JP6581405B2 - Silicon carbide powder, method for producing the same, and method for producing silicon carbide single crystal - Google Patents

Description

  The present invention relates to a silicon carbide powder, a method for producing the same, and a method for producing a silicon carbide single crystal.

Silicon carbide powder has a large hardness and is excellent in thermal conductivity and heat resistance, and is therefore used as a raw material for molded whetstones and ceramic parts. Further, when the physical properties of silicon carbide and silicon are compared, the band gap of silicon carbide is about 3 times that of silicon, and the breakdown electric field strength of silicon carbide is about 10 times that of silicon. It has been attracting attention as a material for substrates for power semiconductors, which can be used as an alternative.
Here, the power semiconductor substrate made of silicon carbide can be manufactured by cutting a silicon carbide single crystal. As a method for producing a silicon carbide single crystal, there is a sublimation recrystallization method in which a silicon carbide powder as a raw material is sublimated under a high temperature condition of 2,000 ° C. or higher to grow a silicon carbide single crystal on a silicon carbide seed crystal. well known. This sublimation recrystallization method is widely used industrially.

Silicon carbide powder, which is a raw material used in the sublimation recrystallization method, is required to be easily sublimated.
As a method for producing a silicon carbide powder having a particle size exhibiting a stable sublimation rate, Patent Document 1 discloses a high purity silicon source, and a high purity as a carbon source that contains oxygen in the molecule and retains carbon by heating. A mixture obtained by homogeneously mixing an organic compound is heated and fired in a non-oxidizing atmosphere to obtain a silicon carbide powder, and 1,700 of the obtained silicon carbide powder is obtained. And a heat treatment step of performing a heat treatment at a temperature of 2,100 ° C. to 2,500 ° C. during the holding at the holding temperature, and the silicon carbide powder production step And by performing the heat treatment step, a silicon carbide powder having an average particle diameter of 100 μm to 300 μm and a content of each impurity element of 0.1 ppm or less is obtained. A method for producing silicon powder is described.

  In addition, as another method for producing silicon carbide powder having a particle size exhibiting a stable sublimation rate, Patent Document 2 discloses one type selected from high-purity tetraalkoxysilane, tetraalkoxysilane polymer, and silicon oxide. The above is used as a silicon source, oxygen is contained in the molecule, and a high-purity organic compound that retains carbon by heating is used as the carbon source. The silicon carbide production step for obtaining silicon carbide powder, and the obtained silicon carbide powder is maintained at a temperature of 1,700 ° C. or higher and lower than 2,000 ° C. A post-treatment step of performing at least one treatment for 5 to 20 minutes at a temperature of 2,100 ° C., and performing the above-mentioned two steps, whereby the average particle size is 10 μm to 500 μm, and each There is described a method for producing a high-purity silicon carbide powder for producing a silicon carbide single crystal, characterized in that a silicon carbide powder having an impurity element content of 0.5 ppm or less is obtained.

JP 2009-173501 A JP 09-48605 A

As a technology for industrially mass-producing silicon carbide, a siliceous raw material containing silicon (Si) and a carbonaceous raw material containing carbon are used as raw materials, and an electric current is passed through a heating element disposed in the raw materials, A method for producing silicon carbide by heating the raw material (Acheson method) is known.
In the Atchison method, silicon carbide is produced as a lump produced from the vicinity of the heating element toward the outside. At this time, in the Atchison furnace, a temperature gradient is generated from the center portion of the furnace (near the heating element) to the outside, so that the silicon carbide as a lump has its mode (crystals of silicon carbide, impurities depending on the part). The total content and type etc.) are different.
In general, a lump of silicon carbide produced by the Atchison method is pulverized to a predetermined particle size to be silicon carbide powder without being distinguished by the above-described aspect of silicon carbide.
When the silicon carbide powder thus obtained is used as a raw material for the sublimation recrystallization method, even if the particle size of the silicon carbide powder is the same, the sublimation speed varies, or the sublimation speed is May be smaller.
Accordingly, an object of the present invention is to provide a silicon carbide powder with little variation in sublimation speed and high sublimation speed.

As a result of intensive studies to solve the above problems, the present inventor has found that the above object can be achieved by silicon carbide powder having a lightness L ^* of 37 or more in the L ^* a ^* b ^* color system. The present invention has been completed.
That is, the present invention provides the following [1] to [5].
[1] A silicon carbide powder having a lightness L ^* in the L ^* a ^* b ^* color system of 37 or more.
[2] The silicon carbide powder according to [1], wherein the chromaticity b ^* in the L ^* a ^* b ^* color system is 0 or more.
[3] The silicon carbide powder according to [1] or [2], wherein a ratio of the powder having a particle size of 10 μm or more in the silicon carbide powder is 80% by mass or more.
[4] A method for producing the silicon carbide powder according to any one of [1] to [3], wherein a mixed raw material obtained by mixing a siliceous raw material and a carbonaceous raw material is heated in a heating furnace. A firing step of firing to obtain a fired product, a grinding step of pulverizing the fired product to obtain a pulverized product divided into a plurality according to a plurality of parts of the fired product, and a pulverization separated into the plurality A method for producing silicon carbide powder, comprising: measuring a value of L ^* a ^* b ^* color system for each product, and obtaining a color of the silicon carbide powder based on the measurement result .
[5] A method for producing a silicon carbide single crystal using the silicon carbide powder according to any one of [1] to [3], wherein the silicon carbide powder is heated and sublimated to obtain a surface of a seed crystal. And a method for producing a silicon carbide single crystal, comprising growing a silicon carbide single crystal.

  The silicon carbide powder of the present invention has little variation in the sublimation rate and a large sublimation rate, and can be suitably used as a raw material for the sublimation recrystallization method.

It is sectional drawing which shows notionally the carbon crucible used for the sublimation recrystallization method, and its content.

[Silicon carbide powder]
The lightness L ^* in the L ^* a ^* b ^* color system of the silicon carbide powder of the present invention is 37 or more, preferably 40 or more, particularly preferably 43 or more. When the lightness L ^* is less than 37, the sublimation rate of the silicon carbide powder becomes small.
The chromaticity b ^* in the L ^* a ^* b ^* color system of the silicon carbide powder of the present invention is preferably 0 or more, more preferably 10 or more. If the chromaticity b ^* is 0 or more, the sublimation rate of the silicon carbide powder is increased.
The chromaticity a ^* in the L ^* a ^* b ^* color system of the silicon carbide powder of the present invention is not particularly limited, but is usually 0 or less, preferably −2 or less.

In the L ^* a ^* b ^* color system, the lightness L ^* , chromaticity b ^* , and chromaticity a ^* are commercially available spectrophotometers (for example, trade name “CM-700d” manufactured by Konica Minolta). Can be measured.
In the above measurement, it is preferable to use a silicon carbide powder having a particle size of 100 μm or less (preferably 50 μm or less, more preferably 10 μm or less) from the viewpoint of performing measurement more accurately. When the particle size of the silicon carbide powder to be measured exceeds 100 μm, the silicon carbide powder may be pulverized before measurement.
When the silicon carbide powder is pulverized, the pulverization medium used for pulverization and the container containing the silicon carbide powder are preferably made of metal. This is because when pulverization is performed using a metal pulverization medium or the like, the metal powder mixed into the silicon carbide powder from the pulverization medium or the like can be easily removed by an acid. On the other hand, a pulverizing medium or container made of ceramic is not preferable because it is difficult to remove foreign matters (ceramic powder or the like) mixed in the silicon carbide powder.
When the foreign matter (metal powder or the like) derived from the grinding media mixed when grinding is insufficient, the lightness L ^* or the like cannot be measured accurately. Moreover, when the said foreign material remains in silicon carbide powder, since the sublimation speed of this silicon carbide powder becomes small, the silicon carbide powder used for the measurement cannot be used as a raw material for the sublimation recrystallization method.

The proportion of the powder having a particle size of 10 μm or more in the silicon carbide powder of the present invention is preferably 80% by mass or more, more preferably 85% by mass or more, and particularly preferably 90% by mass or more. If the ratio is 80% by mass or more, the silicon carbide powder is hardly sintered by heating, so that the sublimation rate of the silicon carbide powder is hardly lowered.
The proportion of the powder having a particle size of 100 μm or more in the silicon carbide powder of the present invention is preferably 60% by mass or more, more preferably 70% by mass or more, and particularly preferably 80% by mass or more. If the ratio is 60% by mass or more, the silicon carbide powder is hardly sintered by heating, so that the sublimation rate of the silicon carbide powder is hardly lowered.
The upper limit of the particle size of the silicon carbide powder of the present invention is not particularly limited, and is appropriately determined depending on the heating conditions in the sublimation recrystallization method and the sublimation rate of the silicon carbide powder required in the sublimation recrystallization method. However, it is preferably 5 mm or less, more preferably 4 mm or less, and particularly preferably 3 mm or less from the viewpoint of preventing a decrease in the sublimation rate of the silicon carbide powder due to a decrease in the specific surface area of the silicon carbide powder.

  Since the silicon carbide powder of the present invention has a small variation in sublimation rate and a large sublimation rate, it can be used as a raw material for the sublimation recrystallization method to stabilize the silicon carbide single crystal on the silicon carbide seed crystal And can be grown in a short time.

[Method for producing silicon carbide powder]
As an example of the method for producing the silicon carbide powder of the present invention, a mixed raw material obtained by mixing a siliceous raw material and a carbonaceous raw material is fired in a heating furnace to obtain a fired product (step (a)). And crushing the baked product to obtain a pulverized product divided into a plurality according to a plurality of parts of the baked product (step (b)), and each of the pulverized product separated into the plurality , L ^* a ^* b ^* Color system value is measured, and based on the measurement result, a method including a color measurement step (step (c)) to obtain the silicon carbide powder is mentioned. Hereinafter, each process will be described in detail.

[Step (a); Firing step]
This step is a step of obtaining a fired product by firing a mixed raw material obtained by mixing a siliceous raw material and a carbonaceous raw material in a heating furnace.
Examples of siliceous raw materials include crystalline silica such as silica stone, and amorphous silica such as silica fume and silica gel. These are used singly or in combination of two or more.
From the viewpoint of obtaining a high-purity silicon carbide powder, the total content of impurities in the siliceous raw material (atoms such as Al and Fe other than Si (excluding oxygen atoms)) is preferably 500 ppm or less, More preferably, it is 200 ppm or less.

Examples of the carbonaceous material include crystalline carbon such as natural graphite and artificial graphite, and amorphous carbon (amorphous carbon) such as carbon black, coke and activated carbon. These are used singly or in combination of two or more.
From the viewpoint of obtaining high-purity silicon carbide powder, the total content of impurities in the carbonaceous raw material (atoms other than C such as Al and Fe (excluding oxygen atoms)) is preferably 500 ppm or less. Preferably it is 200 ppm or less.

By mixing the siliceous raw material and the carbonaceous raw material, a mixed raw material for producing silicon carbide can be obtained. At this time, the mixing method of each raw material is arbitrary, and both wet mixing and dry mixing can be adopted.
The mixing molar ratio (C / Si) of the carbonaceous raw material and the siliceous raw material at the time of mixing is optimum in consideration of the environment during firing, the particle size and reactivity of the raw material for silicon carbide production. Just choose one. The term “optimum” as used herein means improving the yield of silicon carbide obtained by firing, and reducing the amount of the remaining unreacted siliceous material or carbonaceous material.

In the present invention, by using a heating furnace, a reaction represented by the following formula (1) occurs, and a lump made of silicon carbide is obtained.
SiO ₂ + 3C → SiC + 2CO (1)
Examples of the heating furnace include an Atchison furnace (electric current heating; batch type), a fluidized bed furnace (external heating; batch type), and the like.
Among them, the Atchison furnace is suitable for the production method of the present invention from the viewpoint of industrially mass-producing silicon carbide, easily discharging impurities, and obtaining high-purity silicon carbide. .
In the present specification, “Acheson furnace” means a box-type indirect resistance heating furnace opened upward. Here, indirect resistance heating means that the current to be heated (mixed raw material) does not flow directly to the heated object (mixed raw material), but the heated object (mixed raw material) is heated by a heating element that generates heat by passing an electric current. Is what you get.

The type of the heating element of the Atchison furnace is not particularly limited as long as it can conduct electricity. For example, graphite powder (for example, obtained by heat treatment of carbon black), carbon rod, etc. Is mentioned.
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.

The firing temperature when firing using the Atchison furnace is preferably 1,600 ° C. or higher, more preferably 2,000 ° C. or higher, and particularly preferably 2,400 ° C. or higher.
The firing atmosphere in the Atchison furnace is preferably a reducing atmosphere. This is because the yield of silicon carbide decreases when firing is performed in an atmosphere other than the reducing atmosphere. At this time, if amorphous silica is used as the siliceous material, the reactivity is good, so that the furnace can be easily controlled.

[Step (b); Grinding step]
This step is a step of pulverizing the fired product obtained in the previous step to obtain a pulverized product separated into a plurality according to a plurality of portions of the fired product.
A method for pulverizing the obtained fired product (a lump made of silicon carbide) is not particularly limited, and examples thereof include a method for pulverizing using a jaw crusher, a ball mill, a disk mill, or the like.
When performing pulverization, the baked product is cut using a disc grinder or the like, so that the pulverized product can be divided into a plurality of parts and pulverized for each of the divided parts to obtain a pulverized product that is divided into a plurality of parts. it can.

The method for separating the plurality of parts is not particularly limited, and the fired product may be appropriately cut and separated into any plurality of parts. For example, each layer (ingot zone, β crystal zone, altered zone, etc.) that is formed concentrically from a heating element in the Atchison method based on the difference in color tone of the fired product (visually) ) Can be cut into portions corresponding to) and separated into a plurality of portions.
In addition, among the portions of the fired product, the lightness L ^* increases as the distance from the heating element increases, and the lightness L ^* tends to decrease as the distance decreases. Further, among the parts of the burned material, the more becomes the site of upper vertical portion, lightness L ^* becomes smaller and becomes part of the vertically lower, they tend to lightness L ^* increases.
In addition, after pulverization, the obtained pulverized product is classified, and the particle size distribution of the silicon carbide powder may be arbitrary (for example, silicon carbide powder having a particle size distribution in the range of 100 to 3,000 μm).

[Step (c); Color measurement step]
This step measures the value of the L ^* a ^* b ^* color system for each of the pulverized products divided into a plurality, and has a specific lightness L ^* (37 or more), etc., based on the measurement results. This is a step of obtaining the silicon carbide powder targeted by the present invention (silicon carbide powder of the present invention).
The silicon carbide powder of the present invention may consist of only one type of pulverized product, or a combination of two or more types of pulverized product to have a specific lightness L ^* or the like. It may be prepared as described above.

[Method for producing silicon carbide single crystal]
The silicon carbide single crystal can be produced by heating and sublimating the silicon carbide powder described above to grow the silicon carbide single crystal on the surface of the seed crystal. Hereinafter, an example of a method for producing a silicon carbide single crystal will be described with reference to FIG.
On the lower surface of the upper cover 3 of the carbon crucible 1 composed of the main body 2 and the upper cover 3, a single crystal plate having a Si surface appearing as a silicon carbide seed crystal 4 by polishing is installed. On the other hand, the silicon carbide powder (single crystal raw material) 5 is accommodated in the carbon crucible 1 so that a space for sublimation is formed above the internal space of the carbon crucible 1. Then, the silicon carbide single crystal 6 can be grown on the seed crystal 4 by heating for a predetermined time and sublimating the silicon carbide powder 5.

The heating temperature (heating temperature for the raw material) in the sublimation recrystallization method is preferably 2,000 to 2,500 ° C.
The heating is preferably performed by providing a temperature gradient so that the temperature around the seed crystal 4 is lower than the temperature around the silicon carbide powder 5. By providing the temperature gradient, the sublimated silicon carbide easily moves to the seed crystal 4, so that the growth rate of the silicon carbide single crystal 6 can be increased. The difference between the ambient temperature of silicon carbide powder 5 and the ambient temperature of seed crystal 4 is preferably 20 ° C. or higher.
The heating time is not particularly limited, and is usually performed until the silicon carbide powder 5 does not sublime.

After the silicon carbide powder 5 is accommodated in the carbon crucible 1, the body 2 is covered with the upper lid 3, and then an inert gas (for example, argon gas) is put in the carbon crucible 1, under an inert gas atmosphere. Heating may be performed. The pressure of the inert gas atmosphere is preferably 100 Pa to 15 kPa, more preferably 500 to 10 kPa. By heating in such an atmosphere, a higher purity silicon carbide single crystal can be obtained. Alternatively, the carbon crucible 1 may be sealed by bonding the main body 2 and the upper lid 3 with a carbon-based adhesive.
As described above, a silicon carbide single crystal can be produced.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the present specification, ppm is based on mass.
[Materials used]
(1) Silicic raw material A: high purity silica (silica gel which is amorphous silica; total content of impurities excluding oxygen atoms: 10 ppm or less)
(2) Silicate raw material B: high purity silica (silica gel which is amorphous silica; Al content: 50 ppm, Fe content: 120 ppm, total content of impurities excluding Al, Fe and oxygen atoms : 10 ppm or less)
(3) Carbonaceous raw material: carbon black (amorphous carbon; total content of impurities excluding oxygen atoms: 10 ppm or less)
(4) Heating element: Graphite powder for heating element (crystalline graphite powder obtained by heat treatment of carbon black at 3,000 ° C.)

[Examples 1 to 5 and Comparative Examples 1 to 3]
[Production of silicon carbide powders a to c]
Silica raw material A and carbonaceous raw material are mixed using a biaxial mixer so that the molar ratio of carbon to silicic acid (C / SiO ₂ molar ratio) is 3.0 to obtain a mixed raw material. It was.
800 kg of the obtained mixed raw material and the above heating element were stored in an Atchison furnace (inner dimensions of the Atchison furnace: length 2500 mm, width 1,000 mm, height 850 mm), and then the center temperature (mixing in contact with the heating element) Firing was carried out for 12 hours so that the temperature of the raw material was 2500 ° C. or higher, and a silicon carbide lump was obtained.
The obtained silicon carbide lump was fractionated into three parts using a disc grinder according to the color tone by visual observation.
Each of the three fractionated portions was ground using a jaw crusher and a ball mill. The obtained pulverized product is sieved using a sieve, and silicon carbide powder having a particle size range of 100 to 3,000 μm (carbonization passing through a sieve having an opening of 3,000 μm and not passing through a sieve having an opening of 100 μm). Silicon powder) was obtained. This silicon carbide powder was acid-washed to obtain silicon carbide powders a to c.
Of the sieve residue generated when obtaining the silicon carbide powders a to c, for the silicon carbide powder having a particle size of 10 μm or less, a spectroscopic colorimeter (trade name “CM-700d” manufactured by Konica Minolta Co., Ltd.) is used. The lightness L ^* , chromaticity b ^* , and chromaticity a ^* in the L ^* a ^* b ^* color system of the silicon carbide powders a to c were measured. The measurement method was an SCI (regular reflection light included) method that measures color without removing regular reflection light.

[Production of silicon carbide powders d to h]
After obtaining the silicon carbide lump by using the silicic acid raw material B instead of the siliceous raw material A and setting the baking time to 18 hours, the lump is placed in five parts according to the difference in color tone. Except for fractionation, silicon carbide powders d to h were obtained in the same manner as the method for producing silicon carbide powders a to c.
The lightness L ^* , chromaticity b ^* , and chromaticity a ^* in the L ^* a ^* b ^* color system of the silicon carbide powders d to h were measured in the same manner as the silicon carbide powders a to c.

[Production of silicon carbide single crystal]
About each of the obtained silicon carbide powder ah, the quantity of 200g was accommodated in the carbon crucible 1 shown in FIG. A single crystal plate having a Si surface appearing as a seed crystal 4 by polishing was installed on the lower surface of the upper lid 3 of the carbon crucible 1.
In the carbon crucible 1, the temperature of the lower part of the carbon crucible 1 (around the silicon carbide powder 5) is 2300 ° C. under an argon atmosphere and a pressure of 1 kPa, and the upper part of the carbon crucible 1 (seed crystal) 4), the silicon carbide powder 5 in the carbon crucible 1 was sublimated to grow a silicon carbide single crystal 6 on the seed crystal 4. The heating time was 6 hours.

Each sublimation rate of the silicon carbide powders a to h was calculated using the following formula (1). A high sublimation rate means a high sublimation rate.
Sublimation rate (mass% / hour) = [mass of silicon carbide powder reduced by heating for 6 hours] ÷ [mass of silicon carbide powder before heating; 200 g] ÷ 6 (hour) (1)
The results are shown in Table 1.

From Table 1, the sublimation rate (15 to 18% by mass / hour) of the silicon carbide powder of the present invention (Examples 1 to 5) has little variation, and the silicon carbide powder not corresponding to the present invention (Comparative Examples 1 to 1). It can be seen that it is larger than the sublimation rate of 3) (6 to 10% by mass / hour).
Moreover, the silicon carbide powder manufactured from the example (Examples 4-5 and Comparative Examples 1-3) using the "silicic acid raw material B" of Table 1 and the same particle size is manufactured. Even so, it can be seen that there is variation (6 to 16% by mass / hour) in the sublimation rate (sublimation rate).

DESCRIPTION OF SYMBOLS 1 Carbon crucible 2 Main body 3 Upper cover 4 Silicon carbide seed crystal 5 Silicon carbide powder (raw material of a single crystal)
6 Silicon carbide single crystal

Claims (3)

A firing process for obtaining a fired product by firing a mixed raw material obtained by mixing a siliceous raw material and a carbonaceous raw material in a heating furnace,
After the fired product is cut and separated into a plurality of parts, each of the plurality of parts is pulverized to include a powder having a particle size of 10 μm or less and a powder having a particle size of 100 μm or more . A pulverization step for obtaining a pulverized product divided into a plurality according to a plurality of sites;
For each of the pulverized products classified into a plurality of the above, a powder having a particle size of 10 μm or less was measured, and the value of L ^* a ^* b ^* color system was measured. Based on the measurement result, L ^* a color measurement step for obtaining silicon carbide powder satisfying a condition that the lightness L ^* in the a ^* b ^* color system is 40 or more ;
Specified in the color measurement step, consisting of only one kind of pulverized product obtained in the pulverization step or prepared by combining two or more pulverized products. A single crystal growth step of heating and sublimating only the silicon carbide powder satisfying the above conditions to grow a silicon carbide single crystal on the surface of the seed crystal;
A method for producing a silicon carbide single crystal , comprising: In the color measurement step, a silicon carbide powder satisfying the condition that the lightness L ^* is 40 or more and the chromaticity b ^* is 0 or more is obtained, and in the single crystal growth step, the conditions specified in the color measurement step The method for producing a silicon carbide single crystal according to claim 1, wherein only the silicon carbide powder satisfying the condition is heated and sublimated . Prior to the single crystal growth step, the silicon carbide powder is classified, and includes a classification step of obtaining silicon carbide powder having a particle size range of 100 to 3,000 μm as the heating object in the single crystal growth step. The manufacturing method of the silicon carbide single crystal of Claim 1 or 2.

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