JPH10242307A - Nonvolatile semiconductor memory and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the threshold voltage variation due to capture of electrons to stabilize the initial characteristics by sequentially lowering the lowest energy of the conduction band in an insulation film from a floating gate electrode toward a control gate electrode. SOLUTION: Unnecessary parts of a polycrystalline Si film 7, double layer film 6, polycrystalline Si film 5 and Si oxide film 4 are sequentially etched off to form control gate electrodes 7 having a predetermined shape, interlayer insulation film 6, floating gate electrodes 5 and gate insulation film 4, it is thermally oxidized to form a side wall Si oxide film on the side faces of the electrodes 5 etc., sources 8 and drains 9 are formed by ion-implanting, and an insulation film 10, source and drain electrodes 3 are formed. The lowest energy of the conduction band of the film 6 decreases from the floating gate electrode 5 to the control gate electrode 7, no well type potential structure is formed and no electron is confined in the film 6, thus stabilizing the initial characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-volatile semiconductor memory device and a method of manufacturing the same, and more particularly, to a semiconductor memory device in which electrons emitted from a floating gate electrode are not captured by an interlayer insulating film and the operating characteristics of a memory cell are improved. The present invention relates to a stable nonvolatile semiconductor memory device and a method for manufacturing the same.

[0002]

2. Description of the Related Art In a nonvolatile semiconductor memory device shown in FIG. 1 in which a gate portion has a stack structure, a control gate electrode 7 is changed by changing the number of electrons in a floating gate electrode 5.
The threshold voltage as viewed from above is controlled, and information 1 and 0 are defined. Therefore, it is important to stably hold the electrons in the floating gate electrode 5 in the operation stability of the nonvolatile semiconductor memory device. Therefore, the floating gate electrode 5
It is necessary to reduce leakage current of the interlayer insulating film 6 between the gate electrode 7 and the control gate electrode 7 and the gate insulating film 4 between the floating gate electrode 5 and the substrate 1 to maintain good information retention characteristics. is there.

Therefore, a laminated film of a silicon oxide film and a silicon nitride film, that is, a silicon oxide film / silicon nitride film / silicon oxide film (abbreviated as ONO film) having a three-layer structure is widely used as the interlayer insulating film 6. . In the ONO film, since both the upper film and the lower film are silicon oxide films having a large forbidden band width, leakage current in a low electric field can be reduced.

[0004] Conventionally, since a silicon nitride film is formed by a chemical vapor deposition method using ammonia, a deep level is formed in a forbidden band. Therefore, ONO
When an electric field is applied to the film, the conduction of the electrons injected into the silicon nitride film becomes pool-Frenkel conduction dominated by the deep level of the silicon nitride film, and is caused by a high electric field during rewriting of the nonvolatile semiconductor memory device. , The leakage current is kept low, and good rewriting efficiency can be obtained.

In the structure shown in FIG. 1 and the step of forming a wiring structure thereon, it is necessary to perform dry etching a plurality of times. However, at that time, the control gate electrode 7
Electrons are introduced into the floating gate electrode 5 by a high electric field applied between the substrate and the substrate 1, and the threshold value deviates from a target value. Therefore, in order to obtain a thermal equilibrium state in which electrons are not accumulated in the floating gate electrode 5, ultraviolet rays are irradiated after manufacturing the memory cell for the purpose of emitting electrons in the floating gate electrode 5.

As a material of the floating gate electrode 5, a polycrystalline silicon film is generally used, and an energy band diagram of a nonvolatile semiconductor memory device having a stack structure is as shown in FIG. As is clear from FIG. 2, when the ultraviolet rays are irradiated and the electrons absorb the energy of the ultraviolet rays (the energy barrier for the electrons at the silicon oxide / polycrystalline silicon interface of 3.1 eV or more), the electrons exceed the energy barrier. It is possible to move from the floating gate electrode 5 to the outside.

[0007]

However, the interlayer insulating film 6
Is formed of an ONO film, as shown in FIG. 3, since the silicon oxide film and the silicon nitride film have different band gaps, the interlayer insulating film has a well-type potential structure. Therefore, when the electrons in the floating gate electrode 5 are introduced into the silicon nitride film of the ONO film by the irradiation of the ultraviolet light, the electrons are confined due to an energy barrier between the silicon nitride film and the silicon oxide film. Moreover, since a silicon nitride film formed by a conventional method such as CVD has a deep level, electrons injected into the silicon nitride film are captured by this deep level and It becomes difficult to get out. These interlayer insulating films 6
The electrons trapped therein cause the threshold voltage to fluctuate similarly to the electrons in the floating gate electrode 5.

Therefore, in order to stabilize the operating characteristics of the nonvolatile semiconductor device, it is necessary to prevent electrons emitted from the floating gate electrode 5 to the side of the interlayer insulating film 6 by irradiation of ultraviolet rays from being captured by the interlayer insulating film 6. It is essential to have a structure.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, and prevent electrons emitted from a floating gate electrode from being captured by an interlayer insulating film. It is an object of the present invention to provide a nonvolatile semiconductor memory device having the same and a method of manufacturing the same.

[0010]

According to a first aspect of the present invention, there is provided a nonvolatile semiconductor memory device formed at a predetermined interval in a surface region of a semiconductor substrate having a first conductivity type. A source region and a drain region having a second conductivity type opposite to the first conductivity type, and a gate insulating film sequentially formed on the main surface of the semiconductor substrate between the source region and the drain region; A floating gate electrode, an interlayer insulating film including a stacked film of a plurality of insulating films, and a control gate electrode, wherein the lowest energy of the conduction electron band of the plurality of insulating films is from the floating gate electrode to the control gate electrode. And gradually decreases.

That is, since the interlayer insulating film has a structure without a well-type potential and a deep level, electrons emitted from the floating gate electrode to the interlayer insulating film side by irradiation of ultraviolet rays are reduced by the interlayer insulating film. It is prevented from being captured. In order to form a film having such a structure, the lowest energy of the conduction electron band needs to decrease from the floating gate electrode toward the control gate electrode.

When the ultraviolet rays are irradiated, the electrons in the floating gate electrode are excited and injected into the gate insulating film and the interlayer insulating film by the electric field generated by the electrons in the floating gate electrode. Accelerated towards the electrode. At this time, as shown in FIG. 4, if the lowest energy of the conduction electron band decreases from the floating gate electrode toward the control gate electrode, electrons are scattered at the interface between the films and even to the control gate electrode. To reach. That is, since the electrons are not captured in the interlayer insulating film, the threshold does not change due to the irradiation of the ultraviolet rays.

If the interlayer insulating film contains a film in which the diffusion constant of the oxidizing species is smaller than that of the silicon oxide film, an obstacle due to the oxidizing species (oxygen, ozone, oxygen radical or water), for example, the thickness of the interlayer insulating film 6 The increase can be prevented, and a silicon oxynitride film or a silicon nitride film can be used as such a film.

As the interlayer insulating film, a two-layer film of a silicon oxynitride film or a silicon nitride film formed in contact with the lower surface of the control gate electrode and a silicon oxide film formed in contact with the upper surface of the floating gate electrode Can be used. A two-layer film may be formed by forming a silicon oxynitride film in contact with the lower surface of the control gate electrode and forming a silicon oxynitride film in contact with the upper surface of the floating gate electrode.

As the floating gate electrode and the control gate electrode, a low-resistance polycrystalline silicon film doped with a large amount of impurities can be used.

In these nonvolatile semiconductor devices, a gate insulating film, a floating gate electrode, an interlayer insulating film including a silicon oxide film and a film having a smaller diffusion coefficient of an oxidizing species than the silicon oxide film, and a control gate electrode are provided on the main surface of the semiconductor substrate. Forming a film having a diffusion coefficient of an oxidizing species smaller than that of the silicon oxide film by forming a silicon film and then changing the silicon film to a silicon oxynitride film or a silicon nitride film. It can be manufactured by a manufacturing method characterized by being performed. As the silicon film,
For example, a favorable result can be obtained by using an amorphous silicon film, and the silicon film can be formed by a chemical vapor deposition method.

The silicon oxynitride film or silicon nitride film can be formed by heat-treating the silicon film in a gas containing nitrogen radicals, nitric oxide or nitrous oxide. The silicon film can be formed over the silicon oxide film.

As described above, since the silicon film is nitrided or oxynitrided by the heat treatment in an atmosphere containing no ammonia, an interlayer insulating film having no deep level is formed. Further, since water and hydrogen are not contained in the atmosphere in this case, the deep level is reduced, and even if electrons are introduced into the interlayer insulating film, the electrons are not captured, Acceleration by the electric field causes the film to escape from the film and is not trapped in the interlayer insulating film.

A film having a smaller diffusion coefficient of oxidizing species than the silicon oxide film is formed by repeating the formation of the silicon film and the heat treatment a plurality of times. Since the thickness of a silicon oxynitride film or a silicon nitride film formed by one heat treatment is small, it is practically preferable to repeatedly form a thin silicon film and perform the heat treatment to obtain a predetermined film thickness.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a nonvolatile semiconductor memory device of the present invention, a control gate electrode and a floating gate electrode are made of a polycrystalline silicon film doped with a large amount of impurities, and an interlayer insulating film is made of a silicon oxide film and a silicon oxynitride film. If the silicon oxynitride film is formed on the control gate electrode side and the silicon oxide film is formed on the floating gate electrode side, respectively, the lowest energy of the conduction electron band of the interlayer insulating film will be floating. As it goes from the gate electrode to the control gate electrode, it becomes lower, and no well-type potential structure is formed. Therefore, electrons are not confined in the interlayer insulating film, and a very favorable result in practical use is obtained.

The silicon oxynitride film is preferable in view of the fact that the diffusion constant of oxidizing species (oxygen, ozone, oxygen radicals, water) is smaller than that of the silicon oxide film together with the silicon nitride film, so that the oxidizing species does not easily pass therethrough.

A silicon oxynitride film or a silicon nitride film is formed by a heat treatment in an atmosphere of nitrogen radicals, nitric oxide or nitrous oxide after forming a silicon film instead of a commonly used CVD method. In this manner, a film having a low hydrogen content is formed, the deep level is reduced, and the fluctuation of the threshold value is effectively prevented. By repeatedly performing the formation of the silicon film and the heat treatment several times, a desired thickness can be obtained.

[0023]

【Example】

<Embodiment 1> FIG. 1 is a sectional view of a memory cell for explaining an embodiment of the present invention. On the surface of the silicon substrate 1,
After forming a thick insulating film 2 for element isolation using a well-known thermal oxidation method, oxygen and hydrogen are flowed simultaneously, and a 8.5-nm-thick silicon oxide film is formed on the silicon substrate 1 by well-known pyrogenic oxidation. did. The flow rates of the oxygen and hydrogen were 10 liters / minute and 0.5 liters / minute, respectively.
Min and the temperature was 850 ° C.

Next, monosilane and phosphine were added to the source
By the well-known reduced pressure chemical vapor deposition method used as a gas,
After forming a 200 nm-thick polycrystalline silicon film 5 containing phosphorus at a concentration of 1 × 10 ²⁰ cm ^−3, the polycrystalline silicon film 5 is formed by a known low pressure chemical vapor deposition method using nitrous oxide and monosilane. A 10-nm-thick silicon oxide film was formed thereon. Subsequently, an amorphous silicon film having a thickness of 0.5 nm was formed on the silicon oxide film by using a known low pressure chemical vapor deposition method. At this time, the gas pressure 73P
a, Using a nitrogen gas as a carrier gas at a flow rate of 2 liters / minute, disilane was flowed at a flow rate of 0.15 liters / minute, and the formation temperature was 425 ° C.

A heat treatment was performed in nitrogen monoxide at 850 ° C. for 10 minutes to convert all the amorphous silicon films into silicon oxynitride films. The formation of the amorphous silicon film and the heating in nitrogen monoxide were repeated three times, and a 3-nm-thick silicon oxynitride film was stacked on the 10-nm-thick silicon oxide film to form a two-layer film 6. .

By a well-known reduced pressure chemical vapor deposition method using monosilane and phosphine as a source gas, a concentration of 3
A 200 nm-thick polycrystalline silicon film 7 containing phosphorus of × 10 ²⁰ cm ⁻³ was formed on the two-layer film 6.

Next, unnecessary portions of the polycrystalline silicon film 7, the two-layer film 6, the polycrystalline silicon film 5, and the silicon oxide film 4 are sequentially etched and removed using a well-known photo-etching using a mask. A control gate electrode 7, an interlayer insulating film 6, a floating gate electrode 5, and a gate insulating film 4 having predetermined shapes were formed.

After thermal oxidation is performed to form a side wall silicon oxide film on the side portions of the floating gate electrode 5 and the like, the source 8 and the drain 9 are formed by well-known ion implantation. The insulating film 10 and the source / drain electrodes 3 were formed by using the same, and the memory cell for the nonvolatile semiconductor memory device shown in FIG. 1 was manufactured.

Next, the threshold voltages of the nonvolatile semiconductor memory device obtained according to the present embodiment and the conventional nonvolatile semiconductor memory device using the ONO film as an interlayer insulating film were measured and compared. . The ONO film is a 6-nm-thick silicon oxide film formed on a floating gate electrode by a well-known low-pressure chemical vapor deposition method using nitrous oxide and monosilane, and a well-known low-pressure chemical gas using ammonia and dichlorosilane. Film thickness 8 formed by phase growth method
A silicon nitride film having a thickness of 4 nm and a silicon oxide film having a thickness of 4 nm formed by a known low pressure chemical vapor deposition method using nitrous oxide and monosilane were sequentially laminated to form a three-layer film.

As a result, as shown in FIG. 5, the distribution of the threshold voltage before the memory cell is irradiated with the ultraviolet light is changed to the ON state.
The threshold voltage of the present example was about 0.40 V lower than the conventional case using the O film. As shown in FIG. 6, in the case of the present invention, the threshold voltage after ultraviolet irradiation was lower by about 0.6 V than the conventional case using the ONO film, and the variation was small.

As a result, in the conventional memory cell using the ONO film as the interlayer insulating film, the ON
While electrons were accumulated in the O film and the threshold voltage was increased, it was confirmed in the present example that electrons were not accumulated in the interlayer insulating film and the film was in a stable state.

Embodiment 2 In this embodiment, a silicon oxynitride film having a low nitrogen concentration is formed on a floating gate electrode, and a silicon oxynitride film having a high nitrogen concentration is formed on the silicon oxynitride film. The steps up to the step of forming the polycrystalline silicon film 5 used as the floating gate electrode are the same as those in the first embodiment.

After performing the same process as in Example 1 until the step of forming the polycrystalline silicon film 5, a heat treatment is performed at 850 ° C. for 10 minutes in nitrous oxide to obtain the polycrystalline silicon film 5. Was oxynitrided to form a silicon oxynitride film.

Next, an amorphous silicon film having a thickness of 0.5 nm was formed on the silicon oxynitride film by using a known low pressure chemical vapor deposition method. The reduced pressure chemical vapor deposition method was performed at a formation temperature of 425 ° C. using a nitrogen gas as a carrier gas at a gas pressure of 73 Pa and a flow rate of 2 liters / minute, flowing disilane at a flow rate of 0.15 liters / minute.

Next, a heat treatment was performed in nitrogen monoxide at 850 ° C. for 10 minutes to completely convert the amorphous silicon film into an oxynitride film. This process of forming an amorphous silicon film and heating in nitrous oxide was repeated eight times to obtain a film thickness of 12
An nm-thick silicon oxynitride film was formed on the silicon oxynitride film.

On this silicon oxynitride film, a 200 nm-thick polycrystalline silicon film containing phosphorus at a concentration of 3 × 10 ²⁰ cm ^-3 is formed by a well-known reduced pressure chemical vapor deposition method using monosilane and phosphine as a source gas. After forming 7,
Unnecessary portions are sequentially removed using a well-known photo-etching using a mask and processed into a predetermined shape to form a control gate electrode 7, an interlayer insulating film 6 composed of a two-layer film of a silicon oxynitride film and a silicon nitride film, The gate electrode 5 and the gate insulating film 4 were formed.

After thermal oxidation is performed to form a side wall silicon oxide film on the side portions such as the floating gate electrode 5 and the like, the source 8 and the drain 9 are formed by well-known ion implantation. The insulating film 10 and the source and drain electrodes 3 were formed by using the same, and a memory cell for a nonvolatile semiconductor memory device having the structure shown in FIG. 1 was manufactured.

The threshold voltages of the obtained nonvolatile semiconductor memory device and the conventional nonvolatile semiconductor memory device were measured, and both were compared.

The interlayer insulating film of the conventional nonvolatile semiconductor memory device has an ONO structure, and is a 10 nm-thick silicon oxide film formed by a known low pressure chemical vapor deposition method using nitrogen oxide and monosilane. An 8-nm-thick silicon nitride film formed by a known low-pressure chemical vapor deposition method using ammonia and dichlorosilane, and a film thickness formed by a known low-pressure chemical vapor deposition method using nitrous oxide and monosilane It is composed of a three-layer film of a 4 nm silicon oxide film.

FIG. 7 shows the result of comparing the threshold voltages of the present embodiment and the conventional nonvolatile semiconductor memory device.
It was shown to. As is clear from FIG. 7, the distribution of the threshold voltage before the irradiation with the ultraviolet light was about 0.55 V lower than that in the conventional case using the ONO film. FIG. 8 shows a comparison between the threshold voltages after ultraviolet irradiation.
As shown in the figure, the threshold voltage of the present example was lower by about 0.65 V and less varied than the conventional case using the ONO film. This is because in the conventional case, O
This is because electrons are accumulated in the NO film and the threshold voltage is increased, whereas in the present embodiment, such electrons are not accumulated and the NO film is in a stable state.

In this example, the heat treatment was performed using nitric oxide and nitrous oxide, but the same effect was obtained by using nitrogen radicals. The thickness of a silicon oxynitride film or a silicon nitride film that can be formed differs depending on a nitrogen introduction temperature and a nitrogen introduction method, and conditions may be appropriately selected.

In Examples 1 and 2, the thicknesses of the silicon oxide film and the silicon oxynitride film were 10 nm and 3 nm (Example 1), or 0 nm and 13 nm, respectively.
(Example 2) However, these film thicknesses are not particularly limited, and can be appropriately selected.

[0043]

As is apparent from the above description, according to the present invention, the electrons emitted from the floating gate electrode by the irradiation of ultraviolet rays are not trapped in the interlayer insulating film. A non-volatile semiconductor memory device with stable initial characteristics can be obtained without fluctuation of threshold voltage caused by capture.

Since the silicon oxynitride film contained in the interlayer insulating film is less likely to diffuse oxidizing species than the silicon oxide film, the gate of the peripheral circuit of the nonvolatile semiconductor memory device is exposed with the interlayer insulating film exposed. Even if the insulating film is formed, the thickness of the interlayer insulating film does not greatly change. Although a pyrogenic oxidation method is widely used for forming a gate insulating film, this method is performed in an atmosphere containing oxygen or water. However, the method can be performed without any trouble because the silicon oxynitride film is present. it can. Further, even when oxidation is performed using ozone or oxygen radicals, the silicon oxynitride film is less likely to diffuse ozone and oxygen radicals than the silicon oxide film.
This is effective for stabilizing the interlayer insulating film thickness.

[Brief description of the drawings]

FIG. 1 is a sectional view for explaining Embodiments 1 and 2 of the present invention;

FIG. 2 is an energy band diagram of a memory cell of a conventional nonvolatile semiconductor memory device;

FIG. 3 is an energy band diagram of a memory cell of a conventional nonvolatile semiconductor memory device;

FIG. 4 is an energy band diagram for explaining the configuration of the present invention;

FIG. 5 is a diagram for explaining an effect of the present invention;

FIG. 5 is a diagram for explaining an effect of the present invention;

FIG. 6 is a diagram for explaining an effect of the present invention;

FIG. 7 is a diagram for explaining an effect of the present invention;

FIG. 8 is a diagram for explaining the effect of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Si substrate, 2 ... Element isolation insulating film, 3 ... Electrode, 4 ... Gate insulating film, 5 ... Floating gate electrode, 6 ... Interlayer insulating film, 7
... Control gate electrode, 8 ... Source, 9 ... Drain, 10 ...
Insulating film.

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[Procedure amendment]

[Submission date] April 17, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Brief description of drawings

[Correction method] Change

[Correction contents]

[Brief description of the drawings]

FIG. 1 is a sectional view for explaining Embodiments 1 and 2 of the present invention;

FIG. 2 is an energy band diagram of a memory cell of a conventional nonvolatile semiconductor memory device;

FIG. 3 is an energy band diagram of a memory cell of a conventional nonvolatile semiconductor memory device;

FIG. 4 is an energy band diagram for explaining the configuration of the present invention;

FIG. 5 is a diagram for explaining an effect of the present invention;

FIG. 6 is a diagram for explaining an effect of the present invention;

FIG. 7 is a diagram for explaining an effect of the present invention;

FIG. 8 is a diagram for explaining the effect of the present invention.

[Description of Symbols] 1 ... Si substrate, 2 ... element isolation insulating film, 3 ... electrode, 4 ... gate insulating film, 5 ... floating gate electrode, 6 ... interlayer insulating film, 7
... Control gate electrode, 8 ... Source, 9 ... Drain, 10 ...
Insulating film.

Claims (13)

[Claims] 1. A source region and a drain region having a second conductivity type opposite to the first conductivity type and formed at predetermined intervals in a surface region in a semiconductor substrate having a first conductivity type. A gate insulating film, a floating gate electrode, an interlayer insulating film and a control gate electrode each formed of a stacked film of a plurality of insulating films, which are sequentially stacked on the main surface of the semiconductor substrate between the source region and the drain region. A non-volatile semiconductor memory device, wherein the lowest energy of the conduction electron band of the plurality of insulating films decreases sequentially from the floating gate electrode toward the control gate electrode. 2. The nonvolatile semiconductor memory device according to claim 1, wherein said interlayer insulating film includes a film having a diffusion constant of an oxidizing species smaller than that of a silicon oxide film. 3. The nonvolatile semiconductor memory device according to claim 2, wherein the film having a diffusion constant of the oxidizing species smaller than the silicon oxide film is a silicon oxynitride film or a silicon nitride film. 4. An interlayer insulating film comprising a silicon oxynitride film or a silicon nitride film formed in contact with a lower surface of the control gate electrode and a silicon oxide film formed in contact with an upper surface of the floating gate electrode. 4. The nonvolatile semiconductor memory device according to claim 3, wherein the nonvolatile semiconductor memory device is made of a film. 5. An interlayer insulating film comprising: a silicon oxynitride film formed in contact with a lower surface of the control gate electrode; and a silicon nitride film formed in contact with an upper surface of the floating gate electrode.
4. The nonvolatile semiconductor memory device according to claim 3, comprising a layer film. 6. A floating gate electrode and a control gate electrode each comprising a low-resistance polycrystalline silicon film doped with a large amount of impurities.
The nonvolatile semiconductor memory device according to any one of the above. 7. The nonvolatile semiconductor memory device according to claim 2, wherein said oxidizing species is oxygen, ozone, oxygen radical or water. 8. A gate insulating film, a floating gate electrode, an interlayer insulating film including a silicon oxide film and a film having a smaller diffusion coefficient of an oxidizing species than the silicon oxide film, and a control gate electrode are sequentially stacked on the main surface of the semiconductor substrate. A film having a smaller diffusion coefficient of oxidizing species than the silicon oxide film,
A method for manufacturing a nonvolatile semiconductor memory device, comprising: forming a silicon film, and then changing the silicon film to a silicon oxynitride film or a silicon nitride film. 9. The method according to claim 8, wherein the silicon film is formed by a chemical vapor deposition method. 10. The method for manufacturing a nonvolatile semiconductor memory device according to claim 8, wherein said silicon film is an amorphous silicon film. 11. The method of manufacturing a nonvolatile semiconductor memory device according to claim 8, wherein said silicon oxynitride film or silicon nitride film is formed on said silicon oxide film. Method. 12. The silicon oxynitride film or the silicon nitride film is formed by heat-treating the silicon film in a gas containing nitrogen radicals, nitric oxide or nitrous oxide. 12. The method for manufacturing a nonvolatile semiconductor memory device according to any one of items 1 to 11. 13. The film according to claim 12, wherein the film having a smaller diffusion coefficient of the oxidizing species than the silicon oxide film is formed by repeating the formation of the silicon film and the heat treatment a plurality of times. A method for manufacturing a nonvolatile semiconductor memory device.