JPH10223783A - Semiconductor device and fabrication thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a gate oxide against deterioration by employing silicon oxynitride having interface level density of different injected charge dependence in a nonvolatile semiconductor memory and as the gate insulator of a MOS transistor. SOLUTION: A nonvolatile semiconductor memory and an MOS transistor are formed in different regions on a same semiconductor substrate 1. The gate insulator 2 of the nonvolatile semiconductor memory is deposited by heat treating a silicon oxide in an atmosphere containing nitride monoxide and the gate insulator 2 of the MOS transistor is deposited by heat treating a silicon oxide in an atmosphere containing nitrous oxide. Thus obtained gate insulators 2 having interface level density of different injected charge dependence are employed in a nonvolatile semiconductor memory and a MOS transistor. This structure prevents generation of a level in the gate insulator 2 due to high field stress.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a method of manufacturing the same, and more particularly, to a non-volatile semiconductor memory device and a MOS transistor having a low interface state at an interface between a gate insulating film and a silicon substrate and having high characteristics. The present invention relates to a semiconductor device formed on the same semiconductor substrate and a method for manufacturing the same.

[0002]

2. Description of the Related Art As is well known, a non-volatile semiconductor memory device having a stack structure has a floating gate electrode and a control gate electrode. , Information is written, held and erased. As a typical structure, a gate insulating film made of a thin silicon oxide film having a thickness of about 10 nm and source and drain electrodes are formed on a silicon substrate, and a floating gate made of a polycrystalline silicon film is formed on the gate insulating film. An electrode, an insulating film, and a control gate electrode made of a polycrystalline silicon film are sequentially stacked.

Further, for example, 18 V, 0 V, and 20 V are applied to the control gate electrode, the source, the drain, and the silicon substrate, respectively.
When a voltage of 0 V or 0 V is applied for 1 millisecond, a Fowler-Nordheim (hereinafter abbreviated as FN) current flows from the silicon substrate to the floating gate electrode, and charges (electrons) flow into the floating gate electrode. It is stored and goes into the "erase" state.

On the other hand, the control gate electrode, the source, the drain and the silicon substrate have, for example,-
When a voltage of 9 V, 0 V, 4 V, and 0 V is applied for 1 millisecond, electrons in the floating gate electrode are extracted by the FN current to be in a “write” state. In order to “read” the data, for example, a power supply voltage of 3.3 V may be applied to the control gate electrode and a voltage of about 1 V may be applied to the drain electrode. From the threshold voltage of the drain current, it is possible to know the charge accumulation state of the floating gate. This is the principle of operation of a nonvolatile semiconductor memory device having a stack structure.
331403.

On the other hand, in a peripheral circuit of a nonvolatile semiconductor memory device having a stack structure, a MOS (Metal Oxide Semiconductor) is used.
Onductor) transistors are used. M
The OS transistor has, for example, 3.3 V, 0 V, and 1 V on the gate, source, drain, and silicon substrate, respectively.
It operates by applying a voltage of 0 V and 0 V. The operation at this time is the same as the operation at the time of “reading” of the nonvolatile semiconductor memory device having the stack structure.

[0006]

In the conventional nonvolatile semiconductor memory device having the above-mentioned stack structure, when the FN current flows between the silicon substrate and the floating gate electrode, the film thickness becomes 1
A high electric field of about 10 MV / cm is applied to a thin gate insulating film of about 0 nm. As a result, the gate insulating film deteriorates during repeated writing and erasing, resulting in good writing and
Erasing characteristics cannot be maintained, and it is difficult to maintain high reliability of the device without improving the breakdown voltage of the gate insulating film against electric stress.

Therefore, as a nonvolatile semiconductor memory device, the gate insulating film has a high withstand voltage against electric stress, prevents deterioration of the gate insulating film due to the FN tunnel current, and maintains good writing and erasing characteristics. It is extremely important.

Also, MOS used in peripheral circuits
In order to maintain the high-speed operation and high reliability required for recent LSI circuits, MO transistors are also required.
It is necessary that the resistance to hot carriers generated during the operation of the S transistor be high.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a nonvolatile semiconductor memory device having a high withstand voltage against electrical stress of a gate insulating film, preventing deterioration of the gate insulating film due to an FN tunnel current, and maintaining good write and erase characteristics. A semiconductor device in which a MOS transistor capable of maintaining high speed operation and high reliability by effectively preventing deterioration of a gate insulating film due to a semiconductor storage device and hot carriers is formed on the same semiconductor substrate, and a method of manufacturing the same. It is to provide.

[0010]

In order to achieve the above object, a semiconductor device according to the present invention comprises a gate insulating film, a floating gate electrode, an interlayer insulating film formed on a first region of a semiconductor substrate. A nonvolatile semiconductor memory device having a control gate electrode, and a MOS transistor having a gate insulating film and a gate electrode formed by being stacked on a second region different from the first region of the semiconductor substrate; The gate insulating film of the nonvolatile semiconductor memory device and the MO
The gate insulating films of the S transistors are characterized in that the dependence of the interface state density on the injected charge is different from each other.

That is, as is apparent from the band structure of the silicon substrate (semiconductor), gate insulating film (silicon oxide film), and polysilicon (metal) shown in FIG. When the FN tunnel current is injected into the film, high-energy hot electrons are simultaneously generated and strike out high-energy hot holes, which enter the inside of the gate insulating film. As a result, a deep trap level is formed near the interface in the gate insulating film, and the trap level degrades the gate insulating film.

However, when a part of the gate insulating film is nitrided, entry of hot holes into the gate insulating film is effectively prevented, and the trap level is not formed near the interface with the silicon substrate. Therefore, deterioration of the gate insulating film is prevented.

In order to nitride the substrate side of the gate insulating film, heat treatment may be performed using nitrous oxide (N ₂ O) or nitric oxide (NO). For example, silicon oxide can be oxynitrided by flowing N ₂ O gas for 5 minutes while heating the silicon substrate on which the silicon oxide film is formed at 1050 ° C. in an electric furnace.

However, according to the study of the present inventors, the characteristics of a silicon oxynitride film obtained by oxynitriding a silicon oxide film are different from each other when the oxynitridation method used is different, and the characteristics depend on the type of device. It has become clear that it is preferable to appropriately select the oxynitridation method.

That is, FIG. 4 shows the same film thickness (7.6 n
and m) a silicon oxide film (SiO ₂ film), an oxynitride film formed using N ₂ O (SiN ₂ O film), and a MOS using an oxynitride film formed using NO (SiNO film) as insulating films. The result of examining the dependence of the interface state density on the injected charge is shown by measuring the interface state density by the CV measurement method after a capacitor is fabricated and stress charges are injected.

As is clear from FIG. 4, the interface state density of the N ₂ O oxynitride film and the NO oxynitride film is lower than the interface state density of the silicon oxide film. The inclination angle of the straight line showing the dependence on the injected charge differs between the N ₂ O oxynitride film and the NO oxynitride film, and the order of the interface state density differs depending on the magnitude of the stress injection current. Therefore, if a gate insulating film suitable for the nonvolatile semiconductor memory device and the MOS transistor is selected so that the interface state density becomes the lowest, an extremely favorable result can be obtained.

That is, instead of using the same silicon oxynitride film as the gate insulating film, the silicon oxynitride films having different interfacial state densities depending on the injected charge are used for the gate insulating films of the nonvolatile semiconductor memory device and the MOS transistor, respectively. By using the film, the reliability of the semiconductor device in which the nonvolatile semiconductor memory device and its peripheral circuits are formed on the same semiconductor substrate is significantly improved.

It is preferable that the interface state density of the gate insulating film of the nonvolatile semiconductor memory device at an injected charge of 10 C / cm ² is lower than the interface state density of the gate insulating film of the MOS transistor. As the gate insulating film of the semiconductor memory device, a film formed by performing a heat treatment on a silicon oxide film in a gas containing nitrogen monoxide may be used.

Similarly, the interface state density of the gate insulating film of the MOS transistor when the injected charge is 0.1 C / cm ² is preferably lower than the interface state density of the gate insulating film of the nonvolatile semiconductor memory device. As the gate insulating film of the MOS transistor, a film formed by heat-treating a silicon oxide film in a gas containing nitrous oxide may be used.

That is, as shown in FIG.
When an electric charge of cm ² was injected, as shown by arrow A, the NO oxynitride film had a lower interface state density than the N ₂ O oxynitride film, and the injected electric charge was 0.1 C / cm 2. ^{In the case of 2,} the interface density of the N ₂ O oxynitride film was smaller than that of the NO oxynitride film, as is apparent from the arrow B.

Therefore, in the case of a device such as a flash memory cell into which a charge of about 10 C / cm ² is injected, the NO oxynitride film having the lowest interface state density when the injected charge amount is about this is used as the gate insulating film. By using this, the interface state density at the interface between the silicon substrate and the gate insulating film can be reduced most effectively.

Similarly, in the case of a MOS transistor or a MOS capacitor into which a charge of about 0.1 C / cm ² is injected, N ₂ O oxynitride having the lowest interface state density when the amount of the injected charge is this level is used. A film may be used.

Preferred results can be obtained if the thickness of the gate insulating film of the nonvolatile semiconductor memory device is 5 nm to 12 nm and the thickness of the gate insulating film of the MOS transistor is 3 nm to 10 nm.

According to the semiconductor device of the present invention, a step of forming a silicon oxide film on a predetermined region of a semiconductor substrate and then performing a heat treatment in a gas containing nitrogen monoxide to form a gate insulating film; A floating gate electrode made of a first polycrystalline silicon film doped with a large amount of impurities, an interlayer insulating film, and a control gate electrode made of a polycrystalline silicon film doped with a large amount of impurities are laminated on the non-volatile semiconductor The semiconductor device can be manufactured by a method for manufacturing a semiconductor device, including a step of forming a memory device.

As the above-mentioned gas, a gas containing 0.1% to 100% of nitrogen monoxide can be used, and more preferable results can be obtained if the content of nitrogen monoxide is 1% to 10%. In this case, the heat treatment can be performed at 800 to 950 ° C.

Further, in the semiconductor device of the present invention, a step of forming a gate insulating film by forming a silicon oxide film on a predetermined region of a semiconductor substrate and then performing a heat treatment in a gas containing nitrous oxide. A method of manufacturing a semiconductor device, comprising a step of forming a MOS transistor by forming a MOS transistor by stacking a gate electrode on a polycrystalline silicon film doped with a large amount of impurities on an insulating film.

In this case, the above-mentioned gas is 0.1% to
A gas containing 100% nitrous oxide can be used,
If the content of nitrous oxide is 5% to 100%, more preferable results can be obtained. The heat treatment in this case is 80
It is performed at 0 ° C to 1,100 ° C.

The above-mentioned nonvolatile semiconductor memory device and MOS
The transistor is formed in a first region of the same semiconductor substrate and in a second region different from the first region.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a nonvolatile semiconductor memory device and a MOS transistor are formed in different regions of the same semiconductor substrate, respectively, and a gate insulating film having different interface state densities depending on injected charges is formed by a nonvolatile semiconductor memory device. Used for a non-volatile semiconductor memory device and a MOS transistor.

A gate insulating film of a nonvolatile semiconductor memory device is formed by heat-treating a silicon oxide film in an atmosphere containing nitric oxide. A gate insulating film of a MOS transistor contains a silicon oxide film containing nitrous oxide. It is formed by heat treatment in an atmosphere.

As a nonvolatile semiconductor memory device, a rewritable nonvolatile semiconductor memory device having a stack structure of a control gate electrode / interlayer insulating film / floating gate electrode / gate insulating film / silicon substrate such as a flash memory. Can be applied to

A preferable result can be obtained even if the same type of insulating film as the gate insulating film of the MOS transistor is used for the MOS capacitor.

According to the present invention, the state of generation of hot carriers in each semiconductor element to be formed is checked in advance, and a silicon oxynitride film having the lowest interface state density is selected in response to the check, thereby providing a nonvolatile semiconductor memory. The reliability of the device and peripheral circuits is significantly improved.

[0034]

【Example】

<Embodiment 1> A first embodiment of the present invention will be described with reference to FIG. 1 showing a sectional structure of a memory cell. As shown in FIG. 1, after the silicon substrate 1 is immersed in an aqueous solution containing ammonia and hydrogen peroxide, the surface oxide film is removed using a hydrofluoric acid aqueous solution, and the field oxide film is formed using a known selective oxidation method. (Not shown). Next, a flow rate of 10 liters /
The silicon substrate 1 is heated in a wet oxidizing atmosphere for 1 minute to form a silicon oxide film having a thickness of 9 nm at a substrate temperature of 850 ° C., and is immediately transferred to an oxynitriding furnace, and a nitrogen diluted 5% NO gas flow rate 3 SLM (Standard Litter per Minut
e), oxynitriding was performed at a substrate temperature of 850 ° C. to form a silicon oxynitride film 2.

Next, a 200 nm-thick amorphous silicon film containing 3 × 10 ²⁰ cm ⁻³ of phosphorus was formed by a well-known reduced pressure chemical vapor deposition method using monosilane and phosphine. Crystallization was performed by heating at 20 ° C. for 20 minutes to form a polycrystalline silicon film 5.

The surface of the polycrystalline silicon film 5 is thermally oxidized in a 10% oxygen atmosphere diluted with nitrogen at a substrate temperature of 800 ° C. to form a silicon oxide film having a thickness of 5 nm. A 13-nm-thick silicon nitride film was formed by the well-known chemical vapor deposition method used, and the surface of the silicon nitride film was changed to a silicon oxide film by performing thermal oxidation at 900 ° C. in a wet oxidizing atmosphere to form an interlayer insulating film. A three-layer film (hereinafter, referred to as an ONO film) 2 ′ composed of a silicon oxide film, a silicon nitride film, and a silicon oxide film was formed.

A polycrystalline silicon film 6 containing phosphorus (having a thickness of 200 nm) is formed on the ONO film 2 'by a well-known reduced pressure chemical vapor deposition method using monosilane and phosphine. Heat treatment was performed for 20 minutes.

The polycrystalline silicon film 6 is turned on by the well-known photo-etching using a common etching mask.
Unnecessary portions of the O film 2 ′, the polycrystalline silicon film 5, and the silicon oxynitride film 2 were sequentially removed to form a control gate electrode 6, an interlayer insulating film 2 ′, a floating gate electrode 5, and a gate insulating film 2.

The control gate electrode 6, the interlayer insulating film 2 ',
After the exposed portions of the floating gate electrode 5 and the gate insulating film 2 are covered with the silicon oxide film 11, impurities having a conductivity type opposite to that of the silicon substrate 1 are removed by using a well-known ion implantation method. To form a source-side diffusion layer 4 and a drain-side diffusion layer 3. Further, after a silicon oxide film containing arsenic and phosphorus was formed on the entire surface, the upper surface of the silicon oxide film was flattened by heating. A contact hole for exposing the surface of the source-side diffusion layer 4 and the drain-side diffusion layer 3 is formed by using a known method,
Further, electrodes were formed to produce a memory cell.

The rewriting characteristics of the nonvolatile semiconductor memory device manufactured in this example were evaluated as follows. An FN current flows from the substrate side 1 to the floating gate electrode 5 and electrons are injected into the floating gate electrode 5 to perform an “erasing” operation, and the electrons in the floating gate electrode 5 are diffused as a FN current on the drain side. The “writing” operation was performed by pulling out the layer 3. In the erasing operation, the control gate electrode, the source-side diffusion layer, the drain-side diffusion layer, and the substrate each have 18 V, 0 V,
V, 0 V, and 0 V pulse voltages are applied for 1 millisecond, and in the write operation, 9 V, 0 V, 4 V, and 0 V, respectively.
Was applied for 1 millisecond. “Reading” was performed by applying a power supply voltage of 3.3 V to the control gate and a voltage of about 1 V to the drain electrode. Such a measurement can be performed using NO
Performed for the conventional case using the present embodiment a silicon oxide film using ₂ oxynitride films were compared with each other. From the threshold voltage of the drain current, it is possible to know the charge accumulation state of the floating gate.

FIG. 6 shows the obtained write / erase characteristics. In FIG. 6, the number of rewrites is plotted on the horizontal axis, and
The vertical axis indicates the threshold voltage when the erase operation is performed. As is apparent from FIG. 6, NO was used as the gate insulating film.
When the oxynitride film is used, the change in the threshold voltage due to the increase in the number of rewrites is smaller than in the conventional case using the silicon oxide film, and the change in the threshold voltage after 100,000 rewrites is performed. By about 30%.

<Embodiment 2> The second embodiment of the present invention
This will be described with reference to FIG. 2 illustrating a cross-sectional structure of an OS transistor. After immersing the silicon substrate 1 in an aqueous solution containing ammonia and hydrogen peroxide, the surface oxide film was removed with a hydrofluoric acid aqueous solution, and a field oxide film (not shown) was formed using a known selective oxidation method. Next, a flow rate of 10 liters /
The silicon substrate 1 is heated in a wet oxidizing atmosphere for
A silicon oxide film 2 having a thickness of 9 nm was formed at a substrate temperature of 850 ° C. Immediately, the substrate was transferred into an oxynitriding furnace and oxynitrided under the conditions of a 100% N ₂ O gas flow rate of 3 SLM and a substrate temperature of 850 ° C. to form a gate insulating film 2 made of a silicon oxynitride film.

Next, a 200 nm-thick amorphous silicon film containing 3 × 10 ²⁰ cm ⁻³ of phosphorus was formed by a well-known reduced pressure chemical vapor deposition method using monosilane and phosphine. A polycrystalline silicon film 7 was formed by heating at 20 ° C. for 20 minutes, and further processed into a predetermined shape using a known 0.3 μm process to form a gate electrode 7 having a width of 0.3 μm. After the surface of the gate electrode 7 was covered with a silicon oxide film, an impurity having a conductivity type opposite to that of the silicon substrate 1 was ion-implanted to form the source-side diffusion layer 4 and the drain-side diffusion layer 3.

Next, a silicon oxide film (not shown) containing arsenic and phosphorus is formed on the entire surface, and the surface is flattened by heating. Then, a contact hole is formed in the insulating film to form the source side diffusion layer. 4 and the surface of the drain-side diffusion layer 3 are exposed,
Further, source and drain electrodes (not shown) are formed and M
An OS transistor was manufactured.

In the MOS transistor formed in this embodiment and the conventional MOS transistor using a silicon oxide film as a gate insulating film, the mutual conductance with respect to the gate voltage (the change in the drain current with respect to the change in the gate voltage per unit gate width). The rate of change was measured and the two were compared, and the results shown in FIG. 7 were obtained.

As is apparent from FIG. 7, the maximum value of the mutual conductance is almost the same, but when the gate voltage becomes higher than approximately 1.5 V, the MO according to the present embodiment is reduced.
The S transistor has higher transconductance than the conventional MOS transistor. This effect is obtained because the Si—H bond replaces the Si—N bond by the oxynitridation reaction to stabilize the bond, and the interface state due to the Si—H bond existing at the interface between the silicon oxide film and the silicon substrate disappears. It is thought that it was done.

Further, even when hot carriers are injected, the transconductance of the MOS transistor according to the present embodiment is always 5% higher than that of the conventional MOS transistor.
It was high. This is because the bonding between the gate insulating film and the silicon substrate is stabilized by the Si—N bond generated by the oxynitridation reaction, so that even if hot carriers are injected, a new interface state is hardly generated. it is conceivable that.

<Embodiment 3> A third embodiment of the present invention will be described with reference to FIG. As is clear from FIG. 5, the flash memory chip 8 of this embodiment has a flash memory area 9 and a peripheral circuit area 10 in which MOS transistors are formed.

In the flash memory region 9, the nonvolatile semiconductor memory device having a stack structure shown in FIG. 1 was formed, and a NO oxynitride film was used as the gate insulating film 2. Further, the MOS shown in FIG.
A transistor is formed, and N ₂ is used as the gate insulating film _2.
An O oxynitride film was used. These NO oxynitride films and N ₂ O
The oxynitride film was formed in the same manner as in Example 1 and Example 2, respectively.

Writing and erasing were performed 10 ⁶ times on the flash memory 9, and a charge retention life when an electric field of 3 MV / cm was applied was obtained from an acceleration test on threshold voltage fluctuation. The same measurement was performed for a conventional flash memory using a silicon oxide film as a gate insulating film, and the two were compared.

As a result, the charge retention life of the conventional flash memory was 7 years, but the charge retention life of the flash memory of this embodiment using the NO oxynitride film as the gate insulating film 2 was 14 years. And improved significantly.

Since the MOS transistor in the peripheral circuit region 10 also uses the N ₂ O oxynitride film as the gate insulating film 2, the hot carrier resistance is improved and the fluctuation of the voltage applied to the flash memory is reduced. The synergistic effect further improved the reliability of the entire chip.

[0053]

According to the present invention, the generation of a level in a gate insulating film due to a high electric field stress is suppressed, and the reliability of the write / erase characteristics and the charge retention of a nonvolatile semiconductor memory device having a stack structure are suppressed. Life is improved and MO
The hot carrier resistance of the S transistor has been improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention;

FIG. 2 is a sectional view showing a second embodiment of the present invention;

FIG. 3 is a view showing a band structure of a silicon substrate, a gate insulating film, and polysilicon;

FIG. 4 is a diagram for explaining an effect of the present invention;

FIG. 5 is a plan view showing a third embodiment 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.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 2 ... Gate insulating film, 2 '... Interlayer insulating film, 3 ... Drain side diffusion layer, 4 ... Source side diffusion layer, 5 ...
Floating gate electrode, 6 control gate electrode, 7 gate electrode, 8 flash memory chip, 9 flash memory cell region, 10 peripheral circuit region, 11 silicon oxide film.

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI H01L 29/78

Claims (13)

[Claims] A non-volatile semiconductor memory device having a gate insulating film, a floating gate electrode, an interlayer insulating film, and a control gate electrode formed on a first region of a semiconductor substrate;
A MOS transistor having a gate insulating film and a gate electrode formed by being stacked on a second region of the semiconductor substrate different from the first region, wherein the gate insulating film of the nonvolatile semiconductor memory device and A semiconductor device characterized in that gate electrode insulating films of MOS transistors have different injected state dependencies of interface state density. 2. The non-volatile semiconductor memory device according to claim 1, wherein an interface state density at an injected charge of 10 C / cm ² is lower in a gate insulating film of the nonvolatile semiconductor memory device than in a gate insulating film of the MOS transistor. Semiconductor device. 3. The non-volatile semiconductor memory device according to claim 2, wherein the gate insulating film is a film formed by heat-treating a silicon oxide film in a gas containing nitrogen monoxide. Semiconductor device. 4. The device according to claim 1, wherein the interface state density at an injected charge of 0.1 C / cm ² is lower in the gate insulating film of the MOS transistor than in the nonvolatile semiconductor memory device. 13. The semiconductor device according to claim 1. 5. The semiconductor device according to claim 4, wherein the gate insulating film of the MOS transistor is a film formed by heat-treating a silicon oxide film in a gas containing nitrous oxide. 6. The nonvolatile semiconductor memory device according to claim 1, wherein the gate insulating film has a thickness of 5 nm to 12 nm, and the MOS transistor has a gate insulating film having a thickness of 3 nm to 10 nm. 6. The semiconductor device according to any one of 5. 7. A step of forming a silicon oxide film on a predetermined region of a semiconductor substrate, followed by heat treatment in a gas containing nitrogen monoxide to form a gate insulating film;
A nonvolatile semiconductor memory device is formed by stacking a floating gate electrode made of a first polycrystalline silicon film doped with a large amount of impurities, an interlayer insulating film, and a control gate electrode composed of a polycrystalline silicon film doped with a large amount of impurities. A method for manufacturing a semiconductor device, comprising a step of forming. 8. The method according to claim 7, wherein said gas contains 0.1% to 100% of nitrogen monoxide. 9. The method according to claim 8, wherein the heat treatment is performed at 800 ° C. to 950 ° C. 10. A step of forming a gate insulating film by forming a silicon oxide film on a predetermined region of a semiconductor substrate and then performing heat treatment in a gas containing nitrous oxide, and forming a large amount of impurities on the gate insulating film. And a step of forming a MOS transistor by laminating a gate electrode made of a polycrystalline silicon film doped with GaN. 11. The method according to claim 10, wherein said gas contains 0.1% to 100% of nitrous oxide. 12. The method according to claim 11, wherein the heat treatment is performed at 800 ° C. to 1,100 ° C. 13. The non-volatile semiconductor storage device and the MO
13. The semiconductor according to claim 7, wherein the S transistor is formed in a first region of the same semiconductor substrate and in a second region different from the first region. Device manufacturing method.