Raw material powder for silicon carbide production and method for producing the same

Abstract

This invention provides a silicon carbide production raw material powder with reduced metal impurity content, suitable for use in semiconductor materials such as semiconductor wafers. [Solution] A method for producing raw material powder for silicon carbide production, comprising metallic silicon and / or carbon, is provided, comprising: a coarse crushing step in which metallic silicon and / or carbon with a maximum longest part length exceeding 3 mm is crushed so that the maximum longest part length of the metallic silicon and / or carbon after crushing is 300 μm to 3 mm; a fine grinding step in which the metallic silicon and / or carbon that has undergone the coarse grinding step is ground so that the median diameter in the particle size distribution by laser diffraction and scattering method is less than 100 μm, and a classification step to remove fine powder before the fine grinding step is provided.

Description

Technical Field

[0001] The present invention relates to a raw material powder for producing silicon carbide and a method for producing the same. Specifically, the present invention relates to a raw material powder for producing silicon carbide with a reduced content of metallic impurities, which can be used as a raw material for semiconductor wafers, and a method for producing the same.

Background Art

[0002] Silicon carbide (SiC) has excellent properties such as high hardness, high strength, high heat resistance, and high thermal conductivity, and thus has been used in abrasives, refractories, heating elements and the like. In recent years, demand has also been increasing as a raw material for SiC semiconductor wafers. Silicon carbide powders corresponding to these uses have been manufactured, and particularly high-purity silicon carbide powders are required for raw materials for SiC semiconductor wafers and raw materials for SiC sintered bodies for semiconductor manufacturing applications and the like.

[0003] As methods for producing silicon carbide powder, (1) the Acheson method in which silica sand and coke are heated to a high temperature by electrical heating (for example, Patent Documents 1 and 2), (2) a method in which a mixture of silica and carbon powder is externally heated to cause reduction and carbonization reactions (for example, Patent Document 3), and (3) a method in which metal silicon powder is directly carbonized by reaction with carbon powder (also referred to as self-propagating high-temperature synthesis method or combustion synthesis method, for example, Patent Documents 4 and 5) are known.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of Invention

[0005] For use in semiconductor materials, silicon carbide powder with a purity of 5N or higher is required. As a method to obtain high-purity silicon carbide powder, attempts have been made to improve purity by removing impurities from the manufactured silicon carbide powder, as described in, for example, Patent Documents 1 and 4, but there have been limitations to the purity improvement.

[0006] Furthermore, the manufacturing method described in (3) (self-propagating high-temperature synthesis method) is a method that directly carbonizes metallic silicon powder, but it is attracting attention as a manufacturing method that can produce high-purity products because it yields silicon carbide powder corresponding to the purity of a mixed powder obtained by uniformly mixing metallic silicon powder and / or carbon powder, which are raw material powders for silicon carbide production (sometimes simply referred to as "raw material powder"), in a predetermined molar ratio. On the other hand, it is known that if impurities are present in the raw material powder and mixed powder, the silicon carbide powder obtained by the above manufacturing method will also be contaminated with impurities originating from the raw material powder and mixed powder.

[0007] In addition, in order to produce high-purity silicon carbide powder using the self-propagating high-temperature synthesis method described above, it is preferable to react the metallic silicon powder and carbon powder in an equimolar amount as close to equimolar as possible. For this reason, it is necessary to mix the metallic silicon powder and carbon powder in the mixed powder in an equimolar amount and uniformly. Furthermore, in order to complete the reaction, it is necessary to obtain a fine mixed powder with a median diameter of, for example, about 10 μm or less. For this reason, if the metallic silicon and carbon have a shape such as lumps, it is necessary to grind them until the metallic silicon and carbon reach the particle size described above. However, the inventors' research has revealed that impurities may be introduced during the grinding of metallic silicon and carbon, and high-purity silicon carbide powder may not be obtainable.

[0008] Therefore, the object of the present invention is to provide a silicon carbide production raw material powder with reduced metal impurity content that can be used as a semiconductor material, such as a raw material for semiconductor wafers. [Means for solving the problem]

[0009] The inventors of this invention conducted intensive research to solve the above problems. As mentioned above, when using lumpy metallic silicon and carbon as raw materials, it is necessary to pulverize these lumps. In particular, in order to efficiently pulverize large lumps with a diameter of more than 1 cm, it is necessary to combine coarse crushing and fine grinding to adjust the particle size in multiple stages. Analysis of the amount of metallic impurities in metallic silicon and carbon before and after coarse crushing and fine grinding revealed that the amount of metallic impurities increased significantly, especially after coarse crushing. Furthermore, electron microscopy observation revealed that deposits smaller than 10 μm were attached to the surface of the coarsely crushed material (metallic silicon or carbon) of several cm in size obtained from the coarse crushing device, and elemental analysis of these deposits revealed elements contained in the crushing device. From this, we obtained the finding that contamination originating from the coarse crushing device is smaller than 10 μm in size and is attached to the surface of the coarsely crushed material.

[0010] Therefore, we investigated methods for removing metallic impurities from the crushed material after coarse crushing. As a result, we found that by performing classification at the stage when the above-mentioned lump material is coarsely crushed to a few centimeters, fine powder can be removed from the coarsely crushed material, metallic impurities of about 10 μm can be effectively separated. Furthermore, by finely crushing the metallic silicon and carbon to a size of 10 μm or less, high-purity metallic silicon and / or carbon raw material powder can be obtained. By uniformly mixing the obtained metallic silicon and / or carbon raw material powder in a predetermined molar ratio and using the mixed powder in the above-mentioned self-propagating high-temperature synthesis method, the purity of the silicon carbide powder can be greatly improved, thus completing the present invention.

[0011] In other words, the first aspect of the present invention is a method for producing raw material powder for silicon carbide production, comprising metallic silicon and / or carbon raw materials, the method comprising: a coarse crushing step of crushing metallic silicon and / or carbon with a maximum longest part length exceeding 3 mm so that the maximum longest part length of the metallic silicon and / or carbon after crushing is 300 μm to 3 mm; and a fine grinding step of grinding the metallic silicon and / or carbon that has undergone the coarse grinding step so that the median diameter in the particle size distribution by laser diffraction and scattering method is less than 100 μm, wherein the method for producing raw material powder for silicon carbide production comprises a classification step of removing fine powder before the fine grinding step.

[0012] Furthermore, the second aspect of the present invention is a raw material powder for silicon carbide production, comprising metallic silicon and / or carbon raw materials, wherein the median diameter in the particle size distribution is less than 100 μm, and the total amount of Al, B, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, S, W, Y, Zn, and Zr is 5 ppmwt or less.

[0013] Furthermore, the third aspect of the present invention is a silicon carbide powder having a total metal impurity content of 5 ppmwt or less, an average particle size of 10 μm to 1 mm, and a polytype of type 6H. [Effects of the Invention]

[0014] According to the present invention, a raw material powder for silicon carbide production with a highly reduced total amount of metal impurities can be obtained. Furthermore, by using the above raw material powder in self-propagating high-temperature synthesis, high-purity silicon carbide powder with a highly reduced total amount of metal impurities can be obtained. As a result, high-purity silicon carbide semiconductor wafers can be manufactured.

[0015] Furthermore, according to the present invention, even if the raw material for silicon carbide production is not in powder form from the beginning but in lump form, it can be used for the synthesis of high-purity silicon carbide powder regardless of the form of the raw material by performing coarse crushing, purification by classification, and fine grinding. [Modes for carrying out the invention]

[0016] <Method for producing raw material powder for silicon carbide production> The present invention provides a method for producing raw material powder for silicon carbide production, comprising a coarse crushing step of crushing lump-like metallic silicon and / or carbon to a predetermined particle size, and a fine grinding step of further grinding the metallic silicon and / or carbon that has undergone the coarse grinding step to a degree that allows for production by a self-propagating high-temperature synthesis method, characterized in that it includes a classification step to remove fine powder before the fine grinding step. By this production method, raw material powder for silicon carbide production that can be used for the synthesis of high-purity silicon carbide powder can be produced.

[0017] In this specification, unless otherwise specified, the notation "A~B" for numerical values ​​A and B means "A or greater and B or less". If a unit is attached only to numerical value B in such notation, that unit shall also apply to numerical value A. The silicon carbide raw material powder and the method of manufacturing the same of the present invention will be described in detail below.

[0018] [Metallic silicon and / or carbon raw materials] The manufacturing method of the present invention uses metallic silicon and / or carbon (hereinafter also simply referred to as "lumps") whose longest part length exceeds 3 mm. Metallic silicon and / or carbon of this size need to be finely crushed and pulverized to obtain a powder (e.g., median diameter less than 100 μm) suitable for production by the self-propagating high-temperature synthesis method. However, performing this in a single crushing and pulverizing process is not economical; therefore, finely crushed metallic silicon and / or carbon powder can be obtained by performing crushing and pulverizing multiple times. The longest part of metallic silicon and / or carbon refers to the longest distance between two opposing points in the lump or powder. The lump of metallic silicon and / or carbon subjected to the above crushing and pulverizing may consist of only metallic silicon or carbon, or it may contain both in any proportion. When both metallic silicon and carbon are included, the particle size distribution of the metallic silicon and / or carbon powder obtained after the coarse crushing and fine grinding described later may differ significantly, potentially reducing the uniformity of metallic silicon and carbon. Therefore, it is preferable that the content of either metallic silicon or carbon is less than 10% by mass when the total amount of metallic silicon and carbon is 100 parts by mass. Specific examples of the agglomerate include polycrystalline silicon, single-crystal silicon (silicon wafers), graphite, activated carbon, carbon black, and metallic silicon-carbon composite materials, but are not limited to these, and various metallic silicon and / or carbon can be used. Furthermore, the shape of the agglomerate is not particularly limited and may be any size and volume within the range where coarse crushing is possible. To avoid increasing the number of coarse crushing steps and accumulating impurities originating from the crusher, it is preferable that the longest part of the particle does not exceed 10 cm.

[0019] Furthermore, since other components become sources of impurities and are difficult to remove, it is preferable that the lump material does not contain any components other than elemental metallic silicon and elemental carbon. Accordingly, the total amount of metallic impurities other than metallic silicon and carbon in the lump material is preferably 1 ppm or less, more preferably 10 ppb or less, and even more preferably 0.1 ppb or less. The lump material may contain a small amount of silicon carbide, such as 0.1 wt% or less, in which case a portion of the raw material may be siliconized. Since silicon carbide has high hardness, if the content exceeds this range, coarse crushing and fine grinding may become difficult.

[0020] The purity of the above massive material, or the total amount of metal impurities other than metal silicon and carbon, can be measured by impurity analysis after pulverizing the massive material to 1 cm or less by a method that prevents impurities from being mixed in as much as possible. Specifically, when metal silicon is used as the massive material, the massive material is pulverized and then dissolved in hydrofluoric nitric acid, evaporated to dryness by heating, the dried solid is dissolved in dilute nitric acid, and the solution is measured by inductively coupled plasma optical emission spectrometry (ICP-OES), whereby the total amount of impurities in the massive material can be evaluated. When carbon is used as the massive material, the massive material is pulverized, mixed with high-purity metal silicon powder having an average particle diameter of about 10 μm, then heated in an oxidizing atmosphere to remove carbon, the heated metal silicon powder is made into a solution by the same method as described above, and the solution is analyzed by ICP-OES, whereby the total amount of impurities in the massive material can be evaluated. Furthermore, when a massive raw material containing both metal silicon and carbon is used, the massive material is pulverized, then heated in an oxidizing atmosphere to remove carbon, the heated metal silicon powder is made into a solution by the same method as described above, and the solution is analyzed by ICP-OES, whereby the total amount of impurities in the massive material can be evaluated.

[0021] [Rough Pulverization Step] In the production method of the present invention, a rough pulverization step is performed in which the above massive material is roughly pulverized so that the maximum value of the longest portion length of the pulverized metal silicon and / or carbon (hereinafter also simply referred to as "rough pulverized material") is 300 μm to 3 mm. If the maximum value of the longest portion length of the rough pulverized material is less than 300 μm, separation from fine powder containing a large amount of metal impurities in the classification step described later becomes difficult, which is not preferable. On the other hand, if the maximum value of the longest portion length of the rough pulverized material exceeds 3 mm, the particles cannot be sufficiently refined in the fine pulverization step described later, which is not preferable.

[0022] The particle diameter of the above rough pulverized material is determined by analyzing the projected image of the rough pulverized material as the longest portion length. Specifically, it is calculated by acquiring a projected image of the rough pulverized material with a digital camera or a microscope, arbitrarily extracting 100 or more specimens, and determining the maximum value of the longest portion of them.

[0023] The above-mentioned coarse crushing method is not particularly limited, and in addition to hammers and presses, jaw crushers, hammer crushers, roll crushers, etc., can be used. In order to suppress the amount of impurities mixed in, it is preferable to use hard materials such as silicon carbide, silicon nitride, tungsten carbide, and alumina in the parts that come into contact with the raw material, and to select a crushing method that minimizes the number of contacts with the raw material.

[0024] The coarse crushing process is preferably completed in one step to avoid the accumulation of impurities and to obtain coarse crushed material industrially and efficiently. However, it may be performed multiple times, taking into consideration the size of the obtained coarse crushed material.

[0025] [Classification process] In the manufacturing method of the present invention, a classification step is performed to remove fine powder after the coarse crushing step. Here, in any classification method, if separation is performed with a certain particle size as the boundary, one side is classified as fine powder containing 90 wt% or more of particles of that particle size or smaller, and the other side as coarse powder.

[0026] Observation using a scanning electron microscope revealed that the surface of the coarsely crushed material, which was several centimeters in size and obtained from the coarse crushing device, had deposits smaller than 10 μm in size. Furthermore, elemental analysis of these deposits detected large amounts of elements contained in the crushing device. Therefore, the contamination originating from the coarse crushing device is smaller than 10 μm and adheres to the surface of the coarsely crushed material. By removing the fine powder, which has a large impurity content and is generated after the classification process, from the coarse powder and using that coarse powder in the subsequent coarse crushing or fine grinding process, it is possible to produce a high-purity raw material powder.

[0027] The classification method is not particularly limited as long as it does not increase the amount of impurities, and methods such as hand-shaking sieves, vibrating sieves, and airflow classification can be used. When using sieves, the mesh size specified in JIS Z 8801 is preferably 50 μm to 1 mm, and more preferably 100 to 500 μm. If it exceeds this range, the recovery rate of coarse powder obtained after classification may decrease, and if it is smaller than this range, efficient separation of coarse powder and fine powder after classification becomes difficult, and there is a risk that the classification efficiency will decrease due to clogging. The material of the mesh is not particularly limited, but it is preferable to use a resin mesh such as polyethylene or nylon in order to suppress contamination.

[0028] The number of times the classification process can be performed is not particularly limited; it may be performed only once after any coarse crushing process, or it may be performed two or more times after each of multiple coarse crushing processes. In particular, when using a crushing device with highly brittle parts that come into contact with the crushed material, performing the classification process after a coarse crushing process where the inclusion of impurities is a particular concern can effectively remove impurities.

[0029] Furthermore, after the classification process, wet washing may be performed to remove impurities as needed. The washing solution is not particularly limited and can be, for example, pure water, hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, or potassium hydroxide aqueous solution. If necessary, ultrasonic waves, a stirrer, or heating of the washing solution may also be used in conjunction with washing with the above-mentioned washing solution.

[0030] [Fine grinding process] In the manufacturing method of the present invention, the metallic silicon and / or carbon obtained in the coarse grinding step and the classification step are subjected to a fine grinding step in which the particles are ground to a median diameter of less than 100 μm in the particle size distribution. Here, the median diameter refers to the particle size (D50) at which the cumulative frequency of volume is 50% in the particle size distribution curve obtained by laser diffraction and scattering method.

[0031] The particle size of the finely ground material obtained in the fine grinding process can be measured using a laser diffraction / scattering particle size analyzer. Both solvent-circulating and dry-type particle size analyzers can be used.

[0032] The metallic silicon and / or carbon powder obtained in the fine grinding process is mixed in an appropriate ratio and used in the production of silicon carbide described later. However, it is known that if the molar ratio of metallic silicon to carbon in the mixed powder deviates locally from 1.0, the reaction does not proceed stoichiometrically, and silicon-based impurities and free carbon increase. Therefore, in order to improve the uniformity of the molar ratio of metallic silicon to carbon in the mixed powder, it is preferable that the particle size of the finely ground material obtained in the fine grinding process be small, and more specifically, it is more preferable that the median diameter be less than 10 μm. On the other hand, if the particle size of the finely ground material is too small, it tends to adsorb air and moisture, and the purity of the silicon carbide powder synthesized using the raw material tends to decrease, so it is preferable that the median diameter be greater than 10 nm.

[0033] Similarly, from the viewpoint of uniformity of the molar ratio of metallic silicon to carbon in the mixed powder, it is preferable that the particle size (D90) at the cumulative frequency of 90% by volume in the particle size distribution curve of the finely ground material is 100 μm or less. If the D90 after fine grinding exceeds 100 μm, the coarse powder may be removed by classification. The classification method is not particularly limited, and hand-shaking sieves, vibrating sieves, airflow classification, etc., can be used. When using a sieve, it is preferable to use a mesh with an opening size of 300 μm or less, and more preferably 106 μm or less, as specified in JIS Z 8801, in order to selectively separate the coarse powder and fine powder after classification. The material of the mesh is not particularly limited, but it is preferable to use a resin mesh in order to suppress the inclusion of impurities.

[0034] The above-mentioned fine grinding method is not particularly limited as long as it can be finely ground to achieve the above-mentioned particle size distribution. Specific fine grinding methods include vibrating ball mills, planetary ball mills, and jet mills. To suppress the amount of impurities mixed in, it is preferable to select a hard material with a low content of elements other than silicon and carbon for the parts that come into contact with the raw material. For example, ball mill grinding using media made of high-purity silicon carbide is a suitable example. The diameter of the balls should be selected to ensure that the metallic silicon and / or carbon powder is homogeneously mixed, with a diameter of 3 to 20 mm being preferred. Any rotational speed can be selected, but 50 to 500 rpm is preferred. The fine grinding process may be included two or more times, but it is more preferable to perform the fine grinding process only once to avoid the accumulation of impurities.

[0035] Furthermore, after the fine grinding process, further heat treatment or halogen purification may be performed as needed to reduce the amount of impurities. Wet washing using a washing solution such as an acid, alkali, or oxidizing agent may be performed, but since filtration and drying are difficult, it is preferable to perform this after the coarse crushing process rather than after the fine grinding process.

[0036] <Raw material powder for silicon carbide production> By the manufacturing method of the present invention described above, raw material powder for silicon carbide production (hereinafter sometimes simply referred to as "raw material powder") can be obtained. Specifically, raw material powder for silicon carbide production can be obtained which is metallic silicon and / or carbon powder in which the median diameter in the particle size distribution by laser diffraction and scattering method is less than 100 μm, and the total amount of Al, B, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, S, W, Y, Zn, and Zr is 5 ppmwt or less.

[0037] The particle size of the raw material powder is preferably such that the median diameter is 10 nm or more and less than 100 μm, more preferably 2.0 μm to 50.0 μm, and particularly preferably 4.0 μm to 35.0 μm. If the particle size is smaller than this range, it becomes easier to adsorb air and moisture, and the proportion of the surface oxide film on the metallic silicon powder tends to increase. For this reason, when synthesis is performed using this raw material powder, unreacted silicon and / or carbon remain, and the purity of the silicon carbide powder tends to decrease. On the other hand, if the particle size is larger than this range, it becomes difficult to uniformly mix the metallic silicon powder and the carbon powder, and the reaction rate for silicon carbide formation does not become sufficiently high, and the amount of unreacted silicon and / or carbon tends to increase.

[0038] Furthermore, if the raw material powder contains metal impurities, the concentration of metal impurities in the silicon carbide powder tends to increase. Therefore, the total amount of metal impurities Al, B, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, S, W, Y, Zn, and Zr in the metallic silicon powder is preferably 5 ppmwt or less, more preferably 1 ppmwt or less, and even more preferably 0.1 ppmwt or less. The form of the impurities is not particularly limited and may exist as elements, compounds such as oxides, carbides, nitrides, and complexes, or as mixtures. The method for analyzing the total amount of impurities in the raw material powder is not particularly limited and can be inductively coupled plasma emission spectrometry, inductively coupled plasma mass spectrometry, glow discharge mass spectrometry, atomic absorption spectrometry, etc.

[0039] If the content of metallic silicon and / or carbon in the above-mentioned silicon carbide production raw material powder satisfies the required molar ratio of metallic silicon to carbon when producing silicon carbide powder, as described later, the raw material powder can be used directly in the self-propagating high-temperature synthesis described later. On the other hand, if the raw material powder contains metallic silicon or carbon, or metallic silicon and carbon but the molar ratio of metallic silicon to carbon deviates significantly from 1.0, the obtained silicon carbide production raw material powder can be mixed to obtain a silicon carbide production mixed powder by adjusting the molar ratio of metallic silicon to carbon to the desired ratio. The method for producing the silicon carbide production mixed powder will be described in detail below.

[0040] <Method for producing mixed powder for silicon carbide production> [Mixing process] In the manufacturing method of the present invention, the mixed powder for silicon carbide production is obtained by mixing the raw material powder for silicon carbide production with metallic silicon and / or carbon powder, or two or more raw material powders for silicon carbide production with different molar ratios of metallic silicon / carbon, while appropriately adjusting the molar ratio of metallic silicon / carbon. Generally, at temperatures above 2000°C, the reaction between metallic silicon powder and carbon powder is accelerated, and almost the entire amount can be reacted. However, at the same time, due to the volatilization of metallic silicon and the presence of less reactive, highly crystalline carbon, the Si / C molar ratio of the produced silicon carbide powder will differ significantly from the mixing ratio of the raw materials. Therefore, the molar ratio is preferably 0.5 to 1.2.

[0041] In the manufacturing method of the present invention, preferred methods for mixing metallic silicon powder and carbon powder include blenders, mixers, and ball mills. Methods that apply load to the raw materials during mixing, such as ball mills, are particularly preferable because they increase the homogeneity of the metallic silicon powder and carbon powder. For example, when mixing by ball mill, the material of the container and balls in which the metallic silicon powder and carbon powder are filled should be such that they do not wear down during mixing and easily mix with the raw materials, and high-purity silicon carbide is more preferable. The diameter of the balls should be selected to ensure homogeneous mixing of the metallic silicon powder and carbon powder, with a diameter of 3 to 20 mm being preferred. Any rotation speed can be selected, but 50 to 500 rpm is preferred. Furthermore, in the case of methods that apply load to the raw materials during mixing, such as ball mills, if mixing is performed in the presence of oxidation, the newly formed surface of metallic silicon may be oxidized, increasing the amount of unreacted silicon and / or carbon in the silicon carbide powder. Therefore, it is preferable to suppress oxidation by mixing in a non-oxidizing atmosphere (especially in a noble gas atmosphere such as argon) and removing the mixture after cooling to room temperature.

[0042] <Method for producing silicon carbide powder> The present invention provides a method for producing silicon carbide powder, which involves uniformly mixing raw material powders produced by the above-mentioned method for producing raw material powders for silicon carbide production in a predetermined molar ratio to prepare a mixed powder, and then synthesizing silicon carbide powder by self-propagation high-temperature synthesis.

[0043] [Self-propagating high-temperature synthesis] In the manufacturing method of the present invention, a heat treatment step is performed to obtain silicon carbide powder by self-propagation high-temperature synthesis of a mixed powder for silicon carbide production, which is prepared by uniformly mixing the raw material powder produced by the above-mentioned method for producing silicon carbide raw material powder in a predetermined molar ratio. The apparatus is not particularly limited as long as it is capable of self-propagation high-temperature synthesis, but it is preferable to fill the mixed powder for silicon carbide production into an electric furnace, heat the inside of the electric furnace, and ignite a portion of the mixed powder for silicon carbide production as needed to produce silicon carbide powder by self-propagation high-temperature synthesis.

[0044] When producing silicon carbide powder using the method described above, the presence of oxygen in the electric furnace will result in the production of by-products such as silicon oxide due to side reactions. Furthermore, the presence of nitrogen in the electric furnace will increase the nitrogen content in the produced silicon carbide. Therefore, the manufacturing process is preferably carried out under an inert atmosphere or under reduced pressure. For example, a noble gas such as helium, neon, or argon can be used as the inert atmosphere. The pressure when carrying out the process under an inert atmosphere 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. By setting the pressure within this range, it becomes easier to remove nitrogen, moisture, and low-boiling-point substances adsorbed on the raw materials that volatilize during preheating and self-propagating high-temperature synthesis. The lower limit of the pressure is not particularly limited; for example, it may be 0.5 Pa or higher. When creating an inert atmosphere inside the reaction vessel after placing the raw materials in it, it is preferable to reduce the pressure inside the reaction vessel to 0.5 Pa or more and 10 Pa or less, then introduce an inert gas, and restore the pressure to the predetermined level at least once. Furthermore, if the process of reducing the pressure inside the reaction vessel to 0.5 Pa or more and then introducing an inert gas and restoring the pressure to a predetermined level is performed two or more times, the pressure during preheating and / or self-propagating high-temperature synthesis can be carried out at atmospheric pressure. When the heat treatment process is carried out under atmospheric pressure, the volatilization of metallic silicon is suppressed, so silicon carbide powder with a free carbon content of 0.04% or less can be obtained after the heat treatment process.

[0045] Furthermore, regarding the heating temperature inside the electric furnace, from the viewpoint of ensuring that the silicon carbide production reaction is carried out reliably, it is preferable to heat the temperature inside the electric furnace to 900 to 2500°C, and more preferably to 1200 to 2500°C.

[0046] The heating method is not particularly limited. For example, the mixed powder, packed in a heat-resistant reaction vessel made of ceramic, graphite, or other materials, can be placed in an electric furnace, the atmosphere can be adjusted, and then the temperature inside the electric furnace can be raised from room temperature to the production temperature. The heating time is not particularly limited, but it is preferable to raise the temperature over a period of one hour or more to ensure uniform heating. There is no particular upper limit to the heating time, but from the viewpoint of efficient production, it is preferable to keep it to 24 hours or less. Alternatively, the production temperature can be set higher to initiate a self-propagating high-temperature synthesis reaction by spontaneous ignition. Furthermore, to allow crystal growth, the heating temperature can be maintained at any temperature, but from the viewpoint of efficient production, it is preferable to keep it within 24 hours.

[0047] [Decarburization process] In the manufacturing method of the present invention, a decarburization step is performed by heating the silicon carbide powder obtained in the heat treatment step under an oxidizing atmosphere as needed. Although the silicon powder and carbon powder in the silicon carbide production mixed powder are almost consumed by the heat treatment step, some unreacted carbon powder may remain. Therefore, by heat treating the silicon carbide powder after the manufacturing step under an oxidizing atmosphere, the remaining carbon can be oxidized and converted into carbon monoxide or carbon dioxide, thereby consuming some of the unreacted carbon powder. In the manufacturing method of the present invention, the decarburization step may be performed immediately after the heat treatment step, or the silicon carbide powder obtained after the heat treatment step may be filled into a separate oxidizing atmosphere furnace and the decarburization treatment performed therein.

[0048] In the decarburization process, an oxidizing atmosphere can be provided by an oxidizing gas such as air or oxygen. The pressure is not particularly limited, but atmospheric pressure is preferred. Air may be circulated into the heating furnace using a blower, fan, etc.

[0049] The temperature in the decarburization process is preferably 600 to 1200°C, more preferably 600 to 1000°C, and particularly preferably 700 to 900°C. If the heating temperature is lower than the above range, the oxidation of residual carbon will not proceed sufficiently, and if it is higher than the above range, the oxidation of silicon carbide will proceed excessively.

[0050] The decarburization time is not particularly limited and should be kept until the carbon powder in the silicon carbide powder obtained in the manufacturing process has reacted and been completely consumed, which can be, for example, 1 to 10 hours.

[0051] <Silicon Carbide Powder> The silicon carbide powder of the present invention is characterized by being a 6H-type silicon carbide powder with a low total amount of metal impurities and an average particle size of 10 μm to 1 mm.

[0052] The above-mentioned impurities may exist as elemental particles or as compounds such as oxides. The total amount of metallic impurities is preferably 5 ppmwt or less, more preferably 1 ppmwt or less, and even more preferably 0.1 ppmwt or less. The total amount of the above-mentioned impurities can be analyzed, for example, by glow discharge mass spectrometry. Furthermore, the amount of free carbon in the silicon carbide powder can be calculated from the weight loss before and after the heating process after performing the decarburization process, and the amount of nitrogen can be determined using secondary ion mass spectrometry.

[0053] When used for growing silicon carbide single crystals using manufactured silicon carbide powder, the median diameter of the silicon carbide powder is preferably 10 μm to 1 mm, and more preferably 100 μm to 800 μm, in order to stabilize the sublimation rate.

[0054] The silicon carbide powder of the present invention has no particular limitations on its uses, but it can be used as a filler for resins, an abrasive, or a raw material for ceramics. Since the total amount of metal impurities in the silicon carbide powder of the present invention is extremely low, it can be used particularly suitably for semiconductor applications where high purity is required, such as as a raw material for silicon carbide single crystals produced by sublimation recrystallization, or as a raw material for silicon carbide sintered bodies in semiconductor manufacturing.

[0055] <Summary> As can be understood from the above description, the present invention encompasses the following aspects.

[0056] Embodiment 1: A method for producing a raw material powder for silicon carbide production, comprising metallic silicon and / or carbon, comprising: a coarse crushing step in which metallic silicon and / or carbon with a maximum longest part length exceeding 3 mm is crushed so that the maximum longest part length of the metallic silicon and / or carbon after crushing is 300 μm to 3 mm; a fine grinding step in which the metallic silicon and / or carbon that has undergone the coarse grinding step is ground so that the median diameter in the particle size distribution by laser diffraction and scattering method is less than 100 μm, wherein the method for producing a raw material powder for silicon carbide production comprises a classification step to remove fine powder before the fine grinding step. Embodiment 2: The method for producing raw material powder for silicon carbide production according to Embodiment 1, wherein the classification step is sieve classification using a sieve with an opening size of 50 μm to 1 mm.

[0057] Embodiment 3: A method for producing a mixed powder for silicon carbide production, comprising a mixing step of preparing the raw material powder for silicon carbide production obtained by the manufacturing method described in Embodiment 1 or 2 so that the molar ratio of metallic silicon to carbon is 0.5 to 1.2.

[0058] Embodiment 4: A method for producing silicon carbide powder, comprising a heat treatment step to obtain silicon carbide powder by self-propagation high-temperature synthesis using a raw material powder for silicon carbide production obtained by the manufacturing method described in Embodiment 1, or a mixed powder for silicon carbide production obtained by the manufacturing method described in Embodiment 3, wherein the heat treatment step is performed in an inert atmosphere at a temperature of 900°C to 2500°C.

[0059] Embodiment 5: A method for producing silicon carbide powder according to Embodiment 4, comprising a decarburization step of heating the silicon carbide powder obtained in the heating step at a temperature of 600°C to 1200°C in an oxidizing atmosphere.

[0060] Embodiment 6: A raw material powder for silicon carbide production, comprising metallic silicon and / or carbon, wherein the median diameter in the particle size distribution obtained by laser diffraction and scattering is less than 100 μm, and the total amount of Al, B, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, S, W, Y, Zn, and Zr is 5 ppmwt or less.

[0061] Embodiment 7: The raw material powder for producing silicon carbide according to Embodiment 1, wherein the molar ratio of metallic silicon to carbon is 0.5 to 1.2.

[0062] Embodiment 8: A method for producing silicon carbide powder, comprising a heat treatment step of obtaining silicon carbide powder by self-propagation high-temperature synthesis using a raw material powder for silicon carbide production obtained by the manufacturing method described in Embodiment 6 or 7, wherein the heat treatment step is performed in an inert atmosphere at a temperature of 900°C to 2500°C.

[0063] Embodiment 9: A method for producing silicon carbide powder according to Embodiment 8, comprising a decarburization step of heating the silicon carbide powder obtained in the heating step at a temperature of 600°C to 1200°C in an oxidizing atmosphere.

[0064] Embodiment 10: Silicon carbide powder having a total amount of metal impurities of 5 ppmwt or less, an average particle size of 10 μm to 1 mm, and a polytype of type 6H. [Examples]

[0065] The present invention will be described in more detail below, but the present invention is not limited to these examples. Various physical properties in the examples and comparative examples were measured by the following methods.

[0066] (1) Particle size distribution measurement The particle size distribution was measured using a wet method with a laser diffraction / scattering particle size analyzer (HORIBA LA-950S2). The mixed powder was dispersed in pure water or ethanol, and the particle size distribution was measured. From the obtained particle size distribution, the particle size D50 (median diameter) at a cumulative frequency of 50% by volume and the particle size D90 at a cumulative frequency of 90% by volume were determined.

[0067] (2) Impurity content in raw material powder The total amounts of Al, B, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, S, W, Y, Zn, and Zr in the mixed powder were measured using ICP-OES (Thermo Fisher Scientific, iCAP6500DUO). Samples containing carbon components in the raw materials were pre-treated by decarburization in an oxidizing atmosphere at 850°C before being subjected to ICP-OES measurement.

[0068] (3) Impurity content in silicon carbide powder The impurity content was determined by measuring the total amount of alkali metals, alkaline earth metals, and transition metals with atomic numbers 3 to 92 in the silicon carbide powder using glow discharge mass spectrometry (ThermoFishier Scientific ELEMENT GD PLUS).

[0069] (4) Identification of polytypes of silicon carbide powder The polytype of silicon carbide powder was identified using X-ray diffraction (Rigaku SmartLab). CuKα radiation was used as the X-ray source.

[0070] <Example 1> In a silicon manufacturing facility using the Siemens process, after silicon production, carbon material (average Si / C mass ratio = 0.01) with a volume of approximately 800 cm³ (longest part approximately 15 cm) of silicon precipitated from each reactor was coarsely crushed using a jaw crusher equipped with tungsten carbide blades to a maximum longest part length of 10 mm, and then using a roll crusher equipped with alumina rolls to a maximum longest part length of 3 mm.

[0071] The coarsely crushed material obtained by the above coarse crushing process was classified using a nylon sieve with a mesh size of 300 μm as specified in JIS Z 8801 (hereinafter sometimes referred to as sieve A) to remove the fine powder that passed through the sieve, and the coarse powder remaining on the sieve was recovered (carbon coarsely crushed material).

[0072] Bulky polycrystalline silicon (rectangular parallelepiped shape, approximately 10cm x 10cm x 10cm) was processed using the same coarse crushing process as for coarse crushed carbon to obtain coarse crushed silicon.

[0073] Next, the coarse carbon and coarse silicon fragments obtained in the classification process were finely ground using a vibrating ball mill to a median diameter of 10 μm. The balls used in this fine grinding process were made of high-purity silicon carbide, and the pots were made of nylon resin. Subsequently, the two types of finely ground materials were mixed so that the Si / C molar ratio was 1 to obtain a raw material powder for silicon carbide production.

[0074] The silicon carbide production raw material powder was packed into a graphite crucible and placed in a firing furnace. After reducing the pressure inside the furnace to between 0.5 Pa and 10 Pa, the process of introducing 99.99% pure argon and restoring pressure to atmospheric pressure was repeated twice. While maintaining atmospheric pressure, argon was circulated into the electric furnace at a flow rate of 5 liters / minute while preheating from room temperature to 2200°C over 4 hours. After the self-propagating combustion synthesis was completed, decarburization treatment was performed in the electric furnace at 800°C in an oxygenated atmosphere to obtain silicon carbide powder. The polytype of the silicon carbide powder was identified as 6H type by X-ray diffraction. The evaluation results of the raw material powder and the obtained silicon carbide powder are shown in Tables 1 and 2. Note that "Coarse powder recovery rate after sieving" shows the average value of the coarse powder recovery rate of coarse carbon and coarse silicon fragments.

[0075] <Example 2> Silicon carbide powder was obtained by processing under the same conditions as in Example 1, except that the raw materials used were the end portion of a silicon rod containing a carbon electrode on which silicon had been deposited by chemical vapor deposition after silicon production in a Siemens silicon manufacturing facility (volume approximately 500 cm³, longest part approximately 10 cm, average Si / C mass ratio = 0.9) and a carbon component with a small amount of silicon deposited on it (volume approximately 800 cm³, longest part approximately 15 cm) (average Si / C mass ratio = 0.01). The evaluation results of the raw material powder and the obtained silicon carbide powder are shown in Tables 1 and 2. The "Coarse powder recovery rate after sieving" shows the average value of the coarse powder recovery rate of the two types of coarse crushed materials mentioned above.

[0076] <Example 3> After obtaining the coarse crushed carbon material described in Example 1 following the coarse crushing process, silicon carbide powder was obtained in the same manner as in Example 1, except that the coarse crushed carbon material and granular silicon with a particle size of 2 mm were used in the fine grinding process using a vibrating ball mill. The evaluation results of the raw material powder and the obtained silicon carbide powder are shown in Tables 1 and 2. The "Coarse powder recovery rate after sieving" shows the actual value of the coarse powder recovery rate of the coarse crushed carbon material.

[0077] <Example 4> Silicon carbide powder was obtained using the same method as in Example 1, except that a high-manganese steel blade was used in the jaw crusher. The evaluation results of the raw material powder and the obtained silicon carbide powder are shown in Tables 1 and 2. The "Coarse powder recovery rate after sieving" shows the average value of the coarse powder recovery rate of the coarse crushed carbon and coarse crushed silicon.

[0078] <Example 5> In the classification process, silicon carbide powder was obtained using the same method as in Example 1, except that a nylon sieve with a mesh size of 2 mm as specified in JIS Z 8801 (hereinafter sometimes referred to as sieve B) was used. The evaluation results of the raw material powder and the obtained silicon carbide powder are shown in Tables 1 and 2. The "Coarse powder recovery rate after sieving" shows the average value of the coarse powder recovery rate of the coarse crushed carbon and coarse crushed silicon.

[0079] <Comparative Example 1> Silicon carbide powder was synthesized in the same manner as in Example 1, except that classification was not performed after the rough crushing step. The evaluation results of the raw material powder and the obtained silicon carbide powder are shown in Tables 1 and 2.

[0080] <Comparative Example 2> Silicon carbide powder was synthesized in the same manner as in Example 3, except that classification was not performed after the rough crushing step. The evaluation results of the raw material powder and the obtained silicon carbide powder are shown in Tables 1 and 2.

[0081] [Table 1]

[0082] Table 2

Claims

1. A method for producing a raw material powder for silicon carbide production, comprising metallic silicon and / or carbon, comprising: a coarse crushing step of crushing metallic silicon and / or carbon with a maximum longest part length exceeding 3 mm so that the maximum longest part length of the metallic silicon and / or carbon after crushing is 300 μm to 3 mm; a fine grinding step of grinding the metallic silicon and / or carbon that has undergone the coarse grinding step so that the median diameter in the particle size distribution by laser diffraction / scattering method is less than 100 μm, wherein the method for producing a raw material powder for silicon carbide production comprises a classification step of removing fine powder before the fine grinding step.

2. The method for producing a raw material powder for silicon carbide production according to claim 1, wherein the classification step is sieve classification using a sieve with an opening size of 50 μm to 1 mm.

3. A method for producing a mixed powder for silicon carbide production, comprising a mixing step of preparing the raw material powder for silicon carbide production obtained by the manufacturing method according to claim 1 or 2 so that the molar ratio of metallic silicon to carbon is 0.5 to 1.

2.

4. A method for producing silicon carbide powder, comprising a heat treatment step to obtain silicon carbide powder by self-propagation high-temperature synthesis using a raw material powder for silicon carbide production obtained by the manufacturing method described in claim 1, or a mixed powder for silicon carbide production obtained by the manufacturing method described in claim 3, wherein the heat treatment step is performed in an inert atmosphere at a temperature of 900°C to 2500°C.

5. A method for producing silicon carbide powder according to claim 4, comprising a decarburization step of heating the silicon carbide powder obtained in the heating step at a temperature of 600°C to 1200°C in an oxidizing atmosphere.

6. A raw material powder for silicon carbide production, comprising metallic silicon and / or carbon, wherein the median diameter in the particle size distribution obtained by laser diffraction / scattering is less than 100 μm, and the total amount of Al, B, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, S, W, Y, Zn, and Zr is 5 ppmwt or less.

7. The raw material powder for producing silicon carbide according to claim 6, wherein the molar ratio of metallic silicon to carbon is 0.5 to 1.

2.

8. A method for producing silicon carbide powder, comprising a heat treatment step of obtaining silicon carbide powder by self-propagation high-temperature synthesis using the silicon carbide raw material powder described in claim 6 or 7, wherein the heat treatment step is performed in an inert atmosphere at a temperature of 900°C to 2500°C.

9. A method for producing silicon carbide powder according to claim 8, comprising a decarburization step of heating the silicon carbide powder obtained in the heating step at a temperature of 600°C to 1200°C in an oxidizing atmosphere.

10. Silicon carbide powder having a total metal impurity content of 5 ppm wt or less, an average particle size of 10 μm to 1 mm, and a polytype of type 6H.

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