Starting material for silicon carbide production and method for producing silicon carbide powder

Abstract

[Problem] To provide a new starting material for silicon carbide production, the starting material being suitable as a starting material for producing silicon carbide especially by combustion synthesis. [Solution] Provided is a starting material for silicon carbide production which is a composite comprising a carbon member and silicon chemically vapor-deposited on the carbon member, wherein the molar ratio between the carbon and the silicon (Si / C molar ratio) is 0.5 or higher. Also provided is a method for producing silicon carbide which comprises: a pulverization step in which the starting material for silicon carbide production is pulverized to obtain a powder mixture of silicon and carbon; and a reaction step in which the powder mixture obtained in the pulverization step is used as some or all of reactant materials to synthesize silicon carbide.

Description

Raw materials for producing silicon carbide and method for producing silicon carbide powder

[0001] The present invention relates to a novel raw material for producing silicon carbide and a method for producing silicon carbide powder using the raw material for producing silicon carbide.

[0002] Silicon carbide (SiC) has excellent properties such as high hardness, high strength, high heat resistance, and high thermal conductivity, and has been used in abrasives, refractories, heating elements, etc. In recent years, demand for SiC as a raw material for SiC semiconductor wafers has also been increasing.

[0003] Known methods for producing silicon carbide include: (1) the Acheson method, in which silica sand and coke are heated to high temperatures by electrical current; (2) a method in which a mixture of silica and carbon powder is heated externally to cause a reduction and carbonization reaction; (3) a method in which a mixture of silicon powder and carbon powder is heated externally to carbonize it (see Patent Document 1); and (4) the so-called combustion synthesis method, in which a mixture of silicon powder and carbon powder is preheated and then part of the sample is ignited and burned (see Patent Document 2).

[0004] Of the above methods, manufacturing methods (3) and (4) use silicon powder and carbon powder as raw materials. High-purity silicon carbide can be obtained by using high-purity powder as a raw material. These methods are also attracting attention as manufacturing methods that can produce high-purity products with minimal impurity contamination. However, silicon powder is in high demand for semiconductor applications, and there are concerns that it will be difficult to secure the necessary quantities to meet the increasing demand for silicon carbide.

[0005] Currently, the use of recovered semiconductor silicon waste as high-purity silicon powder is being considered, but there is a limit to the amount that can be produced. As demand for silicon carbide continues to grow, there is an urgent need to diversify raw materials.

[0006] International Publication No. 2012-157293 Japanese Patent Application Laid-Open No. 53-25300

[0007] FIG. 1 is a cross-sectional view showing one embodiment of the Si—C composite of the present invention. FIG. 2 is a cross-sectional view showing another embodiment of the Si—C composite of the present invention.

[0008] Therefore, an object of the present invention is to provide a novel raw material for producing silicon carbide, which is suitable as a raw material for producing silicon carbide, particularly for production by combustion synthesis.

[0009] While considering diversifying raw materials for producing silicon carbide, the inventors focused on silicon-carbon composites (hereinafter also referred to as Si-C composites) present in the manufacturing processes of other products. That is, when it is difficult to obtain silicon alone, they considered using silicon-carbon composites produced in the manufacturing processes of other products as raw materials. However, silicon and carbon easily react at temperatures near or above the melting point of silicon, and a mixed layer containing silicon and carbon is formed at the interface of the Si-C composite. Furthermore, in high-temperature reactions, silicon becomes molten, and the molten silicon that flows down the carbon surface contains a large amount of SiC.

[0010] The ratio of silicon to carbon in a mixed layer containing silicon and carbon is not constant. Therefore, in an Si-C composite containing such a mixed layer, even if the volume ratio of silicon to carbon is measured, the ratio of silicon to carbon cannot be accurately determined. Furthermore, the mixed layer is extremely hard, making it difficult to sufficiently pulverize it for use as a raw material for producing silicon carbide. Due to the above reasons, it was found that there are problems with using Si-C composites as raw materials for producing silicon carbide. Therefore, as a result of further investigation, it was found that composites in which silicon is deposited on a carbon member by chemical vapor deposition at a temperature below the melting point of silicon have almost no mixed layer of carbon and silicon. Because there is almost no mixed layer with an unknown composition, in such composite members, the ratio calculated from the volume ratio of silicon to carbon can be accurately determined as the raw material ratio of Si to C. Furthermore, because the thickness of the highly hard mixed layer is extremely thin or there is no mixed layer, it can be uniformly pulverized to the particle size of the raw material used as a raw material for producing silicon carbide. Therefore, by crushing such a composite material, it is possible to accurately blend Si and C when feeding the material for the combustion synthesis reaction. Furthermore, silicon deposited by chemical vapor deposition is highly pure, making it extremely suitable for production by combustion synthesis. Based on these findings, the present invention has been completed.

[0011] That is, according to the present invention, there is provided a raw material for producing silicon carbide, which is a composite comprising a carbon member and silicon chemically vapor-deposited onto the carbon member at a temperature below the melting point of silicon, wherein the molar ratio of carbon to silicon (Si / C molar ratio) is 0.5 or more.

[0012] The thickness of the Si--C mixed layer at the interface between the carbon member and silicon is preferably 5 μm or less.

[0013] The concentration of metal impurities in the carbon member is preferably 10 ppm or less.

[0014] The present invention also provides a method for producing silicon carbide using the raw material for producing silicon carbide, comprising: a pulverization step of pulverizing a composite containing a carbon member and silicon chemically vapor-deposited on the carbon member (hereinafter also referred to as an Si-C composite) to obtain a mixed powder of silicon and carbon (hereinafter also referred to as an Si-C mixed powder), and a reaction step of synthesizing silicon carbide using the mixed powder obtained in the pulverization step as part or all of the reaction raw material.

[0015] It is preferable that the production method further includes a composite recovery step of recovering, after completing the deposition of silicon by chemical vapor deposition in a reactor equipped with a carbon member therein, the portion of the carbon member where silicon has been chemically vapor deposited as a composite.

[0016] The molar ratio of carbon to silicon (Si / C) in the portion recovered as the composite is preferably 0.5 to 20.

[0017] Furthermore, it is preferable to adjust the Si / C molar ratio of the reaction raw materials to 0.5 to 0.9, since this eliminates the need to separately add expensive silicon and carbon for component adjustment.

[0018] The raw material for producing silicon carbide made from the Si-C composite of the present invention has very little SiC at the interface between silicon and carbon (a mixed layer containing silicon and carbon). Therefore, the ratio of silicon to carbon in the Si-C composite can be accurately determined. Therefore, the Si to C ratio of the powder obtained by pulverizing the Si-C composite can be accurately determined, enabling accurate raw material composition adjustment. While conventional manufacturing methods require separate preparation of silicon and carbon, the present invention allows the Si-C composite to be used as a reaction raw material, comparable to conventional methods. Furthermore, because there is very little mixed layer at the interface between silicon and carbon that is difficult to pulverize, pulverization failure is unlikely to occur, making it possible to obtain a raw material for producing silicon carbide with a uniform particle size.

[0019] Furthermore, in the method of producing silicon by the CVD method, the carbon member after the silicon is recovered after the reaction is completed may be treated as waste, but according to the present invention, it can be effectively utilized, thereby contributing to the achievement of the SDGs.

[0020] The Si-C composite, a raw material for producing silicon carbide according to the present invention, contains a carbon member and silicon chemically vapor-deposited on the carbon member. As described above, because chemical vapor deposition is carried out at a temperature below the melting point of silicon, the silicon deposited on the carbon member hardly reacts with the carbon. Therefore, the mixed layer at the interface between the carbon member and the silicon is not visible, or if present, is only 5 μm thick.

[0021] In the present invention, the Si-C mixed layer includes a layer consisting of only SiC and a layer in which C or SiC is dispersed in Si. Such a mixed layer has an extremely high hardness or an extremely high elastic modulus, making it difficult to crush.

[0022] Here, it is recommended that the Si-C composite not be subjected to a thermal history at a temperature equal to or higher than the melting point of silicon, since if the Si-C composite is subjected to a thermal history at a temperature equal to or higher than the melting point of silicon, the mixed layer tends to expand.

[0023] In the present invention, the Si-C composite chemically vapor-deposited on the carbon member can be obtained by known means, typically by contacting a compound gas such as chlorosilane and hydrogen or monosilane with a carbon member heated to a temperature lower than the melting point of silicon but equal to or higher than the reaction temperature.

[0024] The silicon produced by the chemical vapor deposition can be purified to a high purity of 10-N (purity 99.99999999%) by purifying the raw material. Therefore, by using a high-purity carbon member, the purity as a raw material for producing silicon carbide can be improved. Therefore, the total concentration of metal impurities such as iron, aluminum, chromium, and lead in the carbon member is preferably 10 ppm or less, more preferably 1 ppm or less, even more preferably 0.1 ppm or less, and particularly preferably 100 ppb or less.

[0025] In the present invention, the Si / C molar ratio in the Si-C composite is preferably 0.5 or more, particularly 0.7 or more. During the production of the Si-C composite, the Si / C molar ratio of the resulting Si-C composite may be inappropriate for the production of silicon carbide. If the Si / C molar ratio of the Si-C composite generated in the manufacturing process of other products described below is less than 0.5, the amount of silicon added to adjust the Si / C molar ratio to a value suitable for the production of silicon carbide increases, reducing the effect of the present invention, which aims to procure silicon. Furthermore, because carbon is more difficult to pulverize than silicon, a lower carbon ratio is preferable.

[0026] On the other hand, if the Si / C molar ratio of the composite material is too high, it will reduce the silicon yield in other manufacturing processes in which silicon is used as a product, which is not economical. Therefore, a Si / C molar ratio of 10 or less, particularly less than 1, is recommended.

[0027] In the present invention, a representative method for obtaining the Si-C composite is a silicon production process by chemical vapor deposition (CVD). For example, in silicon production by the Siemens process, a silicon rod is produced by passing an electric current through a silicon core wire held by a carbon electrode in a bell jar, which is a reaction vessel, to heat the silicon core wire and deposit silicon on the silicon core wire by chemical vapor deposition. In this case, silicon deposition also occurs on carbon members such as the carbon electrode that holds the silicon core wire and the carbon heater that preheats the silicon core wire.

[0028] Conventionally, silicon deposited on such carbon members has been separated and recovered. For example, silicon deposited on a carbon electrode is separated and recovered by etching a carbon end, which is an end portion cut from a polycrystalline silicon rod, with an alkaline anisotropic etching solution. Also, silicon deposited on a carbon heater is recovered by removing the carbon heater from a reactor after silicon deposition is completed, inductively heating it, and melting and dropping the silicon deposited on the carbon heater.

[0029] In the present invention, the silicon is not separated or recovered from the carbon member on which the silicon is deposited, but the composite of the carbon member and silicon is recovered as it is, and this is used as a raw material for producing silicon carbide.

[0030] FIG. 1 shows, for example, the state in which silicon 1 has been chemically vapor deposited on a carbon heater 2 in the Siemens process. Carbon heaters are generally rod-shaped, with a square cross section with a side length of 5 to 30 mm or a circular cross section with a diameter of 5 to 30 mm. At the portion of the carbon member where silicon has been deposited, the weight of the carbon is calculated from the length of the carbon heater 2 and the carbon density, and the weight of the deposited silicon is calculated from the difference between the total weight and the carbon weight. A portion where the Si / C molar ratio calculated from these falls within the above-mentioned range is extracted and recovered as an Si-C composite, which can be used as a raw material for silicon carbide production. Of course, as long as the average Si / C molar ratio of the entire carbon heater after silicon deposition falls within the above-mentioned range, the entire carbon heater can be used as an Si-C composite for silicon carbide production. FIG. 2 also shows the state in which silicon 1 has been chemically vapor deposited on a carbon electrode 3. Although not shown, at the end of silicon deposition, the silicon extends upward in the figure. In this case, a portion is extracted so that the Si / C molar ratio calculated based on the known volume of electrode 3 and the precipitated weight of silicon 1 falls within the above range, and recovered as an Si-C composite, which can be used as a raw material for producing silicon carbide.

[0031] When multiple Si-C composites with different Si / C molar ratios are used as raw materials for producing silicon carbide, the raw material components can be adjusted using the average Si / C molar ratio of these Si-C composites. A composite in which silicon is precipitated on the carbon heater is preferred as the carbon member, as the cross-sectional area of ​​the carbon heater is constant, allowing the Si / C molar ratio to be calculated directly. Furthermore, if the shape of the carbon is unknown, a portion of the carbon may be sampled after pulverization to measure the Si / C molar ratio.

[0032] In the present invention, the method for producing silicon carbide using an Si-C composite as a reaction raw material is not particularly limited, but examples include the method described in the above patent document in which a mixture of silicon powder and carbon powder is externally heated to carbonize it, and the so-called combustion synthesis method in which a mixture of silicon powder and carbon powder is preheated and then part of the sample is ignited and burned.

[0033] The present invention provides a method for producing silicon carbide using the Si-C composite, comprising: a pulverization step of pulverizing the Si-C composite to obtain a mixed powder of silicon and carbon (Si-C mixed powder); and a reaction step of synthesizing silicon carbide using the mixed powder obtained in the pulverization step as part or all of the reaction raw materials.

[0034] As shown in the example of the Siemens process silicon production method, the above production method preferably further includes a composite recovery step of recovering, after silicon deposition by chemical vapor deposition in a reactor equipped with a carbon member therein, the portion of the carbon member where silicon has been chemically vapor deposited as a Si-C composite.

[0035] In the production method of the present invention, the pulverization step is a step of pulverizing the Si-C composite to obtain a Si-C mixed powder. The pulverization method for the Si-C composite is not particularly limited, and any pulverization method using a known pulverizer, such as a jaw crusher, roll crusher, hammer mill, pin mill, ball mill, or mass colloider, can be used without any particular limitation.

[0036] If the Si / C molar ratio of the Si-C composite differs from the Si / C molar ratio of the reactant, as described below, carbon and / or silicon can be added to adjust the composition. Furthermore, if the amount of the Si-C composite does not reach the required amount of reactant, carbon powder and silicon powder can be added to adjust the amount. The adjustment can be performed by adding carbon or silicon alone, or by adding carbon and silicon simultaneously, depending on the Si / C molar ratio and amount of the Si-C composite. In some cases, if the composition and recovered amount of the mixed powder are sufficient, the adjustment is not necessary. That is, the mixed powder obtained after pulverizing the Si-C composite can be used as part or all of the reactant. When using the Si-C composite as part of the reactant, it is preferable that the Si-C composite account for 50% or more, 60% or more, or even 70% or more of the reactant, based on silicon, in consideration of the objectives of the present invention.

[0037] The carbon and / or silicon added to adjust the composition and amount of the reaction raw materials may be added during the step of pulverizing the Si—C composite, or, if the carbon and silicon are in the form of powder, they may be mixed after pulverization.

[0038] In the method for producing silicon carbide of the present invention, the synthesis method employed in the reaction step is not particularly limited as long as it is a method for reacting carbon and silicon. Hereinafter, a method for producing silicon carbide by combustion synthesis, which is known as a representative method among the synthesis methods, will be described as an example.

[0039] In the production method of the present invention, it is preferable to use a mixed powder containing the mixed powder obtained in the pulverization step as part or all of the reaction raw materials and having a Si / C molar ratio of 0.5 to 0.9 in order to prevent unreacted silicon from remaining.

[0040] The average particle size of the mixed powder used as a raw material for the reaction is not particularly limited, but may be preferably 1.0 to 1000 μm, more preferably 1.0 to 20.0 μm, and even more preferably 2.0 to 10.0 μm. The particle size may be adjusted in the pulverization step or by providing a separate pulverization step.

[0041] The average particle size of the silicon used for the composition adjustment is not particularly limited, but may be a powder of 0.5 μm to 20.0 μm, preferably 2.0 μm to 10.0 μm. It may also be similar to that of the mixed powder. The purity of the silicon used for the composition adjustment may be such that the heavy metal concentration is less than 0.1 ppm, preferably less than 10 ppb, and more preferably 1 ppb. The purity of the silicon can be confirmed by dissolving the silicon powder in a mixture of hydrofluoric acid and nitric acid, evaporating it, and measuring the residual solution by ICP emission or ICP-MS. The average particle size of the carbon used for the composition adjustment is not particularly limited, but may be a powder of 10 nm to 1 μm. It may also be similar to that of the mixed powder. The metal impurity concentration is 50 ppm or less, more preferably 10 ppm or less, and even more preferably 5 ppm or less. The type of carbon, including the carbon of the Si-C composite, is not particularly limited, and examples of carbon black, graphite, etc. can be used. The carbon black can be produced by various methods such as the furnace method (furnace black), the channel method (channel black), and the acetylene method (acetylene black).

[0042] In addition to silicon powder and carbon powder, silicon carbide powder may be added as a diluent to the reaction raw materials in order to control the reaction temperature, etc., within the range that does not impair the effects of the present invention.

[0043] Silicon carbide is synthesized by combustion synthesis by preheating the reactant materials to a temperature of 900°C to 1300°C in an inert atmosphere, then igniting a portion of the reactant materials and burning the entire material by self-propagation.

[0044] In the above reaction, the inert atmosphere can be, for example, a rare gas such as helium, neon, argon, etc. The pressure is not particularly limited, but is preferably 500 Pa or less, more preferably 100 Pa or less, and even more preferably 20 Pa or less.

[0045] Other conditions in the manufacturing method of the present invention are not particularly limited, and the ignition method and the like may be performed by a known method.

[0046] Since the silicon carbide obtained by the manufacturing method of the present invention is rich in carbon, it is desirable to carry out a decarburization treatment to remove the remaining carbon in an oxidizing atmosphere to obtain SiC with a purity of 99 mass % or more.

[0047] In the present invention, the silicon carbide powder obtained by the above-mentioned production method may be recrystallized at a temperature higher than the synthesis temperature, if necessary. The silicon carbide powder obtained by the above-mentioned production method can also be used as a filler for resins.

[0048] The present invention will be described in more detail below, but is not limited to these examples. Various physical properties in the examples and comparative examples were measured by the following methods.

[0049] (1) Si / C molar ratio of Si-C composite The total volume of the Si-C composite and the volume of the carbon member constituting the Si-C composite were calculated, and the Si / C molar ratio was calculated. In cases where the shape of the Si-C composite made it difficult to calculate the volume, the Si / C molar ratio was determined by crushing the composite and measuring it by XRF.

[0050] (2) Thickness of Si / C mixed layer in composite material The mixed layer at the interface between the carbon member and silicon was observed using an electron microscope, and the atomic ratio of Si to C was measured using EDS (Energy Dispersive X-ray Spectroscopy). The thickness of the mixed layer was determined so that the ratio of the peak heights of Si to C was between 1:9 and 9:1.

[0051] (3) Metallic Impurities The amount of metallic impurities was measured by glow discharge mass spectrometry to determine the total amount of alkali metals with atomic numbers 3 to 92, alkaline earth metals, transition metals, zinc, cadmium, and mercury.

[0052] (4) Average particle size (average particle size D50) The average particle size was measured as a 50% cumulative diameter using a laser diffraction particle size distribution analyzer.

[0053] (5) Unreacted Materials In the examples, the amounts of unreacted Si and carbon remaining in the silicon carbide powder obtained by the reaction were measured to confirm that the Si / C molar ratio calculated from the volume of the Si-C composite was accurate. The measurements were performed using XRF (X-ray Fluorescence).

[0054] Example 1 In a silicon manufacturing facility using the Siemens method, after silicon was manufactured, a carbon preheater on which silicon had been deposited by chemical vapor deposition was removed from the reactor. The volume of the preheater was approximately 400 cm. 3 The Si-C composite was then broken into multiple pieces with a length of 0.7 μm and collected as a Si-C composite. The breaking was done to prevent contamination by the cutting device. The Si / C molar ratio of the composite was calculated to be 0.7 on average. The thickness of the mixed layer at the interface between the carbon member and silicon in the obtained Si-C composite was measured and found to be approximately 3 μm.

[0055] The Si—C composite was coarsely crushed using a jaw crusher made of tungsten carbide, and then finely crushed using a ball mill to obtain a mixed powder with an average particle size of 5.3 μm, which was used as a reaction raw material for the combustion synthesis reaction. The balls and pot were made of silicon carbide.

[0056] The reaction raw materials were filled into a graphite crucible and placed in a firing furnace. After reducing the pressure inside the furnace to 0.5 Pa to 10 Pa, argon with a purity of 99.99% was introduced to restore the pressure to normal pressure, and then the pressure was reduced again to 0.5 Pa to 20 Pa. While maintaining a vacuum of 0.5 Pa to 20 Pa, the temperature was raised from room temperature to 1200 ° C over 3 hours for preheating. Immediately after the temperature reached 1200 ° C, a portion of the reaction raw materials was electrically ignited to obtain a crude silicon carbide powder by a combustion synthesis reaction. After the combustion synthesis reaction was completed, the crude silicon carbide powder was crushed in a ball mill to isolate agglomerated particles, and then decarburized in a high-purity electric furnace at 800 ° C in an oxygen atmosphere to obtain a silicon carbide powder.

[0057] The evaluation results of the obtained silicon carbide powder are shown in Table 1.

[0058] Example 2 In a silicon manufacturing facility using the Siemens method, after silicon was manufactured, the end of a silicon rod (volume: approximately 500 cm) containing a carbon electrode was removed from each reactor from a plurality of silicon rods on which silicon had been deposited by chemical vapor deposition. 3) were cut and collected as Si-C composites. The Si / C molar ratio of the composites was calculated to be 12 on average. The thickness of the mixed layer at the interface between the carbon member and silicon in the obtained Si-C composite was measured and found to be approximately 4 μm.

[0059] The Si-C composite was pulverized using a roll crusher and a ball mill in the same manner as in Example 1 to obtain a mixed powder with an average particle size of 5.3 μm. Next, carbon powder consisting of acetylene black with an average particle size of 30 nm and a metal impurity concentration of 0.1 ppm was added to the mixed powder so that the Si / C molar ratio was 0.7, and mixed using a ball mill to obtain a reaction raw material to be subjected to the combustion synthesis reaction. The atmosphere during mixing was argon, and after cooling, the atmosphere was replaced with air. The material of the balls and pot was silicon carbide.

[0060] The obtained reaction raw materials were subjected to combustion synthesis, crushing, and decarburization in the same manner as in Example 1 to produce silicon carbide powder.

[0061] The evaluation results of the obtained silicon carbide powder are shown in Table 1.

[0062] <Reference Example> Silicon powder with an average particle size of 45 μm and a heavy metal content of 0.1 ppm or less was pulverized to obtain silicon particles with an average particle size of 5.1 μm and an impurity content of 1 ppm. This silicon powder and acetylene black as carbon powder with an average particle size of 30 nm and a metal impurity concentration of 0.1 ppm were weighed in a molar ratio of 0.7:1.00 (Si / C molar ratio 0.7) and mixed using a planetary ball mill to obtain a reaction raw material. The atmosphere during mixing was argon, and after cooling, the atmosphere was replaced with air. The material of the ball and pot was silicon carbide.

[0063] The obtained reaction raw materials were subjected to combustion synthesis, crushing, and decarburization in the same manner as in Example 1 to produce silicon carbide powder.

[0064] The evaluation results of the obtained silicon carbide powder are shown in Table 1.

[0065]

[0066] Comparative Example 1: A silicon melt was placed in a carbon crucible for 1 hour and then cooled to form a composite. The thickness of the mixed layer at the interface between the carbon member and silicon in this Si-C composite was measured and found to be approximately 20 μm. When the composite was pulverized using the same procedure as in Example 1, the average particle size reached only approximately 40 μm.

[0067] 1 Silicon 2 Carbon heater 3 Carbon electrode

Claims

1. A raw material for producing silicon carbide, which is a composite material comprising a carbon member and silicon chemically vapor deposited on the carbon member, characterized in that the molar ratio of carbon to silicon (Si / C molar ratio) is 0.5 or more.

2. A raw material for producing silicon carbide as recited in claim 1, wherein the thickness of a mixed layer of Si and C at the interface between the carbon member and silicon in said composite is 5 μm or less.

3. The raw material for producing silicon carbide according to claim 1, wherein the concentration of metal impurities in said carbon member is 10 ppm or less.

4. A method for producing silicon carbide, comprising: a grinding step of grinding a composite containing a carbon member and silicon chemically vapor-deposited on the carbon member to obtain a mixed powder of silicon and carbon; and a reaction step of synthesizing silicon carbide by using the mixed powder obtained in the grinding step as a part or all of the reaction raw material.

5. A method for producing silicon carbide as set forth in claim 4, further comprising a composite recovery step of recovering, after completion of deposition of silicon by chemical vapor deposition in a reactor equipped with a carbon member therein, the portion of the carbon member on which silicon has been chemically vapor deposited as said composite.

6. The method for producing silicon carbide according to claim 5, wherein the molar ratio of carbon to silicon (Si / C) in the portion recovered as the composite is 0.5 to 20.

7. The method for producing silicon carbide according to claim 4, wherein the Si / C molar ratio of the reaction raw materials is adjusted to 0.5 to 0.9.

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