JPH07206422A - Production of synthetic quartz glass powder - Google Patents

Abstract

PURPOSE:To efficiently produce ultrahigh purity synthetic quartz glass powder. CONSTITUTION:When powder of silica gel obtd. by hydrolyzing tetraalkoxysilane is fired to produce synthetic quartz glass powder, the particle size of the silica gel powder is regulated to the range of 10-2,000mum before firing.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the field of semiconductor manufacturing, in particular 1.
The present invention provides a silica glass powder suitable as a raw material for an ultra-high purity quartz glass product used in a high temperature range of 000 ° C or higher.

[0002]

2. Description of the Related Art Conventionally, crucibles and jigs for manufacturing semiconductor single crystals have been manufactured by melting natural quartz powder obtained by crushing natural quartz, but natural quartz is of high quality. Also contains various metal impurities, and was not sufficiently satisfactory in terms of purity. In particular, in a high-purity single crystal that is required as the semiconductor industry becomes more sophisticated, if metal impurities are mixed, the performance of the semiconductor will be adversely affected. Cannot be used. For this reason, recently, high-purity silica glass powder made of an alloy has been required.

In recent years, as a highly pure silica source,
Quartz glass produced by sol-gel method using alkoxysilane as a raw material has been introduced. For example, JP-A-62-176
Japanese Patent Publication No. 928 discloses a method of producing a silica glass powder by hydrolyzing an alkoxysilane in the presence of an acid and an alkali to prepare a gel, crushing and drying the gel, and then firing the silica glass powder.

[0004]

In the production of synthetic quartz glass powder by the sol-gel method, first, alkoxysilane is used as a raw material, and this is hydrolyzed and polycondensed to form a wet gel, which is a by-product of alcohol or water. Is removed by drying to give a dry gel. This dry gel is 1,000-1,4
A synthetic quartz glass is obtained by firing to 00 ° C. and making it non-porous. However, the product obtained after firing is very hard and difficult to pulverize, so normally, when powder is required, it is preferable to perform pulverization in a relatively soft dry gel or wet gel stage. However, it is industrially advantageous. However, the pulverized powder contains a large amount of very small fine particles, large particles, or agglomerates of fine powder, as compared with the particle size actually required as a product. If firing is performed in such a state, particularly for fine powder, since the firing is fast, particles are likely to agglomerate and stick together. Water vapor and C generated in the lower part of the body
O ₂ is accumulated in pressure and bumps, and powder is blown out from the crucible for firing, leading to a reduction in yield. Also, in the production of synthetic quartz glass powder, the most costly is the firing step. In this firing step, firing fine powder, which is essentially unnecessary as a product, together with powder of the product grain size is an industrial process. It is also disadvantageous. On the other hand, if very large particles or agglomerates of fine particles are mixed in at the time of firing as compared with the product particle size, it is difficult for residual carbon to come off, and black foreign matter tends to occur. When this black foreign substance melts, it becomes CO or CO ₂ and causes foaming. However, in a quartz crucible or core tube containing bubbles, dimensional stability during high temperature use and bubbles popping when pulling a single crystal. There is a problem that the liquid level fluctuates and crystal defects occur.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in order to obtain synthetic quartz glass powder free from the above-mentioned inconveniences. As a result, in the production of synthetic quartz glass powder by the sol-gel method, dry silica gel was produced. Before firing the powder, 1
0 to 2,000 μm, preferably 50 to 1,000 μm
By preliminarily classifying to a particle size of m, productivity can be significantly improved, and in terms of quality, during melt molding,
The inventors have found that a quartz glass product having a small amount of bubbles can be obtained, and have reached the present invention.

The present invention will be described in more detail below. The synthetic quartz glass powder targeted in the present invention is obtained by drying silica gel obtained by hydrolyzing alkoxysilane,
It is a quartz glass powder obtained by firing. Hydrolysis of alkoxysilane by the sol-gel method is performed by reacting alkoxysilane with water according to a known method. The alkoxysilane used as a raw material is preferably a C ₁ -C ₄ lower alkoxysilane such as tetramethoxysilane or tetraethoxysilane or an oligomer thereof.

The amount of water used is usually selected from 1 to 10 times the equivalent of the alkoxy groups in the alkoxysilane. At this time, organic solvents such as alcohols and ethers may be mixed if necessary. As alcohol, methanol, ethanol, propanol, butanol, etc.,
Acetone etc. are mentioned as ether. Further, an acid such as hydrochloric acid or acetic acid or an alkali such as ammonia may be used as a catalyst.

As a matter of course, in order to obtain a high-purity silica glass powder, it is necessary that all materials such as the raw material alkoxysilane, water, solvent, etc. introduced into this reaction system are of high purity. is there. To gel the hydrolysis product, you can obtain the gel immediately by heating, but it will gel in several hours even if left at room temperature, so the gelling time can be adjusted by adjusting the degree of heating. It can be adjusted. The gel obtained may be subdivided and then dried. It may be dried and then subdivided.

The degree of drying of the gel is usually from 1 to 10% by weight based on the H ₂ O content, and it is usually carried out by heating the gel to 100 to 200 ° C. in vacuum or in an inert gas. .

The dried silica gel powder produced as described above is added to 10 to 2,000 μm, preferably 50 to
The particle size is adjusted within the range of 1,000 μm. When particles smaller than this range are mixed, they enter the voids between the particles and become densely packed, and the steam generated during firing is
It is not discharged smoothly to the outside of the system, pressure is accumulated inside the powder, and as a result, bumping and powder spillage are likely to occur, which is not preferable. Further, when particles larger than the above particle size range are mixed, the carbon content is not completely oxidized during firing, and unburned carbon is likely to be trapped inside the particles and black foreign matter is likely to occur. Black foreign matter is not preferable because it causes CO or CO ₂ gas during melt molding and causes foaming. As a means for adjusting the particle size, a sieve shaker or the like is sufficient, but it is not particularly limited.

The dried silica gel powder whose particle size has been adjusted in this manner is fired to 1,000 to 1,400 ° C.,
It becomes non-porous and becomes synthetic quartz glass powder, but there is no spilling of powder during firing. Further, since fine powder and coarse particles, which are unnecessary as a product, have been removed in advance, the productivity in the firing step is greatly improved.

[0012]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. [Example 1] Tetramethoxysilane and water in an amount 5 times equivalent thereto were charged in a stirring tank and stirred at a temperature of 30 ° C for 1 hour to obtain a uniform sol solution by hydrolysis reaction. Further, this was transferred to a vinyl chloride vat and left for 24 hours for gelation. The gel was dried for 12 hours using a vacuum dryer at 140 ° C., crushed using a roll mill, and the particle size was adjusted to 125 to 500 μm using a sieve shaker. Silica glass powder 5 thus obtained
Each of 0 kg was charged into 10 quartz crucibles of 550 mmφ × 430 mmH, which were set in an electric furnace having a frontage of 2 × 2 m and a depth of 5 m. Then, the temperature was raised to 1200 ° C. at a heating rate of 200 ° C./Hr, and the temperature was maintained for 20 hours. When the state of the crucible and the powder was examined after natural cooling, no blowout of the powder was found, and the entire amount of the fired product could be recovered. The recovery amount at this time is 410k
and the particle size after firing had shrunk to 100 to 400 μm. In addition, 100 g of the fired product was sampled, and the number of foreign matters of different colors therein was visually counted, and it was found that none.

Comparative Example 1 In Example 1, the dry gel was crushed using a roll mill, and then the particle size was adjusted without adjusting the particle size.
50 pieces for each 50mmφ × 430mmH quartz crucible
The gel was charged in units of kg and baked under the same conditions as in Example 1. When the particle size distribution of the gel charged at this time was measured, 10% or less was 6% and 10 to 50 μm was 8%.
%, 50-100 μm was 13%, 100-500 μm was 67%, and 500 μm or more was 6%. After firing, it was naturally cooled and the state of the crucible and the powder was examined.
About three out of zero crucibles, about one-fifth to one-fourth of the amount of powder charged was blown to the peripheral portion of the crucible. After all, among the powders collected in the crucible, powder having a particle size of 100 to 400 μm was sieved and collected, and the collected amount was 251 kg. This is 1
The firing efficiency per batch was 61% of that of Example 1. Further, when 100 g of the baked product was sampled and the number of black foreign matters was examined in the same manner as in Example 1, it was 6 pieces. When a 15 mmφ × 50 mm ingot was prepared from the fired product containing the black foreign matter by the Bernoulli method using an acid-hydrogen flame, all the black foreign matter became bubbles of 1 mmφ or more.

[0014]

The present invention enables efficient production of high-purity quartz glass powder.

Claims (1)

[Claims] 1. In producing a synthetic quartz glass powder by firing silica gel powder obtained by hydrolysis of tetraalkoxysilane, 10 to 2,000 before firing.
A method for producing a synthetic quartz glass powder, which comprises adjusting the particle size in the range of μm.