JPH02204318A - Method for refining silicon carbide powder - Google Patents

Abstract

PURPOSE:To easily produce the high-purity silicon carbide powder from inexpensive silicon carbide by crushing the silicon carbide, recrystallizing the crushed material by heating and removing the remaining impurities by pickling. CONSTITUTION:The inexpensive silicon carbide contg. impurities is precrushed into the powder having <=100mu average grain diameter, and the powder is heated at 1500-2200 deg.C in a nonoxidizing atmosphere. Consequently, the powder is recrystallized, and the metallic impurities such as iron, Ca and Cr other than Si are moved to the surface from between the crystals in the powder. The heat-treated powder is cleaned with an inorg. acid such as hydrochloric acid, nitric acid, hydrofluoric acid and a mixture of hydrochloric acid and nitric acid to remove the impurities such as iron, Ca and Cr other than Si. By this method, the high-purity silicon carbide powder is easily and inexpensively obtained, and the powder is effectively utilized as the material for a liner tube in a diffusion furnace for producing semiconductors.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for refining silicon carbide powder.

[Conventional technology]

In recent years, silicon carbide sintered bodies with excellent strength and thermal conductivity have been used as constituent materials for liner tubes in diffusion furnaces for semiconductor manufacturing. Additionally, if impurities such as iron, calcium, and chromium remain in the silicon carbide sintered body, the impurities will diffuse into the semiconductor wafer and contaminate the wafer, depending on the impurity concentration. things are required.

Therefore, when producing a sintered body that requires high purity, it is necessary to use high purity silicon carbide powder.

[Problem to be solved by the invention]

However, although silicon carbide powder produced by a gas phase reaction method using SiH4,5iC14 and CH3SiCl3 as starting materials has high purity, it is expensive, and cheap silicon carbide powder contains a large amount of metal impurities. and to remove it, use
After treatment with a strong acid under high temperature and pressure using an autoclave or the like, it becomes necessary to perform a cleaning treatment, which requires expensive equipment.

This invention was made in consideration of the above circumstances, and its purpose is to be able to remove most of the impurities from inexpensive silicon carbide powder in which many impurities remain, and to significantly reduce the concentration thereof. The object of the present invention is to provide a method for refining silicon carbide powder that can be highly purified extremely easily and inexpensively.

[Means and operations for solving the problem] In order to achieve the above object, in this invention, after heating and recrystallizing silicon carbide powder that has been crushed in advance, impurities remaining in the silicon carbide powder are removed. It is removed by acid cleaning. This is because if the raw material is not pulverized, the proportion of impurities trapped within the silicon carbide powder particles will increase. The heating temperature is desirably 1500° C. or higher and lower than 2200° C., because if the heating temperature is 2200° C. or higher, grain growth of the powder will occur, making molding and sintering difficult. Moreover, if the heating temperature is less than 1500° C., recrystallization of the silicon carbide powder will not proceed and impurities will be difficult to move to the powder surface. Also, the average particle size of silicon carbide powder is 1
00 μm or less, and even more preferably 10 μm or less.
A non-oxidizing atmosphere such as one or a combination of two or more of e, Co, vacuum, etc. is preferred.

According to the heat treatment, metal impurities other than silicon, such as iron, calcium, and chromium, move from between the crystals inside the silicon carbide powder toward the surface. Therefore, if the powder is washed using an inorganic acid that dissolves the impurities, a highly purified silicon carbide powder can be obtained.

Next, this invention will be explained in detail.

Commercially available, inexpensive silicon carbide powder is obtained by pulverizing an ingot and then removing impurities mixed in during pulverization by acid washing. However, this silicon carbide powder is iron,
It contains impurities such as calcium and chromium on the order of several 10 ppm to several 100 pp+n. When heating the silicon carbide powder under normal pressure to recrystallize it, the heating temperature is set in a range of 1500°C or more and less than 2200°C. If the heating temperature is less than 1500° C., recrystallization of the silicon carbide powder does not proceed, impurity atoms remain trapped in the crystal lattice inside the silicon carbide powder, and cannot be removed by acid washing. Also, the heating temperature is 2200℃
If the temperature is above, the specific surface area of the silicon carbide powder will be significantly reduced, and the sublimation of silicon carbide will proceed rapidly, so the above temperature range is desirable.

As cleaning acids, hydrochloric acid, nitric acid, and hydrofluoric acid can be used alone, and three types of mixed acids (HCl + HNO3, HF + HNO3, HC
l+HF) can also be used. In particular, it is desirable to use a mixed acid containing hydrochloric acid and nitric acid. The reason for this is that hydrochloric acid is inexpensive and impurities have a high solubility in hydrochloric acid.

In acid washing, an acid is added to the heated powder to prepare a turbid liquid, and the turbid liquid is left for a predetermined period of time. It is more preferable that this cloudy liquid is heated to a temperature of 50 to 80°C, and various impurities are dissolved in the acid solution during this standing period.Next, the silicon carbide powder in the cloudy liquid is filtered out by a filter. After washing and drying, the purification of the silicon carbide powder is completed. By sintering purified silicon carbide powder, a sintered body with high purity, high strength, and excellent thermal conductivity can be obtained.

Next, examples and comparative examples of the present invention will be described.

As starting materials, α-type and β-type raw materials are crushed from ingots and impurities mixed in during crushing are removed by acid washing.
type silicon carbide powder (hereinafter abbreviated as α-type powder and β-type powder, respectively) was used. There are three types of α-type powders with different particle sizes (C, Ca2O3, GC#2000.
GC#8000) were prepared, each having the physical properties shown in Table 1, and containing a large amount of impurities consisting of iron, calcium, and chromium. In addition, as the β-type powder, those synthesized by carbonizing silica sand with coke and those obtained by pulverizing the same are used, and they have the physical properties shown in Table 1 and do not contain the same impurities as the α-type powder. It was. Note that the concentration of each impurity was measured by emission spectrometry.

JLL- Type Particle size Specific surface area Impurity (pμm) (μ11
) (rrr/g) Fe Ca Cr
l α 300 560 200 182
α 8.1 1.07 510 210 12
3 α 0.9 10.6 720 290 1
64 β 8.1 3.8 830 170
95 β 0.5 16.1 920 260
12 The obtained cloudy liquid was left to stand at room temperature and normal pressure for 24 hours.

Next, the turbid liquid was filtered to remove solids through a membrane filter, washed with distilled water until the pH of the filtrate reached 7, and dried.

The graphite crucible contained only 0.2 pμm of iron and trace amounts of calcium and chromium.

Also shown in Table 2 are the acids used on each side.

Further, in each Example and Comparative Example, experiments were conducted according to the following procedure. That is, in a graphite crucible with an inner diameter of 50111
g of various powder samples were filled. Then, this sample was inserted into a Tammann furnace and heated at normal pressure at a pre-selected temperature within the range of 1200°C to 2000°C.Next, 100cc of various acid solutions were added to the various heat-treated powder samples. Table 2 Type of inhibitor AHC135χ reagent special grade [manufactured by Kanto Kagaku Co., Ltd.] B
) lNO3652 Same as above CHF 46χ Same as above D HCI, ) 1:1 mixture of INO3 (volume ratio) E volume, l of HNO3! Mixed liquid (volume ratio)
F 1:1 mixture of HCI and IP (volume ratio) [Examples 1 to 3] In Examples 1 to 3, each pre-selected powder sample (m3.Ik5 in Table 1) was placed in a Tamman furnace. After heating at normal pressure, the sample was washed with an acid selected from the various acids shown in Table 2, washed with distilled water, and then dried. The impurity concentration of the obtained powder sample was measured by emission spectrometry, and the specific surface area after heat treatment was also measured. Table 3 shows the results and heating conditions.

LL- Example Sample heating acid ratio impurity (ppw) evaluation
Conditions Area Fe Ca Cr1315
00℃HCI 4.1 20 10<1<
◎(α)lhr 232000℃MCI 0.14 8 - - ◎(
α) Ihr 351600℃HCI -810<1<◎(β
) lhr In Table 3 above, the symbol "<" means "less than", the Greek letters in the sample stock column indicate the crystal type, and the evaluation column indicates the degree of purification, ■, ○. It is divided into four stages of △ and ×, and the same applies hereafter.

According to the above experimental results, if silicon carbide powder with an average particle size of 1 μm or less is heated at a temperature of 1500°C or higher for 1 hour or more under normal pressure and then washed with acid, the crystal structure of the silicon carbide powder can be changed. Regardless, the concentration of each impurity is significantly reduced to 1/100 to 10/100 of the initial concentration,
It can be seen that the silicon carbide powder has been highly purified.

[Comparative examples ■, ■]

A comparative experiment was conducted on β-type silicon carbide powder under the conditions shown in Table 4. The results are also shown in Table 4.

-J-like- Example Sample Heating Acid Ratio Table Impurity (pμm) Evaluation
Disease condition Area Fe Ca Cr■ 4
1400″t HCI-7801608X(β)l
hr ■ 4 Without heating HCI -8101609x (β) Comparing this result with the results of Example 3, it is found that it is difficult to achieve high purity of β-type silicon carbide powder even when heated at 1400°C. I understand.

Without heating, the amount of decrease in impurity concentration is extremely small.

[Comparative Examples 1 to 0] The following comparative experiment was conducted on α-type silicon carbide powder in order to confirm the significance of heating conditions and types of acids. The results are shown in Table 5.

Example Sample Na floor ■ 3 (α) ■ 3 (α) ■ 3 (α) ■ 3 (α) ■ 3 (α) ■ 3 (α) ■ 3 (α) (α) 1200℃ hr 1300℃ 0.17hr 1300℃ 0.5hr! Heating Acid Surface Impurity (pμm) Evaluation Conditions Product
Fe Ca Cr heating HCI-660190
15 .

× HCI 10゜1350
)lhr [Phase] 3 1300℃ lIc1 8.5 80
- - To (α)3hr @ 1 1600℃ HCI -84513,
9Δ(α)lhr 02 Same as above 11cI -44282,00(α) According to the above experimental results, when α-type silicon carbide powder is only acid-washed without heating (Comparative Examples ■ to ■), When the cleaning solution contains hydrofluoric acid, impurities are reduced to about 10/100 of the initial concentration, but it is difficult to reduce them to less than that.

Furthermore, when the heating temperature of α-type silicon carbide powder is 1300°C (Comparative Examples ■~@), even if the heating time is extended to 3 hours, the impurity concentration can only be reduced to about 10/100. , the heating condition was 1200°C.

The same applies to the case of 1 hour (Comparative Example ■).

When silicon carbide powder is heated at 1500℃, the particle size is 8μ
m or more, the impurity concentration can be reduced to about 10/100.

〔Effect of the invention〕

Claims (1)

[Scope of Claims] 1. A method for purifying silicon carbide powder, which comprises heating and recrystallizing pre-pulverized silicon carbide powder, and then removing impurities remaining in the silicon carbide powder by acid washing. 2. The method for refining silicon carbide powder according to claim 1, wherein the average particle size of the silicon carbide powder is 100 μm or less. 3. The method for refining silicon carbide powder according to claim 1 or 2, wherein the heating temperature is 1500°C or higher and lower than 2200°C in a non-oxidizing atmosphere. 4. The silicon carbide powder according to any one of claims 1 to 3, wherein the impurities include metals other than silicon, such as iron, calcium, and chromium, and the acid is an inorganic acid that dissolves them. Purification method.