / oxide film interface after oxidation. By forming the buffer oxide film 45 by oxidation radical oxidation and flattening the substrate surface before the gate oxidation step, an extremely flat substrate / gate oxide film interface can be obtained even with an extremely thin oxide film.

For forming the gate oxide film 46, for example, oxygen radicals were used. For example, the flow rate is approximately 800 sccm
2.45 GHz frequency, output 2
A microwave plasma of 00 W was set up, and a silicon substrate heated to, for example, a temperature of 900 ° C. was exposed to the downflow atmosphere for, for example, 1 minute. The ambient pressure was, for example, 5 Torr, and the thickness of the formed silicon oxide film was, for example, 3 nm. The cross section of this oxide film is
Observation with a (transmission electron microscope) revealed that the oxide film / substrate interface was flat at the atomic level. As shown in FIG. 20, a normal silicon substrate surface is subjected to radical oxidation to a thickness of 3n.
Even if an oxide film of m is formed, the oxide film / substrate interface is not flat because the surface of the substrate has a roughness of about three atomic layers before oxidation.

For forming the gate oxide film 46, dry oxidation may be used. For example, the silicon substrate is exposed to a dry oxygen atmosphere at a normal pressure of 900 ° C. for 2 minutes, for example, to a thickness of 3
A silicon oxide film having a thickness of nm was formed.

A wet oxide film may be used for forming the gate oxide film 46. For example, the silicon substrate was exposed, for example, to a normal-pressure hydrogen combustion atmosphere diluted with a nitrogen gas to 50% for 2 minutes to form a silicon oxide film having a thickness of, for example, 3 nm.

An ozone atmosphere may be used for forming the gate oxide film 46. An ozone-containing gas of O ₃ / O ₂ ７7% is formed by an ozonizer, and the surface of the silicon substrate heated to, for example, 900 ° C. is exposed to the ozone-containing gas atmosphere for, for example, 5 minutes to form a silicon oxide film having a thickness of, for example, 3 nm. Formed. The atmosphere pressure was, for example, 5 Torr.

As a gate oxide film, a silicon nitride film may be used. For example, when a silicon substrate at a temperature of about 950 ° C. is exposed for 60 seconds, for example, in an ammonia gas atmosphere diluted to about 0.1% with nitrogen gas, the thickness becomes about 2 nm.
Was formed.

Next, as shown in FIG. 27 (i), an arsenic-doped polysilicon film is deposited as a gate electrode 47 over the entire surface of the substrate at 650 ° C. by using a low-pressure CVD method. The gate oxide film 46 is continuously etched using a reactive ion etching method.

Next, as shown in FIG. 27J, arsenic ions are implanted into the surface of the silicon substrate 41 using the gate electrode 47 as a mask under the conditions of an acceleration voltage of 40 keV and a dose of 2 × 10 ¹⁵ cm ^−2. And source / drain regions 48 are formed in a self-aligned manner. Thereafter, a silicon oxide film 49 is formed on the entire surface of the substrate by using a low-pressure CVD method.

Next, as shown in FIG. 27 (k), a contact hole for making a connection to the gate electrode 47 and the source / drain region 48 is opened, and then Al is formed on the entire surface of the substrate.
A film is formed and is patterned to form wiring layers 50 and 51 connected to the gate electrode 47 and the source / drain regions 48.

A cross section of the n-channel MOS transistor manufactured according to the method of this embodiment was observed with a transmission electron microscope. As for the trench groove, the flatness of the interface between the substrate and the buried oxide film on the bottom surface and the side wall is improved as compared with the conventional one using thermal oxidation for buffer oxidation. Regarding the substrate / gate oxide film interface, a flat substrate / oxide film interface at the atomic level, which cannot be obtained by the prior art, was obtained. Further, the dielectric breakdown voltage and Qbd (total amount of electrons passing through the oxide film before the dielectric breakdown) of these trench grooves with respect to the buried oxide film and the gate oxide film become larger than before, and the electric charge flowing under the gate oxide film is reduced. Has also become larger than before. On the other hand, the interface state density of the oxide film was reduced, and electrical characteristics were improved.

If the surface of the silicon substrate before oxidation is flattened, the surface of the gate oxide film after oxidation (oxidation atmosphere side) is also flattened, and the interface between the gate electrode and the gate oxide film formed on the gate oxide film is also flattened. Performance is improved than before. To improve the electrical characteristics of the gate oxide film obtained by the present invention,
This flattening effect at the gate electrode / gate oxide film interface also contributes.

The method of the present embodiment differs from the conventional method only in the difference of the oxidizing species. Therefore, there is almost no problem that the number of processes increases or the processes become complicated.

Before the gate oxide film 46 is formed, the surface of the substrate 41 is flattened by using the method of the present invention.
The interface flatness between the source / drain region 48 and the interlayer insulating film 49 and the wiring layer 51 is also improved as compared with the related art.

After the opening of the contact hole shown in FIG. 27 (k), a buffer oxide film is formed by performing oxygen radical oxidation on the substrate exposed surface at the bottom of the contact hole.
This buffer oxide film is peeled off in the same manner as in the steps shown in FIGS. 23 (a1) to 23 (d1).
And 51 may be formed. By doing so, for example, the bottom of the contact hole damaged at the time of opening the contact hole by RIE is repaired, and the bottom of the contact hole can be flattened. Note that it is preferable to lower the oxygen radical oxidation temperature in order to prevent deformation and deterioration around the contact hole due to heating during buffer oxidation. For example, 700 ° C., O ₂ pressure 5 Torr
A buffer oxide film having a thickness of 10 nm was formed at a plasma discharge power of 200 W and an oxidation time of 90 minutes. Thereafter, the entire substrate was immersed in, for example, a 0.25% aqueous hydrofluoric acid solution for, for example, 12 minutes to remove the buffer oxide film. By adding such a step, the contact resistance between the wiring layers 50 and 51 and the underlying silicon (the substrate 41 and the gate electrode 47) was reduced, and the life of the wiring layers was improved. This is probably because the wiring layer grew uniformly on the flat bottom surface.

In the above example, the wiring layers 50 and 51 are formed in the step of FIG. 27K. However, instead of the wiring layers, the surface of the silicon substrate 41 is silicided to form a metal silicide layer. Is also good. Also in this case, as described above, after opening the contact hole, a buffer oxide film is formed by performing oxygen radical oxidation on the exposed substrate surface of the contact hole bottom surface, and after removing the buffer oxide film, What is necessary is just to form a silicide layer.

In the oxygen radical oxidation used for forming the buffer oxide film and the gate oxide film, the oxygen active species are generated by microwave plasma discharge of O ₂ gas as described above. It is also possible to generate oxygen active species using the method.

As a method for exciting the O ₂ gas, a parallel plate plasma, a helicon wave plasma, an electron cyclotron resonance plasma, a radical beam source or the like can be used.

Further, a buffer oxide film or a gate oxide film may be formed by ozone oxidation using ozone instead of oxygen gas (O ₂ ). In this case, the valve 74c shown in FIG. 4 is closed, and oxygen gas is introduced into the quartz tube 201 by passing oxygen gas through the ozonizer 80.

As a source gas for forming oxygen radicals, molecular gas containing oxygen atoms may be used in addition to oxygen gas. For example, ozone (O ₃ ), nitric oxide (N
O), nitrous oxide (N ₂ O), nitrogen dioxide (N
O ₂ ), water vapor (H ₂ O), hydrogen peroxide (H ₂ O ₂ ), and the like. These gases and oxygen gas may be used singly or a mixture of a plurality of gases, such as helium, neon,
It may be used by mixing with an inert gas such as argon.

Further, oxygen gas or ozone gas may be irradiated with excitation light to generate oxygen atom radicals, which may be used for oxygen radical oxidation.

To irradiate oxygen gas or ozone gas with excitation light, the light sources 203 and 220 shown in FIG. 4 are used. Since the light source 220 irradiates the surface of the substrate 101, the radical concentration on the substrate surface can be increased. Further, the light source 203 can suppress damage to the substrate surface due to irradiation with the excitation light. The number of excitation photons may be one-photon excitation or two- or more-photon excitation. Further, a plurality of light sources may be used in combination.

The types of oxygen atom radicals generated by irradiation with excitation light include O ( ³ P, s =
1), O ( ¹ D, s = 0) in the first excited state, O ( ¹ S, s = 0) in the second excited state,... s is the electron spin quantum number of the entire oxygen atom. here,
The four valence electrons of the 2p orbitals bound to oxygen atoms have an upward spin (↑: spin quantum number ２) or a downward spin (↓: spin quantum number-／), respectively, and each valence electron Is considered to be reflected in s. Note that S, P, and D correspond to the azimuthal quantum numbers 1 = 0, 1, and 2 of the valence electrons as the entire oxygen atom.

Any of these various oxygen atoms can be used for the above-described oxygen radical oxidation. As shown in FIG. 6A, O ( ¹ D) and O ( ³ P) in a high-temperature atmosphere exceeding 550 ° C. have high reactivity, so that Si is oxidized one atomic layer at an oxide film / substrate interface. This interface becomes flat at the atomic level. On the other hand, in the conventional dry oxidation, as shown in FIG. 6B, since the reactivity is low, unreacted Si atoms remain at the oxide film / substrate interface, and irregularities remain at this interface. More preferably, the excited state such as O ( ¹ D) increases the concentration of oxygen atom radicals in a singlet state.

That is, O ( ¹ D) and O ( ¹ S) are represented by s =
0, and the spin directions of the valence electrons form a pair (↑ ↓). Accordingly, since O atoms easily enter Si-Si bonds (valence electrons: ↑ ↓), the reactivity is high, the oxide film formation rate is high, and the flattening effect of the substrate / oxide film interface is also high. In contrast, O ( ³ P) has s = 1, and the spins of the two valence electrons are both upward (↑↑) or downward (↓↓). Therefore, it is harder to enter a Si—Si bond (valence electron: ↑ ↓) than O ( ¹ D) or O ( ¹ S),
Therefore, the reactivity is slightly inferior.

To increase the concentration of the active species O ( ¹ D), for example, in the apparatus shown in FIG. 4, dinitrogen monoxide (N ₂ O) gas is introduced into the quartz tube 201 through the mass flow controller 212, the valve 211, and the pipe 209. Then, the N ₂ O gas is excited by light having a wavelength of 197 nm emitted from the light source 203. According to this method, O ( ¹ D) is selectively formed as an oxygen atom radical.

FIG. 4 shows an example of an apparatus configuration corresponding to many methods as described above. For example, when only plasma discharge of oxygen gas is used as a method for generating oxidizing atom radicals, FIG. When only a part of the device configuration shown in FIG. 4 is used, the device configuration of only that portion may be used.

(Tenth Embodiment) After an oxide film is formed by using oxygen active species for buffer oxidation, a gas phase atmosphere is used for the oxide film removal step, and the buffer oxidation step and the step after the oxide film removal are performed. If performed in a gas phase atmosphere, buffer oxidation →
The oxide film removal → post-process can be continuously performed in the same semiconductor manufacturing apparatus without exposing the semiconductor device to at least the outside air. Here, the post-process is, for example, a gate oxidation process, a nitriding process, an insulating film deposition process, a conductive film deposition process, or a process of forming a compound of a metal and a semiconductor (for example, a metal silicide). Performing buffer oxidation → removal of oxide film → post-process continuously means that the semiconductor surface is prevented from deteriorating electrical characteristics, such as deterioration of dielectric breakdown resistance of insulating film due to contamination of semiconductor surface and poor contact between wiring layer and semiconductor surface. This is extremely effective for improving the performance and yield of the device, improving the throughput of the semiconductor device manufacturing, and saving labor.

Although a gas phase atmosphere is used in the step of removing an oxide film formed by buffer oxidation in this specification, the gas phase atmosphere is used in a buffer oxidation step and a post-step (for example, a gate oxidation step) before and after the oxide film is removed. If it is possible to prevent the influence of the mixing of water or the like, a wet process using a chemical such as a hydrofluoric acid process or a CMP (chemical mechanical polishing) process may be used in the oxide film removing step.

FIG. 28 shows an example of a semiconductor manufacturing apparatus for continuously performing a buffer oxidation step, an oxide film removing step, and a subsequent step without exposing the semiconductor device to at least the outside air.

In FIG. 28, each container is arranged in a line, assuming that each step is performed in an individual container. However, each container may be arranged in another arrangement such as a circle. Further, all the steps may be performed in the same container, or only some of the steps may be performed in the same container. An apparatus for performing the next step, such as selectively or entirely etching the film formed in FIG. 28, may be added to each drawing. As an etching method, for example, chemical dry etching, reactive ion etching, wet treatment using a chemical solution, or chemical mechanical polishing is used. FIG.
May be used in combination as appropriate.

In FIG. 28, the pretreatment for buffer oxidation is also a treatment in a gas phase atmosphere, and is continuously performed until after the buffer oxidation. However, this pretreatment is performed by another apparatus, for example, wet.
The processing may be performed.

The transfer of the substrate between the containers is performed in a vacuum or in an atmosphere of an inert gas such as nitrogen or argon.

Although the dry process in a gaseous phase atmosphere is used for the steps in the pre-oxidation treatment chamber and the oxide film removal chamber, other steps such as a buffer oxidation step and a gate oxidation step after removal of the oxide film) are used. If it can be devised so as not to be affected by the incorporation of moisture into the surface, for example, a wet process using a chemical such as a hydrofluoric acid process or a CMP (chemical mechanical polishing) process may be used in these steps.

FIG. 28A shows the basic configuration of a semiconductor manufacturing apparatus according to the present invention. By continuously performing the buffer oxidation and the oxide film removal according to the present invention without exposing the semiconductor device to at least the outside air, it is possible to continue the post-process without exposing the highly flat semiconductor surface to the outside air. Thus, it is possible to prevent deterioration of electrical characteristics such as deterioration of dielectric breakdown resistance of the insulating film due to contamination of the semiconductor surface and poor contact between the wiring layer and the semiconductor surface.

FIG. 28B shows an example of a semiconductor manufacturing apparatus in which the present invention is applied to a gate oxide film forming step. For example, as shown in FIG. 16, gas pipes, heating devices, active species generation devices, and the like necessary for each process are connected to each process container. Note that unnecessary piping in FIG. 16 may be omitted.

For example, a semiconductor substrate from which an element has been separated is placed in an oxidation pretreatment chamber, and as shown in FIG. 26E, the substrate surface is cleaned using, for example, a photoexcited chlorine radical atmosphere and / or an anhydrous hydrogen fluoride vapor atmosphere. Wash.

For example, for an oxygen gas flow at a flow rate of approximately 800 sccm, a discharge frequency of 2.45 GHz and an output of 200
A microwave plasma of W was set up, and a silicon substrate heated to, for example, a temperature of 900 ° C. was exposed to the downflow atmosphere for, for example, 30 minutes. Atmospheric pressure is, for example, 5T
and the thickness of the formed silicon oxide film was, for example, 10 nm.

Next, the substrate is transferred to a buffer oxidation chamber, and as shown in FIG. 26 (f), an oxide film is formed by oxidation using the above-described oxygen active species, and a flat oxide film / substrate is formed. Form an interface.

Next, the substrate is transported to the oxide film removal chamber,
As shown in FIG. 6 (g), the oxide film formed by the buffer oxidation is removed using, for example, an anhydrous hydrogen fluoride vapor atmosphere to expose a flat substrate surface.

The substrate is exposed to a 7% anhydrous hydrogen fluoride / nitrogen vapor atmosphere diluted with nitrogen for, eg, 1 minute. In order to accelerate the etching of the oxide film, it is preferable to heat the substrate to approximately 100 ° C. After removing the oxide film, in order to remove F atoms remaining on the substrate surface, the substrate is preferably kept in, for example, a reduced pressure atmosphere at 200 ° C. for 10 minutes, for example.

Next, the substrate is fed into the gate oxidation chamber,
As shown in FIG. 6H, the planarized substrate surface is oxidized to perform gate oxidation. For the gate oxidation, for example, an oxygen radical was used. A microwave plasma with a frequency of 2.45 GHz and an output of 200 W is set up for an oxygen gas flow at a flow rate of approximately 800 sccm, and in this down-flow atmosphere,
For example, a silicon substrate heated to a temperature of 900.degree.
Exposure for a minute. The ambient pressure is, for example, 5 Torr.
r, the thickness of the formed silicon oxide film is, for example, 3n
m. Note that, for example, nitridation or oxynitride may be performed instead of gate oxidation, and a gate insulating film of another material such as an oxide film or an oxynitride film may be formed.

Next, the substrate is transferred to a gate electrode layer deposition chamber, and an arsenic-doped polysilicon film is deposited on the entire surface of the substrate by, for example, low pressure CVD using silane. The gate electrode layer deposition step is preferably performed continuously after the gate oxidation, but may be performed by a different apparatus from the buffer oxidation to the oxide film removal to the gate oxidation.

Finally, the substrate on which the gate oxide film and the polysilicon film have been formed is taken out of the gate electrode layer deposition chamber, and the substrate is taken to an apparatus for performing the next step such as selective etching of these films.

FIG. 28 (c) shows an example of a semiconductor manufacturing apparatus in which the present invention is applied to an insulating film deposition step. In each processing vessel, for example, as shown in FIG.
A heating device, an active species generation device, and the like are appropriately connected.

For example, a semiconductor substrate selectively etched by reactive ion is set in an oxidation pre-treatment chamber, and FIG.
25A to 25C, as in FIG. 28B, pretreatment in an oxidation pretreatment chamber, oxidation treatment in a buffer oxidation chamber, and removal of an oxide film in an oxide film removal chamber. Are sequentially performed to flatten the inner wall of the trench for element isolation.

Next, the substrate was transported to the insulating film deposition chamber,
As shown in FIG. 5D, an insulating film is deposited using a CVD method such as liquid phase CVD, and the trench is filled.

For example, the inner wall and bottom surface of the trench for device isolation having a thickness of 0.5 μm and a depth of 0.4 μm are flattened using radical oxidation as a buffer oxidation.
By a CVD method using S (Si (OC ₂ H ₅ ) ₄ ),
A silicon oxide film was embedded. For example, the flow rate of TEOS is 500 sccm, the pressure is approximately 1 Torr, and 700
The substrate heated to ° C. was exposed, for example, for 30 minutes to fill the groove with a silicon oxide film.

Finally, the substrate on which the insulating film is formed is taken out, and the next step of removing the film on the element region by, for example, hydrofluoric acid or the CMP method is performed. The container for performing the next step is shown in FIG.
8 (c), the next step may be performed continuously from the deposition of the insulating film without exposing the substrate to the outside air. Further, the next step may be performed in the insulating film nursery.

FIG. 28D shows an example of a semiconductor manufacturing apparatus in which the present invention is applied to a step of forming a contact between a care layer and a semiconductor layer. For example, as shown in FIG. 16, gas pipes, heating devices, active species generation devices, and the like necessary for each process are connected to each process container.

For example, a semiconductor substrate having a contact hole opened in an insulating film is placed in an oxidation pretreatment chamber, and a semiconductor substrate shown in FIG.
1) to 23 (c1), as in FIG. 28 (b), the pretreatment in the oxidation pretreatment chamber, the oxidation treatment in the buffer oxidation chamber, and the removal of the oxide film in the oxide film removal chamber are performed. Then, the silicon surface at the bottom of the contact hole is planarized. The width of the contact hole was, for example, 0.3 μm, and the depth was, for example, 500 nm.

Next, the substrate was transferred to a conductive film forming chamber,
As shown in FIG. 3 (d1), an Al layer having a thickness of, for example, 200 nm is formed on the entire surface of the substrate including the planarized silicon surface by, for example, magnetron sputtering.

[0398] Finally, the substrate on which the conductive film is formed is taken out, and for example, a selective etching step of an Al layer is performed. Note that since this step is performed continuously after the formation of the conductive film, a container used in the next step may be connected to the conductive film formation chamber.

FIG. 28E shows an example of a semiconductor manufacturing apparatus in which the present invention is applied to a step of forming a contact between a wiring layer and a semiconductor layer. As in FIG. 28D, the pretreatment in the oxidation pretreatment chamber, the oxidation treatment up to the buffer oxidation, and the removal of the oxide film in the oxide film removal chamber are sequentially performed to flatten the silicon surface on the bottom surface of the contact hole.

Next, the substrate is transferred to a metal silicide formation chamber, and a metal silicide layer is formed on the flattened silicon surface at the bottom of the contact hole. The silicide layer is formed, for example, by depositing a titanium layer having a thickness of 20 nm on the substrate by a magnetron sputtering method.
It was formed by performing a heat treatment for 0 second.

Finally, the substrate on which the metal silicide layer is formed is taken out, and for example, an Al layer is formed on the entire surface of the substrate.
In addition, since the next step is performed continuously after the formation of the metal silicide, a container used in the next step may be connected to the metal silicide formation chamber.

FIG. 28 (f) shows an example of a semiconductor manufacturing apparatus in which the present invention is applied to a step of flattening a semiconductor surface having large surface irregularities. In each processing container, for example, as shown in FIG.
Gas pipes, heating devices, active species generation devices, and the like required for each process are appropriately connected.

For example, after preprocessing, a semiconductor substrate having been subjected to element isolation as shown in FIG. 22A is placed in a buffer oxidation chamber (1), and as shown in FIG. A second oxidation is performed. More preferably, the pretreatment of the first buffer oxidation is performed continuously with the main buffer oxidation.
The first buffer oxidation includes conventional methods such as oxidation using active oxygen species, dry oxidation, wet oxidation in a steam atmosphere, oxidation in a hydrochloric acid atmosphere, and oxidation in a liquid phase containing ozone or hydrogen peroxide. Oxidation may be used.

Next, the substrate is transferred to the oxide film removing chamber (1), and the oxide film is removed, for example, in an anhydrous hydrogen fluoride vapor atmosphere, as shown in FIG. By the first buffer oxidation, a semiconductor surface having a somewhat improved flatness is formed.

Next, the substrate is transferred to the buffer oxidation chamber (2), and a second buffer oxidation is performed as shown in FIG. In order to improve the flatness of the semiconductor surface after removing the oxide film, it is preferable to use oxygen active species for the second buffer oxidation.

Next, the substrate is transported to the oxide film removal chamber (2), and the oxide film is removed, as shown in FIG.
A semiconductor surface with significantly improved roughness can be obtained.

Next, the substrate is taken out of the oxide film removing chamber (2), and a post-process such as an insulating film deposition process is performed. Alternatively, the container for performing the post-process is connected to the oxide film removal chamber (2), and the post-process such as, for example, the insulating film volume process is continuously performed on the planarized semiconductor surface without exposing the substrate to the outside air. Do.

In a semiconductor manufacturing apparatus in which the buffer oxidation-oxide film removal-post-process is continuously performed without exposing the semiconductor device to at least a small amount of outside air, an oxide film formed by the buffer oxidation is removed. F, which has a film etching action
It is preferable to use a gaseous atmosphere containing a molecule or an active species having one or more of atoms, Cl atoms, Br atoms, and I atoms.

In the various oxygen radical oxidations described above, even if the process conditions such as the oxidation temperature, the gas flow rate, the atmospheric pressure, the excitation light intensity, the excitation light wavelength, the processing time, the plasma discharge output, etc. are different, the flatness can be improved. Can obtain an improved semiconductor / buffer oxide film interface.

When the buffer oxide film is peeled off, for example, even if the peeling method, the type and concentration of the etching species and the etching time are different, the substrate surface having higher flatness than the conventional one and the inner surfaces of the holes and grooves (bottom and side walls) are obtained. ) Can be obtained.

[0411] As described above, in the oxygen radical oxidation, a buffer oxide film having a flat interface with the underlying semiconductor can be formed at a lower temperature than in the conventional thermal oxidation, so that deformation and alteration due to high-temperature treatment are suppressed. Therefore, in addition to the above-described pretreatments for the gate oxidation, the burying of the trench for element isolation, the burying of the contact holes, and the like, it can be widely used for the flattening treatment of the surface where the semiconductor is exposed or the inner surface of the hole or groove. For example, the present invention can be applied to a flattening process of a bottom surface and a side wall of a hole for a trench capacitor.

As a semiconductor to be subjected to a buffer oxide film forming process by oxygen radical oxidation, it is possible to use a GaAs substrate or an InP substrate in addition to a silicon substrate. The present invention is also applicable to a polycrystalline layer, an amorphous layer, or an epitaxially grown layer of a semiconductor such as Si, GaAs, and InP.

In each of the above embodiments, hydrofluoric acid or an aqueous solution of ammonium fluoride is used as a method for removing an oxide film formed by buffer oxidation. However, as another method, the oxide film is removed in a gas phase atmosphere. It is possible.

[0414] If a gas phase atmosphere is used for the oxide film removing step and the buffer oxidation step and the gate oxidation step after the oxide film removal are performed in a gas phase atmosphere, the semiconductor device is continuously exposed at least without exposing the semiconductor device to the outside air. Oxidation → oxide film removal → gate oxidation step (or nitridation step, insulating film deposition step, conductive film deposition step, compound formation step of metal and semiconductor) can be performed in the same semiconductor manufacturing apparatus. As a result, it is possible to prevent deterioration of electrical characteristics such as deterioration of dielectric breakdown resistance of the insulating film due to contamination of the semiconductor surface and poor contact between the wiring layer and the semiconductor surface, thereby improving the performance and yield of the semiconductor device and improving the semiconductor device. This is extremely effective for improving manufacturing throughput and saving labor.

[0415] The vapor phase atmosphere for removing the oxide film formed by the buffer oxidation may be a molecule having at least one of F atom, Cl atom, Br atom, and I atom having an action of etching the oxide film, or an active gas. Preferably, it contains a species.
For example, a nitrogen dilution atmosphere of anhydrous hydrogen fluoride (HF / N ₂
(7%), an oxide film up to about 100 nm can be removed in one minute.

[0416] The removal of the oxide film in the gas phase atmosphere can be performed, for example, by the following steps.
What is necessary is just to perform using the apparatus shown in FIG. That is, the buffer oxidation is performed using a part of the configuration of the apparatus shown in FIG.
Is exposed to a 7% anhydrous hydrogen fluoride / nitrogen vapor atmosphere diluted with nitrogen for 1 minute. Hydrogen fluoride is supplied to the mass flow controller 222
₂ , valve 223 ₂ , 223 ₁₅ , 223 ₁₈ , 223
_19, and then introduced via 217 _5, nitrogen, to merge with hydrogen fluoride through a mass flow controller 222 ₁ and the valve 223 _1. At this time, when the temperature of the substrate is set to approximately 100 ° C., the etching of the oxide film is promoted.
Preferably, after removing the oxide film, the substrate is heated to approximately 200 ° C. in a reduced pressure atmosphere in order to remove F atoms remaining on the substrate surface.

For removing an oxide film in the gas phase, besides anhydrous hydrogen fluoride vapor, for example, an ultraviolet-excited F ₂ / H ₂ gas,
HF / CH ₃ CO paper, CDE (chemical dry etching), RIE (reactive ion etching), sputtering by hydrogen radical atmosphere plasma, or the like may be used.

[0418] As a substrate processing method in a gaseous-phase atmosphere, the above-described oxide film removing method may be combined with, for example, the following method mainly for removing metal contamination and organic contamination. For example, ultraviolet excitation Cl ₂ , ClF ₃ vapor, HFAC (1,
1,1,5,5,5-hexafluoro-2,4-pentanedione vapor, TFAA (trifluoroacetic acid) vapor, hydrogen radical deammonia hexahexamethyldisilazane (NH
[Si (CH ₃ ) ₃ ] ₂ ) atmosphere or hydrogen radical atmosphere is performed before or after the above oxide film removing method.

[0419] When the gas used for the gas-phase atmosphere treatment of the substrate excited by plasma discharge, the gas and through valve ₂₂₃ 16, _{223 17,} using the electrode 202 and the excitation light source 203. Further, the substrate may be heated as required for the processing.

In the semiconductor manufacturing method and apparatus used for flattening the semiconductor surface in the above embodiment,
To enhance the flatness, preferably the oxidation active species O (1 ^D)
It is preferable to use an atmosphere containing as a main component for buffer oxidation.

(Eleventh Embodiment) In the present embodiment, the oxide film formed in the third embodiment is oxidized to prevent boron from penetrating from the gate electrode through the oxide film to the substrate. An example in which a nitrogen atom has been introduced into the above will be described. Here, boron is used as a dopant for the polysilicon film for the gate electrode.

For example, as shown in FIG. 8A, the surface of a silicon substrate from which an element is separated is oxidized with oxygen radicals,
As shown in (b), a silicon oxide film 103 was formed.

Oxygen radicals are produced, for example, at a discharge frequency of 2.
It was formed by applying a microwave discharge of 45 GHz and a discharge output of 200 W to a low-pressure oxygen gas. Exposing the silicon substrate in the downflow atmosphere, it was oxidized by oxygen radical O (3 ^P). The oxygen flow rate is, for example, 800 scc
m and the atmospheric pressure were, for example, 5 Torr. For example, a silicon oxide film having a thickness of, for example, 6 nm was formed at a temperature of 900 ° C. and an oxidation time of 5 minutes.

Immediately after the formation of the oxide film, the introduced gas was changed from oxygen gas to nitrogen gas, and nitrogen atoms were introduced into the surface of the silicon oxide film using a nitrogen radical atmosphere. For example,
A microwave discharge with a discharge frequency of 2.45 GHz and a discharge output of 100 W was applied to a nitrogen gas at a flow rate of 800 sccm, and the silicon substrate was exposed to a nitrogen gas plasma downflow atmosphere. The pressure was, for example, 5 Torr. The substrate temperature was, for example, 900 ° C., and the processing time was, for example, 30 minutes. After the surface nitriding, the oxidized surface was examined by X-ray photoelectron spectroscopy (XPS). As a result, approximately 1% of N atoms had been introduced near the surface of the oxide film.

[0425] As a reference, a conventional oxide film formed by dry oxidation was formed on another substrate surface. For example, 20
The silicon substrate is exposed to a dry oxygen atmosphere at 900 ° C. for 1 minute, for example, for 10 minutes to form a silicon oxide film having a thickness of, for example, 6 nm. Next, a boron-doped polysilicon layer is formed on the entire surface of the substrate. For example, using a low pressure CVD method using disilane and diborane as raw materials, for example, at a temperature of 4
The thickness of the polysilicon deposited at 50 ° C. is approximately 20
0 nm, boron concentration is approximately 3 × 10 ²⁰ atoms / c
It was m ^3.

Thereafter, the substrates for forming the MOS transistor and for examining the penetration of boron are separated from each other. The substrate for forming the MOS transistor is subjected to annealing at 900 ° C. for 30 seconds in nitrogen gas for annealing the polysilicon layer. Heat treatment was performed. Thereafter, as shown in FIGS. 27 (i) to 27 (k), a MOS transistor was formed as in the ninth embodiment.

In the substrate for boron penetration study, in order to increase the amount of penetration and make it easier to observe, the annealing condition of the polysilicon layer was set to a strong condition. For example, heat treatment was performed at 1000 ° C. for 90 minutes in a nitrogen gas. After this heat treatment, the polysilicon layer is chemically dry-etched (CD
E), the amount of boron that passed through the oxide film by heat treatment and penetrated the substrate was examined using secondary ion mass spectrometry (SIMS).

FIG. 29 shows the result of using SIMS to examine the directional distribution of boron penetrating the oxide film through the gate electrode and penetrating the substrate for various oxide films. FIG.
Is an insulating film in which nitrogen radicals are introduced into the surface of a silicon oxide film formed using oxygen radicals. FIG. 30 is a conventional thermal oxide film. FIG. 31 shows a case where the annealing process is not performed after the annealing process at 90 ° C. for 90 minutes. As shown in FIG. 29, in the radical oxide film having nitrogen atoms introduced near the surface, the boron concentration in the substrate is almost equal to that in FIG. 31 before annealing, indicating that penetration of boron is suppressed. I have. On the other hand, in the conventional thermal oxide film, as shown in FIG. 29, as compared with FIG. 31 before the annealing, the boron concentration in the substrate was increased by the annealing treatment, indicating that a large amount of boron penetrated. I have. On the other hand, in the conventional thermal oxide film, as shown in FIG. 30, the boron concentration in the substrate was increased by the annealing treatment, as compared with FIG. 31 before the annealing, and a large amount of boron penetrated the oxide film. It is shown that. In addition,
The penetration concentration of the radical oxidized oxide film into which nitrogen atoms were not introduced near the surface was intermediate between FIGS. 29 and 30.

On the other hand, when a MOS transistor formed using these oxide films as a gate oxide film was examined, it was found that a radical oxide film in which nitrogen atoms were introduced reflects an improvement in boron penetration resistance as compared with a conventional thermal oxide film. As a result, the threshold voltage was stabilized.

The substrate on which the semiconductor device is formed is oxidized one atomic layer at a time (layer-by-layer) to obtain a flat oxide film / semiconductor substrate interface at the atomic level. Preferably, the angle is close to 0 ° (for example, the substrate surface is parallel to the Si (100) plane) and the substrate surface has high flatness.

The active species used for the oxidation of the semiconductor, the removal of the oxide film, and the nitridation in this embodiment are not limited to the active species in the atmosphere in which the source gas is decomposed by the plasma discharge, the excitation light, or the catalyst. And other feed gas,
Alternatively, an active species generated by reacting with another chemical species may be used.

[0432] The present invention is not limited to the above embodiments of the present invention, and it is needless to say that various modifications can be made without departing from the scope of the present invention.

[0433]

According to the present invention, the following effects can be obtained.

(1) Since an oxidizing gas source containing oxygen radicals in a singlet state as a main component is supplied to the silicon layer, oxidation proceeds efficiently, and a silicon oxide film is formed at a lower temperature than before. As well as eliminating trap sites such as lattice defects in the silicon oxide film, resulting in dense film quality, flattening the interface between the silicon layer and the silicon oxide film, and improving the electrical reliability of the silicon oxide film. can do.

(2) By oxidizing the surface of the semiconductor in an atmosphere containing active oxygen species to form a buffer oxide film, the interface between the semiconductor and the buffer oxide film can be extremely flattened. The surface of the semiconductor after the removal is also flattened. Therefore, when an insulating layer or a conductive layer is formed on the surface of the semiconductor exposed after removing the buffer oxide film, the interface between the two is extremely flattened, and a semiconductor device having excellent reliability and characteristics can be manufactured.

(3) Since the semiconductor substrate can be oxidized at an optimum temperature in an atmosphere containing oxygen active species,
The same effect as (2) can be obtained.

(4) Since a series of steps can be performed without exposing to the outside air, deterioration of electrical characteristics such as deterioration of insulation breakdown resistance of an insulating film due to contamination of a semiconductor surface and poor contact between a wiring layer and a semiconductor surface. Prevention is very effective in improving the performance and yield of the semiconductor device, as well as improving the throughput and saving labor in the manufacture of the semiconductor device.

[Brief description of the drawings]

FIG. 1 shows an EEPRO according to a first embodiment of the present invention.
FIG. 13 is a cross-sectional view illustrating an element structure of an M memory cell.

FIG. 2 is a process sectional view illustrating the method of manufacturing the memory cell in FIG. 1;

3 is a process sectional view illustrating the method for manufacturing the memory cell of FIG.

FIG. 4 is a schematic view showing an oxidation device used for forming a tunnel oxide film.

FIG. 5 shows a difference in flatness of an interface between a gate oxide film and a silicon substrate due to a difference in oxidizing species. .

FIG. 6 is a view for explaining the reason why the flatness of the interface between the gate oxide film and the silicon substrate is different depending on the type of oxidization.

FIG. 7 is a view showing flattening of an interface between an oxide film and a base substrate by O ( ¹ D) oxidation.

FIG. 8: O ( ¹ D) Si-Si due to difference in plane orientation
The figure which shows the difference in the way of joining.

FIG. 9 is a diagram showing energy required to form various oxygen active species from oxygen molecules O ₂ .

FIG. 10 is a diagram showing energy required to excite the ground state O ( ³ P) of an oxygen atom.

FIG. 11 is a diagram showing energy required to excite oxygen molecules O ₂ (a ¹ Δ _g ) in an excited state.

12 is a diagram illustrating the energy required to excite the oxygen molecule _O 2 excited state ^{(b 1} Σ _g ^+).

FIG. 13 shows an EEPR according to the second embodiment of the present invention.
Sectional drawing which shows the manufacturing method of the memory cell of OM.

FIG. 14 is a diagram showing a difference in an oxide film formation rate depending on a difference in oxidizing species.

FIG. 15 is a view showing a difference in dielectric breakdown resistance of an oxide film due to a difference in oxidizing species.

FIG. 16 is a view showing a schematic configuration of a semiconductor manufacturing apparatus according to a third embodiment of the present invention.

FIG. 17 shows an EEPR according to a fourth embodiment of the present invention.
Sectional drawing which shows the manufacturing method of the memory cell of OM.

FIG. 18 is a diagram showing a fifth embodiment of the present invention in comparison with a conventional technique.

FIG. 19 is a diagram showing a sixth embodiment of the present invention in comparison with a conventional technique.

FIG. 20 is a view showing the oxide film thickness dependency of the silicon oxide film / silicon substrate interface roughness.

FIG. 21 is a graph showing dependence of an oxide film thickness on an oxidation time.

FIG. 22 is a process cross-sectional view showing a part of the manufacturing process according to the seventh embodiment of the present invention.

FIG. 23 is a diagram showing an eighth embodiment of the present invention in comparison with a conventional technique.

FIG. 24 is a sectional view schematically showing a semiconductor device manufactured by the steps of the ninth embodiment of the present invention.

FIG. 25 is a process cross-sectional view showing a part of the manufacturing process according to the ninth embodiment of the present invention.

FIG. 26 is a process cross-sectional view showing a part of the manufacturing process according to the ninth embodiment of the present invention.

FIG. 27 is a process cross-sectional view showing a part of the manufacturing process according to the ninth embodiment of the present invention.

FIG. 28 is a view showing a schematic configuration of a semiconductor manufacturing apparatus according to a tenth embodiment of the present invention.

FIG. 29 is a diagram showing a difference in the amount of boron penetration from a gate electrode to a substrate depending on the type of an oxide film.

FIG. 30 is a view showing a difference in the amount of boron penetration from a gate electrode to a substrate depending on the type of an oxide film.

FIG. 31 is a diagram showing a difference in the amount of boron penetration from a gate electrode to a substrate depending on the type of an oxide film.

FIG. 32 is a view showing a difference in oxidation rate due to a difference in oxidizing species.

FIG. 33: Gate voltage shift ΔV due to difference in oxidizing species
FIG.

FIG. 34 is a view showing a difference in Qbd due to a difference in oxidizing species.

FIG. 35 is a view showing a difference in electron mobility at a substrate-side interface of a silicon oxide film formed on a silicon substrate due to a difference in oxidizing species.

FIG. 36 is a view showing a difference in flatness of an interface between a silicon substrate and a silicon oxide film due to a difference in oxidizing species.

FIG. 37 is a view for explaining the reason why the flatness of the interface between the silicon oxide film and the silicon substrate is different depending on the type of oxidized species.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 101 ... p-type silicon substrate 102 ... silicon oxide film 103 ₁ ... tunnel oxide film 103 ₂ ... insulating film between gate electrodes 104 ₁ ... floating gate electrode 104 ₂ ... control gate electrode 105 ... source region 106 ... drain region 107 ... silicon oxide film 108: Source electrode 109: Gate electrode wiring 110: Drain electrode

Claims (40)

[Claims] 1. A method for manufacturing a semiconductor device, comprising: oxidizing a surface of a semiconductor layer in an atmosphere containing oxygen active species at a temperature exceeding 550 ° C. to form an oxide film. 2. The method for manufacturing a semiconductor device according to claim 1, wherein the atmosphere containing the pre-oxygen active species is a plasma atmosphere of a gas containing molecules having oxygen atoms. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the atmosphere containing the oxygen active species includes ozone molecules. 4. The method for manufacturing a semiconductor device according to claim 1, wherein the oxygen active species is generated by irradiating a gas containing a molecule having an oxygen atom with light. 5. The method of manufacturing a semiconductor device according to claim 1, wherein said oxygen-active species is generated by exposing a metal or a metal oxide to a gas containing a molecule having an oxygen atom. Production method. 6. A semiconductor manufacturing apparatus, wherein an oxide film is formed by oxidizing a surface of a semiconductor layer in an atmosphere containing oxygen active species at a temperature exceeding 550 ° C. 7. The semiconductor manufacturing apparatus according to claim 6, wherein the atmosphere containing the oxygen active species is a plasma atmosphere of a gas containing molecules having oxygen atoms. 8. The semiconductor manufacturing apparatus according to claim 6, wherein the atmosphere containing the active oxygen species contains ozone molecules. 9. The semiconductor manufacturing apparatus according to claim 6, wherein the oxygen active species is generated by irradiating a gas containing a molecule having an oxygen atom with light. 10. The semiconductor manufacturing apparatus according to claim 6, wherein said oxygen active species is generated by exposing a metal or a metal oxide to a gas containing a molecule having an oxygen atom. 11. A method comprising: oxidizing a surface of a semiconductor in an atmosphere containing oxygen active species to form an oxide film; and removing the oxide film to expose a surface of the semiconductor. Semiconductor device manufacturing method. 12. The method of manufacturing a semiconductor device according to claim 11, further comprising a step of forming an insulating film by oxidizing or nitriding the exposed surface of the semiconductor. 13. The method of manufacturing a semiconductor device according to claim 11, further comprising a step of depositing an insulating film on the exposed surface of the semiconductor. 14. The method of manufacturing a semiconductor device according to claim 11, further comprising a step of depositing a conductive film on the exposed surface of the semiconductor. 15. The method of manufacturing a semiconductor device according to claim 11, further comprising a step of forming a layer containing the semiconductor and a desired metal as main components on the exposed surface of the semiconductor. A method for manufacturing a semiconductor device. 16. A method for manufacturing a semiconductor device according to claim 11, wherein a first oxide film is formed by oxidizing a surface of the semiconductor with the semiconductor containing the oxygen active species. Removing the oxide film and exposing the surface of the semiconductor;
Forming a second oxide film and exposing a surface of the semiconductor by removing the second oxide film one or more times. 17. The method of manufacturing a semiconductor device according to claim 11, wherein the step of removing the oxide film and exposing the surface of the semiconductor further comprises removing the oxide film in a gas phase atmosphere. A method for manufacturing a semiconductor device, comprising: 18. The method of manufacturing a semiconductor device according to claim 17, wherein said gaseous phase atmosphere includes F atoms, Cl atoms, and B atoms.
A method for manufacturing a semiconductor device, comprising using a gaseous atmosphere containing a molecule having at least one of r atoms and I atoms or an active species. 19. A method for forming an oxide film by oxidizing the surface of a semiconductor in an atmosphere containing oxygen active species, and exposing the surface of the semiconductor by removing the oxide film without exposing the semiconductor device to at least outside air. A semiconductor manufacturing apparatus characterized by being continuously performed. 20. The semiconductor manufacturing apparatus according to claim 19, further comprising a step of forming an insulating film by oxidizing or nitriding the surface of the exposed semiconductor while maintaining at least a state of not being exposed to the outside air. Characteristic semiconductor manufacturing equipment. 21. The semiconductor manufacturing apparatus according to claim 19, further comprising a step of depositing an insulating film on the exposed surface of the semiconductor while maintaining at least a state of not being exposed to the outside air. apparatus. 22. The semiconductor manufacturing apparatus according to claim 19, further comprising a step of depositing a conductive film on the exposed surface of the semiconductor while maintaining at least a state of not being exposed to outside air. apparatus. 23. The semiconductor manufacturing apparatus according to claim 19, wherein a layer mainly composed of the semiconductor and a desired metal is formed on the surface of the exposed semiconductor while maintaining at least a state of not being exposed to the outside air. A semiconductor manufacturing apparatus comprising: 24. A step of forming a first oxide film by oxidizing a surface of the semiconductor in an atmosphere containing the oxygen active species, and a step of exposing the surface of the semiconductor by removing the first oxide film. The step of oxidizing the surface of the semiconductor to form a second oxide film and the step of removing the second oxide film to expose the surface of the semiconductor are performed at least once at least without exposing to outside air. A semiconductor manufacturing apparatus characterized in that the method is performed in an integrated manner. 25. The semiconductor manufacturing apparatus according to claim 19, wherein removing the oxide film and exposing the surface of the semiconductor includes removing the oxide film in a gas phase atmosphere. Characteristic semiconductor manufacturing equipment. 26. The semiconductor manufacturing apparatus according to claim 25, wherein the gaseous phase atmosphere is a gaseous phase atmosphere containing molecules or active species having at least one of F atom, Cl atom, Br atom and I atom. A semiconductor manufacturing apparatus characterized by being used. 27. The method of manufacturing a semiconductor device according to claim 11, wherein the step of oxidizing a surface of the semiconductor in an atmosphere containing the oxygen active species to form an oxide film comprises:
A method for manufacturing a semiconductor device, wherein the method is performed at a temperature exceeding 550 ° C. 28. The semiconductor manufacturing apparatus according to claim 19, wherein the step of oxidizing a surface of the semiconductor in an atmosphere containing the oxygen active species to form an oxide film is performed.
A semiconductor manufacturing apparatus characterized by performing at a temperature exceeding ℃. 29. Claims 1 to 5 and 11
17. The method of manufacturing a semiconductor device according to claim 16,
The method for manufacturing a semiconductor device, wherein the oxygen active species is mainly composed of an oxygen atom radical whose excited state is a singlet state. 30. The semiconductor manufacturing apparatus according to claim 6, wherein the oxygen active species is mainly composed of an oxygen atom radical whose excited state is a singlet state. Characteristic semiconductor manufacturing equipment. 31. An oxidizing gas containing an oxygen atom radical in a singlet state as an excited state as a main component is supplied to a silicon layer.
A method for manufacturing a semiconductor device, comprising oxidizing a surface thereof to form a silicon oxide film. 32. The method for manufacturing a semiconductor device according to claim 28, wherein the oxygen source gas has a wavelength of 175 nm.
A method for manufacturing a semiconductor device, comprising irradiating light of m or less to generate oxygen atom radicals in the singlet state. 33. The method of manufacturing a semiconductor device according to claim 28, wherein the singlet state oxygen is irradiated by irradiating a plasma atmosphere of a gas containing a molecule having an oxygen atom with light having a wavelength of 175 nm or less. A method for manufacturing a semiconductor device, characterized by generating atomic radicals. 34. The method of manufacturing a semiconductor device according to claim 33, wherein said plasma atmosphere is divided into a plasma generation region and an oxidation region. 35. The method of manufacturing a semiconductor device according to claim 28, wherein the generation efficiency of the singlet-state oxygen atom radical is reduced to a triplet state in a gas atmosphere containing a molecule having an oxygen atom. A method for manufacturing a semiconductor device, comprising irradiating light having a wavelength higher than that of an atomic radical to generate the oxygen atom radical in the singlet state. 36. The method of manufacturing a semiconductor device according to claim 28, wherein the oxidizing source gas containing the singlet-state oxygen atom radicals converts the singlet-state oxygen atom radicals into a triplet-state oxygen atom radical. The rate constant of the reaction for deactivating oxygen radicals is 4 × 10 ¹¹ c at a temperature of 298K.
A method for manufacturing a semiconductor device, comprising gas molecules of less than m ³ mol ⁻¹ s ⁻¹ . 37. The method of manufacturing a semiconductor device according to claim 28, wherein the atmosphere containing dinitrogen monoxide gas is irradiated with light having a wavelength of 341 nm or less to convert the oxygen atom radicals in the singlet state. A method for manufacturing a semiconductor device, comprising: 38. The method of manufacturing a semiconductor device according to claim 28, wherein the oxidation is performed under a condition that a partial pressure of oxygen molecules in the oxidation source gas is 10 Torr or less and an oxidation temperature is 550 ° C. or less. A method for manufacturing a semiconductor device, comprising: 39. An oxide film formed by oxidizing the surface of a semiconductor layer in an atmosphere containing oxygen active species at a temperature exceeding 550 ° C., and an interface between the semiconductor layer and the oxide film is flat at an atomic level. A semiconductor device having a degree. 40. A silicon oxide film formed by oxidizing a surface of a silicon layer supplied with an oxidizing gas mainly containing oxygen atom radicals in an excited state as a singlet state. A semiconductor device, wherein an interface with a silicon oxide film has an atomic level flatness.