JP2011102205A - METHOD FOR CONTROLLING PARTICLE SIZE OF alpha-SILICON CARBIDE POWDER AND SILICON CARBIDE SINGLE CRYSTAL - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for controlling the particle size of α-silicon carbide powder for efficiently obtaining silicon carbide powder of the objective particle size, and to provide a homogeneous silicon carbide single crystal including few impurities by using the α-silicon carbide powder whose particle size is controlled by the method. <P>SOLUTION: In the method for controlling the particle size of the α-silicon carbide powder produced by heating β-silicon carbide or a silicon carbide precursor in a non-oxidizing atmosphere and subjecting the β-silicon carbide or β-silicon carbide produced from the silicon carbide precursor to phase transition to α-silicon carbide, the temperature of phase transition from the β-silicon carbide to the α-silicon carbide is controlled by changing the pressure of the atmosphere, so that the α-silicon carbide powder having an average particle size of ≥10 μm is produced. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for controlling the particle size of an α-type silicon carbide powder and a silicon carbide single crystal, and more specifically, the particles of α-type silicon carbide powder used for growing a silicon carbide single crystal by an improved Rayleigh method. The present invention relates to a diameter control method and a silicon carbide single crystal synthesized based on an α-type silicon carbide powder whose particle size is controlled by this particle size control method.

  Conventionally, an improved Rayleigh method is well known as a method for producing a silicon carbide single crystal. In this improved Rayleigh method, a temperature gradient is provided in a silicon carbide single crystal production apparatus, and a single crystal raw material made of silicon carbide sublimated in a high temperature part is supplied to the seed crystal in a low temperature part where the seed crystal is installed. In this method, a silicon carbide single crystal is grown using this seed crystal as a nucleus. In order to sublimate the single crystal raw material, a temperature of 2200 ° C. or higher is required (Patent Documents 1 to 4).

Further, in order to obtain a stable sublimation rate of the single crystal raw material, it is necessary to use a high-purity silicon carbide powder having a particle diameter of 100 μm or more and 300 μm or less and not mixed with impurities.
Such a single crystal raw material is not preferable if it is produced by pulverizing coarse particles or block-like lumps because impurities may be mixed therein.
Therefore, in order to obtain a silicon carbide powder having a high purity and a particle size of 100 to 300 μm that is suitable as a raw material for a silicon carbide single crystal, when a silicon carbide precursor is fired to synthesize a silicon carbide powder, 2000 A method has been proposed in which the temperature is temporarily maintained at a temperature of ℃ or lower and then raised to a phase transition temperature that causes grain growth of 2,000 ℃ or higher (Patent Documents 5 and 6).

JP 2008-74653 A JP 2008-74662 A Japanese Patent No. 3898278 JP 2009-46367 A JP 2009-173501 A Japanese Patent No. 3934695

By the way, in the conventional method for producing a silicon carbide single crystal, the sublimation conditions and the like of the silicon carbide powder vary depending on the structure of the production apparatus and the like. In order to control the sublimation conditions of the silicon carbide powder, It is necessary to control the particle size of the silicon carbide powder as a raw material.
As a conventional method for controlling the particle size of a powder, a method of grain growth utilizing diffusion of the particle surface by heating is common. However, in the case of silicon carbide powder, heating is performed because of strong covalent bonding. Even if the temperature is changed, the diffusion on the particle surface is weak, and therefore the particle diameter does not change much. As described above, there is a problem that silicon carbide powder having an arbitrary particle size cannot be obtained only by controlling the temperature condition during heating.

  The present invention has been made to solve the above-described problems, and a method for controlling the particle size of an α-type silicon carbide powder capable of efficiently obtaining a silicon carbide powder having a target particle size, and this An object of the present invention is to provide a homogeneous silicon carbide single crystal with few impurities by using an α-type silicon carbide powder whose particle size is controlled by a particle size control method.

  As a result of intensive studies to solve the above problems, the present inventors have heated β-type silicon carbide or silicon carbide precursor in a non-oxidizing atmosphere to convert β-type silicon carbide into α-type silicon carbide. When changing the pressure of the atmosphere to control the phase transition temperature from β-type silicon carbide to α-type silicon carbide, the silicon carbide powder with a large particle size suitable for the raw material of silicon carbide single crystal In addition, it has been found that impurities can be efficiently removed by controlling the atmospheric pressure at the time of phase transition from β-type silicon carbide to α-type silicon carbide. It came to completion.

  That is, in the method for controlling the particle size of the α-type silicon carbide powder of the present invention, the β-type silicon carbide or the silicon carbide precursor is heated in a non-oxidizing atmosphere, and the β-type silicon carbide or the silicon carbide precursor is heated. A method for controlling the particle size of an α-type silicon carbide powder produced by phase transition of β-type silicon carbide generated from a body to α-type silicon carbide, wherein the pressure of the atmosphere is changed to change α-type from β-type silicon carbide A phase transition temperature to silicon carbide is controlled to produce an α-type silicon carbide powder having an average particle size of 10 μm or more.

It is preferable to control the phase transition temperature in the range of 2000 ° C. to 2400 ° C. by changing the pressure of the atmosphere in the range of 2 × 10 ⁵ Pa to 10 ⁷ Pa.
It is preferable to raise the temperature to 2000 ° C. or more and 2400 ° C. or less by the heating, and then reduce the pressure of the atmosphere while maintaining this temperature to cause the β-type silicon carbide to undergo phase transition to the α-type silicon carbide.
The α-type silicon carbide powder to be produced preferably has an average particle size of 100 μm or more and 300 μm or less, and a metal impurity content of 1 ppm or less.

  The silicon carbide single crystal of the present invention is characterized by crystal growth using an α-type silicon carbide powder whose particle size is controlled by the particle size control method of the α-type silicon carbide powder of the present invention.

According to the particle size control method for α-type silicon carbide powder of the present invention, β-type silicon carbide or silicon carbide precursor is heated in a non-oxidizing atmosphere, and the β-type silicon carbide or silicon carbide precursor is heated. When the β-type silicon carbide produced from the body is phase-transformed to α-type silicon carbide, the pressure of the atmosphere is changed to control the phase transition temperature from the β-type silicon carbide to the α-type silicon carbide. The particle size of the silicon carbide powder can be controlled to a desired particle size suitable for the raw material of the silicon carbide single crystal.
Moreover, since the pressure of the atmosphere at the time of phase transition from β-type silicon carbide to α-type silicon carbide is changed, impurities can be removed from the generated α-type silicon carbide powder.
Furthermore, if the atmospheric pressure is reduced, impurities can be efficiently removed.

  According to the silicon carbide single crystal of the present invention, since the crystal growth is performed using the α-type silicon carbide powder whose particle size is controlled by the particle size control method of the α-type silicon carbide powder of the present invention, impurities and defects are eliminated. Less and homogeneous.

The form for implementing the particle size control method and silicon carbide single crystal of the α-type silicon carbide powder of the present invention will be described.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[Method of controlling particle size of α-type silicon carbide powder]
The particle size control method of the α-type silicon carbide powder according to the present embodiment includes heating the β-type silicon carbide or the silicon carbide precursor in a non-oxidizing atmosphere, and the β-type silicon carbide or the silicon carbide precursor. Is a particle size control method of an α-type silicon carbide powder produced by phase transition of β-type silicon carbide produced from α-type silicon carbide, and the α-type silicon carbide is changed from β-type silicon carbide by changing the pressure of the atmosphere. This is a method for producing an α-type silicon carbide powder having an average particle diameter of 10 μm or more by controlling the phase transition temperature.

Next, the particle diameter control method for the α-type silicon carbide powder of the present embodiment will be described in detail.
First, β-type silicon carbide as a raw material, or a silicon carbide precursor containing a silicon element and a carbon element for producing β-type silicon carbide is prepared.
Here, the β-type silicon carbide is preferably a β-type silicon carbide fine powder obtained through a synthesis reaction, and the β-type silicon carbide fine powder is preferably a β-type silicon carbide fine powder having a particle size of 10 μm or less. .

  The silicon carbide precursor may be a mixture or compound containing both a silicon source containing silicon element and a carbon source containing carbon element, and known silicon sources and carbon sources used for the production of silicon carbide may be used. It can be used as appropriate.

As such a silicon source, a solid or liquid source is used.
Examples of the solid silicon source include silica sol (a colloidal ultrafine silica-containing liquid containing a hydroxyl group (—OH) and an alkoxyl group inside), silicon dioxide (silica gel, fine silica, quartz powder), and the like. . In order to uniformly mix these solid silicon sources with the carbon source, it is preferable to use a fine particle size powder.

Examples of the liquid silicon source include those obtained by acid decomposition or dealkalization of an alkali silicate aqueous solution, for example, a silicate polymer obtained by dealkalization of water glass; a hydroxyl group (—OH). An ester of an organic compound having silicic acid; an alkoxide such as tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ) and tetramethoxysilane (Si (OCH ₃ ) ₄ ); Examples thereof include esters with organic compounds or organometallic compounds.

On the other hand, as the carbon source, solid carbon such as carbon black, carbon nanotube, fullerene, or an organic compound that is liquid and has a high residual carbon ratio when heated, for example, phenol resin, furan resin, xylene resin, Resin monomers and prepolymers such as polyimide, polyurethane, polyacrylonitrile, polyvinyl alcohol, and polyvinyl acetate are preferably used.
In addition, cellulose, sucrose, pitch, tar and the like are also preferably used.

  As such β-type silicon carbide fine powder or silicon carbide precursor, it is preferable to use a high-purity metal impurity of 1 ppm or less so that the obtained silicon carbide single crystal has a necessary function.

  The free carbon content in the β-type silicon carbide fine powder is preferably 0.1% by mass or less. Further, when the content of free carbon in the β-type silicon carbide fine powder exceeds 0.1% by mass, the free carbon in the fine powder is burned and removed by performing a heat treatment in the air in advance. The content is preferably 0.1% by mass or less.

On the other hand, the molar ratio (C / Si ratio) of carbon atoms (C) and silicon atoms (Si) contained in the silicon carbide precursor is preferably 2.0 or more and 3.0 or less, more preferably 2. 2 or more and 2.7 or less.
Here, the reason why the C / Si ratio is set to 2.0 or more and 3.0 or less is that when the C / Si ratio is less than 2.0, the amount of Si source that does not become silicon carbide increases. On the other hand, if the C / Si ratio exceeds 3.0, free carbon remains at the stage when the β-type silicon carbide fine powder is produced, and particles of the β-type silicon carbide fine powder are left behind. This is because it inhibits growth.

Next, the β-type silicon carbide or silicon carbide precursor is heated in a non-oxidizing atmosphere.
As an apparatus for heating, a heat treatment furnace capable of generating α-type silicon carbide from this β-type silicon carbide or silicon carbide precursor in a non-oxidizing atmosphere is suitable. It is preferable that the pressure control range and the maximum operating temperature in this non-oxidizing atmosphere can be appropriately selected according to the conditions of use.

  Specifically, this β-type silicon carbide or silicon carbide precursor is put into a heat treatment furnace vessel such as a graphite crucible, and then the heat treatment furnace is filled with an inert gas such as argon or nitrogen gas. A non-oxidizing gas such as a reducing gas containing a slight amount of hydrogen is substituted to form a non-oxidizing atmosphere, and then the temperature is raised to a predetermined temperature and firing is performed at the predetermined temperature.

Here, when the β-type silicon carbide or silicon carbide precursor is introduced, in order to efficiently obtain the α-type silicon carbide powder from the β-type silicon carbide or silicon carbide precursor, it is preferable to increase the packing density. .
For example, when β-type silicon carbide fine powder is used, it is preferable to compress the β-type silicon carbide fine powder into a predetermined shape by pressing the β-type silicon carbide fine powder before being charged.

The filling density of the β-type silicon carbide or silicon carbide precursor or the density of the molded body is preferably 1 g / cm ³ or more.
Here, the reason why the packing density or the green body density is set to 1 g / cm ³ or more is that the particles can be sufficiently in contact with each other by setting the density within the above range, and thus uniform and efficient grain growth. It is because it can be performed.
The higher the packing density or the compact density, the better, but generally the upper limit is about 70% of the theoretical density.

  Next, the β-type silicon carbide or silicon carbide precursor is heated at a predetermined temperature increase rate, and at a predetermined temperature, for example, a temperature in the range of 2000 ° C. or higher and 2400 ° C. or lower for 1 minute or longer and 24 hours. The following is held and fired.

Here, the rate of temperature rise is not particularly limited. For example, when a silicon carbide precursor is used, in the temperature range (1600 ° C. to 1800 ° C.) where the silicon carbide precursor undergoes a chemical reaction to produce silicon carbide. Preferably, the temperature is 0.1 ° C./min or more and 10 ° C./min or less.
Moreover, when there is much quantity of the volatile component from a silicon carbide precursor in a 1000 degrees C or less temperature range, it is preferable to perform preliminary baking once at the temperature of 1000 degrees C or less, and to remove a volatile component.

The atmosphere at the time of firing needs to be an atmosphere in which silicon carbide is not oxidized, and an inert atmosphere or a non-oxidizing atmosphere that is a reducing atmosphere is preferable, and argon gas or nitrogen gas is particularly preferable.
In particular, when a silicon carbide precursor is used, it is preferable to detoxify the carbon monoxide generated when the β-type silicon carbide fine particles are produced from the silicon carbide precursor by discharging it to the outside of the furnace.

Control of the pressure in this atmosphere may be performed from room temperature (25 ° C.), or may be performed at 1800 ° C. or higher at which the phase transition from β-type to α-type begins.
For example, when a silicon carbide precursor is used, it is preferable to control the atmospheric pressure from a temperature of 1800 ° C. or higher at which the silicon carbide precursor reacts to form β-type silicon carbide.
It is preferable to control the atmospheric pressure from at least 1800 ° C. or higher, after reaching the holding temperature, until the holding temperature is finished.
It should be noted that the pressure can be appropriately changed both during the temperature rise and during the holding.

As for the pressure of this atmosphere, the temperature may be raised to the holding temperature by either a pressure higher than atmospheric pressure or a pressure lower than atmospheric pressure. However, if the atmospheric pressure is increased, the phase transition temperature becomes higher. In order to obtain α-type silicon carbide powder of particles, it is preferable to increase the atmospheric pressure.
In addition, when obtaining α-type silicon carbide powder having particles smaller than those undergoing phase transition under atmospheric pressure, it is preferable to lower the atmospheric pressure and lower the phase transition temperature.

About holding | maintenance temperature, it can set suitably in the temperature of the range of 2000 degreeC or more and 2400 degrees C or less mentioned above.
The holding temperature may be higher than the temperature at which phase transition from β-type silicon carbide to α-type silicon carbide occurs, but when the holding temperature is made lower than the phase transition temperature and this holding temperature is reached, no phase transition occurs, and this holding temperature. It is preferable to start the phase transition by lowering the atmospheric pressure while maintaining.

Unlike the temperature, the atmospheric pressure at this holding temperature is applied almost simultaneously to the entire container, so that the entire β-type silicon carbide in the container can be phase-shifted at the same time. The body is easy to obtain.
The atmospheric pressure at the time of this phase transition is not particularly limited as long as it is lower than the pressure at the start of holding the holding temperature. For example, in the case of phase transition at the same temperature as the holding temperature, the smaller the pressure, the larger the particles Can be easily obtained, and impurities contained in silicon carbide can be efficiently removed.

There is no particular limitation on the control of the atmospheric pressure, but when the pressure higher than the atmospheric pressure is maintained during the holding temperature, the pressure is preferably set to be equal to or higher than atmospheric pressure and equal to or lower than 10 ⁷ Pa. In the case where a low pressure is maintained, the pressure is preferably 10 ² Pa or more and atmospheric pressure or less.
Here, the lower limit value of the atmospheric pressure is set to 10 ² Pa because, if the atmospheric pressure is less than 10 ² Pa, silicon carbide that volatilizes outside the apparatus at the time of phase transition increases, and the yield for obtaining a single crystal raw material deteriorates. It is.

When the phase transition from β-type silicon carbide to α-type silicon carbide occurs at this phase transition temperature, grains grow rapidly. Furthermore, by controlling the atmospheric pressure, the temperature at which phase transition occurs can be controlled, and the particle size of the α-type silicon carbide powder having a large particle size suitable for the raw material of the silicon carbide single crystal can be controlled.
Furthermore, impurities can be efficiently removed by controlling the atmospheric pressure at the time of phase transition.

[Silicon carbide single crystal]
The silicon carbide single crystal of the present embodiment is a silicon carbide single crystal obtained by crystal growth using the α-type silicon carbide powder whose particle size is controlled by the particle size control method of the α-type silicon carbide powder of the present embodiment. It is.
This silicon carbide single crystal has few impurities and defects and is homogeneous.

As described above, according to the particle size control method for α-type silicon carbide powder of the present embodiment, β-type silicon carbide is heated by heating β-type silicon carbide or a silicon carbide precursor in a non-oxidizing atmosphere. When the phase transition to α-type silicon carbide is performed, the pressure of this atmosphere is changed to control the phase transition temperature from β-type silicon carbide to α-type silicon carbide. Can be controlled to a particle size of 100 μm or more and 300 μm or less suitable for a raw material of silicon carbide single crystal, and α-type silicon carbide powder having a target particle size can be obtained efficiently.
Moreover, since the pressure of the atmosphere at the time of phase transition from β-type silicon carbide to α-type silicon carbide is changed, impurities can be removed from the generated α-type silicon carbide powder.
Furthermore, if the atmospheric pressure is reduced, impurities can be efficiently removed.

  According to the silicon carbide single crystal of this embodiment, since the crystal growth was performed using the α-type silicon carbide powder whose particle size was controlled by the particle size control method of the α-type silicon carbide powder of this embodiment, impurities and There are few defects and it is homogeneous.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these Examples.

"Example 1"
As the silicon carbide raw material, β-type silicon carbide fine powder having an average particle diameter of 1 μm and metal impurities of 1 ppm or less was used.
The silicon carbide fine powder was pressure-molded to a compact density of 1.3 g / cm ³ and then filled into a graphite crucible.
Next, using a heat treatment furnace capable of performing heat treatment in an argon atmosphere, the temperature was raised to 2100 ° C. with an atmospheric pressure of 10 ⁶ Pa and held for 2 hours, and then held for 2 hours with an atmospheric pressure of 10 ⁴ Pa. Example 1 The silicon carbide powder was obtained.
The crystal phase of the silicon carbide powder was α-type, the average particle size was 140 μm, and the metal impurities were 0.1 ppm or less.

"Example 2"
A silicon carbide powder of Example 2 was obtained according to Example 1 except that the holding temperature of Example 1 was changed from 2100 ° C. to 2400 ° C.
The crystal phase of the silicon carbide powder was α-type, the average particle size was 280 μm, and the metal impurities were 0.1 ppm or less.

"Example 3"
A silicon carbide powder of Example 3 was obtained according to Example 1 except that the holding temperature of Example 1 was changed from 2100 ° C. to 2300 ° C.
The crystalline phase of the silicon carbide powder was α-type, the average particle size was 480 μm, and the metal impurities were 0.1 ppm or less.

Example 4
A silicon carbide powder of Example 4 was obtained according to Example 3 except that the atmospheric pressure after maintaining at 2300 ° C. for 2 hours in Example 3 was changed to atmospheric pressure.
The crystal phase of the silicon carbide powder was α-type, the average particle size was 278 μm, and the metal impurities were 0.1 ppm or less.

"Example 5"
The temperature of Example 1 was set to 2 × 10 ⁵ Pa, raised to 2100 ° C. and held for 2 hours, and then maintained for 2 hours with the atmospheric pressure set to 10 ³ Pa. A silicon carbide powder was obtained.
The crystal phase of this silicon carbide powder was α-type, the average particle size was 233 μm, and the metal impurities were 0.1 ppm or less.

"Example 6"
The silicon carbide of Example 6 according to Example 1 except that the atmospheric pressure in Example 1 was raised to 2000 ° C. while maintaining atmospheric pressure and maintained for 2 hours, and then maintained for 2 hours at 10 ³ Pa. A powder was obtained.
The crystal phase of the silicon carbide powder was α-type, the average particle size was 147 μm, and the metal impurities were 0.1 ppm or less.

"Example 7"
Carbonization of Example 7 according to Example 1 except that the atmospheric pressure in Example 1 was 10 ⁷ Pa, the temperature was raised to 2400 ° C. and held for 2 hours, and then the atmospheric pressure was returned to atmospheric pressure and held for 2 hours. Silicon powder was obtained.
The crystal phase of the silicon carbide powder was α-type, the average particle size was 560 μm, and the metal impurities were 0.1 ppm or less.

"Comparative Example 1"
The silicon carbide powder of Comparative Example 1 was obtained in the same manner as in Example 1 except that the atmospheric pressure was not controlled in Example 1 and the atmospheric pressure was kept at atmospheric pressure at 2100 ° C. for 4 hours.
The crystal phase of this silicon carbide powder was a mixture of α type and β type. The average particle diameter was 41 μm, and when the particle size distribution curve of the particle diameter was observed, two peaks were observed at 80 μm and 7 μm.

"Comparative Example 2"
The silicon carbide powder of Comparative Example 2 was obtained in the same manner as in Example 3 except that the atmospheric pressure was not controlled in Example 3 and the atmospheric pressure was maintained at 2300 ° C. for 4 hours.
The crystal phase of this silicon carbide powder was α-type, the average particle size was 80 μm, and the metal impurities were 0.1 ppm or less.

“Comparative Example 3”
A silicon carbide powder of Comparative Example 3 was obtained in the same manner as in Example 3 except that the atmospheric pressure was not controlled in Example 3 and maintained at 2450 ° C. under atmospheric pressure for 4 hours.
The crystal phase of the silicon carbide powder was α-type, the average particle size was 83 μm, and the metal impurities were 0.1 ppm or less.

“Comparative Example 4”
A silicon carbide powder of Comparative Example 4 was obtained in the same manner as in Example 1 except that the atmospheric pressure was changed from room temperature to 5 × 10 ⁴ Pa in Example 1 and maintained at 2200 ° C. for 4 hours.
The crystal phase of this silicon carbide powder was α-type, the average particle size was 90 μm, and the metal impurities were 0.1 ppm or less.

“Comparative Example 5”
A silicon carbide powder of Comparative Example 5 was obtained in the same manner as in Example 1 except that the atmospheric pressure was changed from room temperature to 10 ⁶ Pa in Example 1 and maintained at 2200 ° C. for 4 hours.
The crystal phase of this silicon carbide powder was β-type, and the average particle size was 10 μm.

Claims (5)

β-type silicon carbide or a silicon carbide precursor is heated in a non-oxidizing atmosphere, and the β-type silicon carbide or β-type silicon carbide produced from the silicon carbide precursor is phase-shifted to α-type silicon carbide. A method for controlling the particle size of α-type silicon carbide powder to be produced,
Α-type carbonization characterized in that the pressure of the atmosphere is changed to control the phase transition temperature from β-type silicon carbide to α-type silicon carbide to produce α-type silicon carbide powder having an average particle size of 10 μm or more. A method for controlling the particle size of silicon powder. 2. The phase transition temperature is controlled in a range of 2000 ° C. to 2400 ° C. by changing the pressure of the atmosphere in a range of 2 × 10 ⁵ Pa to 10 ⁷ Pa. Particle diameter control method for α-type silicon carbide powder.   The temperature is raised to a temperature of 2000 ° C. or higher and 2400 ° C. or lower by the heating, and then the pressure of the atmosphere is lowered while maintaining this temperature to cause β-type silicon carbide to undergo phase transition to α-type silicon carbide. The method for controlling the particle size of the α-type silicon carbide powder according to claim 1 or 2.   4. The α-type according to claim 1, wherein the α-type silicon carbide powder to be produced has an average particle size of 100 μm to 300 μm and a metal impurity content of 1 ppm or less. A method for controlling the particle size of silicon carbide powder.   Carbonization characterized by crystal growth using α-type silicon carbide powder whose particle size is controlled by the particle size control method for α-type silicon carbide powder according to any one of claims 1 to 4. Silicon single crystal.