JP2011146580A - Method of manufacturing silicon carbide semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem in nitriding processing on an insulating film/silicon carbide interface, wherein when an NO gas or N<SB>2</SB>O gas is introduced into a high-temperature reaction furnace, those gases are thermally decomposed and a new interface level is generated by re-oxidation by oxygen produced during the thermal decomposition, so reducible interface level density is suppressed. <P>SOLUTION: The method of manufacturing a silicon carbide semiconductor device includes a step of forming an insulating film on a wafer whose surface is formed of a silicon carbide layer, and a nitriding processing step of nitriding an interface between the silicon carbide layer and an insulating film by heat-treating the wafer after insulating film formation at a predetermined processing temperature in a nitrogen oxide gas atmosphere to which carbon monoxide gas is added. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a silicon carbide semiconductor device, and more particularly to a method for reducing the on-resistance of a silicon carbide MOSFET.

Silicon carbide (SiC) has a wider band gap than silicon (Si) and has excellent physical properties such as dielectric breakdown field strength, saturation electron velocity and thermal conductivity, and is an excellent property as a semiconductor power device material. Have What is expected to be realized as a power device using silicon carbide is a high output insulated gate field effect transistor (MOSFET) with high breakdown voltage and low loss. Since silicon carbide has an excellent feature that an insulating film made of high-quality silicon dioxide (SiO ₂ ) can be formed by a thermal oxidation method, a silicon dioxide (SiO ₂ ) film is used as a gate insulating film of a silicon carbide MOSFET. Can be used. The SiO ₂ film on silicon carbide can be formed by a method such as a thermal oxidation method or a chemical vapor deposition (CVD) method.

Although silicon carbide has excellent physical property values as described above, even if a silicon carbide MOSFET is manufactured by a conventional manufacturing method, the mobility of the channel layer (inversion layer) is small, and the performance expected from the physical property values is still Not realized. This is because a large number of interface states (traps) are generated at the so-called MOS interface of silicon dioxide (SiO ₂ ) / silicon carbide (SiC) formed by the conventional thermal oxidation method, so that it can move sufficiently within the channel layer. This is because it is difficult to cause a large number of majority carriers to exist, and the channel conductance (channel mobility μch) becomes very low. As a result, there is a problem that the on-resistance (source / drain resistance during conduction) of the element increases and the loss during the on-operation increases.

Various methods have been studied and reported in order to reduce the interface state existing at the MOS interface. For example, a method of nitriding under a reduced pressure atmosphere disclosed in Patent Document 1, a method of nitriding by diluting a nitrogen oxidizing gas with an inert gas disclosed in Patent Document 2, a cold wall disclosed in Patent Document 3 A method of nitriding using a furnace has been reported. Further, heat treatment is performed while irradiating with ultraviolet rays in a single gas or mixed gas atmosphere of nitrogen monoxide (NO), nitrogen dioxide (N ₂ O), ammonia (NH ₃ ), and hydrogen (H ₂ ) disclosed in Patent Document 4. A method has also been reported.

JP-A-2005-136386 JP 2006-210818 A JP 2005-109396 A JP 2000-286258 A

As described above, the high-temperature heat treatment (nitriding treatment) in the NO gas or N ₂ O gas atmosphere after forming the insulating film by the thermal oxidation method is promising as a means for improving the channel mobility. However, when NO gas or N ₂ O gas is introduced into a high-temperature reactor in such nitriding treatment, these gases are thermally decomposed, and new interface states are generated due to re-oxidation by oxygen generated during the thermal decomposition. Therefore, there is a problem that the interface state density that can be reduced is suppressed.

The inventions described in Patent Documents 1, 2, and 3 described above are techniques for reducing the oxidation rate by reducing the oxygen partial pressure in the nitriding atmosphere and preventing reoxidation at the gate insulating film / silicon carbide interface. In addition, since it is extremely difficult to prevent the decomposition of NO gas and N ₂ O gas itself, there is a problem that a trace amount of oxygen is generated. Similarly, in the method of performing high-temperature heat treatment while irradiating ultraviolet rays, reoxidation with radical oxygen (—O—) having high oxidizing power in NO gas or N ₂ O gas atmosphere causes NO gas or N ₂ O gas and NH ₃ to be reoxidized. In a mixed atmosphere of gas or H ₂ gas, re-oxidation by H ₂ O caused by the reaction of both occurs, and a new interface state is generated, so that the effect of reducing the interface state density by nitriding treatment is suppressed. was there. The present invention has been made to solve the above-described problems.

  In the processing temperature region of 1100 ° C. or higher effective for nitriding, the present inventors re-oxidize the gate insulating film / silicon carbide interface even with such an oxygen amount (partial pressure), and reduce the interface state by nitriding. The inventors have found that the effect is suppressed for the first time, and have invented a method for manufacturing a semiconductor device described in detail below.

  The method of manufacturing a semiconductor device according to the present invention includes a step of forming an insulating film on a wafer having a silicon carbide layer on the surface, and a nitrogen oxide gas atmosphere in which carbon monoxide gas is added to the wafer after the insulating film is formed. And a nitriding treatment step of nitriding the interface between the silicon carbide layer and the insulating film by performing a heat treatment at a predetermined treatment temperature.

  According to the method for manufacturing a semiconductor device according to the present invention, the generation of interface states due to reoxidation can be suppressed, so that the amount of interface states reduced by nitriding treatment is increased and the channel mobility is improved. As a result, a low-loss semiconductor device with low on-resistance can be manufactured.

It is a figure which shows roughly the cross-section of the silicon carbide semiconductor device which concerns on Embodiment 1 of this invention. It is process sectional drawing of the manufacturing method of the silicon carbide semiconductor device which concerns on Embodiment 1 of this invention. It is process sectional drawing of the manufacturing method of the silicon carbide semiconductor device which concerns on Embodiment 1 of this invention. It is process sectional drawing of the manufacturing method of the silicon carbide semiconductor device which concerns on Embodiment 1 of this invention. It is process sectional drawing of the manufacturing method of the silicon carbide semiconductor device which concerns on Embodiment 1 of this invention. It is a schematic diagram of the reactor used for manufacture of the silicon carbide semiconductor device which concerns on Embodiment 1 of this invention. It is a figure which shows the temperature profile in each process process time series relevant to gate insulating film preparation in manufacture of the silicon carbide semiconductor device which concerns on Embodiment 1 of this invention. It is the figure which showed typically the flow of each gas and the reaction which arises in the reactor in the reactor used for the manufacturing method of the silicon carbide semiconductor device which concerns on Embodiment 1 of this invention. It is process sectional drawing of the manufacturing method of the silicon carbide semiconductor device which concerns on Embodiment 1 of this invention. It is process sectional drawing of the manufacturing method of the silicon carbide semiconductor device which concerns on Embodiment 1 of this invention. It is a figure which shows the temperature profile in each process process time series relevant to gate insulating film preparation in manufacture of the silicon carbide semiconductor device which concerns on Embodiment 2 of this invention. It is a figure which shows roughly the cross-section of the silicon carbide semiconductor device which concerns on Embodiment 3 of this invention.

Embodiment 1 FIG.
1 is a schematic cross-sectional view of a silicon carbide semiconductor device manufactured by the method for manufacturing a silicon carbide semiconductor device of the first embodiment. As an example of the silicon carbide semiconductor device, a cross-sectional structure of an n-channel silicon carbide MOSFET is shown.

  In FIG. 1, the silicon carbide semiconductor device has an n-type silicon carbide drift layer 20 formed on the first main surface of low-resistance n-type silicon carbide substrate 10 and a predetermined surface side of silicon carbide drift layer 20. And a p-type base region 30 containing aluminum (Al) as the first impurity as a p-type impurity, and a surface layer portion on the inner side with respect to the respective cross-sectional directions of the base region 30 The n-type source region 40 is formed shallower than the base region 30 and contains the second impurity nitrogen (N) as an n-type impurity, and the surface of the silicon carbide drift layer 20 including the base region 30 and the source region 40. The gate insulating film 50 made of silicon dioxide and a portion including a region between the pair of source regions 40 on the gate insulating film 50 are formed except for a part on the surface side of the source region 40. A gate electrode 60 provided at a position where the gate insulating film 50 is not formed, a source electrode 70 provided on the surface of the source region 40 where the gate insulating film 50 is not formed, and a second electrode opposite to the first main surface of the silicon carbide substrate 10. And a drain electrode 80 provided on the back surface side.

  In FIG. 1, a region in the base region 30 that faces the gate electrode 60 through the gate insulating film 50 and in which a channel layer is formed during the ON operation is referred to as a channel region. Further, the distance between which the channel region is sandwiched between the region where the ion implantation is not performed at the surface layer portion of silicon carbide drift layer 20 and source region 40 is referred to as a channel length.

  First, an outline of the operation of the silicon carbide semiconductor device shown in FIG. 1 will be described. In the silicon carbide semiconductor device of FIG. 1, when a voltage is applied to gate electrode 60, a channel layer is formed on the surface of base region 30 immediately below the gate electrode, and a charge is generated between source region 40 and silicon carbide drift layer 20. Is formed. When the silicon carbide MOSFET is an n-channel MOSFET, majority carriers are electrons, and electrons flowing from the source region 40 into the silicon carbide drift layer 20 are generated along the electric field generated by the voltage applied to the drain electrode 80 and the silicon carbide drift layer 20 and It reaches the drain electrode 80 through the n-type silicon carbide substrate 10. Therefore, a current flows from the drain electrode 80 to the source electrode 70 by applying a voltage to the gate electrode 60.

  On the other hand, when the silicon carbide MOSFET is a p-channel MOSFET and the majority carriers are holes, the holes injected from drain electrode 80 flow through silicon carbide drift layer 20 and reach base region 30, and then Then, it flows into the source region 40 according to the potential of the source electrode 70 through the channel layer formed on the surface of the base region 30. As a result, holes flow from the drain electrode 80 to the source electrode 70.

  A method of manufacturing an n-channel MOSFET that is the silicon carbide semiconductor device of the first embodiment will be described with reference to FIGS. 2 to 5 and FIGS. 9 and 10 are schematic cross-sectional views in the respective manufacturing steps of the n-channel MOSFET.

As shown in FIG. 2, first, on the surface of the low resistance n-type silicon carbide substrate 10 whose first main surface has a (0001) plane and has a 4H polytype, for example, a chemical vapor phase is formed. Silicon carbide drift layer 20 having an n-type impurity concentration of 1 × 10 ¹⁵ cm ⁻³ to 1 × 10 ¹⁸ cm ⁻³ and a layer thickness of 5 to 50 μm is epitaxially grown by a deposition method (Chemical Vapor Deposition: CVD). By forming the silicon carbide drift layer 20 under such conditions, a vertical high breakdown voltage MOSFET having a breakdown voltage of several hundred V to 3 kV or more can be realized.

Next, as shown in FIG. 3, first implantation mask 100 is formed on the surface of silicon carbide drift layer 20, and using p-type first impurity Al as a silicon carbide drift, using first implantation mask 100 as a mask. Ions are implanted into the layer 20. At this time, the depth of ion implantation of Al is set to a level that does not exceed the thickness of the silicon carbide drift layer 20, that is, about 0.5 to 3 μm. Further, the impurity concentration of the ion-implanted Al is set in advance within a range of 1 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ and higher than the n-type impurity concentration of the silicon carbide drift layer 20. Set. A region in which Al is ion-implanted in silicon carbide drift layer 20 and becomes p-type conductivity functions as base region 30.

After removing first implantation mask 100, a second implantation mask 110 having a width wider than that of first implantation mask 100 in the channel length direction is formed on the surface of silicon carbide drift layer 20, as shown in FIG. Nitrogen (N), which is an n-type second impurity, is ion-implanted into the surface of the silicon carbide drift layer 20 on which the second implantation mask 110 is formed. The ion implantation depth of N is set so as to be shallower than the thickness of the base region 30. Further, the impurity concentration of the ion-implanted N is set in advance so as to exceed the p-type impurity concentration of the base region 30 within a range of 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ²¹ cm ⁻³ . Of the region into which N is implanted in silicon carbide drift layer 20, the n-type region functions as source region 40. After removing the second implantation mask 110, annealing is performed in a heat treatment apparatus in an inert gas atmosphere such as argon (Ar) gas at a treatment temperature of 1300 to 1900 ° C. for 30 seconds to 1 hour. By such annealing treatment, ion-implanted N and Al are electrically activated.

Subsequently, as shown in FIG. 5, the surface of the silicon carbide drift layer 20 including the source region 40 and the base region 30 is thermally oxidized, and a gate insulating film made of SiO ₂ having a desired thickness of 100 nm or less. 50 is formed.
Next, a characteristic manufacturing process, that is, a nitriding process in the method for manufacturing the silicon carbide semiconductor device of the first embodiment will be described in detail below.

Using the reaction furnace 200 shown in FIG. 6, nitriding is performed according to the sequence shown in FIG. In FIG. 7, the vertical axis represents the temperature in each processing step, and the horizontal axis represents time, and the nitriding step in an NO gas or N ₂ O gas atmosphere is shown with a temperature profile in time series.

  The operation of the reaction furnace 200 of FIG. 6 will be described below. First, a wafer on which a large number of semiconductor manufacturing apparatuses are formed is installed in the boat 201 in the reaction furnace 200. By using the boat 201, it is possible to process a plurality of wafers at the same time, and the manufacturing cost can be reduced. A dummy substrate 204 is installed in the vacant part of the boat 201 to prevent the vacant part from becoming dirty during film formation. After the wafer is placed in the reaction furnace 200, each gas for processing is introduced from the gas inlet 203, and the inside of the reaction furnace 200 is heated by the heater 202 attached to the periphery of the reaction furnace 200. A desired processing temperature can be controlled with high accuracy by electronically controlling the output of the heater 202.

Next, the nitriding process will be described. After the wafer 300 is introduced into the reaction furnace 200, it is evacuated until the pressure in the reaction furnace 200 and the gas piping reaches 1.3 Pa or less. Such evacuation is performed for the purpose of removing the oxidizing gas in the reaction furnace 200. After reaching the target pressure, an inert gas is caused to flow into the reaction furnace 200 from the gas inlet 203 to return to atmospheric pressure, and then the temperature is raised while maintaining the same atmosphere. After reaching a desired heat treatment temperature, NO gas or N ₂ O gas and CO gas highly reactive with oxygen are introduced into the reaction furnace 200 from the gas inlet 203. The CO gas has a property of changing NO gas or N ₂ O gas into a gas having low oxidizing power such as CO ₂ gas. Incidentally, CO gas is extremely stable even in a heat treatment region at a high temperature such as nitriding the surface of the silicon carbide layer, and has a feature that it does not thermally decompose.

FIG. 8 is a diagram schematically showing the flow of each gas in the reaction furnace 200 and the reaction that occurs. Oxygen (O ₂ ) generated by thermal decomposition of a nitric oxide-based gas represented by NO gas or N ₂ O gas during nitriding treatment reacts with CO gas, and CO ₂ is a stable gas with low oxidizing power. (CO + O ₂ → 2CO ₂ ) gas. The same effect can be obtained by nitriding in an atmosphere diluted with an inert gas such as N ₂ or Ar or a reduced pressure atmosphere in addition to the above mixed gas.

By the nitriding treatment by the above-described method, generation of oxygen (O ₂ ) that may re-oxidize the gate insulating film / silicon carbide interface and generate an interface state is prevented, so that the nitriding treatment can be effectively performed. . Further, there is no limitation on the nitriding time, and it is possible to select an optimal time according to the gate insulating film material and film thickness. The treatment temperature during nitriding is preferably in the range of 1100 ° C. or higher and 1300 ° C. or lower where the nitriding effect is high. The above-mentioned inert gas or mixed gas atmosphere is suitable for the temperature drop.
In addition, since CO gas has a property which corrodes the material containing nickel (Ni) and iron (Fe), attention is required for the gas piping and the exhaust piping to be SUS piping.

The optimum mixing ratio of CO gas will be discussed below. As an example, the optimum mixing ratio (volume ratio) of NO gas and CO gas will be described.
When NO gas and CO gas are mixed, the following three reactions occur.
2NO → N ₂ + O ₂ (1)
2CO + O ₂ → 2CO ₂ (2)
2NO + 2CO → 2CO ₂ + N ₂ (3)
Reaction (1) is a reaction in which oxygen is generated by thermal decomposition of NO gas. Reaction formula (2) is a reaction in which the O ₂ gas generated in the reaction (1) is changed to CO ₂ gas by CO gas. Reaction (3) is a reaction in which NO gas, which plays a role in reducing the interface state, is consumed by CO gas.

In order to change all of the O ₂ gas generated by the reactions (1) and (2) into CO ₂ gas, it is necessary to set the CO gas flow rate to at least twice the O ₂ gas generation amount. However, it must also be taken into account that NO gas reacts with CO gas and is consumed from reaction (3). Therefore, the CO gas flow rate needs to be smaller than the NO gas flow rate. In other words, the optimum condition is that the mixing ratio [CO] / [NO] (hereinafter, the volume ratio) of NO gas and CO gas is 1 or less, and more than twice the amount of generated O ₂ gas is generated. Become. Calculation of the O ₂ gas generation amount produced | generated according to Reaction Formula (1)-(3) is possible by the calculation method of Table 2 using the NO gas reaction equation shown in Table 1. That is, by substituting the heat treatment temperature and the NO gas flow rate flowing in the reactor into Table 2, the amount of O ₂ gas generated after t seconds can be obtained. It can be calculated by calculating t seconds until the gas reaches the wafer time.

上述の表中で、Ｅa, E-aは矢印方向（⇔）の活性化エネルギーを表し、ka、k-aは矢印方向（⇔）の反応測定定数を表す。Ｅb, E-b, kb、k-b以下も同様である。また、Ｒは気体定数を、Ｔは温度、ｔは時間をそれぞれ表す。

In the above table, Ea and Ea represent activation energy in the arrow direction (⇔), and ka and ka represent reaction measurement constants in the arrow direction (⇔). The same applies to Eb, Eb, kb, and below kb. R represents a gas constant, T represents temperature, and t represents time.

For example, when the heat treatment temperature is 1250 ° C. and the time that the gas stays before reaching the wafer in the reaction furnace 200 is 30 seconds, the amount of O ₂ gas generated is 0.1 × NO gas flow rate. That is, O ₂ gas corresponding to 10% of the NO gas flow rate is generated. The optimum mixing ratio [CO] / [NO] of the NO gas flow rate and the CO gas flow rate in this case is larger than 0.1 from the viewpoint that the CO gas flow rate is larger than the O ₂ gas generation amount, and the CO gas flow rate is NO gas. It is within a range smaller than 1 from the viewpoint of less than the flow rate.

Even when an inert gas such as Ar or N ₂ is mixed, the amount of O ₂ gas generated can be calculated by the same calculation method, so that the optimum range of the mixing ratio [CO] / [NO] can be estimated.

  By using a mixed gas having a mixture ratio [CO] / [NO] optimized in accordance with the above calculation, it is possible to perform a nitriding process that does not cause reoxidation of the silicon carbide / gate insulating film interface. .

  Next, as shown in FIG. 9, a polycrystalline silicon film having conductivity is formed on the gate insulating film 50 by a low pressure CVD method, and patterned into a predetermined shape, thereby forming a gate electrode 60. At this time, the gate electrode 60 preferably overlaps with the pair of source regions 40 through the gate insulating film 50 in the range of, for example, 10 nm to 5 μm.

  Thereafter, as shown in FIG. 10, the gate insulating film 50 excluding the portion covered with the gate electrode 60 and the vicinity thereof is removed. Finally, source electrode 70 electrically connected to source region 40 is formed and drain electrode 80 is formed on the back surface side of silicon carbide substrate 10 to complete the n-channel MOSFET shown in FIG. Here, examples of the material constituting the source electrode 70 and the drain electrode 80 include an Al alloy.

A silicon carbide MOSFET which is a kind of silicon carbide semiconductor device manufactured in the above-described process effectively generates oxygen (O ₂ ) that may reoxidize the silicon carbide surface by adding CO gas during nitriding. Therefore, the amount of interface states reduced by nitriding increases. As a result, since high channel mobility is obtained in the channel layer, the on-resistance of the silicon carbide MOSFET is reduced, and the loss during the on-operation can be reduced.

  In the present embodiment, the gate insulating film 50 is an example of a silicon oxide film formed by thermally oxidizing silicon carbide. However, the gate insulating film 50 is formed by a CVD method, a vapor deposition method, a sputtering method, an ion cluster beam. It may be a deposited film formed by a method, a molecular beam epitaxy method or the like. The material of the gate insulating film is not limited to silicon oxide, and may be a silicon nitride film, a silicon oxynitride film, an aluminum oxide film, an aluminum nitride film, a hafnium oxide film, a zirconium oxide film, or the like. Further, the gate insulating film may have a laminated structure in which silicon nitride and silicon dioxide are combined, for example.

  Further, as silicon carbide substrate 10, a low resistance n-type silicon carbide substrate 10 having a (0001) plane as a first main surface and a 4H polytype is shown as an example. Is not limited to 4H, and the orientation of the first principal surface may be the (000-1) plane, the (11-20) plane, etc., and is inclined in any direction from these plane orientations. May be. Further, the polytype of the silicon carbide substrate 10 may be 6H or 3C.

  The material of the gate electrode 80 is an example of low-resistance polycrystalline silicon, but the conductivity type may be either n-type or p-type. Further, it may be n-type or p-type low resistance polycrystalline silicon carbide. Further, the material of the gate electrode 80 may be Al, titanium (Ti), molybdenum (Mo), tantalum (Ta), niobium (Nb), tungsten (W), or nitrides of these metals. The material for the source electrode 90 and the drain electrode 100 may also be made of the same metal as that for the gate electrode 80. Moreover, you may anneal at about 1000 degreeC after each electrode formation.

Embodiment 2. FIG.
Although the method for manufacturing the silicon carbide semiconductor device described in the first embodiment relates to the nitriding process after forming the gate insulating film, the method for manufacturing the silicon carbide semiconductor device according to the second embodiment is the same as in the first embodiment. In addition to this step, the present invention relates to a nitriding step that is performed before forming a gate insulating film on the surface of silicon carbide.

  FIG. 11 shows the temperature profile in the reaction furnace in each step from the nitridation process on the surface of the silicon carbide substrate before the formation of the gate insulating film, the silicon dioxide film formation process by chemical vapor deposition, and the subsequent nitridation process. FIG.

In FIG. 11, the vertical axis indicates the temperature in each processing step, and the horizontal axis indicates time. The nitriding step in an NO gas or N ₂ O gas atmosphere, the oxide film forming step by chemical vapor deposition, and the subsequent steps A gate insulating film forming process including a nitriding process process in an atmosphere of NO gas or N ₂ O gas is shown together with corresponding temperature profiles in time series.

First, the wafer after the base region 30 and the source region 40 are formed is introduced into a nitriding reactor in an inert gas atmosphere such as argon (Ar) or nitrogen (N ₂ ).

When the temperature in the nitriding reactor reaches a desired processing temperature, NO gas or N ₂ O gas and CO gas that is highly reactive with oxygen are introduced into the reactor 200. Oxygen (O ₂ ) generated by the thermal decomposition of the nitric oxide-based gas during the nitriding treatment reacts with the CO gas to become CO ₂ (CO + O ₂ → 2CO ₂ ) gas, which is a stable gas with low oxidizing power. The same effect can be obtained by nitriding in an atmosphere diluted with an inert gas such as N ₂ or Ar or a reduced pressure atmosphere in addition to the above mixed gas. By carrying out such a nitriding process, nitrogen atoms (N) are passivated without reoxidizing the silicon carbide surface with oxygen, so that the interface with the silicon dioxide film deposited in the next process is good. Become.

The nitriding temperature is preferably 1100 ° C. to 1300 ° C. The nitriding time is preferably about 30 minutes to 6 hours.
After the nitriding process, the temperature is lowered to the wafer removal temperature. The above-mentioned inert gas or mixed gas atmosphere is suitable for the temperature drop. Thereby, the nitriding process step before forming the gate insulating film is completed. The nitridation process after the formation of the gate insulating film is substantially the same as in the first embodiment, and is omitted.

As in the case of the first embodiment, the above-described treatment effectively performs nitriding while preventing the generation of oxygen (O ₂ ) that may re-oxidize the silicon carbide surface and generate interface states. it can. Further, there is no limitation on the nitriding time, and it is possible to select an optimum processing time according to the gate insulating film material and film thickness.

Embodiment 3 FIG.
FIG. 12 is a schematic cross-sectional view of a silicon carbide MOSFET which is a silicon carbide semiconductor device in the third embodiment of the present invention. In FIG. 12, n-type silicon carbide drift layer 20, p-type well region 30, and n-type source region 40 are sequentially stacked on the first main surface of silicon carbide substrate 10. The n-type silicon carbide drift layer 20, the p-type well region 30, and the n-type source region 40 are provided with trenches that penetrate the well region 30 and the source region 40 and reach the silicon carbide drift layer 20.

  A gate insulating film 50 made of silicon oxide is formed on the surface of the trench and the surface of the source region 40 except for a part on the surface side of the source region 40. Furthermore, a gate electrode 60 is formed on the gate insulating film 50 at a position facing the silicon carbide drift layer 20, the well region 30, and the source region 40. Further, source electrode 70 is formed on the surface of source region 40 where gate insulating film 50 is not formed, and on the second main surface opposite to the first main surface of silicon carbide substrate 10, that is, on the back surface side. Each has a drain electrode 80 formed thereon. Since the silicon carbide MOSFET of the present embodiment is the same as that of the first embodiment except that the structure is a trench structure, detailed description thereof is omitted.

  Also in the silicon carbide MOSFET having the trench structure of the present embodiment, as in the case of manufacturing the silicon carbide MOSFET shown in the first embodiment, the reactivity between the nitrogen oxide-based gas and oxygen is high after the gate insulating film 50 is formed. In addition, after the reaction, an interface state formed at the interface between the silicon carbide layer and the gate insulating film 50 by performing a nitriding process using a mixed gas of CO gas that changes to a gas having a low oxidizing power. As a result, channel mobility can be increased.

  Also, in the case of silicon carbide IGBT (Insulated Gate Bipolar Transistor), as in the case of the present embodiment, after the gate insulating film 50 is formed, a nitriding treatment is performed using a mixed gas of CO gas and nitrogen oxide-based gas. The same effect is produced.

  In the first to third embodiments, an example of an n-channel MOSFET using electrons as carriers has been described. Needless to say, a p-channel MOSFET using holes as carriers also has the same effect.

  10 silicon carbide substrate, 20 drift layer, 30 well region, 40 source region, 50 gate insulating film, 60 gate electrode, 70 source electrode, 80 drain electrode, 200 furnace, 201 boat, 202 heater, 203 gas inlet, 204 dummy Substrate, 300 substrate.

Claims (8)

Forming an insulating film on a wafer having a silicon carbide layer on the surface;
A nitriding treatment step of nitriding an interface between the silicon carbide layer and the insulating film by heat-treating the wafer after forming the insulating film in a nitrogen oxide-based gas atmosphere mixed with carbon monoxide gas;
A method for manufacturing a silicon carbide semiconductor device comprising: 2. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the nitrogen oxide-based gas is one or both of nitrogen monoxide gas and nitrogen dioxide gas. 2. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the heat treatment step is performed in a mixed atmosphere of an inert gas, a nitrogen oxide-based gas, and a carbon monoxide gas. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the heat treatment step heats the wafer at a processing temperature of 1100 ° C. or higher and 1300 ° C. or lower. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the insulating film is a silicon dioxide film. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the heat treatment step includes nitriding in a reduced pressure atmosphere. The nitriding treatment step of nitriding the surface of the silicon carbide layer by heat-treating the wafer before forming the insulating film at a predetermined treatment temperature in a nitrogen oxide gas atmosphere to which carbon monoxide gas is added. The manufacturing method of the silicon carbide semiconductor device of any one of thru | or 5. 8. The silicon carbide according to claim 1, wherein a volume ratio of the carbon monoxide gas flow rate to the nitrogen oxide gas flow rate is 1 or less and twice or more than a generated oxygen gas flow rate. A method for manufacturing a semiconductor device.

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