JPH07157308A - Method for producing synthetic quartz glass powder - Google Patents

Abstract

(57) [Summary] [Purpose] Quartz glass powder suitable as a raw material for ultra-high purity quartz glass products. [Composition] A synthetic quartz glass powder, characterized in that, when a synthetic silica glass powder is produced by firing a silica gel powder obtained by hydrolysis of tetraalkoxysilane, the silica gel powder is fired while flowing during the firing. Manufacturing method.

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 quartz 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 synthesized has been required.

In recent years, as a highly pure silica source,
Silica glass produced by sol-gel method using alkoxysilane as a raw material has been introduced. For example, JP-A-62-17
Japanese Patent No. 6928 discloses a method in which an alkoxysilane is hydrolyzed in the presence of an acid and an alkali to prepare a gel, which is crushed, dried, and fired to produce a quartz glass powder.

[0004]

In the production of synthetic quartz glass powder by the sol-gel method, alkoxysilane is used as a raw material, which is hydrolyzed and polycondensed to form a wet gel, and alcohol and water produced as by-products are further added. Dry and remove to obtain dry gel. However, 100% of the alkoxy groups do not react, and some remain as bonded alkoxy groups in the dry gel. Furthermore, some of the alcohol by-produced in the reaction is left behind in the dry gel. In fact, the carbon concentration in the dry gel is about 10,000 to 15,000 ppm.

When this dry gel is fired, most of the carbon content is burned and removed, but part of it becomes unburned carbon and may be trapped in the glass to become black foreign matter.
If this black foreign substance is mixed in the product of synthetic quartz powder,
When melted to form crucibles or ingots, CO
And becomes CO ₂ gas and causes foaming. The quartz crucible and core tube containing bubbles obtained in this way have problems such as dimensional stability during high temperature use, bubbles popping when pulling a single crystal, and liquid level fluctuations and crystal defects. It was

[0006]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in order to obtain synthetic quartz glass powder without the above-mentioned inconvenience, and as a result, in the production of synthetic quartz glass powder by the sol-gel method, dried silica gel In the step of firing the powder, it was found that by flowing the silica gel powder, it is possible to obtain a synthetic quartz glass powder with less black foreign matter in the product, and consequently less bubbles during melt molding, and arrived at the present invention. did.

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 equivalents 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 ammonium may be used as a catalyst. As a matter of course, in order to obtain a high-purity quartz glass powder, it is necessary that all the raw materials used here such as alkoxysilane, water, and solvent, which are introduced into this reaction system, have a high purity.

In order to gel the hydrolysis product, the gel can be obtained immediately by heating, but even if it is left at room temperature, it will gel in a few hours. Therefore, by adjusting the degree of heating, the gel can be obtained. The aging time can be adjusted. The obtained gel may be subdivided and then dried, or may be dried and subdivided. The particle size of dry silica gel powder is 6
It is 0 to 900 μm, preferably 80 to 800 μm.
Regarding the degree of drying of the gel, the H ₂ O content is usually 1
10 to 10% by weight, 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 fired under the specific firing conditions described below. That is, firing is performed while flowing the silica gel powder in an air atmosphere or an atmosphere having a higher oxygen concentration. This flow may be performed for the entire period of firing, or may be performed effectively only in a specific temperature region in consideration of the requirements described below. For such temperature range,
1000 ° C or less at which the gel becomes non-porous, especially 400 to 800
If the temperature is in the range of ° C and the oxygen temperature is raised in this range, the effect of the present invention can be improved and the firing time can be shortened.
For example, charge silica gel powder into a cylindrical quartz container,
There is a method of flowing the powder layer by rotating the cylindrical container. However, as a method of flowing the powder,
The method is not particularly limited to this method. For example, a method of charging silica gel powder into a crucible and bubbling air or the like from the lower layer portion thereof can be used. Normally, when this silica gel powder is calcined in a stationary state, oxygen is not sufficiently diffused to the lower layer of the powder, the carbon-containing material is not completely oxidized, and it becomes unburned carbon to give a black color. It may cause foreign matter. On the other hand, by constantly flowing the powder layer, each silica gel particle was brought into sufficient contact with oxygen, and it was possible to significantly suppress the generation of black foreign matter. here,
The temperature rising rate during firing is preferably 1000 ° C./Hr or less, and more preferably 500 ° C./Hr or less, particularly at 800 ° C. or less before sealing the gel. When the temperature is raised more rapidly than this, the effect of suppressing the generation of black foreign matter cannot be expected so much because the gel seals before the carbon is completely oxidized. Also, on the way, 4
It is also effective to hold the material in the range of 00 to 800 ° C. for about 0.5 to 5 hours. In this case, it is preferably 1.5 to 5 hours in an air atmosphere and 0.5 to 3 hours under a high oxygen concentration. Thus, finally, 1000-140
The mixture is baked to 0 ° C. to make the gel non-porous to obtain synthetic silica glass powder.

The quartz glass powder thus obtained is
Compared to the product obtained by firing without flowing the powder, the amount of black foreign matter is extremely small. When this silica glass powder containing very few black foreign matters is melt-molded, ingots and crucibles with very few bubbles can be produced.

[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. After drying this gel for 12 hours using a vacuum dryer at 140 ° C., the particle size was adjusted to a particle size of 100 to 500 μm. 1.5 kg of the silica glass powder thus obtained was charged into a quartz glass inner tube of a rotary kiln type electric furnace. 2 rpm while supplying air at 101 / min from the left side of this quartz tube
Rotate the quartz tube at 12 ° C at a heating rate of 200 ° C / Hr.
The temperature was raised to 00 ° C. and the temperature was maintained for 10 hours. After natural cooling, the synthetic quartz glass powder was taken out, and the number of black foreign matters therein was visually examined to find that it was eight. Further, this powder was melted using a Bernoulli type melting device by heating with an oxygen-hydrogen flame to prepare an ingot of 12 mmφ × 50 mm, and the foaming state was examined. As a result, one very small bubble was found.

Example 2 In Example 1, the firing conditions were 200 ° C./hr and 60
After raising the temperature to 0 ° C. and holding at this temperature for 2 hours, the temperature was further raised to 1200 ° C. at 200 ° C./Hr and the
It was carried out by holding for 0 hour. Then, when the number of black foreign matters in the synthetic quartz glass powder obtained in the same manner was visually inspected, it was one. Furthermore, when a 12 mmφ × 50 mm ingot was produced from this powder by the Bernoulli method, no bubbles were found.

Comparative Example-1 A dried silica gel powder was prepared in the same manner as in Example 1,
1.5 kg was charged into a 150 mmφ × 150 mmH quartz glass crucible. At this time, the powder bed height is 120 m
It was m. This crucible was set in an electric furnace, and air was flowed on the surface of the crucible at a rate of 101 / min at 200 ° C.
The temperature was raised to 1200 ° C. with / Hr, and the temperature was maintained for 10 hours. After natural cooling, the number of black foreign matters in the obtained synthetic quartz glass powder was visually inspected and found to be 45 / kg. Furthermore, by this Bernoulli method with this powder, 12 mm
When a φ × 50 mm ingot was produced, a very large number of bubbles (including 3 large bubbles of 0.5 mmφ or more) were observed.

[0015]

Industrial Applicability According to the present invention, it is possible to obtain a silica glass powder containing less black foreign matter.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hiroaki Nagai 1-1 Kurosaki Shiroishi, Hachimansai-ku, Kitakyushu City Mitsubishi Kasei Co., Ltd. Kurosaki Plant

Claims (2)

[Claims] 1. A synthetic quartz glass powder produced by hydrolyzing a tetraalkoxysilane, which is calcined while flowing the silica gel powder when the synthetic silica glass powder is produced. Glass powder manufacturing method. 2. The method according to claim 1, wherein the silica gel powder is made to flow at 400 to 800 ° C. in the firing step.