JP2018118874A - Silicon carbide powder, method for manufacturing the same and method for manufacturing silicon carbide single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a silicon carbide powder capable of stabilizing the growth rate of a silicon carbide single crystal to suppress the occurrence of a defect, such as a silicon droplet, a method for manufacturing the same; and a method for manufacturing a silicon carbide single crystal.SOLUTION: The method for manufacturing silicon carbide powder comprises: mixing an inorganic siliceous raw material with a carbonaceous raw material to obtain a silicon carbide manufacturing raw material; sintering the silicon carbide manufacturing raw material at a temperature of 2200°C or higher to form a massive material consisting of silicon carbide; cooling the massive material consisting of the silicon carbide obtained in the sintering step while blocking to contact the massive material to oxygen; pulverizing the cooled massive material; and classifying the pulverized material to obtain silicon carbide powder having a free carbon concentration of 0.05 mass% or more in a region from a particle surface to a depth of 10 μm. The silicon carbide powder is used as a raw material when manufacturing a silicon carbide single crystal by a sublimation recrystallization method.SELECTED DRAWING: None

Description

  The present invention relates to a silicon carbide powder that is a raw material for producing a silicon carbide single crystal by a sublimation recrystallization method (an improved Rayleigh method), a method for producing the same, and a method for producing a silicon carbide single crystal.

  Silicon carbide powder is used as a material for molding wheels, ceramic parts and the like because of its high hardness, high thermal conductivity, and high temperature heat resistance. In addition, silicon carbide single crystal is attracting attention as a power semiconductor substrate material that replaces silicon because it has a physical property of about three times the band gap and about ten times the dielectric breakdown electric field strength compared to silicon.

  As a method for producing a silicon carbide single crystal, a sublimation recrystallization method in which silicon carbide powder as a raw material is sublimated under a high temperature condition of 2000 ° C. or higher to grow a single crystal of silicon carbide is well known and widely used industrially. Has been.

  In a method of obtaining a silicon carbide single crystal by a sublimation recrystallization method, it is important to stabilize the growth rate of the single crystal. If the growth rate is unstable, it tends to cause defects such as micropipe defects, and when doping a single crystal such as by adding boron to form a p-type semiconductor, a dopant added to the single crystal The higher the single crystal growth, the smaller the concentration of becomes and becomes non-uniform.

  As a method for stabilizing the crystal growth rate, Patent Document 1 discloses that the sublimation rate becomes unstable because the sublimation gas Si is absorbed into a graphite crucible used as a heat insulation container during sublimation, thereby insulating the crucible. It is considered that this is because the heating conditions of the crucible change due to changes in the properties, and a method is described in which the heat insulation property of the crucible is suppressed by absorbing Si in advance in the crucible.

  In addition, Patent Document 2 uses a silicon carbide powder precursor having a 6H-type polytype obtained by heating silicon pieces and carbon powder as a sublimation raw material, thereby increasing the growth rate of silicon carbide crystals during sublimation. A method of enhancing is described.

  Further, in Patent Document 3, by using a mixture of silicon carbide and carbon as a raw material as a raw material powder, crystal growth is suppressed while suppressing generation of silicon droplets due to rapid crystal growth in a Si-rich atmosphere. A method is described in which a crystal is grown at high speed under the condition that the temperature difference between the surface and the raw material powder is 200 ° C. or more.

JP 2014-43394 A JP 2013-252998 A JP2013-103848A

  In each of the above documents, the generation mechanism of defects such as deterioration of the heat insulating material due to absorption of Si gas by the heat insulating material and generation of silicon droplets due to excessive Si gas concentration is discussed. When sublimating the silicon, the Si concentration in the sublimation gas is higher than the C concentration, particularly in the initial stage of sublimation, causing defects.

  On the other hand, a method for reducing the influence by increasing the carbon concentration of the raw material, taking into account the generation of Si gas, or a sublimation condition is being studied. Since it is necessary to heat excessively, it leads to a decrease in energy efficiency, and the method of selecting a system and sublimation conditions that take into account the generation of Si gas is a condition such as deterioration of the heat insulating material when repeatedly producing silicon carbide single crystals. Accordingly, it is necessary to review the conditions each time, so it is not suitable for industrial production.

  Therefore, the object of the present invention is to suppress the Si concentration in the sublimation gas from becoming higher than the C concentration in the initial sublimation of the silicon carbide powder, to stabilize the growth rate of the silicon carbide single crystal, It is in providing the silicon carbide powder which can suppress generation | occurrence | production of the defect of this, its manufacturing method, and the manufacturing method of a silicon carbide single crystal.

  To achieve the above object, the silicon carbide powder of the present invention is a silicon carbide powder used as a raw material for producing a silicon carbide single crystal by a sublimation recrystallization method. The silicon carbide powder is free in the region from the particle surface to a depth of 10 μm. The carbon concentration is 0.10 to 3.0% by mass.

  According to the silicon carbide powder of the present invention, since the free carbon concentration in the region from the particle surface to a depth of 10 μm is 0.05% by mass or more, when a silicon carbide single crystal is produced by a sublimation recrystallization method, sublimation is performed. It is possible to delay the sublimation of Si in the initial stage and promote the sublimation of C, the Si in the single crystal in the initial stage of growth does not become excessive, and the generation of defects such as silicon droplets in the initial stage of sublimation can be suppressed, A single crystal can be grown at a stable growth rate. Also, if the free carbon concentration is high only on the surface, it is possible to prevent defects such as carbon inclusion in the later stage of sublimation, unlike the case where the carbonaceous material is mixed as a raw material and the operation is performed under C-rich conditions. be able to.

  And since the free carbon density | concentration in the area | region from the particle | grain surface to a depth of 10 micrometers is 0.10-3.0 mass%, the growth rate of a single crystal can be stabilized more.

  Moreover, in the silicon carbide powder of this invention, it is preferable that the particle size range by the opening dimension of a sieve is 106-2360 micrometers. The particle size range in the present invention means that 95% by mass or more of particles fall within the range when sieving. Fine particles tend to cause carbon inclusion due to fine carbon powder, and coarse particles tend to have low sublimation speed due to a small specific surface area, and silicon droplets tend to occur.

  On the other hand, the method for producing silicon carbide powder according to the present invention is a method for producing silicon carbide powder used as a raw material for producing a silicon carbide single crystal by a sublimation recrystallization method, wherein an inorganic siliceous raw material and a carbonaceous raw material are used. A raw material preparation step for obtaining a raw material for silicon carbide production by mixing, a firing step for forming a lump of silicon carbide by firing the raw material for silicon carbide production at 2200 ° C. or higher, and the firing step. A cooling step of cooling the lump of silicon carbide, and a powder forming step of obtaining a silicon carbide powder of a predetermined particle size by crushing the cooled lump and classifying the lump. In this case, the mass is cooled while blocking contact with oxygen.

  According to the method for producing silicon carbide powder of the present invention, free carbon and oxygen are combusted in the surface region of the particles by cooling while blocking the lump of silicon carbide from coming into contact with oxygen during the cooling step. It is possible to prevent the free carbon concentration on the surface from lowering due to the reaction, and to increase the free carbon concentration on the particle surface of the finally obtained silicon carbide powder. Thereby, silicon carbide powder having the above-described effects can be obtained.

  In the method for producing the silicon carbide powder of the present invention, the cooling is performed while blocking the contact of the lump with oxygen during the cooling step, thereby reducing the depth from the particle surface of the silicon carbide powder finally obtained. It is preferable that the free carbon concentration in the region up to 10 μm is 0.05% by mass or more. According to this, the effect mentioned above can be acquired still more favorably.

  In the manufacturing method of the silicon carbide powder of this invention, it is preferable to perform the said cooling process, spraying water on the said lump. By this method, the periphery of the lump can be blocked by steam so that the lump surface is less susceptible to oxidation by oxygen in the air, and cooling of the high temperature lump is promoted by latent heat of vaporization. By doing this, it is possible to shorten the time during which the lump surface is maintained in a high temperature state in which a combustion reaction easily occurs.

  In the method for producing silicon carbide powder of the present invention, it is preferable that in the powder forming step, the pulverization and classification are performed so that the particle size range depending on the sieve opening size is 106 to 2360 μm. Thereby, when manufacturing a silicon carbide single crystal by the sublimation recrystallization method, a silicon carbide powder in which carbon inclusion and silicon droplets are hardly generated can be obtained.

  Furthermore, the method for producing a silicon carbide single crystal of the present invention is characterized in that a silicon carbide single crystal is grown by the sublimation recrystallization method using the above-described silicon carbide powder as a raw material. Thereby, the above-described operational effects can be obtained.

  According to the silicon carbide powder of the present invention, when a silicon carbide single crystal is produced by a sublimation recrystallization method, it is possible to delay the sublimation of Si in the initial stage of sublimation and promote the sublimation of C. Si is not excessive, and generation of defects such as silicon droplets in the initial stage of sublimation can be suppressed, and a single crystal can be grown at a stable growth rate. In addition, it is possible to prevent the occurrence of defects such as carbon inclusion in the later stage of sublimation.

  According to the method for producing silicon carbide powder of the present invention, free carbon and oxygen are combusted in the surface region of the particles by cooling while blocking the lump of silicon carbide from coming into contact with oxygen during the cooling step. It is possible to prevent the free carbon concentration on the surface from decreasing due to the reaction, and the free carbon concentration in the region from the particle surface of the finally obtained silicon carbide powder to a depth of 10 μm is 0.05% by mass or more. Can be.

  According to the method for producing a silicon carbide single crystal of the present invention, generation of defects such as silicon droplets in the initial stage of sublimation can be suppressed, and a single crystal can be grown at a stable growth rate.

In the Example of this invention, it is a schematic sectional drawing which shows the structure of the crucible used when manufacturing the silicon carbide single crystal by the sublimation recrystallization method. It is explanatory drawing which shows the state which takes out the grown single crystal and slices in the Example. In the Example, it is explanatory drawing which shows the state which cuts out a sample piece from the sliced single crystal.

  Hereinafter, the present invention will be described in more detail with reference to embodiments of the present invention.

  First, a method for producing silicon carbide powder will be described. Although a method using a solid phase reaction will be described here, a method using a liquid phase reaction or the like may be used.

  The method for producing silicon carbide powder according to the present invention comprises a raw material preparation step of obtaining a raw material for producing silicon carbide by mixing an inorganic siliceous raw material and a carbonaceous raw material, and firing the raw material for producing silicon carbide at 2200 ° C. or higher. By the firing step of forming a lump of silicon carbide, the cooling step of cooling the lump of silicon carbide obtained in the baking step, the cooled lump is pulverized, and the pulverized product is classified And a powder forming step of obtaining a silicon carbide powder having a predetermined particle size. During the cooling step, the free carbon concentration in the region from the particle surface of the finally obtained silicon carbide powder to a depth of 10 μm is 0 by cooling while blocking the mass from coming into contact with oxygen. 0.05% by mass or more.

  Examples of the inorganic siliceous material include crystalline silica such as silica, silica fume, amorphous silica such as silica gel, and granular metal silicon. These may be used alone or in combination of two or more. The average particle size of the inorganic siliceous material is appropriately selected depending on the environment during firing, the state of the material (crystalline or amorphous), the reactivity with the carbonaceous material, and the like. However, it is preferable to use amorphous silica as the inorganic siliceous raw material because the reactivity during firing is good and the furnace is easily controlled.

  Examples of the carbonaceous raw material include crystalline carbon such as natural graphite and artificial graphite, and amorphous carbon such as carbon black, coke, and activated carbon. These may be used alone or in combination of two or more. The average particle diameter of the carbonaceous raw material is appropriately selected depending on the environment during firing, the state of the raw material (crystalline or amorphous), the reactivity with the carbonaceous material, and the like.

  An inorganic siliceous raw material and a carbonaceous raw material are mixed to prepare a raw material for silicon carbide powder. The mixing method at this time is arbitrary, and may be either wet mixing or dry mixing. The mixing molar ratio (C / Si) of the carbonaceous raw material and inorganic siliceous raw material during mixing is selected in consideration of the environment during firing, the particle size of the silicon carbide powder raw material, reactivity, etc. To do. The term “optimum” as used herein means improving the yield of silicon carbide obtained by firing and reducing the unreacted residual amount of the inorganic siliceous raw material and carbonaceous raw material.

  The obtained mixed powder (raw material for silicon carbide production) is fired at 2200 ° C. or higher, preferably 2500 ° C. or higher to obtain bulk silicon carbide.

  The firing method is not particularly limited, and examples thereof include a method using external heating and a method using current heating. Examples of the external heating method include a method using a fluidized bed furnace, a batch type furnace, and the like. Examples of the method using electric heating include a method using an Atchison furnace.

  The firing atmosphere is preferably a reducing atmosphere. This is because the yield of silicon carbide is reduced when fired in an atmosphere having low reducing ability. At this time, if amorphous silica is used as one of the inorganic siliceous raw materials, the furnace is easily controlled due to good reactivity. It is preferable to use a mixture containing amorphous silica.

  In the present specification, the “Atchison furnace” refers to a box-type indirect resistance heating furnace having an open top. Here, the indirect resistance heating does not directly flow an electric current to an object to be heated, but obtains silicon carbide by a heating element that generates heat by flowing an electric current. An example of a specific configuration of such an Atchison furnace is described in Japanese Patent Laid-Open No. 2013-112544.

By using such a furnace, the reaction shown in the following formula (1) occurs, and a lump made of silicon carbide (SiC) is obtained.
SiO ₂ + 3C → SiC + 2CO (1)

  The type of the heating element of the Atchison furnace is not particularly limited as long as it can conduct electricity, and examples thereof include graphite powder and carbon rod.

  The form of the substance constituting the heating element is not particularly limited, and examples thereof include powder and lump. The heating element is provided so as to have a rod-like shape as a whole so as to connect the electrode cores provided at both ends in the energizing direction of the Atchison furnace. Examples of the rod shape here include a columnar shape and a prismatic shape.

  After energization, a lump made of silicon carbide is generated in the furnace. And it cools until the inside of a furnace becomes normal temperature. At this time, by blocking the silicon carbide agglomerates during cooling from coming into contact with oxygen, it is possible to prevent the free carbon and oxygen from burning and reacting in the surface region of the particles, thereby reducing the surface free carbon concentration. .

  As a method for blocking the silicon carbide block during cooling from coming into contact with oxygen, a method of spraying mist-like water onto the silicon carbide block during cooling is preferably employed. By this method, the periphery of the lump can be blocked by steam so that the lump surface is less susceptible to oxidation by oxygen in the air, and cooling of the high temperature lump is promoted by latent heat of vaporization. By doing this, it is possible to shorten the time during which the lump surface is maintained in a high temperature state in which a combustion reaction easily occurs.

  In addition, as a method of blocking the silicon carbide lump being cooled from coming into contact with oxygen, until the inside of the furnace reaches room temperature, a method of introducing an inert gas such as argon gas to perform air cooling, A method of supplying pellet-like carbon particles or metal silicon particles so as to cover the lump can also be adopted.

  And the lump (ingot) which consists of obtained silicon carbide is grind | pulverized. Examples of the pulverization method include a pulverization method using a top grinder, a disk grinder, a jet mill, a ball mill and the like.

  Thereafter, it is preferable to classify the pulverized product so as to obtain a desired particle size range. For classification, a method using a sieve is the simplest and preferable. However, classification is not limited to a method using a sieve, and may be either dry or wet. Further, as a dry classification, for example, a centrifugal classification method using an air flow can be used.

  By classification, the particle size range depending on the sieve opening size is preferably 106 to 2360 μm, more preferably 250 to 2000 μm, and most preferably 355 to 1700 μm. Fine particles tend to cause carbon inclusion due to fine carbon powder, and coarse particles tend to have low sublimation speed due to a small specific surface area, and silicon droplets tend to occur.

  Further, contamination by pulverization may be removed by appropriately washing the pulverized product with hydrochloric acid or the like.

  The silicon carbide powder of the present invention thus obtained has a feature that the free carbon concentration on the particle surface is high. In the present invention, the concentration of free carbon on the particle surface is not the proportion of free carbon in the entire particle, but the proportion of free carbon in the portion corresponding to the surface of the silicon carbide grains. As a result of various studies, the inventors have found that the free carbon concentration in the region up to a depth of about 10 μm contributes to the suppression of silicon droplets in the initial stage of sublimation. I found out. For this reason, in this invention, the area | region from the particle | grain surface of silicon carbide powder to the depth of 10 micrometers is considered as a part corresponded to the surface, and it decided to obtain | require the free carbon concentration of the part. How the free carbon concentration was determined will be described below.

  First, when producing crystalline silicon carbide powder by the sublimation recrystallization method (modified Rayleigh method), free carbon is basically formed only on the surface. This is because, in this method, a gas phase reaction occurs around a small crystal that happens to occur (accordingly, a seed crystal occurs in a place with a high vapor concentration), and the crystal gradually grows. Is excluded from the crystal and not taken into the crystal. Free carbon is generated at the very end of crystal growth by carbonizing the surface or by attaching very small graphite to the surface.

  On the other hand, free carbon may remain in the particles. This is a case where silicon carbide particles grow together by crushing during the reaction, finally becoming one particle, and the carbon source involved in the claw remains. In the particles of the present invention, it is estimated that such carbon is present at a certain ratio.

  However, in the present invention, since it is desired to measure only 10 μm of carbon below the surface, the sample was not pulverized, and the free carbon content was determined by JIS R 6124 “Method for quantifying free carbon”. In this method, when the sample is pulverized, carbon remaining in the crush is exposed and detected by pulverization. However, when not pulverized, carbon remaining in the sample is not detected.

  Here, with respect to “the amount of free carbon relative to the entire particle”, since free carbon is only on the particle surface, the value of the larger particle size becomes relatively smaller. However, even if the particle size is large, the percentage of free carbon on the surface is the same as that having a small particle size in terms of defect suppression, as seen by the evaluation method that “the surface portion contains more than%”. Based on the idea that the effect is exhibited, in the present invention, the “region from the particle surface to a depth of 10 μm” is assumed to be the surface, and the free carbon concentration in that portion is determined.

  Therefore, first, the ratio of the surface portion in the silicon carbide powder to be measured is obtained. The silicon carbide powder is classified with a sieve to obtain the particle size distribution. The particle diameter at which the cumulative weight is 50% is defined as the average particle diameter of the powder. For convenience, it is assumed that the silicon carbide powder is a spherical particle having the average particle diameter obtained here. The particle radius at this time is D (μm). At this time, the ratio R of the surface portion in the silicon carbide powder is obtained by the following formula (2).

  After determining the ratio R of the surface portion in the powder, the content of free carbon is measured by the JIS R 6124 “Quantitative method for free carbon”. Here, the sample is measured without being pulverized regardless of the particle diameter, and no auxiliary combustor is used. The free carbon concentration thus determined is the free carbon concentration on the surface of the powder particles.

  When the obtained free carbon content is X (%), the free carbon concentration S (%) on the particle surface in the present invention is obtained by the following formula (3).

  In the silicon carbide powder of the present invention, the free carbon concentration in the region from the particle surface to a depth of 10 μm determined as described above is 0.05% by mass or more, preferably 0.10 to 3.0% by mass, more preferably Is 0.15 to 2.0 mass%. In addition, when there is too much free carbon, it will become C excess and may cause the carbon inclusion in a single crystal, and crystal growth may become difficult.

  The method for producing a silicon carbide single crystal of the present invention is a method for growing a silicon carbide single crystal by a sublimation recrystallization method using the silicon carbide powder of the present invention as a raw material. The method for producing the silicon carbide single crystal by the sublimation recrystallization method may be performed according to a conventional method, and is not particularly limited, but the outline is as follows.

  First, the raw material silicon carbide powder is filled into a crucible made of graphite, for example, and this crucible is disposed in a heating device. However, the container in which the silicon carbide powder is filled is not limited to a graphite crucible, and any container may be used as long as it is used when producing single crystal silicon carbide by a sublimation recrystallization method.

  And it heats so that the raw material in a crucible may become 2000-2500 degreeC under pressure reduction which made the crucible inert gas atmosphere, such as argon gas. However, the temperature of the portion where the silicon carbide single crystal grows on the lower surface of the lid of the crucible is about 100 ° C. lower than this.

  This heating is continued for several hours to several tens of hours. Thereby, the silicon carbide powder as a raw material is sublimated to become a sublimation gas, reaches the lower surface of the lid and is single-crystallized, and this single crystal grows, whereby a lump of silicon carbide single crystal can be obtained.

  As described above, the silicon carbide powder of the present invention has a free carbon concentration in the region from the particle surface to a depth of 10 μm of 0.05% by mass or more, and therefore, a silicon carbide single crystal is produced by a sublimation recrystallization method. At this time, the sublimation of Si in the initial stage of sublimation can be delayed and the sublimation of C can be promoted, so that Si in the single crystal in the initial stage of growth does not become excessive, and generation of defects such as silicon droplets in the initial stage of sublimation is suppressed In addition, a single crystal can be grown at a stable growth rate. Also, if the free carbon concentration is high only on the surface, it is possible to prevent defects such as carbon inclusion in the later stage of sublimation, unlike the case where the carbonaceous material is mixed as a raw material and the operation is performed under C-rich conditions. be able to.

  Examples of the present invention will be described below. However, the present invention is not limited to these examples.

Example 1
Mix amorphous siliceous material (amorphous silica) and carbonaceous material (carbon black) using a biaxial mixer so that the molar ratio of carbon to silicon (C / Si) is 3.20. A raw material for producing silicon carbide was obtained.

  850 kg of the obtained raw material for producing silicon carbide and the heating element were placed in an Atchison furnace (inner dimensions of the Atchison furnace: length 2500 mm, width 1000 mm, height 850 mm) and then fired at 2200 ° C. for 13.5 hours. It was.

  Then, while cooling by air cooling, 200 g / min of distilled water at 25 ° C. was sprayed in a mist form from a position 2.0 m higher than the height of the furnace. Here, the mist is sprayed upward and descends toward the furnace at a moderate speed. As a result, a massive silicon carbide powder was obtained.

  The obtained massive silicon carbide was pulverized using a top grinder and a disk mill to obtain silicon carbide powder. The obtained silicon carbide powder was a crystalline silicon carbide powder.

  The obtained silicon carbide powder was classified into a range of 500 to 1700 μm using a sieve having openings of 1700 μm and 500 μm. About this powder, the surface free carbon concentration was measured by the method mentioned above.

  As shown in FIG. 1, a raw material 5 composed of 150.0 g of silicon carbide powder obtained by the above classification was filled in a graphite crucible 1 having an inner dimension of 120 × 200 mm. A single crystal (seed crystal) 4 of silicon carbide cut into a disk shape having a diameter of 50.8 mm and a thickness of 1.0 mm is bonded to the crucible 1 and a graphite plate 3 having a pedestal 2 having a thickness of 5 mm at the center. Then, it was covered with a heat insulating material made of graphite.

  The whole was left in a furnace and heated in an argon atmosphere of 3 Torr (400 Pa) so that the furnace bottom temperature was 2350 ° C. by induction heating.

  Here, the heating rate was controlled to be 10 ° C./min, and heating was performed for 10 hours from the time when the temperature became 2350 ° C. Then, after stopping the furnace and air-cooling to room temperature, the crucible 1 was taken out. The single crystal 4 grown by sublimation was removed from the base 2, and the sublimation rate was calculated from the value obtained by dividing the weight change (g) by the heating time (= 10h).

  Further, as shown in FIG. 2, the removed single crystal 4 was ground at 50 mm in diameter and then sliced at positions 1.2 mm and 2.2 mm from the surface bonded to the pedestal 2. The crystal was cut into a flat plate shape (that is, since the original thickness of the single crystal was 1.0 mm, the first 0.2 to 1.2 mm of crystal growth was cut out).

  For analysis, 15 pieces of 5 mm square samples were cut out from the cut single crystal as shown in FIG. In addition, the number in FIG. 3 is length (mm).

  Of these 15 pieces, each 7 pieces (about 1.1 g) were selected at random, and pulverized into a powder that passed through a 100 μm sieve, and then the method of JIS R 6124 (surface silicic acid by neutralization titration method). Quantification of free silicic acid and free carbon by the determination of free carbon by combustion capacity method. It was determined that silicon droplets were generated for the samples in which free silicic acid was detected, and that carbon inclusions were generated for the samples in which free carbon was detected.

(Example 2)
About Example 2, although the silicon carbide powder was manufactured by the method similar to Example 1, the amount of spray water at the time of cooling was 100 g / min.

(Examples 3 to 11)
Silicon carbide powder was produced in the same manner as in Example 1 for Examples 3 to 6 and in the same manner as in Example 2 for Examples 7 to 8, but the sieve used for classification was changed, and the particle sizes listed in Table 1 were used. Limited to range. In Examples 9 to 11, silicon carbide powder was produced by the same method as in Example 1, except that 25% of the raw amorphous silica powder was converted to metal silicon powder of the same Si mole (purity> 99.999%, grain size). A raw material substituted with a diameter of 150 to 425 μm was used.

(Comparative Examples 1-10)
Agglomerated silicon carbide powder was produced by the same method as in Example 1, and the classification range was changed as shown in Table 1. However, in Comparative Examples 1 to 4, no spraying was performed during cooling. Moreover, in Comparative Examples 5-6, instead of spraying water at the time of cooling, air was injected toward the furnace at a flow rate of 50 L / min (this corresponds to the amount of air consumed when spraying water at 100 g / min). Equivalent to). In Comparative Examples 7 to 8, water was sprayed in the same manner as in Example 1, but a raw material having a carbon to silicon molar ratio (C / Si) of 2.7 was used. In Comparative Examples 9 to 10, water was sprayed in the same manner as in Example 1, but a raw material having a carbon to silicon molar ratio (C / Si) of 3.5 was used.

  For some samples, black spots of carbon inclusions were observed on the surface of the single crystal when the single crystal after crystal growth was sliced.

  Table 1 shows the particle size range, the surface free carbon concentration, and the results of the sublimation test obtained in the experiment for each example and comparative example.

  As shown in Table 1, in each of Examples 1 to 11, the free C concentration indicating the occurrence of carbon inclusion is below the lower limit of quantification, and the free Si concentration suggesting the generation of silicon droplets is also the lower limit of quantification. It was less than the value or less compared with Comparative Examples 1-10.

  On the other hand, all of Comparative Examples 1 to 10 except for Comparative Examples 9 to 10 have a high free Si concentration. On the other hand, not only the surface but also the whole produced under C-rich conditions as in Comparative Examples 9 to 10 It was found that C-rich silicon carbide powder increases free C, although free Si can be suppressed.

From the above, it can be seen that the use of a raw material having a high free carbon concentration on the surface is effective in suppressing carbon inclusion and silicon droplets.

Claims (7)

  In a silicon carbide powder used as a raw material when producing a silicon carbide single crystal by a sublimation recrystallization method, the carbonization concentration in the region from the particle surface to a depth of 10 μm is 0.10 to 3.0 mass%. Silicon powder.   The silicon carbide powder according to claim 1, wherein a particle size range according to a sieve opening size is 106 to 2360 μm. In the method for producing silicon carbide powder used as a raw material when producing a silicon carbide single crystal by a sublimation recrystallization method,
A raw material preparation step for obtaining a raw material for producing silicon carbide by mixing an inorganic siliceous raw material and a carbonaceous raw material;
A firing step of forming a lump of silicon carbide by firing the raw material for producing silicon carbide at 2200 ° C. or higher;
A cooling step for cooling the lump made of silicon carbide obtained in the firing step;
A powder forming step of pulverizing the cooled mass and obtaining a silicon carbide powder having a predetermined particle size by classifying the pulverized product,
In the cooling step, the lump is cooled while being blocked from coming into contact with oxygen.   In the cooling step, cooling is performed while blocking the mass from coming into contact with oxygen, so that the free carbon concentration in the region from the particle surface of the finally obtained silicon carbide powder to a depth of 10 μm is 0.05. The method for producing silicon carbide powder according to claim 3, wherein the content is not less than mass%.   The manufacturing method of the silicon carbide powder of Claim 3 or 4 which performs the said cooling process, spraying water on the said lump.   The method for producing silicon carbide powder according to any one of claims 3 to 5, wherein, in the powder forming step, the pulverization and classification are performed so that a particle size range according to a sieve opening size is 106 to 2360 µm.   A method for producing a silicon carbide single crystal, comprising growing a silicon carbide single crystal by a sublimation recrystallization method using the silicon carbide powder according to claim 1 or 2 as a raw material.