JPH11176828A - Method of forming silicon oxide film - Google Patents

Abstract

(57) Abstract: In a method for forming a silicon oxide film, the roughness of an SiO ₂ / Si interface of a thermal oxide film at the atomic level is reduced. SOLUTION: As a pretreatment of a step of thermally oxidizing a silicon substrate 1 to form a silicon oxide film 4, a protective oxide film 3 is formed on a surface of the silicon substrate 1 having a flat surface 2 at an atomic level.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a silicon oxide film, and more particularly, to a MOS (Metal) method.
The present invention relates to a method for forming a silicon oxide film for forming a gate oxide film having a flat SiO ₂ / Si interface in an oxide semiconductor (semiconductor) type semiconductor device.

[0002]

2. Description of the Related Art At present, as a gate insulating film in a MOS type semiconductor device centering on a semiconductor memory such as a DRAM (Dynamic Random Access Memory), a silicon thermal insulating film formed by thermally oxidizing the surface of a silicon substrate is used. An oxide film is used.

As a general method for forming such a silicon thermal oxide film, first, the surface of a silicon substrate on which a MOSFET is formed is subjected to RCA cleaning (if necessary, W. Kern
and D. A. Puotinen, RCA Revi
ew vol. 31, p. 187, 1970), and then heat-treating in a dry oxygen atmosphere or a steam atmosphere at normal pressure to thermally oxidize the surface of the silicon substrate.

[0004] Incidentally, the RCA cleaning is a cleaning method of silicon wafers that have been developed by RCA Corp., NH ₄ O
H Washing with a mixed solution of H ₂ O ₂ and H ₂ O ₂ , or acid washing with a mixed solution of HCl and H ₂ O ₂ , and may include acid washing with a mixed solution of H ₂ SO ₄ and H ₂ O _2. .

[0005]

However, in recent years, MOS
Atomic level structures at the SiO ₂ / Si interface have begun to become a problem as gate oxide films become thinner with the progress of high integration and miniaturization of semiconductor devices.

Particularly, when a thermal oxide film is formed in a dry oxygen atmosphere after a conventional pretreatment by chemical cleaning, SiO ₂
/ Si interface is known to cause atomic level roughness (if necessary, T. Ohmi, M. Miyashi)
ta, and T.S. Imoka, Proceedin
gs of the Microcontaminate
ion Meeting, San Jose, Cali
Fornia, 1991), this atomic level roughness affects the electrical characteristics of MOS devices.

Accordingly, the present invention provides a method of forming a thermal oxide
It is intended to reduce atomic level roughness of the ₂ / Si interface.

[0008]

FIG. 1 is an explanatory view of the principle configuration of the present invention. Referring to FIG. 1, means for solving the problems in the present invention will be described. 1 (a) to 1 (c) (1) The present invention relates to a method for forming a silicon oxide film,
As a pretreatment before the step of thermally oxidizing the silicon substrate 1 to form the silicon oxide film 4, a protective oxide film 3 is formed on the surface of the silicon substrate 1 having the flat surface 2 at the atomic level.

As described above, an atomically flat silicon substrate
By forming a thin protective oxide film 3 on the surface of the plate 1,
To form silicon oxide film 4 by thermal oxidation.
iO _TwoTo maintain the atomic level flatness of the Si / Si interface
And prevent adverse effects on the electrical characteristics of semiconductor devices
be able to.

(2) In the present invention, the protective oxide film 3 according to the above (1), wherein the substrate temperature of the silicon substrate 1 is 500 to 7
The oxide film is formed by thermally oxidizing the surface of the silicon substrate 1 at a temperature of 00 ° C.

As described above, the protective oxide film 3 is preferably an oxide film formed by thermally oxidizing the surface of the silicon substrate 1 at a low temperature of 500 to 700.degree. That is, 5
00 ° C. In the following, rather than a practical process because the growth rate slows down, and in 700 ° C. or higher, the oxygen pressure currently used (normal pressure), the surface of the silicon substrate 1, SiO ₂ + Si → 2SiOエ ッ チ ン グ causes a problem that the interface after growth is roughened.

(3) In the present invention according to (1) or (2), in order to form a flat surface 2 at the atomic level, the silicon substrate 1 is formed prior to the step of forming the protective oxide film 3. It is characterized in that the surface is flattened.

As described above, in order to obtain a flat surface 2 at the atomic level with good reproducibility, it is preferable to perform a flattening process on the surface of the silicon substrate 1.

(4) The present invention is characterized in that, in the above (3), the flattening process is a flattening method in which the silicon substrate 1 is heat-treated at a temperature of 900 to 1200 ° C. in a vacuum. .

As such a flattening method, a flattening method in which the silicon substrate 1 is heat-treated in a vacuum at a temperature of 900 to 1200 ° C. is preferable. Thereby, a flat surface 2 at the atomic level can be obtained.

(5) In the present invention according to (3), the flattening is performed by forming a flat hydrogen-terminated surface on the surface of the silicon substrate 1 by a solution process, and then performing a heat treatment in a vacuum. It is a flattening method for removing hydrogen from the terminal surface.

As described above, as a planarization method, a specific crystal plane, that is, the main surface of the Si substrate is preferentially exposed and flattened by a solution treatment, and a dangling bond of Si atoms on the surface is formed. A step of forming a hydrogen-terminated surface to which hydrogen atoms are bonded may be used. In this case, in order to prevent a reduction in the oxidation rate in the next oxidation step, hydrogen is released by a heat treatment before the step of forming the protective oxide film 3. There is a need.

(6) The present invention is characterized in that, in the above (5), the temperature in the heat treatment is 550 to 700 ° C.

As described above, since the heat treatment temperature for desorbing hydrogen is sufficient at 550 to 700 ° C., the pretreatment can be performed at a lower temperature of about 400 ° C. than the flattening method of (4). .

(7) The present invention is characterized in that, in the above (3), the flattening treatment is a flattening method of providing an epitaxial growth layer on the surface of the silicon substrate 1.

As described above, the flattening method may be a step of depositing an epitaxially grown layer. By providing a thin epitaxially grown layer, the surface of the silicon substrate 1 can be flattened at the atomic level by the epitaxially grown layer.

(8) Further, according to the present invention, before providing the epitaxial growth layer in the above (7), the silicon substrate 1
A thin chemical oxide film is formed on the surface of the substrate by solution processing, and then heat treatment is performed in a vacuum to thermally desorb the chemical oxide film.

As described above, when an epitaxial growth layer is deposited, a thin chemical oxide film is formed on the surface of the silicon substrate 1 by solution processing, for example, the above-mentioned RCA cleaning before the deposition of the epitaxial growth layer. It is necessary to perform heat treatment in the inside to thermally desorb the chemical oxide film. However, since the heat treatment temperature in this case is about 850 ° C., it is lower at about 150 ° C. than the flattening method of (4). Preprocessing becomes possible.

(9) The present invention is characterized in that in any one of the above (1) to (8), the silicon oxide film 4 is a gate oxide film.

As described above, by applying the step of forming the silicon oxide film 4 of the present invention to the step of forming the gate oxide film of the MOSFET, the electrical characteristics of the miniaturized MOSFET can be made uniform and the high integration can be achieved. The reliability of the MOS semiconductor device can be improved.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Here, a first embodiment of the present invention will be described with reference to FIGS. 2 to 5. Here, for the sake of simplicity, a general silicon oxide film will be described. This will be described as a forming step. FIG. 2 is an explanatory diagram of a manufacturing process according to the first embodiment of the present invention, and FIG. 3 is an explanatory diagram of a surface state of the substrate according to the first embodiment of the present invention. FIG. 4 is an explanatory view of the surface state of a substrate in a comparative example manufactured to show the function and effect of the present invention. FIG.
1) It is explanatory drawing of the process dependence of a spot distribution.

Referring to FIG. 2A, first, a silicon substrate 11 having a (111) plane as a main surface is H
The ₂ mixed solution of SO ₄ and H ₂ O ₂ was chemically cleaned to remove metal contamination and organic surfaces of the silicon substrate 11, followed by a 1% HF aqueous solution, H ₂ SO ₄ and H
After removing an oxide film formed by chemical cleaning with a mixed solution of ₂ O ₂ and metal contamination in the oxide film, NH ₄ O
Particles (dust) are removed by chemical cleaning with a solution consisting of H: H ₂ O ₂ : H ₂ O.

As shown in the figure, a thin oxide film 12 remains on the surface of the silicon substrate 11 after the chemical cleaning, and an interface between the oxide film 12 and the silicon substrate 11, that is, an SiO ₂ / Si interface. Has roughness indicated by irregularities. The surface roughness of the silicon substrate 11 is present when the wafer is purchased, and the roughness is increased by the above-described chemical cleaning.

Next, as shown in FIG. 2B, the silicon substrate 11 is placed in a 1 × 1 through a vacuum introduction chamber.
Higher vacuum than 0 ^-9 Torr, for example, 5 × 10 ^-10 To
rr is introduced into a vacuum processing apparatus, and the silicon substrate 1
Is raised to 900 to 1200 ° C., for example, 1100 ° C., and heat-treated for 1 to 60 seconds, for example, 30 seconds to flatten the surface of the silicon substrate 11.

By this flattening process, the silicon substrate 1
The oxide film 12 on the surface of the substrate 1 is removed by sublimation, and the Si atoms of the silicon substrate 11 are selectively evaporated from the step, so that a flat terrace region 14 sandwiched by one atomic step 13 is formed. (For the heat treatment in vacuum, if necessary, see Booth, Yagi, Tsukada, Aono, ed., Surface Physical Properties Engineering Handbook, published by Maruzen Co., Ltd.).

Further, by such a heat treatment at 1100 ° C., active Si atoms on the surface of the silicon substrate 11 are moved and reconstructed, thereby exhibiting a Si (111) -7 × 7 structure. . Note that this Si (111) -7 × 7 structure means (111)
It means a lattice structure that is seven times (7 × 7) the ideal lattice state of the surface.

Subsequently, oxygen is introduced into the vacuum processing apparatus, and the degree of vacuum is set to 1 × 10 ^-6 to 1 × 10 ^-3 Torr, for example, 2 × 10 Torr.
^Under the condition of ⁻⁶ Torr, the temperature of the silicon substrate 11 is lowered to 500 to 700 ° C., for example, 630 ° C., and then heat-treated for 1 to 30 minutes, for example, 10 minutes to obtain 0.3 to 1.0 nm. For example, a protective oxide film 15 having a thickness of 0.3 nm is formed. Note that this protective oxide film 1
The film thickness of No. 5 was confirmed by measurement by X-ray excitation photoelectron spectroscopy.

Next, after the silicon substrate is once taken out into the atmosphere, as shown in FIG.
Put in a quartz heating furnace at normal pressure, that is, 760 Torr, and in a dry oxygen atmosphere, at 800 to 1000 ° C., for example, 900
By performing heat treatment at a temperature of 1 to 200 minutes, for example, 140 minutes, a silicon oxide film 16 having a thickness of 3 to 50 nm, for example, 48 nm is formed on the surface of the silicon substrate 11.
To form

Next, the surface condition of the substrate according to the first embodiment of the present invention will be described with reference to FIG. FIG. 3 (a) is a simulated SREM (scanning reflection electron microscope) image of the surface of the silicon substrate 11 after the planarization process. , The flat terrace region 14 interposed between the atomic steps 13 indicates that a clean and flat surface is obtained by the above-described flattening process.

Referring to FIG. 3B, FIG. 3B shows 1% HF for observing the surface state of the silicon substrate 11 after the formation of the silicon oxide film 16, that is, the SiO ₂ / Si interface state. SRE when silicon oxide film 16 is thinned to 1 nm or less using a solution
It is a reproduction of the M image, and it is observed that the stripe pattern of the atomic step 13 having substantially the same pattern as that of FIG. 3A is retained.
When 5 was provided as a pretreatment in the thermal oxidation step, the state of the SiO ₂ / Si interface after thermal oxidation was flat and no roughness was found.

When the SREM is used, the surface roughness of the terrace region 14 is at the atomic level in view of the fact that the atomic step 13 which is a step of one atom can be observed.
It is understood that it is very flat. Such a surface state can be observed in all the examples in which the thickness of the silicon oxide film 16 is set to 48 nm or less.

Here, in order to compare and confirm the effects of the present invention, the step of forming the protective oxide film 15 shown in FIG. 2C is omitted, and after leaving it in the air for 15 hours, thermal oxidation is performed. Therefore, the surface state of the substrate of this comparative example will be described with reference to FIG. By leaving the substrate in the air for 15 hours, an oxide film having a thickness of about 0.3 nm is formed on the surface of the silicon substrate 11.

FIG. 4A is a simulated SREM image of the surface of the silicon substrate 11 after the flattening process. The surface is composed of atomic steps 13 and flat terrace regions 14. This indicates that a flat surface is obtained as in the first embodiment of the present invention.

Referring to FIG. 4B, FIG. 4B shows 1% HF in order to observe the surface state of the silicon substrate 11 after the formation of the silicon oxide film 16, that is, the SiO ₂ / Si interface state. SRE when silicon oxide film 16 is thinned to 1 nm or less using a solution
It is a copy of the M image, and the whole is mottled,
It is difficult to observe the atomic steps 13 on the initial surface in FIG.

Therefore, in the case of this comparative example, since it is difficult to observe the atomic steps 13 and the terrace region 14, it can be said that the roughness in the terrace region 14 has increased to such an extent that it cannot be distinguished from the atomic steps 13.

Here, in order to examine the roughness of the SiO ₂ / Si interface in more detail, RHEED (reflection high-speed electron diffraction) is used.
(1, 1) spot profile was measured, and will be described with reference to FIG. FIG. 5 also shows, for comparison, a conventional example in which thermal cleaning is performed without performing a planarization process and a process of forming another protective film after performing chemical cleaning, as in the related art.

FIG. 5 shows the profile of the (1,1) diffraction spot. Position on the horizontal axis shows the position of the pixel of the CCD camera. The peak near 300 corresponds to the (1,1) diffraction corresponding to the substrate vertical component.

In such a profile of the (1,1) diffraction spot, the position from the peak near the position 300 to the position where the position approaches 0 is a streak.
Is shorter, that is, the narrower the width of the diffraction intensity distribution is, the better the flatness of the surface is. Therefore, it is understood that the surface roughness increases in the order of the present invention, the comparative example, and the conventional example. Is done.

As described above, in the first embodiment of the present invention, the step of forming a thin protective oxide film is performed as a pretreatment for the thermal oxidation step, following the planarization processing step by high-temperature heat treatment in vacuum. As a result, a silicon oxide film having a flat interface can be formed.

The flattening process is performed at a high temperature in a vacuum.
Since it is not limited to the heat treatment step, next, referring to FIG.
A second embodiment of the present invention will be described. Referring to FIG. 6A, first, as in the first embodiment, the (111) plane
The silicon substrate 11 whose main surface is H_TwoSO_FourAnd H_TwoO_Two
Chemical cleaning with a mixed solution of
To remove metallic and organic contamination of the surface, then 1% H
Chemical cleaning with an aqueous solution of F_TwoSO_FourAnd H_TwoO_Twoof
An oxide film formed by chemical cleaning with a mixed solution; and
After removing metal contamination in the oxide film, NH 3_FourOH: H_Two
O_Two: H _TwoParty after chemical cleaning with a solution consisting of O
Removes dust (dust).

Next, the silicon substrate 11 is made 1 to 40%,
For example, by dipping in a 40% NH ₄ F solution for 1 to 10 minutes, for example, 5 minutes, hydrogen atoms 18 are bonded to dangling bonds 17 of Si atoms on the surface of the silicon substrate 11 to terminate the hydrogen. Form a surface.

The treatment in this NH ₄ F solution (if necessary, GS Higashi, et al., Ap.
plied Physics Letters, vo
l. 56, p. 659, 1990), the oxide film on the surface of the silicon substrate 11 is removed by etching, and the surface of the silicon substrate 11 is etched so that the (111) plane appears preferentially. , A flat surface is obtained. In this case, since the high-temperature treatment has not been performed, the surface structure is considered to be a Si (111) -1 × 1 structure.

Next, as shown in FIG. 6B, the silicon substrate 11 on which the hydrogen-terminated surface was formed was kept at 1 × 10 ^{-8 to} 5 × 10 ^-11 Torr, for example, 5 × 10 ^-10 through a vacuum introduction chamber. Introduced into vacuum processing equipment,
The silicon substrate 11 is heated to 550-700 ° C., for example, 600
At a temperature of 1 ° C., heat treatment is performed for 1 to 5 minutes, for example, 1 minute, so that hydrogen atoms 18 on the surface of the silicon substrate 11 are heated.
Is detached. In this step, hydrogen atoms 18
Is performed because the oxidation rate becomes slower in the next step of forming the protective oxide film 15 at a low temperature when the oxide semiconductor film is present.

Next, as in the first embodiment, oxygen is introduced into the vacuum processing apparatus to reduce the degree of vacuum from 1 × 10 ⁻⁶ to 1 ×, as in the first embodiment.
In a state of 10 ⁻³ Torr, for example, 2 × 10 ⁻⁶ Torr, the substrate temperature of the silicon substrate 11 is set to 500 to 700.
° C, for example, after cooling to 630 ° C,
For example, 0.3-
A protective oxide film 1 having a thickness of 1.0 nm, for example, 0.3 nm
5 is formed.

Next, after the silicon substrate is once taken out into the atmosphere,
Put in a quartz heating furnace at normal pressure, that is, 760 Torr, and in a dry oxygen atmosphere, at 800 to 1000 ° C., for example, 900
By performing heat treatment at a temperature of 1 to 200 minutes, for example, 140 minutes, a silicon oxide film 16 having a thickness of 3 to 50 nm, for example, 48 nm is formed on the surface of the silicon substrate 11.
To form

In the second embodiment, the heat treatment temperature of the planarization process, that is, the temperature in the hydrogen desorption step is 550 to 700 ° C., so that the temperature is 400 ° C. in comparison with the first embodiment. A low temperature treatment is possible, and therefore, it is desirable as a pretreatment for a silicon substrate on which an impurity diffusion layer has already been formed.

However, since the oxide film is also etched in the solution processing for forming the hydrogen-terminated surface, the LOCOS
(Local Oxidation of Silic
on) Since there is a problem that a device structure such as a structure is etched, it is inappropriate when etching of the device structure is disliked.

In the second embodiment,
Since the (111) silicon substrate is used as the substrate, the flattening process is performed by the treatment in the NH ₄ F solution and the hydrogen desorption treatment. However, the substrate is limited to the (111) silicon substrate. Instead, a silicon substrate having a (100) plane as a main surface may be used.

When a (100) silicon substrate is used, a mixed solution of HF and H ₂ O ₂ may be used instead of the treatment in an NH ₄ F solution (if necessary, C.I.
H. Bjorkman, et al. , Japanes
e Journal of Applied Physi
cs, vol. 34, p. 722, 1995), H
F: H ₂ O ₂ = 1: 8 to 1:20, for example, using a solution having a volume ratio of 1:12, the silicon substrate may be immersed for 1 to 10 minutes, for example, 5 minutes, and subsequent hydrogen desorption The steps and the like may be performed in the same manner.

Next, with reference to FIG. 7, a third embodiment of the present invention in which an epitaxial growth step is employed as a planarization processing step will be described. First, the silicon substrate 11 having the (111) plane as a main surface is H
130 ° C. with a mixed solution of ₂ SO ₄ : H ₂ O ₂ = 5: 1
For 10 minutes to remove metal and organic contamination on the surface of the silicon substrate 11, and then NH ₄ O
After removing particles (dust) by chemical cleaning at 80 ° C. for 10 minutes with a solution consisting of H: H ₂ O ₂ : H ₂ O = 1: 2: 4, HCl: H ₂ O ₂ : H ₂ O = 1. : 2: 4
Is chemically washed at 80 ° C. for 10 minutes. In this step, a chemical oxide film 19 mainly composed of SiO ₂ and having a thickness of about 1 nm is formed on the surface of the silicon substrate.

Next, as shown in FIG. 7B, the silicon substrate 11 was placed in a 5 × 1
The silicon substrate 11 is introduced into a vacuum processing apparatus maintained at 0 ⁻⁸ to 1 × 10 ⁻¹⁰ Torr, for example, 2 × 10 ⁻⁹ , and
At a temperature of 0 to 900 ° C, for example, 850 ° C,
After sublimating the chemical oxide film 19 on the surface of the silicon substrate 11 by performing a heat treatment for 10 minutes, for example, 5 minutes,
The silicon substrate 11 is introduced into a vapor phase growth apparatus, and Si ₂ H
By a thermal decomposition method using _6, at a substrate temperature of 800 to 900 ° C., for example, 850 ° C., a thickness of 5 to 50 nm,
For example, a 10 nm silicon epitaxial growth layer 20
Is grown to planarize the surface of the silicon substrate 11.

Subsequently, as shown in FIG. 7C, the silicon substrate 11 is introduced into a vacuum processing apparatus in the same manner as in the first embodiment, and
After the substrate temperature is set to 500 to 700 ° C., for example, 630 ° C., oxygen is introduced into the vacuum processing apparatus to reduce the degree of vacuum to 1
× 10 ^-6 to 1 × 10 ^-3 Torr, for example, 2 × 10 ^-6 T
In the state of orr, heat treatment is performed for 1 to 30 minutes, for example, 10 minutes, so that 0.3 to 1.0 nm, for example,
A protective oxide film 15 having a thickness of 0.3 nm is formed.

Next, after the silicon substrate is once taken out into the atmosphere,
Put in a quartz heating furnace at normal pressure, that is, 760 Torr, and in a dry oxygen atmosphere, at 800 to 1000 ° C., for example, 900
By performing heat treatment at a temperature of 1 to 200 minutes, for example, 140 minutes, a silicon oxide film 16 having a thickness of 3 to 50 nm, for example, 48 nm is formed on the surface of the silicon substrate 11.
To form

In the third embodiment, the heat treatment temperature for the planarization process, that is, the temperature in the chemical oxide film removing step and the epitaxial growth step is 800 to 900 ° C.
Therefore, compared with the first embodiment,
A low temperature treatment is possible. However, a vapor phase epitaxial growth apparatus is required.

In the thermal oxidation step for forming the silicon oxide film 16 in this case, the entire silicon epitaxial growth layer 20 may be thermally oxidized, or
When the thickness of the silicon epitaxial growth layer 20 is large, a part thereof may be oxidized.

Although the embodiments of the present invention have been described above, in any case, when forming a thermal oxide film on a flattened silicon substrate surface, a thin protective oxide film, particularly, By forming the protective oxide film by thermal oxidation at a low temperature of 500 to 700 ° C., thermal oxidation proceeds while maintaining the surface flatness at the atomic level.
An iO ₂ / Si interface can be formed.

The protective oxide film is not necessarily limited to a thermal oxide film, but may be a CVD-SiO ₂ film formed by a CVD method, for example, SiH ₄ and N _2.
O 2 was used as a source gas and vapor-phase grown at a low temperature of about 400 to 600 ° C. under a pressure of about 1 × 10 ⁻⁴ Torr;
An SiO ₂ film having a thickness of 1 nm or less, more preferably 1 nm or less, may be used.

In the above three embodiments, the first embodiment is superior in terms of the simplicity of the process and the apparatus, and the viewpoint of lowering the processing temperature although etching of the oxide film occurs. Therefore, the second embodiment is excellent, and although the epitaxial growth apparatus is required, the third embodiment is excellent in that the oxide film is not etched and low-temperature processing can be performed. .

Further, in each of the above embodiments, for the sake of simplicity, the description is made as a general process of forming a silicon oxide film.
This step is applied when forming a gate oxide film in a device formation region of a silicon substrate after forming an element isolation oxide film by the process, but is not limited to the gate oxide film.

[0065]

According to the present invention, when a thermal oxide film is formed on the surface of a flattened silicon substrate, a protective oxide film is formed at a low temperature as a pretreatment, so that a flat SiO ₂ film is formed.
/ Si interface can be formed, whereby the interface of the gate oxide film of the miniaturized MOSFET can be made flat at the atomic level, and the reliability of the highly integrated semiconductor integrated circuit device can be improved. .

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a basic configuration of the present invention.

FIG. 2 is an explanatory diagram of a manufacturing process according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a surface state of a substrate according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram of a surface state of a substrate in a comparative example.

FIG. 5 is an explanatory diagram of processing dependency of a (1,1) spot distribution of RHEED.

FIG. 6 is an explanatory diagram of a manufacturing process according to a second embodiment of the present invention.

FIG. 7 is an explanatory diagram of a manufacturing process according to a third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 silicon substrate 2 flat surface at atomic level 3 protective oxide film 4 silicon oxide film 11 silicon substrate 12 oxide film 13 atomic step 14 terrace region 15 protective oxide film 16 silicon oxide film 17 dangling bond 18 hydrogen atom 19 chemical oxide film 20 Silicon epitaxial growth layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Noriyuki Miyata 4-1-1, Kamidadanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Masakazu Ichikawa 1-280-1, Higashi Koigakubo, Kokubunji-shi, Tokyo Within Hitachi Central Research Laboratory (72) Inventor Heiji Watanabe 5-7-1 Shiba, Minato-ku, Tokyo Within NEC Corporation

Claims (9)

[Claims] 1. A method according to claim 1, wherein a protective oxide film is formed on a surface of said silicon substrate having a flat surface at an atomic level, as a pretreatment before a step of thermally oxidizing the silicon substrate to form a silicon oxide film. A method for forming an oxide film. 2. The method according to claim 1, wherein the protective oxide film is an oxide film formed by thermally oxidizing a surface of the silicon substrate while keeping a substrate temperature of the silicon substrate at 500 to 700 ° C. 2. The method for forming a silicon oxide film according to claim 1. 3. The method according to claim 1, wherein the surface of the silicon substrate is flattened prior to the step of forming a protective oxide film in order to form the flat surface at the atomic level. Of forming a silicon oxide film. 4. The method for forming a silicon oxide film according to claim 3, wherein the flattening process is a flattening method in which the silicon substrate is heat-treated at a temperature of 900 to 1200 ° C. in a vacuum. 5. The planarization method according to claim 1, wherein a flat hydrogen-terminated surface is formed on the surface of the silicon substrate by a solution process, and then heat treatment is performed in a vacuum to remove hydrogen from the hydrogen-terminated surface. 4. The method for forming a silicon oxide film according to claim 3, wherein: 6. The temperature in the heat treatment is 550-7.
6. The method for forming a silicon oxide film according to claim 5, wherein the temperature is 00.degree. 7. The method for forming a silicon oxide film according to claim 3, wherein said flattening treatment is a flattening method of providing an epitaxial growth layer on a surface of said silicon substrate. 8. A method of forming a thin chemical oxide film on a surface of the silicon substrate by a solution process before providing the epitaxial growth layer, and then performing a heat treatment in a vacuum to thermally desorb the chemical oxide film. The method for forming a silicon oxide film according to claim 7. 9. The method for forming a silicon oxide film according to claim 1, wherein said silicon oxide film is a gate oxide film.