JP2018030760A - Production method of silicon carbide single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a silicon carbide single crystal capable of improving a sublimation rate of silicon carbide powder which is a raw material.SOLUTION: A crucible is filled with silicon carbide powder which is a raw material, and the silicon carbide powder is sublimed, to thereby produce single crystal silicon carbide. A repose angle of silicon carbide powder which is the raw material is 25° or larger and 45° or smaller, more preferably, 30° or larger and 40° or smaller.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a silicon carbide single crystal.

  Silicon carbide single crystals are used as materials for molding wheels, ceramic parts and the like because of their high hardness, high thermal conductivity, and high temperature heat resistance. In addition, silicon carbide is attracting attention as a power semiconductor substrate material that replaces silicon because it has properties of about 3 times the band gap and about 10 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. Various ideas have been made regarding silicon carbide powder as a raw material in the sublimation recrystallization method.

  For example, in Patent Document 1, silicon carbide powder is placed in a crucible so that silicon carbide powder having a particle diameter of 500 μm to 1000 μm larger than particles filled in other portions in the surface portion and the vicinity thereof is filled. Filling is disclosed.

  In Patent Document 2, a silicon carbide powder is filled in a crucible so that a silicon carbide powder having a small particle size of 50 μm to 200 μm is covered with a silicon carbide powder having a large particle size of 300 μm to 700 μm. Is disclosed.

JP 2000-7492 A JP 2009-51702 A

  In the techniques disclosed in Patent Documents 1 and 2, if the silicon carbide particles have a small diameter, it is preferable because the sublimation speed is high and sublimation is stable. However, if only the small diameter particles are used, sintering is superior to sublimation. Therefore, large-diameter particles are mixed.

  However, when silicon carbide particles having different particle diameters are mixed, the raw materials become non-uniform and the process is likely to become uneasy, and the small-diameter particles sublimate and the sublimation rate decreases.

  Therefore, it is considered that simply defining the particle size range is not enough as a factor of lowering the sublimation speed, and there is another factor.

  An object of this invention is to provide the manufacturing method of the silicon carbide single crystal which can aim at the improvement of the sublimation rate of the silicon carbide powder which is a raw material.

  The present invention is a method of filling a silicon carbide powder as a raw material in a container and sublimating the silicon carbide powder to produce a silicon carbide single crystal, wherein the angle of repose of the silicon carbide powder is 25 ° or more and 45 ° or less. It is characterized by being.

  If the angle of repose is less than 25 °, when silicon carbide powder as a raw material is filled in the container, the gap between the silicon carbide powders is too small and the sublimation rate is slow. On the other hand, if the angle of repose exceeds 45 °, when silicon carbide powder as a raw material is filled in the container, large cavities are formed between the silicon carbide powders, the amount of filling of the container is reduced, and the sublimation rate is reduced. is there. The angle of repose may be measured in accordance with the measurement method described in JIS R9301-2-2: 1999 “Alumina powder—Part 2: Physical property measurement method-2: Angle of repose”.

  According to the present invention, since the angle of repose is 25 ° or more and 45 ° or less, when the silicon carbide powder as the raw material is filled in the container, appropriate cavities are generated between the silicon carbide powders, and the sublimation rate is improved. .

  In the present invention, the angle of repose of the silicon carbide powder is preferably 30 ° or more and 40 ° or less.

  In this case, in particular, since the particles are sintered because there are many contact points between the particles, the decrease in the sublimation rate due to the decrease in the specific surface area of the particles due to the roughness can be suppressed. Increases sublimation speed.

In the present invention, the light bulk density of the silicon carbide powder is preferably 0.8 g / cm ³ or more and 1.5 g / cm ³ or less.

  In this case, when the silicon carbide powder as a raw material is filled in the container, appropriate cavities are generated between the silicon carbide powders, and the sublimation rate is improved. The light bulk density is the same as the light bulk density measurement method described in JIS R9301-2-3: 1999 "Alumina powder-Part 2: Physical property measurement method-3: Light bulk density and heavy bulk density". What is necessary is just to measure according to it.

  Moreover, in this invention, it is preferable that the particle size range of the said silicon carbide powder is 45 micrometers or more and less than 3350 micrometers.

  When the particle size of the silicon carbide powder is less than 45 μm, even if the angle of repose is 25 ° or more and 45 ° or less, the number of contact points where the particles are in contact with each other is extremely large, and the sintering is easily performed and the sintering is excessive. There is a risk of proceeding. On the other hand, when the particle size of the silicon carbide powder is 3350 μm or more, even if the angle of repose is 25 ° or more and 45 ° or less, the particles become coarse and the specific surface area becomes small, so that a sufficient sublimation rate cannot be obtained. .

  Hereinafter, the manufacturing method of the silicon carbide single crystal which concerns on embodiment of this invention is demonstrated.

  First, the manufacturing method of the silicon carbide powder used as a raw material with the manufacturing method of a silicon carbide single crystal is demonstrated. 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 includes a step of mixing a silicon-containing inorganic siliceous raw material and a carbonaceous raw material containing carbon to obtain a silicon carbide production raw material, and firing the silicon carbide production raw material at 2500 ° C. or higher. , A step of obtaining a lump of silicon carbide, a step of introducing an inert gas, air cooling the lump to room temperature, a step of crushing the air-cooled lump, and classifying the obtained pulverized product, Obtaining a desired silicon carbide powder.

  Examples of the inorganic siliceous raw material include crystalline silica such as silica, amorphous silica such as silica fume and silica gel. 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 inorganic siliceous raw 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 the inorganic siliceous raw material at the time of mixing should be optimized in consideration of the environment during firing, the particle size of the raw material for silicon carbide powder, the reactivity, etc. select. 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 powder) is fired at 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. A general furnace may be used as the 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.

  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 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.

  Air cooling is performed by introducing an inert gas such as argon gas until the temperature inside the furnace reaches room temperature. And the lump (ingot) which consists of obtained silicon carbide is grind | pulverized. The pulverization method is not particularly limited, and examples thereof include a pulverization method using a top grinder, a disk mill, a jaw crusher, or the like as a pulverizer.

  Thereafter, the pulverized product is classified using a sieve according to 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.

  Next, a method for producing a silicon carbide single crystal by sublimation recrystallization using this raw material will be described.

  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.

  The shape of the silicon carbide particles obtained by pulverizing the lump obtained by firing in an Atchison furnace or the like is different if the pulverization method is different, and the angle of repose is also different. For example, a silicon carbide powder obtained by pulverization using a top grinder or a disk mill has larger corners and more corners than those pulverized using a ball mill. The corner becomes smaller.

  Furthermore, even if the grinding method is the same, if the particle size is different, the shape is different and the angle of repose is also different. For example, in a silicon carbide powder obtained by pulverization using a top grinder or a disk mill, the smaller the particle size, the smaller the corners and the fewer corners, and the easier it is to collapse, so the angle of repose becomes smaller. Furthermore, the angle of repose becomes larger as the particle size range becomes wider because it becomes more difficult to collapse.

  Thus, silicon carbide particles having different repose angles can be obtained depending on the pulverization method or the particle size range.

  In the present invention, the angle of repose of the silicon carbide powder that is a raw material for producing a silicon carbide single crystal by the sublimation recrystallization method is 25 ° or more and 45 ° or less. Furthermore, the angle of repose is preferably 28 ° or more and 42 ° or less, and more preferably 30 ° or more and 40 ° or less. The angle of repose may be measured in accordance with the measurement method described in JIS R9301-2-2: 1999 “Alumina powder—Part 2: Physical property measurement method-2: Angle of repose”.

  If the angle of repose is less than 25 °, when the crucible is filled with silicon carbide powder, the filled silicon carbide powder is densely packed and the number of contact points between the particles increases, so that the particles sinter during sublimation, Since the surface area of the filling material in which the sublimation gas is generated is reduced, the sublimation speed is reduced.

  On the other hand, particles having an angle of repose exceeding 45 ° have many coarse irregularities, but the irregularities are only coarse, that is, the particles are composed of coarse crystals. The specific surface area of the particles is smaller than that of the resulting particles, and the sublimation rate is reduced.

  If the angle of repose is 25 ° or more and 45 ° or less, when the crucible is filled with silicon carbide powder, moderate cavities are generated between the silicon carbide powders, and the sublimation rate is improved.

  This is because particles with the same particle size and a large angle of repose are more likely to be caught by the irregularities on the surface of the particles, and are filled in a state of leaving irregularly shaped voids in the crucible. In addition, since particles having a large angle of repose have irregularities on the surface, the specific surface area of the particles is large, and the amount of sublimation gas generated from the particle surface tends to increase. In the sublimation recrystallization method, pores of about several μm to several tens of μm existing on the surface of the raw material are blocked by sublimation recrystallization in the raw material in the initial stage of sublimation, and therefore do not necessarily contribute to the generation amount of sublimation gas. .

  Furthermore, when the angle of repose is 28 ° or more and 42 ° or less, and further 30 ° or more and 40 ° or less, the particle shape is particularly preferable from the viewpoint of the contact point and the specific surface area described above, and the sublimation rate is increased.

  Furthermore, when firing the silicon carbide powder in the Atchison furnace, it is preferable to add wood chips in a burned state and quickly burn the carbon monoxide on the furnace surface with air. Thereby, since carbon monoxide is burned and removed at the outer periphery of the furnace, the carbon monoxide partial pressure at the outer periphery of the furnace is lowered, and the gradient of the carbon monoxide partial pressure in the radial direction of the furnace is made constant. As a result, it is considered that a silicon carbide single crystal grows radially and it becomes easier to obtain a needle-like one when pulverized. The silicon carbide powder obtained in this manner has a lot of needle-like powders, and the angle of repose tends to fall within the range of 25 ° to 45 °.

Furthermore, in the present invention, the light bulk density of the silicon carbide powder, which is a raw material for producing a silicon carbide single crystal by the sublimation recrystallization method, is 0.8 g / cm ³ or more and 1.5 g / cm ³ or less. preferable. Further, the light bulk density is 0.9 g / cm ³ or more and 1.5 g / cm ³ or less, and more preferably 1.0 g / cm ³ or more and 1.4 g / cm ³ or less. The light bulk density is the same as the light bulk density measurement method described in JIS R9301-2-3: 1999 "Alumina powder-Part 2: Physical property measurement method-3: Light bulk density and heavy bulk density". What is necessary is just to measure according to it.

If the light bulk density is less than 0.8 g / cm ³ , when silicon carbide powder is filled in the crucible, large cavities are formed between the silicon carbide powders, the filling amount in the crucible is reduced, and the sublimation rate is reduced. It is.

On the other hand, when the light bulk density exceeds 1.5 g / cm ³ , when the silicon carbide powder is filled in the crucible, the gap between the silicon carbide powders is too small, and the sublimation rate becomes slow.

When the light bulk density is 0.8 g / cm ³ or more and 1.5 g / cm ³ or less, when the crucible is filled with silicon carbide powder, appropriate cavities are generated between the silicon carbide powders, and the sublimation rate is improved.

  The particle size range of the silicon carbide powder is preferably 45 μm or more and less than 3350 μm. When the particle size of the silicon carbide powder is less than 45 μm, even if the angle of repose is 25 ° or more and 45 ° or less, the number of contact points where the particles are in contact with each other is extremely large, and the sintering is easily performed and the sintering is excessive. There is a risk of proceeding. On the other hand, when the particle size of the silicon carbide powder is 3350 μm or more, even if the angle of repose is 25 ° or more and 45 ° or less, the particles become coarse and the specific surface area becomes small, so that a sufficient sublimation rate cannot be obtained.

  The particle size range of the particles being A or more and less than B means that D5 of the particle size distribution of the particle powder is A or more and D95 is less than B. That is, it means that the weight under the sieve when sieved with the sieve of A is less than 5%, and the weight of the sieve when sieved with the sieve B is 5% or less.

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

Example 1
First, amorphous silica powder was prepared as an inorganic siliceous material, and carbon black (amorphous carbon) was prepared as a carbonaceous material. These raw materials were mixed using a biaxial mixer so that the molar ratio of carbon to silicon (C / SiO ₂ ) was 3.0 to obtain a raw material for producing silicon carbide powder.

  And this raw material was baked for 12 hours in the Atchison furnace which made the center temperature 2500 degreeC or more. Thereby, a lump of silicon carbide was obtained. The internal dimensions of the Atchison furnace were 2500 mm in length, 1000 mm in width, and 850 mm in height.

  At the time of firing, about 200 g of wood chips ignited and combusted every 2 hours from the start of heating are supplied to the upper part of the furnace, and carbon monoxide generated in the furnace and leaked outside is oxygen in the atmosphere. To quickly burn on contact. In addition, the wood chip used the thing which limited the particle size to 10 mm or more using the sieve with a 10 mm opening as a commercial item.

  The obtained cylindrical lump is first pulverized to a total amount of 3 mm or less using a top grinder while removing the bottom of the sieve using a 3 mm sieve and then reduced to 2 mm or less using a disk mill. By grinding, silicon carbide powder was obtained. The obtained silicon carbide powder was crystalline.

  And the obtained silicon carbide powder was limited to the range whose particle size is 500 micrometers or more and less than 1700 micrometers using the sieve of 500 micrometers and 1700 micrometers of openings. And the angle of repose of this silicon carbide powder was determined.

  Here, the angle of repose was measured according to the measurement method described in JIS R9301-2-2: 1999 “Alumina powder—Part 2: Physical property measurement method-2: Angle of repose”. Specifically, it is as follows.

  As a foundation for measuring the angle of repose, a square plate made of polished stainless steel and having a side of 300 mm and a thickness of 6 mm was prepared. On this foundation, four straight lines intersecting at 45 ° with each other were radiated.

  A stainless steel funnel having a foot inner diameter of 6 mm and an opening angle of 60 ° was installed directly above the intersection of the straight lines so that the distance between the tip of the foot and the base was 40 mm and fixed. Then, the silicon carbide powder was poured at a rate of about 60 g / min until the tip of the powder pile reached the tip of the funnel so as to be transmitted along the side of the funnel.

  In order to measure the size of the spread of the powder at the end of pouring, mark each part where the four straight lines on the base and the spread of the powder (excluding scattered particles) intersect (two on each straight line) The distance between the marks was measured for each of the four straight lines, and the spread diameter of the powder was obtained.

  Compared to the alumina powder described in JIS R9301-2-2, silicon carbide powder tends to scatter and fly irregularly on the base plate, so measure three times and calculate the average spread diameter to calculate the angle of repose. Using.

When the spread diameter of the powder is D (mm), the inner diameter of the funnel foot is d (= 6 mm), and the height of the powder is h (= 40 mm), the angle of repose θ is calculated by the following equation (2).
θ = tan ⁻¹ [(2h / (D−d)] (2)

  The angle of repose of the silicon carbide powder was 31 °.

Further, the light bulk density of the silicon carbide powder was determined. Here, the light bulk density is measured according to JIS R9301-2-3: 1999 "Alumina powder-Part 2: Physical property measurement method-3: Light bulk density and heavy bulk density". Measured in the same manner as above. The light bulk density of the silicon carbide powder was 1.18 g / cm ³ .

  Next, 150 g of silicon carbide powder was filled into a graphite crucible having an inner dimension of 100 mm in diameter and a height of 200 mm and having a side surface thickness of 5 mm and a bottom surface thickness of 8 mm. At this time, carbon paper having a diameter of 100 mm, a thickness of 2 mm, and a weight of about 2.8 g was laid on the bottom of the crucible to facilitate the recovery of the silicon carbide powder. The crucible was covered with a carbon lid having a thickness of 5 mm. No seed crystals were attached to the crucible lid.

  The crucible was placed in a heating apparatus and heated in an argon atmosphere and a pressure of 1 Torr (133 Pa). In this heating, the temperature measured by a radiation thermometer that measures the center of the bottom of the crucible was first increased at a rate of temperature increase of 10 ° C./min. After reaching 2200 ° C., the state was maintained for 10 hours. .

  Thereafter, the inside of the crucible was cooled to room temperature. A lump of silicon carbide single crystal was formed on the lower surface of the lid of the crucible. And the silicon carbide powder which remained in the bottom of the crucible was collect | recovered. At this time, the silicon carbide powder adhering to the inner wall surface of the crucible was not recovered as once sublimated.

  The weight obtained by subtracting the sum of the weights of the silicon carbide powder and the carbon plate recovered after heating from the sum of the weights of the silicon carbide powder and the carbon plate before heating was determined as the weight of the sublimated silicon carbide powder.

  Heating with a crucible was performed three times, and the average value of the weight of the sublimated silicon carbide powder was determined. And the sublimation rate was calculated | required by remove | dividing this average value by 10 hours which are heating time. The sublimation rate was 1.48 g / h.

(Examples 2 to 8)
In Examples 2-8, the particle size was limited to the range described in Table 1 by changing the sieve to be used in the silicon carbide powder obtained by pulverizing the lump in Example 1. As shown in Table 1, the angle of repose is 41 ° from 25 °, loosed bulk density was 1.33 g / cm ³ from 1.01 g / cm ^3.

  This silicon carbide powder was filled in a crucible and heated as in Example 1. As shown in Table 1, the sublimation rate was 1.07 g / h to 1.40 g / h.

(Examples 9 and 10)
The firing time in the Atchison furnace is 2500 ° C. or more, the holding time is 18 hours, and the silicon carbide powder obtained by pulverizing the lump in the same manner as in Example 1 is changed in the sieve to be used. The range was limited. The particle size was adjusted to the same as in Examples 1 and 2. As shown in Table 1, the angle of repose was 28 ° and 26 °, respectively, and the light bulk density was 1.30 g / cm ³ and 1.38 g / cm ³ .

  This silicon carbide powder was filled in a crucible and heated as in Example 1. As shown in Table 1, the sublimation rates were 1.22 g / h and 1.16 g / h, respectively.

(Example 11)
The silicon carbide powder obtained in the same manner as in Example 1 was limited to a particle size range of 45 μm or more and less than 1700 μm using a sieve having openings of 45 μm and 1700 μm. The angle of repose is 32 °, but loosed bulk density was 1.52 g / cm ^3, was greater than 1.5 g / cm ^3.

  This silicon carbide powder was filled in a crucible and heated as in Example 1. As shown in Table 1, the sublimation rate was 1.03 g / h, which was inferior to Examples 1-10.

  This is probably because when the crucible was filled with silicon carbide powder, the gap between the silicon carbide powders was too small, so that the sublimation rate was slow.

(Example 12)
The silicon carbide powder obtained in the same manner as in Example 1 was limited to a particle size range of 45 μm or more and less than 4750 μm using a sieve having openings of 45 μm and 4750 μm. As shown in Table 1, the angle of repose was 34 °, and the light bulk density was 1.41 g / cm ³ .

  This silicon carbide powder was filled in a crucible and heated as in Example 1. As shown in Table 1, the sublimation rate was 1.04 g / h, which was inferior to Examples 1-10.

  This is thought to be due to the presence of coarse silicon carbide powder having a large diameter in the vicinity of 4750 μm, so that the light bulk density was increased, but because a large gap was formed between the silicon carbide powders, the sublimation rate was slowed.

(Comparative Examples 1-4)
In Comparative Examples 1 to 4, silicon carbide powder was fired using an Atchison furnace in the same manner as in Example 1 except that wood chips were not added during firing. And the obtained lump was grind | pulverized with the ball mill and the silicon carbide powder was obtained.

The obtained silicon carbide powder was changed in the sieve to be used, and the particle size was limited to the range shown in Table 1. As shown in Table 1, the angle of repose is 23 ° from 16 °, loosed bulk density was 1.61 g / cm ³ from 1.28 g / cm ^3.

  This silicon carbide powder was filled in a crucible and heated as in Example 1. As shown in Table 1, the sublimation rate was 0.42 g / h to 0.95 g / h, which was inferior to Examples 1-12.

  This is because the obtained lump was pulverized with a ball mill, so that the convex portions at the corners were removed and rounded, and because no wood chips were added during firing, the amount of acicular silicon carbide powder was reduced. This is considered to be because the silicon carbide powder filled in the crucible was clogged too much and the sublimation rate was slow.

(Comparative Examples 5 and 6)
In Comparative Examples 5 and 6, the commercially available silicon carbide powder was limited to the range described in Table 1 by changing the sieve to be used. As shown in Table 1, the repose angles were 23 ° and 21 °, respectively, and the light bulk density was 1.45 g / cm ³ and 1.53 g / cm ³ .

  This silicon carbide powder was filled in a crucible and heated as in Example 1. As shown in Table 1, the sublimation rates were 0.81 g / h and 0.75 g / h, respectively, which were inferior to Examples 1-12.

  This is probably because the angle of repose of the silicon carbide powder is small and the light bulk density is high, so that the silicon carbide powder filled in the crucible is clogged too much and the sublimation rate is slowed.

(Comparative Examples 7 and 8)
In Comparative Examples 7 and 8, as in Example 1, the silicon carbide powder was fired using the Atchison furnace. And the obtained lump was pulverized with a reinforced nylon hammer to obtain silicon carbide powder.

The obtained silicon carbide powder was changed in the sieve to be used, and the particle size was limited to the range shown in Table 1. As shown in Table 1, the angle of repose was 46 ° and 48 °, respectively, and the light bulk density was 1.07 g / cm ³ and 1.03 g / cm ³ .

  This silicon carbide powder was filled in a crucible and heated as in Example 1. As shown in Table 1, the sublimation rates were 0.91 g / h and 0.88 g / h, respectively, which were inferior to those of Examples 1-12.

  This is because the lump obtained was pulverized with a hammer and originally cracked in the direction in which it was easily cracked. This is thought to be because the cavities were formed too much and the sublimation rate was slow.

Claims (4)

In a method for producing a single crystal silicon carbide by filling silicon carbide powder as a raw material in a container and sublimating the silicon carbide powder,
The repose angle of the silicon carbide powder is 25 ° or more and 45 ° or less, and the method for producing a silicon carbide single crystal.   2. The method for producing a silicon carbide single crystal according to claim 1, wherein an angle of repose of the silicon carbide powder is not less than 30 ° and not more than 40 °. The method for producing a silicon carbide single crystal according to claim 1 or 2, wherein a light bulk density of the silicon carbide powder is 0.8 g / cm ³ or more and 1.5 g / cm ³ or less.   4. The method for producing a silicon carbide single crystal according to claim 1, wherein a particle size range of the silicon carbide powder is 45 μm or more and less than 3350 μm. 5.