JP2011023431A - Method of fabricating silicon carbide semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of fabricating a silicon carbide semiconductor device, wherein source gas can be supplied without requiring a vaporizer, production of tar components that hinders cleaning in an annealing furnace is inhibited at the low temperature part in the furnace by stabilizing the deposition rate and forming a high quality carbon film, and the quality of the silicon carbide semiconductor device is stabilized while improving the yield. <P>SOLUTION: A carbon protective film 6 is formed on the entire surface of a silicon carbide wafer WF by chemical vapor deposition while using carbon monoxide as the source gas. More specifically, a deposition device is evacuated by means of a vacuum pump and after removing the residual oxygen as much as possible, the interior of the deposition apparatus is heated under reduced pressure to have a temperature in the range of 500-1,000°C while feeding inert gas such as Ar or He. When this temperature is reached, inflow of the inert gas is stopped, and carbon monoxide is made to flow into the deposition apparatus as the source gas thus forming the carbon protective film 6 on the entire surface of the silicon carbide wafer WF. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a silicon carbide semiconductor device.

  Silicon carbide (SiC) is capable of producing a silicon carbide semiconductor device having higher voltage resistance than conventional silicon (Si), and is expected as a next-generation high-power semiconductor device. In manufacturing a silicon carbide semiconductor device using such silicon carbide, in order to control the conductivity type and conductivity for a silicon carbide wafer having a silicon carbide layer epitaxially grown on a silicon carbide substrate, Impurity ions to be n-type or p-type are implanted, and after the ion implantation, the implanted silicon carbide wafer is activated by argon (Ar) in order to activate the implanted ions and recover crystal defects formed by the ion implantation. There is an annealing treatment step of exposing to a high temperature in an atmosphere of an inert gas. In the case of using a silicon carbide wafer, this annealing treatment is preferably carried out at as high a temperature as possible in order to stabilize the characteristics, and is usually carried out at 1500 ° C. or higher, preferably 1600 ° C. or higher.

  However, when the silicon carbide wafer is annealed at a high temperature, an uneven surface called step bunching is formed on the surface of the silicon carbide wafer. The reason why step bunching is formed is as follows.

  A silicon carbide wafer is usually obtained by epitaxially growing a silicon carbide layer on a silicon carbide substrate. In this case, the epitaxial growth has a crystal form such as 6H type or 4H type in the same crystal plane. In order to prevent them from being mixed and occurring, the growth is performed by tilting the growing crystal axis by 4 degrees or 8 degrees with respect to the C-axis direction (direction perpendicular to the [0001] plane which is the crystal plane).

  When the silicon carbide wafer thus grown with the crystal axis inclined is exposed to a high temperature such as an annealing process, Si and carbon (C) as constituent elements are evaporated from the surface of the silicon carbide wafer. In this evaporation, the evaporation conditions of silicon and carbon are different and the crystal axes are inclined, so that the evaporation amounts of silicon and carbon are different in the silicon carbide wafer surface. Step bunching is formed on the surface.

  The step bunching formed in this manner hinders the formation of a gate oxide film on the silicon carbide wafer after the annealing process, and further hinders the formation of a gate electrode on the gate oxide film. For example, there is a possibility that a decrease in adhesion or a deterioration in leak characteristics may occur due to unevenness at the interface between the silicon carbide wafer and the gate oxide film or the gate oxide film and the gate electrode.

  For this reason, prevention or reduction of step bunching is a major issue for stabilizing the quality of the silicon carbide semiconductor device and improving the yield.

  As a method for preventing or reducing such step bunching, there is a method in which a carbon film is formed on the surface of a silicon carbide wafer, and this carbon film is used as a protective film for preventing evaporation of silicon and carbon during annealing.

  Patent Document 1 discloses that a carbon protective film for annealing with respect to SiC is formed using a hydrocarbon material gas containing oxygen, and this film is used as a protective film for preventing evaporation of silicon and carbon during annealing. ing. In Patent Document 1, by using a hydrocarbon gas containing oxygen (ethyl alcohol or methyl alcohol), a high-quality carbon film is obtained, and tar components are generated in a low-temperature part in the furnace that hinders cleaning in the annealing furnace. Is suppressed.

JP 2009-65112 A

  However, in the method of Patent Document 1, since the source gas is supplied from a liquid, a vaporizer is required to stabilize the gas supply amount and the film formation rate, and the apparatus becomes expensive and complicated.

  The present invention has been made to solve the above problems, and can supply a source gas without a vaporizer, stabilize the film formation rate, and form a high-quality carbon film to prevent the annealing furnace from being cleaned. It is an object of the present invention to provide a method for manufacturing a silicon carbide semiconductor device that suppresses generation of tar components in a low temperature portion in the furnace and realizes stable quality and improved yield of the silicon carbide semiconductor device.

  A first aspect of a method for manufacturing a silicon carbide semiconductor device according to the present invention includes a step (a) of forming an active region of the silicon carbide semiconductor device by ion-implanting impurities into the surface of the silicon carbide wafer; After step (a), a step (b) of forming a carbon protective film having a predetermined thickness on the entire surface of the silicon carbide wafer by chemical vapor deposition using at least carbon monoxide gas as a source gas; And (c) annealing the silicon carbide wafer on which the carbon protective film is formed.

  A second aspect of the method for manufacturing a silicon carbide semiconductor device according to the present invention includes a step (a) of forming an active region of a silicon carbide semiconductor device by ion-implanting impurities into the surface of the silicon carbide wafer, and the step (a) After the step (b), a carbon protective film having a predetermined thickness is formed on the entire surface of the silicon carbide wafer by chemical vapor deposition using a hydrocarbon gas and an oxygen gas or a hydrogen gas as a source gas. And (c) annealing the silicon carbide wafer on which the carbon protective film is formed.

  According to the first aspect of the method for manufacturing a silicon carbide semiconductor device of the present invention, a carbon protective film having a predetermined thickness is formed on the entire surface of the silicon carbide wafer, so that the silicon carbide wafer is subjected to an annealing process. Step bunching can be prevented from occurring on the surface, and a high-quality, high-quality carbon protective film with few impurities can be obtained, so that contamination of the silicon carbide semiconductor device can be prevented. Further, since unbalanced thermal stress generated in the silicon carbide wafer can be prevented, an increase in crystal defects of the silicon carbide wafer due to the thermal stress can also be prevented. Therefore, it is possible to obtain a method for manufacturing a silicon carbide semiconductor device capable of realizing stable quality and improvement in yield. Further, by using carbon monoxide as a source gas, the source gas can be supplied without a vaporizer, and the gas supply amount and the film formation rate can be stabilized.

  According to the second aspect of the method for manufacturing a silicon carbide semiconductor device of the present invention, a carbon protective film having a predetermined thickness is formed on the entire surface of the silicon carbide wafer, so that the silicon carbide wafer is subjected to an annealing process. Step bunching can be prevented from occurring on the surface. In addition, since a high-purity and high-quality carbon protective film with few impurities can be obtained, contamination of the silicon carbide semiconductor device can be prevented. Further, since unbalanced thermal stress generated in the silicon carbide wafer can be prevented, an increase in crystal defects of the silicon carbide wafer due to the thermal stress can also be prevented. Therefore, it is possible to obtain a method for manufacturing a silicon carbide semiconductor device capable of realizing stable quality and improvement in yield. Further, by using a hydrocarbon gas and an oxygen gas or a hydrogen gas as a source gas, the source gas can be supplied without a vaporizer, and the gas supply amount and the film formation rate can be stabilized.

It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is sectional drawing explaining the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention. It is a figure explaining the structure of the manufacturing apparatus used for the manufacturing method of the silicon carbide semiconductor device of Embodiment 1 which concerns on this invention.

<Embodiment 1>
<Manufacturing method>
A method for manufacturing a silicon carbide semiconductor device according to the first embodiment of the present invention will be described by way of example with reference to FIGS. 1 to 8 sequentially illustrating a manufacturing process of a power MOSFET (Power Metal Oxide Semiconductor Field Effect Transistor) 100. The configuration of the power MOSFET 100 is shown in FIG. 8 for explaining the final process.

  Here, the term “MOS” has been used for a metal / oxide / semiconductor laminated structure in the past, and is an acronym for Metal-Oxide-Semiconductor. However, in particular, in a field effect transistor having a MOS structure (hereinafter, simply referred to as “MOS transistor”), materials for a gate insulating film and a gate electrode have been improved from the viewpoint of recent integration and improvement of a manufacturing process.

  For example, in a MOS transistor, polycrystalline silicon has been adopted instead of metal as a material of a gate electrode mainly from the viewpoint of forming a source / drain in a self-aligned manner. From the viewpoint of improving electrical characteristics, a material having a high dielectric constant is adopted as a material for the gate insulating film, but the material is not necessarily limited to an oxide.

  Therefore, the term “MOS” is not necessarily limited to the metal / oxide / semiconductor stacked structure, and is not presumed in this specification. That is, in view of the common general knowledge, “MOS” is not only an abbreviation derived from the word source, but also has a meaning including widely a laminated structure of a conductor / insulator / semiconductor.

First, in the step shown in FIG. 1, an n-type impurity is formed on one main surface of the semiconductor substrate 1 containing a relatively high concentration (n ⁺ ) of an n-type (first conductivity type) impurity by an epitaxial crystal growth method. Is formed at a relatively low concentration (n ⁻ ). Here, as the semiconductor substrate 1, for example, a silicon carbide substrate is suitable. The semiconductor substrate 1 and the silicon carbide layer 2 constitute a silicon carbide wafer WF.

  Next, in the step shown in FIG. 2, a p-type (second conductivity type) impurity is formed in the surface of silicon carbide wafer WF, specifically in the surface of silicon carbide layer 2 using a resist (not shown) as a mask. A plurality of well regions 3 separated from each other are selectively formed. After the ion implantation, the resist is removed. Here, examples of the p-type impurity in the silicon carbide layer 2 include boron (B) and aluminum (Al).

  Next, n-type impurities are ion-implanted into the surface of each well region 3 using a resist (not shown) as a mask to selectively form the source region 4. After the ion implantation, the resist is removed. Here, examples of the n-type impurity in the well region 3 include phosphorus (P) and nitrogen (N).

Next, using a resist (not shown) as a mask, a p-type impurity is ion-implanted so that the source region 4 is in contact with the periphery thereof, so that a contact region 5 containing the p-type impurity at a relatively high concentration (p ⁺ ) is formed. Form. After the ion implantation, the resist is removed. Here, the impurity concentration of the contact region 5 is set to be relatively higher than the impurity concentration of the well region 3. Examples of the p-type impurity include boron (B) and aluminum (Al).

  Next, in the step shown in FIG. 3, carbon monoxide is used as a source gas, and a carbon protective film 6 is formed on the entire surface of the silicon carbide wafer by chemical vapor deposition such as CVD (Chemical Vapor Deposition).

  Specifically, the inside of the film forming apparatus for performing CVD is evacuated by a vacuum pump, and after removing residual oxygen as much as possible, an inert gas such as argon (Ar) or helium (He) is allowed to flow under reduced pressure. The temperature in the film forming apparatus is heated to a range of 500 ° C. to 1000 ° C. When this temperature is reached, the inflow of the inert gas is stopped, and carbon monoxide is caused to flow into the film forming apparatus as a source gas, thereby forming the carbon protective film 6 on the entire surface of the silicon carbide wafer WF.

At this time, the pressure in the film forming apparatus is controlled to be in a range of 1 Pa to 10 ⁷ Pa. However, when the pressure in the film forming apparatus is from a reduced pressure state to atmospheric pressure, the decomposition of carbon monoxide is promoted. Hydrogen gas may be added. Note that in the case where the pressure in the film formation apparatus is set to a pressurized state, it is not necessary to add hydrogen gas.

  When hydrogen gas is added, the flow rate of carbon monoxide gas and hydrogen gas is in the range of carbon monoxide gas: hydrogen gas flow ratio of 1:10 to 10: 1, preferably 1: 4 to 4: 1. To control. The carbon monoxide gas may be diluted with argon gas.

  When carbon monoxide gas and hydrogen gas are used as source gases, a carbon film with fewer defects can be obtained than a carbon protective film obtained only with a hydrocarbon gas. This is because hydrogen gas reacts more with carbon having an amorphous structure during film formation, and has an effect of reducing defects in the film.

  Furthermore, adhesion of unreacted carbon or polymer hydrocarbon film to the low temperature portion in the film forming apparatus is reduced, and the maintainability of the film forming apparatus during production is improved.

  Further, by adding hydrogen gas, carbon monoxide is easily decomposed, and the deposition rate of the carbon film is improved.

  Thus, the carbon protective film 6 formed by a chemical vapor deposition method such as CVD is a high-purity and high-quality carbon film with few impurities. Here, “good quality” refers to a state in which the formed film has few amorphous components and graphitization proceeds.

  The film thickness of the carbon protective film 6 is preferably 1 nm or more, which produces an effect as a protective film, and is preferably 1000 nm or less, which does not cause cracking due to the temperature load applied to the silicon carbide wafer and the temperature difference generated in the silicon carbide wafer WF. The range is not less than 10 nm and not more than 500 nm for easy film thickness control.

  In addition, since the carbon protective film 6 is formed on the entire surface of the silicon carbide wafer, it is possible to simultaneously form a plurality of sheets simultaneously in a batch manner.

  Specifically, a plurality of silicon carbide wafers WF are arranged in a film forming apparatus at a distance so that the carbon protective film 6 is uniformly formed on the entire surface of the silicon carbide wafer, thereby forming a film in a lump. And throughput is improved.

  Next, the silicon carbide wafer WF having the carbon protective film 6 formed on the entire surface is put into an annealing apparatus and annealed in an inert gas atmosphere.

  Here, the substrate holder used in the carbon protective film forming film forming apparatus and the annealing apparatus described above is configured using, for example, carbon, and the annealing apparatus and the film forming apparatus are used in common. The effect of reducing the possibility of contamination in the furnace due to film peeling or the like can be expected while reducing the adhesion of particles and the like and improving the yield. Is obtained.

  Carbon is used as the material for the substrate holder because it is exposed to a high temperature of 1500 ° C. or higher in the annealing process, so that durability is taken into consideration.

  Here, an example of a film forming apparatus and an annealing apparatus will be described with reference to FIG. FIG. 9A shows a configuration of a general CVD apparatus 30 as a film forming apparatus for forming the carbon protective film 6.

  As shown in FIG. 9, a CVD apparatus 30 is used to form a carbon protective film 6 on the entire surface of a gas introduction pipe 31 for introducing carbon monoxide gas and, if necessary, hydrogen gas, and a silicon carbide wafer WF. The film forming furnace 32, the gas exhaust pipe 33 for exhausting the pyrolyzed carbon monoxide gas, and the carbon monoxide gas provided on the outer periphery of the film forming furnace 32 so as not to directly contact the carbon monoxide gas. A heater 34 for thermal decomposition, and a substrate holder 35 for holding the carbon protective film 6 on the entire surface of the silicon carbide wafer WF so that the carbon protective film 6 can be formed and batch processing a plurality of silicon carbide wafers WF at the same time are provided. ing. The substrate holder 35 may be one that can support and hold the peripheral portion of the silicon carbide wafer WF at, for example, three points.

  The configuration of the CVD apparatus 30 shown in FIG. 9 is an example, and the carbon protective film 6 can be formed if a configuration corresponding to this is provided.

  FIG. 9C shows the configuration of an annealing treatment apparatus 40 for annealing the silicon carbide wafer WF on which the carbon protective film 6 is formed.

  In FIG. 9, an annealing apparatus 40 includes an annealing furnace 41, a gas introduction pipe 42 for introducing an inert gas such as argon into the annealing furnace 41, a gas exhaust pipe 43 for exhausting the inside of the annealing furnace 41, and a plurality of carbonizations. A substrate holder 35 on which a silicon wafer can be placed and shared with the CVD apparatus 30, a heater 44 such as a carbon heater provided around the substrate holder 35, at least around the heater 44, A soaking material 45 made of quartz or ceramic for uniformly applying heat of the heater 44 to the silicon carbide wafer, and a coil 46 for inductively heating the heater 44 are provided around the annealing furnace 41.

  Specifically, the annealing is performed after the annealing furnace 41 is evacuated, and then argon gas is introduced from the gas introduction pipe 42 and the heat of the heater 44 induction-heated by the coil 46 in an argon atmosphere set to a predetermined pressure. Then, preheating (about 1000 ° C.) is performed, followed by heating at a predetermined temperature (1500 ° C. or higher, preferably about 1700 ° C.) for a predetermined time, and then quickly cooling. Thereby, the implanted ions are electrically activated, and crystal defects formed by the ion implantation are recovered.

  As described above, the substrate holder 35 is shared by the annealing apparatus 40 and the CVD apparatus 30 and is taken out from the CVD apparatus 30 as shown in FIG. 9B. The substrate holder 35 thus introduced is introduced into the annealing apparatus 40 as it is.

  After the annealing treatment, the carbon protective film 6 is removed by exposing it in an oxygen atmosphere at about 950 ° C. for about 30 minutes. Alternatively, it is removed by ashing using oxygen plasma used for resist removal.

  Here, since carbon protective film 6 is formed on the entire surface of silicon carbide wafer WF, step bunching does not occur on the surface of silicon carbide wafer WF during the annealing process.

  When the unevenness of the surface of the silicon carbide wafer WF after removing the carbon protective film 6 was measured with an AFM (Atomic Force Microscopy), the unevenness of about several tens of nanometers was obtained when the carbon protective film 6 was not provided. Is generated on the entire surface of the silicon carbide wafer, whereas when the carbon protective film 6 is used, only unevenness of 1 nm or less is generated, and the effect was confirmed.

  In addition, according to the manufacturing method of the present invention, since the high-purity carbon protective film 6 with few impurities is formed, the silicon carbide semiconductor device is not contaminated. Furthermore, since carbon protective film 6 is formed on the entire surface of silicon carbide wafer WF, unbalanced thermal stress generated in silicon carbide wafer WF during the annealing process is improved, and distortion generated in silicon carbide wafer WF is reduced. . As a result, it is possible to prevent an increase in defects generated in the crystal of silicon carbide wafer WF.

Next, in the process shown in FIG. 4, heat is applied to one main surface of the silicon carbide wafer WF from which the carbon protective film 6 has been removed, specifically, the main surface on the side where the well region 3 and the like are formed by ion implantation. A gate oxide film 7 made of silicon dioxide (SiO ₂ ) is formed by an oxidation method. The gate oxide film 7 formed in this step is a thermal oxide film.

  Next, in the step shown in FIG. 5, after a polysilicon film is formed on the gate oxide film 7 by chemical vapor deposition, wet etching is performed using a resist mask (not shown) patterned by photolithography. The gate electrode 8 is formed by removing unnecessary portions of the polysilicon film by a dry etching method such as RIE (Reactive Ion Etching). At this time, the gate electrode 8 is formed so as to straddle between the two source regions 4 facing each other, and is in contact with the silicon carbide layer 2 and the well region 3 between the two source regions 4.

Next, in the step shown in FIG. 6, interlayer insulation composed of silicon dioxide (SiO ₂ ) is formed on the surfaces of the gate oxide film 7 and the gate electrode 8 by chemical vapor deposition using TEOS (Tetraethoxysilane) gas. A film 9 is formed. The interlayer insulating film 9 formed in this step is a TEOS oxide film.

  Next, in the step shown in FIG. 7, the contact region 5 and a part of the source region 4 are exposed by a wet etching method or a dry etching method such as RIE using a resist mask (not shown) patterned by photolithography. Thus, the interlayer insulating film 9 and the gate oxide film 7 are removed. At this time, the gate oxide film 7 is formed so as to straddle between the two opposing source regions 4 and to be in contact with a part of the source region 4 so as not to protrude from the gate oxide film 7 thereon. A gate electrode 8 is present. Further, the interlayer insulating film 9 is left so as to cover the upper surface and side surfaces of the gate electrode 8.

  Next, a physical vapor deposition method (PVD: Physical Vapor) such as sputtering is applied so as to cover the exposed contact region 5 and part of the source region 4 after the interlayer insulating film 9 and the gate oxide film 7 are removed. A conductive film is formed by Deposition).

  Thereafter, in the step shown in FIG. 8, a conductive mask formed on the upper surface of the interlayer insulating film 9 by a wet etching method or a dry etching method such as RIE, using a resist mask (not shown) patterned by photolithography. Unnecessary portions are removed to form a source electrode (first main electrode) 10 in contact with the contact region 5 and a part of the source region 4. The source electrode 10 is electrically connected to the contact region 5 and the source region 4.

  The constituent material of the source electrode 10 includes nickel (Ni) and aluminum (Al).

  Finally, in the step shown in FIG. 8, a physical vapor phase such as sputtering is formed on the back surface of the silicon carbide wafer WF, specifically on the main surface opposite to the side where the well region 3 and the like are formed by ion implantation. A conductive film is formed by a growth method to form a drain electrode (second main electrode) 11. Examples of the constituent material of the drain electrode 11 include nickel (Ni) and aluminum (Al).

  Through the above steps, the main part of the power MOSFET 100 is completed as shown in FIG.

<Effect>
As described above, according to the method for manufacturing the silicon carbide semiconductor device according to the first embodiment, the silicon carbide wafer is formed by chemical vapor deposition in which carbon monoxide gas is thermally decomposed after impurity ion implantation. A carbon protective film 6 having a predetermined thickness is formed on the entire surface of the WF. Thereby, step bunching can be prevented from occurring on the surface of silicon carbide wafer WF during the annealing process, and high-purity and good-quality carbon protective film 6 with few impurities can be obtained, so that the silicon carbide semiconductor device is not contaminated. Can be prevented. Further, since unbalanced thermal stress generated in silicon carbide wafer WF can be prevented, an increase in crystal defects of silicon carbide wafer WF accompanying this thermal stress can also be prevented. Therefore, it is possible to obtain a method for manufacturing a silicon carbide semiconductor device capable of realizing stable quality and improvement in yield. Further, by using carbon monoxide as a source gas, the source gas can be supplied without a vaporizer, and the gas supply amount and the film formation rate can be stabilized.

<Embodiment 2>
In the method for manufacturing the silicon carbide semiconductor device of the first embodiment, the structure in which carbon protective film 6 is formed using carbon monoxide gas as the source gas has been shown. However, even if hydrocarbon gas and oxygen gas are used as the source gas, good.

  More specifically, when the CVD apparatus 30 shown in FIG. 9 is used, the film forming furnace 32 mounted on the substrate holder 35 and having the silicon carbide wafer WF disposed therein is evacuated to a reduced pressure state. After the oxygen remaining in the substrate was exhausted as much as possible, an inert gas such as argon (Ar) or helium (He) was allowed to flow as a carrier gas into the film forming furnace 32, and the inside of the apparatus was evacuated while evacuating. Heat the temperature in the range of 850 ° C to 1000 ° C. Thereafter, with the carrier gas stopped or flowing, a hydrocarbon gas such as acetylene, methane and propane and an oxygen gas are supplied at a predetermined pressure, and the hydrocarbon gas is thermally decomposed to the entire surface of the silicon carbide wafer WF. A carbon protective film 6 is formed. The film thickness of the carbon protective film 6 is the same as that formed in the first embodiment.

  Here, the pressure during decompression is desirably 10,000 Pa or less, and more desirably 1000 Pa or less.

  When hydrocarbon gas and oxygen gas are used as the source gas, the flow rate ratio of oxygen gas: hydrocarbon gas flowing into the film forming furnace 32 is in the range of 1: 100 to 4: 1, and gas combustion reaction occurs. Adjust the flow rate and pressure of hydrocarbon gas and oxygen gas so that there is not. For example, when methane gas is used, if it is atmospheric pressure, the combustion reaction does not occur when methane is 5% or less and 14% or more in the mixing ratio (volume ratio) with air. During decompression, the combustion range is narrower than that at atmospheric pressure. For example, at 1000 Pa, the combustion reaction does not occur even if the flow rate ratio of methane gas: oxygen gas is 9: 1.

  As described above, by using the hydrocarbon gas and the oxygen gas as the source gas, the source gas can be supplied without a vaporizer, and the gas supply amount and the film formation rate can be stabilized.

  Further, when oxygen gas is used as a source gas together with hydrocarbon gas, a carbon film having fewer defects can be obtained than a carbon protective film obtained using only hydrocarbon gas. This is because oxygen gas reacts more with carbon having an amorphous structure during film formation, and has an effect of reducing defects in the film.

  Furthermore, adhesion of unreacted carbon or polymer hydrocarbon film to the low temperature portion in the film forming apparatus is reduced, and the maintainability of the film forming apparatus during production is improved.

<Modification>
Note that the same effect can be obtained by using hydrogen gas instead of oxygen gas. When using hydrocarbon gas and hydrogen gas as the source gas, the hydrocarbon gas is set so that the flow ratio of hydrogen gas: hydrocarbon gas flowing into the film forming furnace 32 (FIG. 9) is 1: 100-4: 1. And control the flow rate of hydrogen gas.

  6 Carbon protective film, 35 substrate holder, WF silicon carbide wafer.

Claims (7)

(a) ion-implanting impurities into the surface of the silicon carbide wafer to form an active region of the silicon carbide semiconductor device;
(b) after the step (a), forming a carbon protective film having a predetermined thickness on the entire surface of the silicon carbide wafer by chemical vapor deposition using at least carbon monoxide gas as a source gas;
(c) annealing the silicon carbide wafer on which the carbon protective film is formed. A method for manufacturing a silicon carbide semiconductor device. The step (b)
When the pressure in the film forming apparatus for performing chemical vapor deposition is from a reduced pressure state to atmospheric pressure, hydrogen gas is introduced together with the carbon monoxide gas as the source gas,
The method for manufacturing a silicon carbide semiconductor device according to claim 1, further comprising a step of introducing only the carbon monoxide gas as the source gas when the pressure in the film forming apparatus is in a pressurized state. (a) ion-implanting impurities into the surface of the silicon carbide wafer to form an active region of the silicon carbide semiconductor device;
(b) After the step (a), a carbon protective film having a predetermined thickness is formed on the entire surface of the silicon carbide wafer by chemical vapor deposition using a hydrocarbon gas and an oxygen gas or a hydrogen gas as a source gas. And a process of
(c) annealing the silicon carbide wafer on which the carbon protective film is formed. A method for manufacturing a silicon carbide semiconductor device. The step (b)
The method for manufacturing a silicon carbide semiconductor device according to claim 1, further comprising a step of forming the carbon protective film so that the predetermined thickness is in a range of 1 nm to 1000 nm. The step (b)
The manufacturing method of the silicon carbide semiconductor device of Claim 1 or Claim 3 including the batch process which forms the said carbon protective film collectively with respect to the said several silicon carbide wafer.   4. The method for manufacturing a silicon carbide semiconductor device according to claim 1, wherein the step (b) and the step (c) commonly use a substrate holder for holding a plurality of the silicon carbide wafers.   The method for manufacturing a silicon carbide semiconductor device according to claim 5, wherein the substrate holder is made of carbon.

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