Silicon carbide powder and method for producing same

Abstract

The purpose of the present invention is to provide a silicon carbide powder in which both silicon-based impurities and free carbon are highly reduced. The solution of the present invention is to provide a method for producing a silicon carbide powder by mixing a silicon metal powder and a carbon powder and by self-propagating high-temperature synthesis, the method being characterized by comprising: a mixing step for obtaining a raw material for silicon carbide production by mixing the silicon metal powder and the carbon powder; and a production step for obtaining a silicon carbide powder by self-propagating high-temperature synthesis of the mixed silicon metal powder and carbon powder in an inert gas atmosphere, the bulk density of the silicon metal powder and the carbon powder after mixing in the mixing step is at least twice the bulk density of the silicon metal powder and the carbon powder before the mixing step.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing silicon carbide powder and silicon carbide powder. Specifically, it relates to a method for manufacturing silicon carbide powder with a reduced carbon content and metal impurity content, which can be used as a raw material for semiconductor wafers, and the silicon carbide powder. Background Art

[0002] Silicon carbide (SiC) has excellent properties such as high hardness, high strength, high heat resistance, and high thermal conductivity, and is therefore used in abrasives, refractories, heating elements, etc. In recent years, the demand for raw materials for SiC semiconductor wafers has been increasing. When manufacturing silicon carbide powder suitable for these applications, high-purity silicon carbide powder is particularly required as a raw material for SiC semiconductor wafers and as a raw material for SiC sintered bodies for semiconductor manufacturing applications. As reasons for the decrease in the purity of silicon carbide powder, it is known that there are unreacted silicon and carbon derived from raw materials during manufacturing. When silicon carbide powder containing these components is used as a raw material, it has a negative impact on the product. For example, Patent Document 1 discloses that when the silicon carbide powder used as a raw material for manufacturing SiC single crystals by sublimation recrystallization contains unreacted carbon (free carbon), the carbon enters the SiC single crystal and becomes a cause of defects. In addition, Patent Document 2 discloses that when the silicon carbide powder used as a raw material for manufacturing a silicon carbide sintered body contains free silicon, it hinders sintering or causes the generation of defects in the sintered body.

[0003] As methods for manufacturing silicon carbide, the following are known: (1) the Acheson method of heating silica sand and coke at high temperature by electric heating (for example, Patent Documents 1 and 3); (2) a method of externally heating a mixture of silicon dioxide and carbon powder for reduction and carbonization reactions (for example, Patent Document 4); (3) a method of externally heating a mixture of metal silicon powder and carbon powder for carbonization (for example, Patent Document 5); (4) a method of preheating a mixture of metal silicon powder and carbon powder and then igniting a part of the sample and burning it (also called self-propagating high-temperature synthesis method or combustion synthesis method. For example, Patent Document 6).

[0004] The method of (1) is the most commonly used method for manufacturing silicon carbide powder. It can be manufactured relatively inexpensively using large-scale equipment. However, due to uneven temperature in the furnace, free silicon and free carbon are likely to be generated, and it is difficult to obtain high-purity products. The method of (2) uses high-purity silica and carbon powder as raw materials and can easily obtain relatively high-purity silicon carbide powder. However, when using silica as a raw material, there is a tendency to generate free SiO2. The method of (3) uses high-purity metallic silicon powder and carbon powder as raw materials and can easily obtain relatively high-purity silicon carbide powder. However, silicon will volatilize during high-temperature firing, and free carbon still cannot be highly reduced. The method of (4) can be synthesized at a lower temperature compared to (3), so the volatilization of silicon can be suppressed. However, the low reaction temperature inhibits the conversion rate to silicon carbide, resulting in an increase in free silicon and free carbon. By performing heat treatment in an air atmosphere, free carbon can be removed relatively easily, but silicon-based impurities require treatment with hydrofluoric acid or the like. When the content of free carbon is high, the content of silicon-based impurities will also increase relatively. Therefore, reducing the content of free carbon after the reaction is extremely important for improving the purity of silicon carbide powder.

[0005] Prior art documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Laid-Open No. 2019-151533

[0008] Patent Document 2: Japanese Patent Laid-Open No. 63-17258

[0009] Patent Document 3: Japanese Patent Laid-Open No. 2015-157737

[0010] Patent Document 4: Japanese Patent Laid-Open No. 2012-246165

[0011] Patent Document 5: International Publication No. 2012-157293

[0012] Patent Document 6: Japanese Patent Laid-Open No. 53-25300 Summary of the invention

[0013] Problems to be solved by the invention

[0014] The method described in (1) is the most commonly used method for manufacturing silicon carbide powder. Its advantage is that it can be manufactured relatively inexpensively using large-scale equipment. The aspect to be improved is that due to temperature unevenness in the furnace, free silicon and free carbon are likely to be generated, and it is difficult to obtain a high-purity product. The method in (2) uses high-purity silica and carbon powder as raw materials and can easily obtain silicon carbide powder with a relatively high purity. However, when using silica as a raw material, there is a tendency to generate free SiO2. The method in (3) uses high-purity metallic silicon powder and carbon powder as raw materials and can easily obtain silicon carbide powder with a relatively high purity. However, silicon will volatilize during high-temperature firing, and free carbon still cannot be highly reduced. Compared with the method in (3), the method in (4) can be synthesized at a lower temperature, so the volatilization of silicon can be suppressed. However, the low reaction temperature inhibits the conversion rate to silicon carbide, resulting in an increase in free silicon and free carbon.

[0015] In addition, as described in Patent Documents 1 and 4, attempts have been made to improve the purity by removing impurities from the manufactured silicon carbide powder, but there is a limit to the improvement of purity.

[0016] As described above, there is a need for silicon carbide powder with less Si-based impurities such as free silicon and free SiO2 and less free carbon. However, so far, silicon carbide powder with a high reduction of both has not been obtained. Therefore, the problem of the present invention is to provide silicon carbide powder with a high reduction of both silicon-based impurities and free carbon.

[0017] Means for Solving the Problem

[0018] The present inventors conducted in-depth research to solve the above problems. By discussing the important factors for generating free silicon and free carbon in the self-propagating high-temperature synthesis method of the method in (4) above, the following insights were obtained: When these raw materials are unevenly mixed, there is a tendency to generate free silicon and free carbon. Based on these insights, the preparation method of the mixed powder of metallic silicon powder and carbon powder used in the self-propagating high-temperature synthesis method was repeatedly discussed, and the following facts were found, thus completing the present invention: When adding metallic silicon powder and carbon powder to obtain their mixed powder, by making the volume density after mixing within a specified range relative to the volume density before mixing, a mixed powder with less uneven mixing can be obtained. Then, using this mixed powder to manufacture silicon carbide powder can reduce the contents of free silicon, free carbon, and the content of metallic impurities.

[0019] That is, the first invention is a method for manufacturing silicon carbide powder, which involves mixing metal silicon powder and carbon powder and manufacturing silicon carbide powder through self-propagating high-temperature synthesis. The manufacturing method is characterized in that it includes: a mixing step of mixing metal silicon powder and carbon powder to obtain a raw material for manufacturing silicon carbide; and a manufacturing step of subjecting the mixed metal silicon powder and carbon powder to self-propagating high-temperature synthesis in an inert gas atmosphere to obtain silicon carbide powder, such that the bulk density of the mixed metal silicon powder and carbon powder in the mixing step is more than twice the bulk density of the metal silicon powder and carbon powder before the mixing step.

[0020] In the above first invention, the following solutions are preferably adopted.

[0021] (1) The manufacturing step is carried out in an electric furnace.

[0022] (2) The temperature in the electric furnace is 900 - 2050 °C.

[0023] (3) In the mixing step, at least one selected from a ball mill, a planetary ball mill, a jet mill, and a vibration mill is used as a mixing means.

[0024] (4) Metal silicon powder with an average particle size of 20 μm or less and carbon powder with a primary particle size of 100 nm or less are mixed.

[0025] (5) It includes: a heat treatment step of heating the silicon carbide powder obtained in the manufacturing step in an oxidizing atmosphere.

[0026] (6) In the heat treatment step, the heat treatment temperature is 600 - 1200 °C.

[0027] In addition, the second invention is a silicon carbide powder, wherein the free carbon content is 0.001 - 0.5% by mass and the free metallic silicon is 0.01 - 1.0% by mass.

[0028] In the above second invention, the following solutions are preferably adopted.

[0029] (7) The total content of metal impurities of B, Al, Fe, Cu, Mg, Ni, and Ca is 1 ppm or less.

[0030] (8) The free carbon content is 0.001 - 0.5% by mass, the free metallic silicon is 0.01 - 1.0% by mass, and the total content of metal impurities of B, Al, Fe, Cu, Mg, Ni, and Ca is 1 ppm or less.

[0031] Advantages of the Invention

[0032] According to the present invention, high-purity silicon carbide powder with a low content of unreacted carbon can be obtained. As a result, when used as a raw material for SiC single crystals manufactured by the sublimation recrystallization method, single crystals with fewer defects can be manufactured. In addition, when used as a raw material for sintered bodies, sintered bodies with good sinterability and fewer defects can be manufactured. Moreover, the content of metal impurities in the silicon carbide powder obtained by the manufacturing method of the present invention is low, and it can also be applied to the raw material for SiC semiconductor wafers. Detailed Embodiments

[0033] The present invention is characterized in that when manufacturing silicon carbide powder by mixing metal silicon powder and carbon powder and performing self-propagating high-temperature synthesis, the bulk density of the mixed metal silicon powder and carbon powder is made to be twice or more the bulk density of the metal silicon powder and carbon powder before mixing. By such a manufacturing method of the present invention, high-purity silicon carbide powder with low contents of unreacted free silicon, free carbon, and metal impurities can be obtained. The details of the reason why high-purity silicon carbide powder can be obtained by the manufacturing method of the present invention are not yet clear, and the inventors et al. speculate as follows. That is, as described above, in the self-propagating high-temperature synthesis method, since the reaction temperature is low, the conversion rate to silicon carbide is suppressed, and there is a tendency for free silicon and free carbon to increase. This tendency is particularly likely to occur when the mixing of the metal silicon powder and carbon powder before the reaction is insufficient. The carbon powder forms aggregates relatively frequently, and there is a tendency that it is difficult to mix sufficiently to the extent of adding the carbon powder to the metal silicon powder. In the self-propagating high-temperature synthesis method, after the silicon powder and carbon powder are mixed, they are supplied to the reaction. If the mixing is insufficient, the large-volume aggregates of the carbon powder cannot be sufficiently disintegrated, and the bulk density of the mixed powder will not change significantly. Therefore, by mixing the silicon powder and carbon powder and performing a sufficient mixing process using a mixing means such as a ball mill to disintegrate the carbon powder aggregates that have formed and at the same time sufficiently mix the silicon powder and carbon powder, the bulk density of the above-mentioned mixed powder after mixing is increased. Therefore, it is speculated that by increasing the bulk density of the above-mentioned mixed powder to a ratio equal to or higher than a specified ratio with respect to the bulk density before mixing, the silicon powder and carbon powder can be uniformly mixed. Then, it is speculated that by supplying the uniformly mixed mixed powder for manufacturing, high-purity silicon carbide powder with low contents of unreacted carbon and metal impurities can be obtained.

[0034] In this specification, unless otherwise specified, for numerical values A and B, the term "A to B" means "A or more and B or less". In such a term, when only a unit is attached to numerical value B, the unit should also apply to numerical value A. Hereinafter, the manufacturing method of the silicon carbide powder of the present invention will be described in detail.

[0035] <Manufacturing Method of Silicon Carbide Powder>

[0036] 〔Metal Silicon Powder〕

[0037] In the manufacturing method of the present invention, a mixing step is performed to mix metal silicon powder and carbon powder to obtain a mixed powder (hereinafter also referred to as "raw material for silicon carbide manufacturing"). From the viewpoints of reaction yield and reduction of the content of unreacted metal silicon powder and carbon powder, it is preferred that the mixing ratio of Si / C in the raw material for silicon carbide manufacturing is mixed such that the Si / C molar ratio is 0.98 or more and 1.02 or less.

[0038] In addition, from the viewpoint of reactivity, the particle size of the metal silicon powder is preferably 2.0 μm to 50.0 μm, more preferably 4.0 μm to 35.0 μm. The average particle size of the metal silicon powder is preferably 20 μm or less, more preferably 2.0 μm to 10.0 μm. If the particle size of the metal silicon powder is too small, the proportion of the surface oxide film increases, so the Si-based impurities and free carbon in the silicon carbide powder tend to increase. In addition, if the particle size is too large, it is difficult to uniformly mix with the carbon powder, the reaction rate is not high enough, and the Si-based impurities and free carbon tend to increase. When the metal silicon contains metal impurities, the metal impurity concentration in the silicon carbide powder also tends to increase. Therefore, the total content of metal impurities such as B, Al, Fe, Cu, Mg, Ni, and Ca in the metal silicon powder is preferably 1 ppm or less, more preferably 0.1 ppm or less.

[0039] 〔Carbon powder〕

[0040] In the manufacturing method of the present invention, as the carbon powder, the primary particle size of the used powder is preferably 100 nm or less, more preferably 10 nm or more and 100 nm or less. If the particle size of the carbon powder is too small, it is easy to adsorb air and moisture, and the purity of the silicon carbide powder tends to decrease. If the particle size is too large, it is difficult to uniformly mix with the metal silicon powder, the reaction rate is not high enough, and the Si-based impurities and free carbon tend to increase. When the carbon powder contains metal impurities, the metal impurity concentration in the silicon carbide powder also tends to increase. Therefore, the metal impurity concentration of the carbon powder is 50 ppm or less, more preferably 10 ppm or less, and further preferably 1 ppm or less. The type of the carbon powder is not particularly limited, and for example, carbon black, graphite, activated carbon, etc. can be used. The carbon black can be made by various methods such as furnace method (furnace black), channel method (channel black), and acetylene method (acetylene black).

[0041] 〔Raw material for silicon carbide manufacturing〕

[0042] When mixing the above-mentioned silicon powder and carbon powder to obtain the raw material for silicon carbide manufacturing, it is particularly preferred to use a metal silicon powder with an average particle size of 20 μm or less and a carbon powder with a primary particle size of 100 nm or less.

[0043] 〔Other raw materials〕

[0044] In the raw materials for manufacturing silicon carbide, within the scope of not impairing the effects of the present invention, in addition to metal silicon powder and carbon powder, for the purpose of controlling the reaction temperature, etc., silicon carbide powder can also be added as a diluent. When using silicon carbide powder as a diluent, adjust the Si / C molar ratio of the mixed powder including the diluent silicon carbide powder. The mixing amount of silicon carbide powder is usually 50% by mass or less of the mixed powder. In addition, if the metal impurities contained in the silicon carbide powder used as a diluent are many, the amount of metal impurities in the manufactured silicon carbide powder will also increase. Therefore, the metal impurities in the silicon carbide powder are preferably 200 ppm or less, more preferably 100 ppm or less, and further preferably 50 ppm or less. It should be noted that the silicon carbide powder manufactured by the manufacturing method of the present invention can also be used as the silicon carbide powder for diluent.

[0045] 〔Mixing process〕

[0046] In the manufacturing method of the present invention, the method of mixing the metal silicon powder and the carbon powder to obtain the raw material for manufacturing silicon carbide requires that the bulk density of the raw material powder for manufacturing silicon carbide after mixing is twice or more than the bulk density of the metal silicon powder and the carbon powder before mixing. As described above, the carbon powder is agglomerated, so by mixing with the silicon powder while breaking it up, uniform mixing can be achieved. The method for measuring the bulk density of the raw material for manufacturing silicon carbide after mixing can be confirmed by filling the raw material for manufacturing silicon carbide after mixing into a glass container with an internal volume of 100 cc and measuring the weight. It should be noted that the filling at this time is sparse filling without tapping or applying pressure. In addition, the bulk density before mixing is calculated by separately calculating the bulk density of the metal silicon powder and the carbon powder in the same manner as above, and then weighted-averaging the bulk density of each powder according to the mixing ratio. In the manufacturing method of the present invention, it is sufficient that the bulk density of the metal silicon powder and the carbon powder after mixing is twice or more than the bulk density of the metal silicon powder and the carbon powder before mixing, and it is preferably appropriately carried out within the range of 2 times or more and 10 times or less, and particularly preferably appropriately carried out within the range of 2 times or more and 8 times or less.

[0047] As a method of mixing metallic silicon powder and carbon powder in the manufacturing method of the present invention, specifically, preferred means include mixing means using a blender, a mixer, or a ball mill. In particular, a method of applying a load to raw materials during mixing, such as in a ball mill, can increase the homogeneity of the metallic silicon powder and the carbon powder, and thus is more preferred. For example, when a ball mill is selected for mixing, the materials of the container and the balls filled with the metallic silicon powder and the carbon powder are preferably materials that are not easily worn and mixed into the raw materials during mixing, and more preferably high-purity silicon carbide. In addition, the ball diameter can be selected to be a size that allows homogeneous mixing of the metallic silicon powder and the carbon powder, and the diameter is preferably 3 to 20 mm. The rotation speed can be arbitrarily selected, and is preferably 50 to 500 rpm. In addition, in the case of a method of applying a load to raw materials during mixing in a ball mill, if mixing is carried out in the presence of oxygen, the newly formed surface of the metallic silicon may be oxidized, and the Si-based impurities and free carbon in the silicon carbide powder may increase. Therefore, it is preferably mixed in a non-oxidizing atmosphere (especially in a rare gas atmosphere such as argon), and taken out after cooling to room temperature, thereby suppressing oxidation.

[0048] 〔Manufacturing process〕

[0049] In the manufacturing method of the present invention, a manufacturing process of obtaining silicon carbide powder by self-propagating high-temperature synthesis of the raw materials for manufacturing silicon carbide is carried out. Any device capable of performing self-propagating high-temperature synthesis can be used, and there is no particular limitation. It is preferred to fill the raw materials for manufacturing silicon carbide into an electric furnace, heat the inside of the electric furnace, and ignite a part of the raw materials for manufacturing silicon carbide as needed, thereby manufacturing silicon carbide powder by self-propagating high-temperature synthesis.

[0050] When manufacturing silicon carbide powder by the above method, if oxygen exists in the electric furnace, by-products such as silicon oxide will be generated due to side reactions. In addition, when nitrogen exists in the electric furnace, the nitrogen content in the generated silicon carbide increases. Therefore, the manufacturing process is preferably carried out in an inert atmosphere or under reduced pressure. The inert atmosphere can use rare gases such as helium, neon, and argon, for example. The pressure when carried out in an inert atmosphere is not particularly limited, and it can be carried out under atmospheric pressure or in a pressurized atmosphere. It should be noted that after the raw materials are placed inside the electric furnace, in order to remove oxygen, nitrogen, moisture, etc. inside the electric furnace, it is preferred to carry out the process of reducing the pressure inside the electric furnace to 0.5 Pa or more and 10 Pa or less and then introducing an inert gas to restore the pressure to a specified pressure at least once before the electric furnace is heated. In addition, after replacing the inside of the reaction vessel with an inert gas, the inside of the reaction vessel can be reduced in pressure again to 0.5 Pa or more and 10 Pa or less, and the raw materials for manufacturing silicon carbide can be baked by heating to a temperature lower than the manufacturing temperature.

[0051] In addition, as the heating temperature inside the electric furnace, from the viewpoint of reliably carrying out the silicon carbide formation reaction, the temperature inside the electric furnace is preferably heated to 900 to 2050 °C, more preferably 1000 °C to 1800 °C, and particularly preferably 1200 °C to 1500 °C.

[0052] There is no particular limitation on the heating method. For example, the mixed powder filled in a heat-resistant reaction vessel made of ceramics, graphite, etc. is placed in an electric furnace. After adjusting the atmosphere, the temperature in the electric furnace is raised from room temperature to the manufacturing temperature. The heating-up time is not particularly limited, and it is preferably heated up over 1 hour because it is easy to heat up evenly. The upper limit of the heating-up time is not particularly limited, and from the viewpoint of high-efficiency production, it is preferably 24 hours or less. After rising to the manufacturing temperature, it can be immediately ignited to start the self-propagating high-temperature synthesis reaction, or it can be temporarily held at the manufacturing temperature and then ignited to start the manufacturing process. In the case of temporarily holding at the manufacturing temperature and then igniting to start the self-propagating high-temperature synthesis reaction, from the viewpoint of high-efficiency production, the holding time at the heating temperature is preferably within 24 hours. In addition, a high manufacturing temperature can also be set to initiate the self-propagating high-temperature synthesis reaction by spontaneous combustion.

[0053] 〔Heat treatment process〕

[0054] In the manufacturing method of the present invention, a heat treatment process can also be carried out as needed to heat-treat the silicon carbide powder obtained in the above manufacturing process in an oxidizing atmosphere. Through the above manufacturing process, the silicon powder and carbon powder in the raw materials for manufacturing silicon carbide are almost consumed, but a part of the unreacted silicon powder and carbon powder may still remain. Therefore, by heat-treating the silicon carbide powder after the manufacturing process in an oxidizing atmosphere, the remaining carbon is oxidized and converted into carbon monoxide and carbon dioxide, whereby a part of the unreacted carbon powder can be consumed. In the manufacturing method of the present invention, the heat treatment process can be continued after the manufacturing process, or the silicon carbide powder obtained after the manufacturing process can be filled into a separate heating furnace for heat treatment.

[0055] In the heat treatment process, the oxidizing atmosphere can be, for example, an oxidizing gas such as air or oxygen. The pressure is not particularly limited, and it is preferably under atmospheric pressure. A blower, a fan, etc. can be used to make air flow in the heating furnace.

[0056] The temperature in the heat treatment process is preferably 600 - 1200 °C, more preferably 600 - 1000 °C, and particularly preferably 700 - 900 °C. If the heating temperature is lower than the above range, the oxidation of the remaining carbon will not proceed sufficiently, and if the heating temperature is higher than the above range, the oxidation of silicon carbide will proceed significantly.

[0057] The heating time is not particularly limited as long as it is maintained until the carbon powder in the silicon carbide powder obtained in the manufacturing process reacts and is completely consumed. For example, it can be 1 - 10 hours.

[0058] 〔Crushing process〕

[0059] In the manufacturing method of the present invention, after the heating process, size reduction can be carried out as needed to adjust the particle size. The size reduction method is not particularly limited, and preferred methods include, for example, size reduction by a vibration ball mill, a rotating ball mill, or a jet mill. The materials of the container and the balls can be materials that are not easily worn and mixed into the raw materials, and more preferably high-purity silicon carbide. It should be noted that even if impurities are mixed in, they can be removed by the cleaning process described below.

[0060] 〔Cleaning process〕

[0061] In the manufacturing method of the present invention, cleaning treatment can be carried out as needed to reduce metal impurities and the like. For cleaning, an acidic aqueous solution or an alkaline aqueous solution can be used, and it can be selected according to the element to be reduced. For example, for the acidic aqueous solution, hydrochloric acid, hydrofluoric acid, nitric acid, sulfuric acid, or phosphoric acid can be used, and for the alkaline aqueous solution, an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, etc. can be used. When necessary, the cleaning solution can be heated to promote dissolution.

[0062] <Silicon carbide powder>

[0063] Through the manufacturing method of the present invention, high-purity silicon carbide powder with a low free carbon and low metallic silicon content can be obtained. Specifically, the obtained silicon carbide powder can have a free carbon content of 0.5 mass% or less and free metallic silicon of 1.0 mass% or less, and preferably a free carbon content of 0.001 to 0.5 mass% and free metallic silicon of 0.01 to 1.0 mass%. The carbon content of the silicon carbide powder of the present invention is extremely low, and it can be particularly applied to semiconductor applications that require high purity. The amount of free carbon can be calculated from the weight reduction before and after the heat treatment process by implementing the heat treatment process. In addition, through the heating process after the above manufacturing process, a silicon carbide powder with a carbon content of 0.05 mass% or less, preferably 0.001 to 0.05 mass%, can be obtained.

[0064] Moreover, through the manufacturing method of the present invention, high-purity silicon carbide powder with a total metal impurity content of B, Al, Fe, Cu, Mg, Ni, and Ca of 1 ppm or less can be obtained. The content of metal impurities can be measured by glow discharge mass spectrometry analysis.

[0065] <Uses of silicon carbide powder>

[0066] The uses of the silicon carbide powder of the present invention are not particularly limited. Since the Si-based impurities and free carbon are less, it can be particularly applied to raw materials for SiC single crystals manufactured by the sublimation recrystallization method and raw materials for SiC sintered bodies for semiconductor manufacturing applications, etc., which particularly require high-purity silicon carbide powder.

[0067] Examples

[0068] Hereinafter, the present invention will be described in more detail, but the present invention is not limited to these embodiments. Various physical properties in the examples and comparative examples were measured by the following methods.

[0069] (1) Free carbon concentration

[0070] The free carbon concentration was calculated from the weight reduction during the heating process. Specifically, the following was performed. Approximately 10 g of silicon carbide powder produced by the production method of the present invention was placed in an aluminum / silica porcelain container with a capacity of 28 cc whose weight had been previously measured, and the weight was measured. After placing the porcelain container in an electric furnace, it was heated to 800°C in an air atmosphere and at normal pressure, and maintained at 800°C for 2 hours after reaching 800°C. Then, after cooling to room temperature, the weight was measured, and the free carbon concentration was calculated by dividing the reduced weight before and after the heating process by the weight of the silicon carbide powder after the heating process.

[0071] (2) Free silicon concentration

[0072] The free silicon concentration was determined from the integrated intensity ratio of the 3C-type silicon carbide (111) peak and the metallic silicon (111) peak in the 2θ measurement by X-ray diffraction. Samples were prepared by adding 0.1 to 5.0 mass% of metallic silicon to the silicon carbide powder in advance, and five samples were prepared. X-ray diffraction measurement (SmartLab manufactured by Rigaku) was performed to obtain a calibration curve of the integrated intensity ratio of the 3C-type silicon carbide (111) peak and the metallic silicon (111) peak in the 2θ measurement by X-ray diffraction with respect to the metallic silicon content. The integrated intensity ratio of the 3C-type silicon carbide (111) peak and the metallic silicon (111) peak in the 2θ measurement by X-ray diffraction of the produced silicon carbide powder was substituted into the calibration curve, whereby the free silicon concentration in the silicon carbide powder was calculated.

[0073] (3) Amount of metallic impurities

[0074] The amount of metallic impurities was measured by glow discharge mass spectrometry (ELEMENT GDPLUS manufactured by ThermoFisher Scientific) for the total amount of alkali metals, alkaline earth metals, and transition metals with atomic numbers from 3 to 92.

[0075] (4) Bulk density

[0076] The bulk density after mixing metallic silicon powder and carbon powder was calculated by filling the mixed powder into a 100 cc graduated cylinder up to the 100 cc mark and taking the measured weight as the weight per 100 cc. It should be noted that when filling the mixed powder, the mixed powder was put into the graduated cylinder placed on an electronic balance using a spatula to form a sparse filling state without applying any special pressure to the mixed powder.

[0077] In addition, the bulk density before mixing is obtained by calculating the bulk density of each of the metallurgical silicon powder and the carbon powder in the same manner as the method for measuring the bulk density of the mixed powder, and weighted-averaging the bulk densities of the respective powders according to the mixing ratio.

[0078] (5) Particle size of metallurgical silicon powder, average particle size, and primary particle size of carbon powder

[0079] The particle size and average particle size of the metallurgical silicon powder are measured using a laser diffraction / scattering particle size analyzer (Partica LA-950V2 manufactured by Horiba, Ltd.). Ethanol is used as the dispersion medium. The median diameter (D50) obtained by the measurement is taken as the particle size.

[0080] The primary particle size of the carbon powder is obtained by measuring the length of any particle from an observation image at a magnification of 100,000 times obtained using a scanning electron microscope (FE-SEM JSM-7800Prime manufactured by JEOL Ltd.).

[0081] <Example 1>

[0082] A metallurgical silicon powder with an average particle size of 5.0 μm and a total content of metallic impurities of B, Al, Fe, Cu, Mg, Ni, and Ca of 0.51 ppm and acetylene black with a particle size of 30 nm as the carbon powder are weighed and charged into a ball mill tank at a molar ratio of 1.00:1.00 (Si / C molar ratio of 1.00). The bulk density before mixing is 0.08 g / cm 3 . Using a ball mill, they are mixed at a rotation speed of 125 rpm for 30 minutes to obtain a raw material for manufacturing silicon carbide with a bulk density of 0.35 g / cm 3 (The bulk density after mixing is 4.28 times that before mixing). The atmosphere during mixing is argon, and after cooling, the atmosphere is replaced with air. The material of the grinding balls is silicon carbide.

[0083] The mixed powder is filled into a graphite crucible and placed in an electric furnace. After reducing the pressure in the furnace to 0.5 Pa or more and 10 Pa or less, the operation of introducing argon with a purity of 99.999% and then repressurizing to atmospheric pressure is repeated twice. While maintaining atmospheric pressure, argon is allowed to flow through the electric furnace at a flow rate of 5 liters per minute, and at the same time, the temperature is raised from room temperature to 1200 °C over 3 hours. Silicon carbide powder is obtained by self-propagating high-temperature synthesis that occurs spontaneously during the heating process. The free carbon in the silicon carbide is 0.01% by mass, and the free silicon is 0.1% by mass or less. The evaluation results of the obtained silicon carbide powder are shown in Table 1.

[0084] <Example 2>

[0085] Silicon carbide powder is synthesized in the same manner as in Example 1, except that the mixing time in the ball mill is 60 minutes. The bulk density of the raw material for manufacturing silicon carbide after mixing is 0.48 g / cm3 (The volume density after mixing is 5.93 times that before mixing). In addition, the free carbon of the obtained silicon carbide is 0.01% by mass, and the free silicon is 0.1% by mass or less. The evaluation results of the obtained silicon carbide powder are shown in Table 1.

[0086] <Example 3>

[0087] Silicon carbide powder was synthesized in the same manner as in Example 1 except that the mixing time in the ball mill was 10 minutes. The volume density of the raw material for manufacturing silicon carbide after mixing was 0.17 g / cm 3 (The volume density after mixing is 2.11 times that before mixing). In addition, the free carbon of the obtained silicon carbide is 0.31% by mass, and the free silicon is 0.7% by mass. The evaluation results of the obtained silicon carbide powder are shown in Table 1.

[0088] <Example 4>

[0089] The silicon carbide powder manufactured in the same manner as in Example 1 was filled into an aluminum / silica porcelain container and placed in an electric furnace. The inside of the furnace was maintained in an air atmosphere and at normal pressure, heated to 800 °C in 1 hour, and maintained at 800 °C for 2 hours after reaching 800 °C. After maintaining for 2 hours, it was cooled to room temperature to obtain silicon carbide powder. The free carbon of the obtained silicon carbide is 0.01% by mass, and the free silicon is 0.1% by mass or less. The evaluation results of the obtained silicon carbide powder are shown in Table 1.

[0090] <Comparative Example 1>

[0091] Silicon carbide powder was synthesized in the same manner as in Example 1 except that the mixing time in the ball mill was 5 minutes. The volume density of the raw material for manufacturing silicon carbide after mixing was 0.12 g / cm 3 (The volume density after mixing is 1.44 times that before mixing). In addition, the free carbon of the obtained silicon carbide is 1.09% by mass, and the free silicon is 2.5% by mass. The evaluation results of the obtained silicon carbide powder are shown in Table 1.

[0092] <Comparative Example 2>

[0093] The metal silicon powder and acetylene black with a particle size of 30 nm as the carbon powder were weighed in a molar ratio of 1.00:1.00 (Si / C molar ratio 1.00), and put into a polyethylene bag with a zipper. The polyethylene bag was shaken up and down for 5 minutes to mix the metal silicon powder and the carbon powder to obtain the raw material for manufacturing silicon carbide, and silicon carbide powder was synthesized in the same manner as in Example 1 except for this. The volume density of the raw material for manufacturing silicon carbide after mixing was 0.08 g / cm 3 (The volume density after mixing is 1.02 times that before mixing). In addition, the free carbon of the obtained silicon carbide is 1.79% by mass, and the free silicon is 4.2% by mass. The evaluation results of the obtained silicon carbide powder are shown in Table 1.

[0094] <Comparative Example 3>

[0095] The silicon carbide powder produced in the same manner as in Comparative Example 1 was filled into an alumina / silica porcelain container and placed in an electric furnace. The inside of the furnace was maintained in an atmospheric atmosphere at normal pressure, heated to 800°C over 1 hour, and maintained at 800°C for 2 hours after reaching 800°C. After maintaining for 2 hours, it was cooled to room temperature to obtain silicon carbide powder. The free carbon in the obtained silicon carbide was 0.01% by mass and the free silicon was 2.5% by mass. The evaluation results of the obtained silicon carbide powder are shown in Table 1.

[0096] [Table 1]

[0097]

Claims

1. A method for manufacturing silicon carbide powder, characterized in that, the manufacturing method is a method for manufacturing silicon carbide powder by mixing metal silicon powder and carbon powder and performing self-propagating high-temperature synthesis, and the manufacturing method includes: a mixing step of mixing metal silicon powder and carbon powder to obtain a raw material for manufacturing silicon carbide; and a manufacturing step of obtaining silicon carbide powder by performing self-propagating high-temperature synthesis on the mixed metal silicon powder and carbon powder in an inert gas atmosphere, such that the bulk density of the mixed metal silicon powder and carbon powder in the mixing step is more than twice the bulk density of the metal silicon powder and carbon powder before the mixing step.

2. The method for manufacturing silicon carbide powder according to claim 1, wherein, the manufacturing step is carried out in an electric furnace.

3. The method for manufacturing silicon carbide powder according to claim 2, wherein, in the manufacturing step, the temperature in the electric furnace is 900 - 2050 °C.

4. The method for manufacturing silicon carbide powder according to claim 1, characterized in that, in the mixing step, at least one selected from a ball mill, a planetary ball mill, a jet mill, and a vibration mill is used as a mixing means.

5. The method for manufacturing silicon carbide powder according to claim 1, characterized in that, in the mixing step, metal silicon powder with an average particle size of 20 μm or less and carbon powder with a primary particle size of 100 nm or less are mixed.

6. The manufacturing method of the silicon carbide powder according to claim 1, characterized in that, including: a heat treatment step of heating the silicon carbide powder obtained in the manufacturing step in an oxidizing atmosphere.

7. The method for manufacturing silicon carbide powder according to claim 6, wherein, in the heat treatment step, the heat treatment temperature is 600 - 1200 °C.

8. A silicon carbide powder, wherein, the free carbon content is 0.5 mass% or less and the free metal silicon is 1.0 mass% or less.

9. A silicon carbide powder, wherein, the total content of metal impurities of B, Al, Fe, Cu, Mg, Ni, and Ca is 1 ppm or less.

10. A silicon carbide powder, wherein, the free carbon content is 0.5 mass% or less, the free metal silicon is 1.0 mass% or less, and the total content of metal impurities of B, Al, Fe, Cu, Mg, Ni, and Ca is 1 ppm or less.

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