JP2000022149A - Semiconductor device and manufacturing method thereof - Google Patents

Abstract

(57) Abstract: A semiconductor device having a dual gate electrode and a method of manufacturing the same, wherein boron is prevented from escaping from a P ⁺ gate without lowering the driving capability of an N-type MOS transistor, and a gate is prevented. Provided are a semiconductor device capable of improving the reliability of an insulating film and a method for manufacturing the same. A silicon substrate and a silicon substrate are provided.
A gate insulating film formed on the gate insulating film;
A semiconductor device is constituted by a gate electrode 30 formed thereon and having a silicon film 26 at least on a surface in contact with the gate insulating film 18 and a nitrogen segregation layer having a peak concentration near an interface between the silicon film 26 and the gate insulating film 18. I do.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device having a dual gate electrode and a method of manufacturing the same,
The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device, which suppress heat loss of boron from a P ⁺ gate and a decrease in driving capability of an N-type transistor.

[0002]

2. Description of the Related Art With the recent miniaturization and speeding up of semiconductor devices, P ⁺
A polysilicon film (hereinafter referred to as a P ⁺ gate) is
The gate electrode of the OS transistor N ⁺ polysilicon film (hereinafter, referred to as N ⁺ gate) is used, so-called dual gate electrode is being used.

[0003] Although boron (B) is widely used as a dopant in the P ⁺ gate, the diffusion constant of boron is large, so that boron in the gate electrode diffuses into the silicon substrate in the channel region through the gate insulating film by a heat treatment in a later step. So-called heat loss is a problem. When heat is released from boron, the impurity concentration in the silicon substrate in the channel region changes, which causes deterioration in characteristics such as fluctuation in threshold voltage.

It is known that the heat release of boron from the P ⁺ gate can be reduced by introducing nitrogen into the gate insulating film. Therefore, by forming a gate insulating film using NO, N ₂ O, and NH ₃ , or performing heat treatment in an atmosphere of these gases after forming the gate insulating film,
2. Description of the Related Art A gate oxide film made of a silicon oxynitride film containing about several percent of nitrogen in the film is formed to prevent heat from being released from boron. However, when a gate insulating film made of a silicon oxynitride film is formed by, for example, a thermal oxidation method using N ₂ O, as shown in FIG. 15, the introduced nitrogen segregates at the interface between the silicon substrate and the gate insulating film. And
The driving capability of the N-type MOS transistor may decrease due to an increase in the interface state due to nitrogen.

Also, SV Hattangady et al. Perform a nitrogen plasma treatment after forming a gate oxide film in order to suppress such a decrease in the driving capability of an N-type MOS transistor.
A method has been proposed to segregate nitrogen at the interface between the gate oxide film and the gate electrode (eg, "Ultrathin nitrogen-profil").
e engineered gate dielectric films ", IEDM Technica
l See Digest (1996) p.495. ). However, if the nitrogen plasma treatment is performed after the formation of the gate insulating film, there is a possibility that the gate insulating film may be broken or damaged by the charge-up due to the plasma, which is not preferable from the viewpoint of reliability.

Further, a method of preventing heat from being released from boron by implanting nitrogen ions and performing heat treatment after the formation of the gate electrode, and a method of using a silicon source gas such as SiH ₄ gas at the initial stage of depositing a silicon film serving as a gate electrode. N to Si ₂ H ₆
A method of forming a gate electrode by mixing H ₃ gas and forming a heat release preventing layer of boron is also performed. However, in both methods, a region where nitrogen is distributed is wide, and a part of the electrode where nitrogen is distributed is used. The activation of boron is hindered and the electrode is depleted,
Eventually, the electrical equivalent film thickness of the gate insulating film is increased, and the driving capability of the transistor is sometimes reduced.

[0007]

As described above, according to the conventional method of manufacturing a semiconductor device, when nitrogen is introduced to prevent heat from being released from boron from the P ⁺ gate, the nitrogen reaches the silicon substrate interface and becomes N-type. When the driving capability of the MOS transistor is reduced, or when nitrogen is introduced by performing a nitrogen plasma process, the gate oxide film is broken or damaged by charge-up due to the plasma, which is disadvantageous.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor device capable of preventing heat from being released from boron from a P ⁺ gate without lowering the driving capability of an N-type MOS transistor and improving the reliability of a gate insulating film. It is to provide a manufacturing method.

[0009]

The object of the present invention is to provide a silicon substrate, a gate insulating film formed on the silicon substrate, and a silicon film formed on the gate insulating film and having at least a surface in contact with the gate insulating film. And a first nitrogen segregation layer having a peak concentration near an interface between the silicon film and the gate insulating film. By configuring the semiconductor device in this manner, it is possible to prevent heat from leaking from the gate electrode without deteriorating the driving capability of the N-type MOS transistor.

The object of the present invention is to form a gate insulating film on a silicon substrate, and to form a first insulating film on the gate insulating film.
Forming a silicon film, and segregating nitrogen at an interface between the first silicon film and the gate insulating film. By manufacturing a semiconductor device in this manner, heat can be prevented from leaking from the gate electrode.

In the method of manufacturing a semiconductor device, in the step of segregating nitrogen, nitrogen is introduced from a surface of the first silicon film by annealing the silicon substrate in a gas atmosphere containing nitrogen. , The first
Nitrogen may be segregated at the interface between the silicon film and the gate insulating film. By manufacturing the semiconductor device in this manner, nitrogen can be segregated at the interface between the first silicon film and the gate insulating film without segregating at the interface between the silicon substrate and the gate insulating film. Therefore, N-type MO
It is possible to prevent boron from leaking out of the gate electrode without lowering the driving capability of the S transistor. In addition, since the gate insulating film is not exposed to plasma in the above method, the reliability of the gate insulating film can be improved.

In the method of manufacturing a semiconductor device, in the step of segregating nitrogen, the silicon substrate is annealed after introducing nitrogen into a surface region of the first silicon film, and the first silicon film is annealed. Nitrogen may be segregated at the interface between the gate insulating film and the gate insulating film. By manufacturing the semiconductor device in this manner, nitrogen can be segregated at the interface between the first silicon film and the gate insulating film without segregating at the interface between the silicon substrate and the gate insulating film. Therefore, it is possible to prevent boron from leaking from the gate electrode without lowering the driving capability of the N-type MOS transistor.

In the method of manufacturing a semiconductor device, in the step of segregating nitrogen, the silicon substrate is exposed to a plasma containing nitrogen to introduce nitrogen into a surface region of the first silicon film. Is also good. In this method, the first silicon film is formed on the gate insulating film, and the charge can be released from the edge of the substrate even when nitrogen is introduced by plasma. Nitrogen can be introduced while preventing the increase.

In the above-described method for manufacturing a semiconductor device, the method may further include, after the step of segregating nitrogen, a step of forming a second silicon film on the first silicon film. By manufacturing the semiconductor device in this manner, even when the thickness of the silicon film forming the gate electrode is large, a sufficient concentration of nitrogen can be segregated at the interface between the gate electrode and the gate insulating film. it can.

The object of the present invention is to form a gate insulating film on a silicon substrate and to form a first insulating film on the gate insulating film.
Forming a silicon film, and segregating nitrogen at an interface between the first silicon film and the gate insulating film to form a silicon oxide film on the first silicon film.
Forming a second silicon film on the first silicon film, introducing impurities into the first silicon film and the second silicon film, and forming the second silicon film on the first silicon film. The method is also achieved by a method for manufacturing a semiconductor device, comprising: a step of etching using an oxide film as a stopper; and a step of etching the silicon oxide film. By manufacturing a semiconductor device in this manner, a highly doped thin silicon film can be easily formed on a gate insulating film. Further, since the silicon oxide film formed when introducing nitrogen can be used as the stopper film used for etching the second silicon film, the number of steps is not increased more than necessary.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Principle of the Invention] In order to prevent heat from being released from boron from a gate electrode, it is effective to introduce nitrogen between the gate electrode and the silicon substrate. Further, in order not to lower the driving capability of the N-type MOS transistor, it is necessary to suppress segregation of nitrogen at the interface between the gate insulating film and the silicon substrate. Therefore, in order to satisfy these requirements, it is considered desirable to segregate nitrogen between the gate electrode and the gate insulating film and not segregate nitrogen at the interface between the gate insulating film and the silicon substrate.

From the above viewpoint, the inventors of the present invention have conducted intensive studies. As a result, after forming a silicon oxide film serving as a gate insulating film and a silicon film serving as a gate electrode on a silicon substrate, annealing is performed in an atmosphere containing nitrogen. It has become clear for the first time that nitrogen can be segregated at the interface between the gate electrode and the gate insulating film without segregating nitrogen at the interface between the gate insulating film and the silicon substrate. It has been found that by introducing nitrogen in this way, heat is prevented from being released from boron from the gate electrode, and the driving capability of the N-type MOS transistor is not deteriorated.

Here, it is extremely important to deposit a silicon film on the gate insulating film before annealing in an atmosphere containing nitrogen in order to segregate nitrogen at the interface between the gate insulating film and the silicon film. Take a role. FIG. 1 shows a sample in which a silicon oxide film having a thickness of about 10 nm and a polysilicon film having a thickness of about 10 nm are formed on a silicon substrate by NH _3.
FIG. 2 is a SIMS profile in the case where annealing is performed at 620 ° C. for 20 minutes in an atmosphere, and then a polysilicon film having a thickness of about 30 nm is further deposited.
Is a SIMS profile obtained when a sample in which a silicon oxide film having a thickness of about 10 nm is formed on a silicon substrate is annealed at 620 ° C. for 20 minutes in an NH ₃ atmosphere, and then a polysilicon film having a thickness of about 40 nm is formed. It is.

As shown in the figure, in the sample (FIG. 2) which was annealed before depositing the polysilicon film even though the annealing was performed at the same processing temperature for the same time, nitrogen introduced into the substrate was used. In the sample (FIG. 1) annealed after depositing the polysilicon film, the concentration of about 1% nitrogen was introduced into the substrate. Segregates at the interface between the silicon oxide film and the silicon oxide film.

Therefore, in order to segregate nitrogen between the gate electrode and the gate insulating film without segregating nitrogen at the interface between the gate insulating film and the silicon substrate, it is necessary to perform annealing before annealing in an atmosphere containing nitrogen. Thus, it is understood that it is important to form a silicon film to be a gate electrode on a gate insulating film made of a silicon oxide film. Note that the silicon film formed over the gate insulating film can exhibit the above-described effects when at least one atomic layer exists. Further, as the silicon film, a polysilicon film or an amorphous silicon film can be used.

In FIG. 1, a nitrogen peak is observed at the interface between the polysilicon film and the silicon oxide film, and a nitrogen peak is also observed in the polysilicon film. It corresponds to the surface of the polysilicon film at the time of introduction. That is, when annealing is performed in an NH ₃ atmosphere, nitrogen is segregated at the interface between the polysilicon film and the silicon oxide film, and at the same time, nitrogen is distributed on the surface of the polysilicon film at the time of annealing.

The gas for introducing nitrogen is NH.
_In addition to ₃ , NO, N ₂ O, NO ₂ , NF ₃ , N (CH ₃ ) _{3 and the} like can also be used. Of these gases, NH ₃
Gas and NO gas have a strong nitriding power and can introduce the same concentration of nitrogen at a lower temperature than other gases, and therefore are preferable in view of a low process temperature. The heat treatment temperature and the heat treatment time for introducing nitrogen are desirably adjusted as appropriate depending on the thickness of the silicon film, the gas used, the amount of nitrogen introduced, and the like. The above effects can be obtained by introducing nitrogen near the interface at a peak concentration of at least about 0.05 to 10%.

It is conceivable to perform ion implantation after depositing the silicon film, or to introduce nitrogen by mixing a gas containing nitrogen during the deposition of the silicon film. The behavior was different from the case where annealing was performed in an atmosphere containing nitrogen to introduce nitrogen. That is, the inventors of the present application have studied and found that in the method of introducing nitrogen by ion implantation or at the time of film formation, even if heat treatment is performed thereafter, nitrogen segregation does not occur and remains widely distributed in the silicon film. As a result, the activation of some boron in the silicon film is hindered, resulting in depletion of the electrode. Although it is not clear why nitrogen cannot be segregated by ion implantation or by a method of introducing nitrogen during film formation, nitrogen is contained in order to segregate nitrogen at the interface between the silicon film and the silicon oxide film. It is considered very important to perform annealing in an atmosphere.

Another method other than the method of annealing in an atmosphere containing nitrogen is to introduce nitrogen to the surface of the silicon film and then perform heat treatment to segregate nitrogen at the interface between the gate electrode and the gate insulating film. it can. For example, after introducing nitrogen to the surface of a silicon film by nitrogen plasma treatment, nitrogen can be diffused by heat treatment to segregate nitrogen at an interface between a gate electrode and a gate insulating film.
In this case, a silicon film is formed on the entire surface of the gate insulating film, and the charge during the nitrogen plasma processing can be released from the edge of the substrate. Therefore, the conventional plasma processing in which the gate insulating film is exposed is performed. The charge-up resistance associated with the plasma processing can be improved as compared with the method.

FIG. 3 shows a film having a thickness of about 1 on a silicon substrate.
A sample having a 0 nm silicon oxide film and a polysilicon film having a thickness of about 40 nm was formed at 920 ° C. for 6 hours in an NH ₃ atmosphere.
SIMS in the case of performing 0 second lamp annealing
Profile. As shown in the figure, even when the thickness of the polysilicon film is relatively thick as 40 nm, nitrogen is segregated at the interface between the polysilicon film and the silicon oxide film by annealing in an NH ₃ atmosphere after depositing the polysilicon film. Can be done.

[First Embodiment] FIGS. 4 to 7 show a semiconductor device and a method for fabricating the same according to a first embodiment of the present invention.
This will be described with reference to FIG. FIG. 4 is a schematic sectional view showing the structure of the semiconductor device according to the present embodiment, and FIGS. 5 to 7 are process sectional views showing the method of manufacturing the semiconductor device according to the present embodiment.

First, the structure of the semiconductor device according to the present embodiment will be explained with reference to FIG. Silicon substrate 10
An element isolation film 12 for defining an element region is formed thereon. An N-well 14 is formed in a P-type MOS transistor formation region in the silicon substrate 10, and a P-well 16 is formed in an N-type MOS transistor formation region. Silicon substrate 1 defined by element isolation film 12
The gate insulating film 1 made of a silicon oxide film
8 are formed. On the gate insulating film 18 in the P-type MOS transistor formation region, a gate electrode 30p made of a P ⁺ polysilicon film is formed. On the gate insulating film 18 in the N-type MOS transistor formation region, a gate electrode 30n made of an N ⁺ polysilicon film is formed. Silicon substrate 1 on both sides of gate electrodes 30p and 30n
In 0, source / drain diffusion layers 32p and 32n are formed.

Here, the semiconductor device according to the present embodiment is
It is characterized by the distribution of nitrogen introduced into the polysilicon films constituting the gate electrodes 30p and 30n. That is, in the semiconductor device according to the present embodiment, the nitrogen is
0p and 30n and segregation at the interface between the gate electrodes 30p and 30n and the gate insulating film 18, but not at the interface between the gate insulating film 18 and the silicon substrate 10 (see FIG. 1). By configuring the semiconductor device in this manner, it is possible to suppress the heat loss of boron from the gate electrodes 30p and 30n, and to prevent the driving capability of the N-type MOS transistor from deteriorating.

Hereinafter, the structure of the semiconductor device according to the present embodiment and the method of manufacturing the semiconductor device will be described in detail along the semiconductor device manufacturing steps. First, the element isolation film 12 embedded in the silicon substrate 10 is formed on the silicon substrate 10 by, for example, a shallow trench method. Next, an N well 14 is formed in the P-type MOS transistor formation region of the silicon substrate 10 by using a lithography technique and an ion implantation technique.
A P well 16 is formed in the type MOS transistor formation region.

Subsequently, a silicon oxide film having a thickness of, for example, about 3.5 nm is formed on the silicon substrate 10 in the element region by a thermal oxidation method. Thus, a gate insulating film 18 made of a silicon oxide film is formed (FIG. 5A). After this,
A polysilicon film 20 having a thickness of about 10 nm is deposited on the entire surface by, for example, a thermal CVD method using SiH ₄ gas (FIG. 5B). The substrate temperature is, for example, 620 ° C.
The polysilicon film 20 is for segregating nitrogen at the interface between the gate insulating film 18 and the polysilicon film 20 when nitrogen is introduced in a later step, and has a thickness of at least one atomic layer. The effect can be obtained.

Next, the gas introduced into the CVD furnace is NH 3
₃ was changed to a gas, NH ₃ under atmosphere for example 620 ° C., 20
Anneal for a minute. As a result, nitrogen is distributed near the surface of the polysilicon film 20, and nitrogen is dispersed at the interface between the polysilicon film 20 and the gate insulating film 18 without segregating nitrogen at the interface between the gate insulating film 18 and the silicon substrate 10. It can be segregated (FIG. 5 (c)).

Subsequently, the gas introduced into the CVD furnace is changed to SiH ₄ gas again, and a polysilicon film 22 having a thickness of about 90 nm is additionally grown on the polysilicon film 20. Thus, the polysilicon film 26 having a total thickness of about 100 nm is formed.
Is formed (FIG. 6A). The reason why the annealing is performed in the CVD furnace by changing the gas introduced into the CVD furnace is to prevent the polysilicon film 20 from being exposed to the atmosphere and being oxidized. Therefore, if other measures are taken to prevent the polysilicon film 20 from being exposed to the atmosphere, or if the effect on the polysilicon film 20 is negligible, the annealing is not necessarily performed in the CVD furnace. No need. That is, after the polysilicon film 20 is deposited by the CVD device, annealing is performed by another device, and the polysilicon film 24 is again formed by the CVD device.
May be deposited.

After nitrogen is segregated between the polysilicon film 26 and the gate insulating film 18 as described above, the polysilicon film 26 is doped. For example, boron ions (B ⁺ ) are implanted into the polysilicon film 26 in the P-type MOS transistor formation region at an acceleration energy of 2 keV and a dose of 2 ×.
As 10 ¹⁵ cm ^-2, also the polysilicon 26 of N-type MOS transistor forming region, phosphorus ions (P ^+), acceleration energy 5 keV, ions are implanted as a dose of 2 × 10 ¹⁵ cm ^-2.

Then, for example, at 800 ° C. 6 in a nitrogen atmosphere.
By performing a heat treatment for 0 minutes, the implanted impurities are diffused into the polysilicon film 26 and are electrically activated. In this manner, the polysilicon film 26 in the P-type MOS transistor formation region is set to the P ⁺ polysilicon film 26p, and the polysilicon film 26 in the N-type MOS transistor formation region is set to the N ⁺ polysilicon film 26n (FIG. 6B).

Subsequently, an insulating film 28 functioning as an anti-reflection film when patterning the polysilicon film 26 is formed on the polysilicon film 26 having the conductivity type. For example, an insulating film 28 is formed by depositing a silicon oxynitride film having a thickness of about 30 nm by a CVD method. Thereafter, the insulating film 28 is formed by ordinary lithography and etching.
Then, the polysilicon film 26 is patterned to form gate electrodes 30p and 30n made of the polysilicon film 26 whose upper surface is covered with the insulating film 28 (FIG. 7A).

Next, the source / drain diffusion layer 32 having, for example, an LDD structure is self-aligned with the gate electrodes 30p and 30n in the same manner as in a normal MOS transistor formation method.
By forming p and 32n, a MOS transistor is completed (FIG. 7B). Table 1 summarizes the characteristics of the MOS transistor thus formed and the characteristics of the MOS transistor formed by the conventional method.

[0037]

[Table 1] In Table 1, the characteristics of the "thermal oxide film" MOS transistor forming a gate insulating film by thermal oxidation of the phrase under normal oxidizing atmosphere, "N ₂ O nitride oxide film" highlighting the N ₂ O
MOS with gate insulating film formed by thermal oxidation using silicon
This shows the characteristics of the transistor. The heat loss of boron represents a difference between the threshold voltage Vth of the transistor when BF ₂ is used as an impurity to be introduced into the gate electrode and the threshold voltage Vth of the transistor when B is used. The greater the difference, the greater the degree of heat loss. Moreover, the drive capability of the N-type transistor is expressed by the product of the film thickness t _ox of the channel conductance g _m and the gate insulating film.

As shown in Table 1, as a gate insulating film, N
_It can be seen that in the case of using the ₂ O nitrided oxide film and in the case of the present invention, the heat loss of boron can be suppressed as compared with the ordinary thermal oxide film containing no nitrogen. From the SIMS measurement results, the peak concentration of nitrogen was about 1% in both the case of using the N ₂ O nitrided oxide film and the case of the present invention. The semiconductor device was better.

The driving capability of the N-type transistor is reduced by about 5% when the N ₂ O oxynitride film is used as the gate insulating film. However, the driving capability of the semiconductor device of the present invention is not reduced. I couldn't. As described above, according to the present embodiment, nitrogen can be introduced into the interface between the gate electrode and the gate insulating film without segregating nitrogen at the interface between the gate insulating film and the silicon substrate. It is possible to prevent boron from leaking from the gate electrode without deteriorating the driving capability of the transistor. In addition, since the gate insulating film is not exposed to plasma when introducing nitrogen, there is no possibility that the reliability of the gate insulating film is reduced.

[Second Embodiment] The semiconductor device and the method for fabricating the same according to a second embodiment of the present invention will be described with reference to FIGS.
Explanation will be made using 0. The same components as those of the semiconductor device according to the first embodiment and the method of manufacturing the same are denoted by the same reference numerals, and description thereof will be simplified or omitted. FIG. 8 is a schematic sectional view showing the structure of the semiconductor device according to the present embodiment, and FIGS. 9 and 10 are process sectional views showing the method of manufacturing the semiconductor device according to the present embodiment.

In the first embodiment, the gate electrode 30
NH during the formation of the polysilicon film 26 to be p and 30n.
₃ Heat treatment in a nitrogen atmosphere is performed, and the gate electrode 30p,
Although nitrogen is segregated at the interface between 30n and the gate insulating film 18, nitrogen can be segregated after the entire polysilicon film 26 is formed. In the present embodiment, a semiconductor device in which nitrogen can be segregated at the interface between the gate electrodes 30n, 30p and the gate insulating film 18 after forming a polysilicon film for forming a gate electrode, and a method of manufacturing the semiconductor device will be described.

First, the structure of the semiconductor device according to the present embodiment will be explained with reference to FIG. The basic structure of the semiconductor device according to the present embodiment is the same as that of the semiconductor device according to the first embodiment shown in FIG. 4, but the distribution of nitrogen in the polysilicon film 26 is different from that of the semiconductor device according to the first embodiment. Are different. That is, in the semiconductor device according to the present embodiment, nitrogen is segregated at the interface between the gate electrodes 30p and 30n and the gate insulating film 18, and a region where nitrogen is segregated also exists near the surfaces of the gate electrodes 30p and 30n. (See FIG. 3).

Hereinafter, the structure of the semiconductor device according to the present embodiment and the method for fabricating the semiconductor device will be described in detail along the steps of manufacturing the semiconductor device. First, the gate insulating film 18 is formed on the silicon substrate 10 in the same manner as in the method of manufacturing the semiconductor device according to the first embodiment shown in FIG.
(A)). Next, a polysilicon film 26 having a thickness of about 50 nm is deposited on the entire surface by, for example, thermal CVD using SiH ₄ gas (FIG. 9B). The substrate temperature is, for example, 6
20 ° C. Note that an amorphous silicon film may be used instead of the polysilicon film 26.

Subsequently, for example, 900 in an NH ₃ atmosphere.
Anneal at 60 ° C. for 60 seconds. By performing the annealing in the NH ₃ atmosphere, the nitrogen in the NH ₃ is taken into the substrate as shown in FIG. That is, the nitrogen is distributed near the surface of the polysilicon film 26, diffuses inside the polysilicon film 26, and segregates at the interface between the polysilicon film 26 and the gate insulating film 18. On the other hand, no segregation occurs at the interface between the gate insulating film 18 and the silicon substrate 10. Therefore, by introducing nitrogen in this manner, heat loss of boron introduced into polysilicon film 26 by nitrogen introduced at the interface between polysilicon film 26 and gate insulating film 18 can be suppressed, and silicon Substrate 10
There is no increase in the interface state at the surface (FIG. 9C).

Thereafter, for example, FIG. 6B to FIG. 7B
A P-type MOS transistor and an N-type MOS transistor are formed in the same manner as in the method of manufacturing the semiconductor device according to the first embodiment shown in FIG. 10 (FIGS. 10A to 10C). As described above, according to the present embodiment, annealing is performed after the formation of the polysilicon film serving as the gate electrode, and the gate electrode and the gate insulating film are separated without segregating nitrogen at the interface between the gate insulating film and the silicon substrate. N is introduced at the interface of
It is possible to prevent boron from leaking from the gate electrode without deteriorating the driving capability of the OS transistor. In addition, since the gate insulating film is not exposed to plasma when introducing nitrogen, there is no possibility that the reliability of the gate insulating film is reduced.

In the first and second embodiments, the gate electrode is formed only of the polysilicon film. However, the gate electrode having a polycide structure composed of a laminated film of the polysilicon film and the refractory metal silicide film, A gate electrode having a polymetal structure composed of a laminated film of a silicon film and a high melting point metal may be used. In this case, a high melting point metal silicide film or a high melting point metal film may be formed on the polysilicon film 26 after the formation of the polysilicon film 26 and before the formation of the insulating film 28.

In the first and second embodiments, N
Although nitrogen was introduced by performing annealing in an H ₃ atmosphere, as described in the principle, nitrogen plasma treatment may be performed after depositing a polysilicon film, and then nitrogen may be introduced by performing annealing. . [Third Embodiment] The semiconductor device and the method for fabricating the same according to a third embodiment of the present invention will be explained with reference to FIGS.

FIG. 11 is a schematic sectional view showing the structure of the semiconductor device according to the present embodiment, and FIGS. 12 to 14 are process sectional views showing the method for manufacturing the semiconductor device according to the present embodiment. In the method of manufacturing the semiconductor device according to the second embodiment, a method of performing heat treatment in an NH ₃ atmosphere to segregate nitrogen at the interface between the gate electrodes 30p and 30n and the gate insulating film 18 has been described. A gas containing oxygen such as NO, N ₂ O, and NO ₂ can also be used. In this case, nitrogen can be segregated at the interface between the gate electrodes 30p and 30n and the gate insulating film 18, but the surface of the polysilicon film 20 is oxidized, so that the oxide film thus formed remains. If this is done, the etching may be stopped in the patterning step when forming the gate electrode in a later step.

For this reason, it is desirable to remove the oxide film thus formed, but it is also possible to use this oxide film effectively. In the present embodiment, a method using this oxide film will be described. First, the structure of the semiconductor device according to the present embodiment will be explained with reference to FIG.

An element isolation film 12 for defining an element region is formed on the silicon substrate 10. An N-well 14 is formed in a P-type MOS transistor formation region in the silicon substrate 10, and a P-well 16 is formed in an N-type MOS transistor formation region. On the surface of the silicon substrate 10 defined by the element isolation film 12, a gate insulating film 18 made of a silicon oxide film is formed. P
A gate electrode 30p made of a P ⁺ silicon film 22p and a refractory metal silicide film 36 is formed on the gate insulating film 18 in the type MOS transistor formation region. On the gate insulating film in the N-type MOS transistor formation region, N
^{+ A} gate electrode 30n composed of a silicon film 22n and a refractory metal silicide film 36 is formed. Source / drain diffusion layers 32p and 32n are formed in the silicon substrate 10 on both sides of the gate electrodes 30p and 30n.
Note that the distribution of nitrogen in the substrate is similar to that of the semiconductor device according to the first embodiment. That is, nitrogen is
Refractory metal silicide film 36 and silicon films 22p, 22
n, and segregates at the interface between the gate electrodes 30p and 30n and the gate insulating film, but does not segregate at the interface between the gate insulating film 18 and the silicon substrate 10.

Hereinafter, the structure of the semiconductor device according to the present embodiment and the method for fabricating the semiconductor device will be described in detail along the steps of manufacturing the semiconductor device. First, the gate insulating film 18 is formed on the silicon substrate 10 in the same manner as in, for example, the method of manufacturing the semiconductor device according to the first embodiment shown in FIG.
(A)).

Next, an amorphous silicon film 22 having a thickness of about 30 nm is deposited on the entire surface by, eg, thermal CVD using SiH ₄ gas (FIG. 12B). The substrate temperature is, for example, 450 ° C. Subsequently, annealing is performed at 900 ° C. for 60 seconds in an NO gas atmosphere. This allows
Nitrogen can be segregated at the interface between the amorphous silicon film 22 and the gate insulating film 18 without segregating nitrogen at the interface between the gate insulating film 18 and the silicon substrate 10. Further, the amorphous silicon film 2 is formed by NO gas.
2 is oxidized, and a silicon oxide film 34 having a thickness of about 1.5 nm is formed on the surface of the amorphous silicon film 22 (FIG. 12C). The heat treatment converts the amorphous silicon film 22 into a polysilicon film.
For convenience of explanation, the description will be made hereinafter as the amorphous silicon film 22.

Thereafter, a film thickness of about 50 n is formed on the silicon oxide film 32 by, for example, a thermal CVD method using SiH ₄ gas.
Then, a polysilicon film 24 having a thickness of m is deposited. The substrate temperature is, for example, 620 ° C. (FIG. 13A). Next, the polysilicon film 24 and the amorphous silicon film 22 are doped. For example, in a P-type MOS transistor formation region, boron ions are set to an acceleration energy of 5 keV and a dose is 4 × 10 ¹⁵ cm ⁻² , and in an N-type MOS transistor formation region, phosphorus ions are set to an acceleration energy of 10 keV.
V ions are implanted at a dose of 4 × 10 ¹⁵ cm ⁻² .

Subsequently, for example, at 800 ° C. 6 in a nitrogen atmosphere.
By performing a heat treatment for 0 minutes, the implanted impurities are sufficiently diffused into the amorphous silicon film 22 and are electrically activated. Thus, the polysilicon film 26 in the P-type MOS transistor formation region is replaced with the P ⁺ polysilicon film 26p.
The amorphous silicon film 22 is a P ⁺ amorphous silicon film 22p, the polysilicon film 26 in the N-type MOS transistor formation region is an N ⁺ polysilicon film 26n, and the amorphous silicon film 22 is an N ⁺ amorphous silicon film 22n (FIG. 13 (b)).

Thereafter, the polysilicon film 22 is etched using, for example, a microwave plasma etching method with the silicon oxide film 34 as a stopper. For example, the amorphous silicon film 22 is etched using SF ₆ as an etching gas at a pressure of 0.05 Torr (FIG. 13C). The removal of the amorphous silicon film 22 using the silicon oxide film 34 as a stopper is effective in forming a low-resistance gate wiring.

A gate structure such as a polycide structure or a polymetal structure is known as a method of forming a low-resistance gate wiring. However, in order to form a lower-resistance wiring, the thickness of the underlying polysilicon film must be reduced. It is desired to do.
On the other hand, when a dual gate electrode is employed, it is general that the polysilicon film serving as the gate electrode is doped by ion implantation. In order to perform sufficient doping of the polysilicon film, ions implanted into the channel region are not doped. It is required to deposit a polysilicon film of a certain thickness or more in order to prevent penetration.

In order to satisfy both of these requirements, it is conceivable to deposit a thicker silicon film and perform doping, and then etch back the silicon film. However, simply performing etch back lacks controllability of the thickness of the polysilicon film. In addition, considering the insertion of the stopper film in the middle of the polysilicon film, the number of steps increases.

On the other hand, according to the method for fabricating the semiconductor device according to the present embodiment, in the step of introducing nitrogen into the interface between the gate electrode and the gate insulating film, the silicon oxide film 34 functioning as a stopper can be formed simultaneously. Therefore, a thin amorphous silicon film with sufficient doping can be easily formed. Next, the silicon film 34 on the amorphous silicon film 22 is removed by, for example, dry etching (FIG. 14A).

Subsequently, a refractory metal silicide film 36 having a thickness of about 100 nm is formed on the amorphous silicon film 22 by, for example, a CVD method (FIG. 14B). As the refractory metal silicide film 36, for example, a tungsten silicide film, a molybdenum silicide film, a titanium silicide film, a tantalum silicide film, or the like can be used. Further, a high melting point metal film may be formed instead of the high melting point metal silicide film.

Thereafter, on the high melting point metal silicide film 36, an insulating film 28 functioning as an antireflection film when patterning the high melting point metal silicide film 36 and the amorphous silicon film 22 is formed. Thereafter, the insulating film 28, the refractory metal silicide film 36, and the amorphous silicon film 22 are patterned by a normal lithography technique and an etching technique to form gate electrodes 30p and 30n having a polycide structure whose upper surface is covered with the insulating film 28. I do.

Next, the source / drain diffusion layer 32 having an LDD structure, for example, is self-aligned with the gate electrodes 30p and 30n in the same manner as in a normal MOS transistor formation method.
By forming p and 32n, a MOS transistor is completed (FIG. 14C). Thus, according to the present embodiment,
Using a silicon oxide film formed when introducing nitrogen to the interface between the gate electrode and the gate insulating film as a stopper,
Since the doped polysilicon film is etched back, the thin polysilicon film can be doped at a high concentration while preventing penetration due to ion implantation.

In the above embodiment, the silicon oxide film 34 is formed simultaneously with the segregation of nitrogen by using a gas containing nitrogen and oxygen, but after the nitrogen is introduced by the nitrogen-based gas containing no oxygen. A silicon oxide film 34 may be formed. After introducing nitrogen near the surface of the amorphous silicon film 22 by plasma treatment or the like,
Heat treatment may be performed in an oxidizing atmosphere to diffuse and segregate nitrogen simultaneously with the formation of the silicon oxide film 34.

In the first to third embodiments, the doping of the gate electrode is performed after nitrogen is introduced into the interface between the gate electrode and the gate insulating film. May be performed before. Also,
In the third embodiment, the gate electrode having a polycide structure composed of a laminated film of a polysilicon film and a refractory metal silicide film is formed. However, the gate electrode having a polymetal structure composed of a laminated film of a polysilicon film and a refractory metal is formed. It may be.

In the third embodiment, nitrogen is introduced and a silicon oxide film is formed by annealing in a NO atmosphere. However, after the polysilicon film is deposited and nitrogen is introduced, the oxide film is formed. Heat treatment may be performed while forming.

[0065]

As described above, according to the present invention, a silicon substrate, a gate insulating film formed on the silicon substrate,
A semiconductor device includes a gate electrode formed over a gate insulating film and having a silicon film at least on a surface in contact with the gate insulating film, and a first nitrogen segregation layer having a peak concentration near an interface between the silicon film and the gate insulating film. N
It is possible to prevent boron from leaking out of the gate electrode without deteriorating the driving capability of the type MOS transistor.

A step of forming a gate insulating film on a silicon substrate, a step of forming a first silicon film on the gate insulating film, and a step of segregating nitrogen at an interface between the first silicon film and the gate insulating film. Since the semiconductor device is manufactured by the step of performing, the heat release of boron from the gate electrode can be prevented. In the step of segregating nitrogen,
Annealing the silicon substrate in a gas atmosphere containing nitrogen to introduce nitrogen from the surface of the first silicon film;
By causing nitrogen to segregate at the interface between the first silicon film and the gate insulating film, the nitrogen can be separated from the first silicon film and the gate insulating film without segregating at the interface between the silicon substrate and the gate insulating film. It can segregate at the interface. Therefore, it is possible to prevent boron from leaking from the gate electrode without lowering the driving capability of the N-type MOS transistor. In addition, since the gate insulating film is not exposed to plasma in the above method, the reliability of the gate insulating film can be improved.

In the step of segregating nitrogen,
Nitrogen is introduced into the surface region of the first silicon film, and then the silicon substrate is annealed, and nitrogen is segregated at the interface between the first silicon film and the gate insulating film. Can be segregated at the interface between the first silicon film and the gate insulating film without segregating at the interface. Therefore, it is possible to prevent boron from leaking from the gate electrode without lowering the driving capability of the N-type MOS transistor.

Further, a step of forming a gate insulating film on a silicon substrate, a step of forming a first silicon film on the gate insulating film, and a step of segregating nitrogen at an interface between the first silicon film and the gate insulating film. Forming a silicon oxide film on the first silicon film, forming a second silicon film on the first silicon film, and forming a first silicon film and a second silicon film on the first silicon film.
A semiconductor device is manufactured by the step of introducing impurities into the silicon film, the step of etching the second silicon film using the silicon oxide film as a stopper, and the step of etching the silicon oxide film. In addition, a thin silicon film doped with a high concentration can be easily formed. Further, since the silicon oxide film formed when introducing nitrogen can be used as the stopper film used for etching the second silicon film, the number of steps is not increased more than necessary.

[Brief description of the drawings]

FIG. 1 is a graph showing an atomic concentration distribution in a sample in which a silicon oxide film and a polysilicon film are formed on a silicon substrate and an annealing is performed in an NH ₃ atmosphere during the formation of the polysilicon film.

FIG. 2 is a graph showing an atomic concentration distribution in a sample formed by forming a silicon oxide film on a silicon substrate and then annealing in an NH ₃ atmosphere.

FIG. 3 is a graph showing an atomic concentration distribution in a sample formed by forming a silicon oxide film and a polysilicon film on a silicon substrate and then annealing in a NH ₃ atmosphere.

FIG. 4 is a schematic sectional view showing the structure of the semiconductor device according to the first embodiment of the present invention.

FIG. 5 is a process sectional view (part 1) illustrating the method for fabricating the semiconductor device according to the first embodiment of the present invention;

FIG. 6 is a sectional view (part 2) illustrating the method for manufacturing the semiconductor device according to the first embodiment of the present invention;

FIG. 7 is a process sectional view (part 3) illustrating the method for fabricating the semiconductor device according to the first embodiment of the present invention;

FIG. 8 is a schematic sectional view showing the structure of a semiconductor device according to a second embodiment of the present invention.

FIG. 9 is a process cross-sectional view (part 1) illustrating the method for manufacturing a semiconductor device according to the second embodiment of the present invention.

FIG. 10 is a process sectional view (part 2) illustrating the method for fabricating the semiconductor device according to the second embodiment of the present invention.

FIG. 11 is a schematic sectional view showing the structure of a semiconductor device according to a third embodiment of the present invention.

FIG. 12 is a process cross-sectional view (part 1) illustrating the method for manufacturing a semiconductor device according to the third embodiment of the present invention.

FIG. 13 is a process sectional view (part 2) illustrating the method for fabricating the semiconductor device according to the third embodiment of the present invention.

FIG. 14 is a process sectional view (part 3) illustrating the method for fabricating the semiconductor device according to the third embodiment of the present invention.

FIG. 15 is a graph showing an atomic concentration distribution in a semiconductor device formed by a conventional method of manufacturing a semiconductor device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Silicon substrate 12 ... Element isolation film 14 ... N well 16 ... P well 18 ... Gate insulating film 20 ... Polysilicon film 22 ... Amorphous silicon film 24 ... Polysilicon film 26 ... Polysilicon film 28 ... Insulating film 30 ... Gate electrode 32: source / drain diffusion layer 34: silicon oxide film 36: refractory metal silicide film

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F040 DA06 DA28 DB03 DC01 EC01 EC04 EC05 EC07 EC12 EC13 EC28 EF02 EK05 FA15 FA19 FB02 FB04 FC00 FC10 5F048 AA07 AC03 BA01 BB06 BB07 BB08 BB09 BB12 BC06 BE03 BG14 DA17 DA20 DA21

Claims (12)

[Claims] A silicon substrate; a gate insulating film formed on the silicon substrate; a gate electrode formed on the gate insulating film and having a silicon film on at least a surface in contact with the gate insulating film; A semiconductor device comprising: a first nitrogen segregation layer having a peak concentration near an interface between a film and the gate insulating film. 2. The semiconductor device according to claim 1, further comprising a second nitrogen segregation layer having a peak concentration near a surface of said silicon film opposite to said gate insulating film. 3. The semiconductor device according to claim 1, further comprising a second nitrogen segregation layer having a peak concentration in said silicon film. 4. A step of forming a gate insulating film on a silicon substrate, a step of forming a first silicon film on the gate insulating film, and a step of forming an interface between the first silicon film and the gate insulating film. And a step of segregating nitrogen. 5. The method for manufacturing a semiconductor device according to claim 4, wherein in the step of segregating nitrogen, the surface of the first silicon film is subjected to nitrogen annealing by annealing the silicon substrate in a gas atmosphere containing nitrogen. Wherein a nitrogen is segregated at an interface between the first silicon film and the gate insulating film. 6. The method for manufacturing a semiconductor device according to claim 4, wherein in the step of segregating nitrogen, the silicon substrate is annealed after introducing nitrogen into a surface region of the first silicon film, and A method of manufacturing a semiconductor device, wherein nitrogen is segregated at an interface between the silicon film and the gate insulating film. 7. The method for manufacturing a semiconductor device according to claim 6, wherein in the step of segregating nitrogen, the surface of the first silicon film is exposed to nitrogen by exposing the silicon substrate to plasma containing nitrogen. A method for manufacturing a semiconductor device, which is introduced. 8. The method for manufacturing a semiconductor device according to claim 4, wherein a second silicon film is formed on the first silicon film after the step of segregating nitrogen. A method for manufacturing a semiconductor device, further comprising a step. 9. The method of manufacturing a semiconductor device according to claim 8, wherein the step of forming the first silicon film, the step of segregating nitrogen, and the step of forming the second silicon film are performed on the silicon substrate. A continuous process without exposing the semiconductor device to the atmosphere. 10. A step of forming a gate insulating film on a silicon substrate, a step of forming a first silicon film on the gate insulating film, and a step of forming an interface between the first silicon film and the gate insulating film. Segregating nitrogen to form a silicon oxide film on the first silicon film; forming a second silicon film on the first silicon film; and forming the first silicon film and the second silicon film on the first silicon film. A step of introducing an impurity into the second silicon film, a step of etching the second silicon film using the silicon oxide film as a stopper, and a step of etching the silicon oxide film. Manufacturing method. 11. The method for manufacturing a semiconductor device according to claim 10, wherein the step of segregating nitrogen includes NO, NO _2, or N ₂ O.
Wherein the silicon substrate is annealed in an atmosphere containing nitrogen to segregate nitrogen at an interface between the first silicon film and the gate insulating film and simultaneously oxidize the surface of the first silicon film. Manufacturing method. 12. The method for manufacturing a semiconductor device according to claim 11, wherein in the step of segregating nitrogen, the substrate is annealed in an atmosphere containing oxygen after introducing nitrogen into a surface region of the first silicon film. And a step of segregating nitrogen at an interface between the first silicon film and the gate insulating film and oxidizing the first silicon film at the same time.