JPH06329406A - Production of synthetic silica glass powder - Google Patents

Abstract

PURPOSE:To obtain silica glass powder suitable as a raw material for ultrahigh- purity silica glass products. CONSTITUTION:The synthetic silica glass powder can be obtained by baking silica powder produced by hydrolyzing a tetraalkoxysilane in the presence of 1-10mol%, based on the tetraalkoxysilane, of fine silica powder 0.01-100mum in particle diameter.

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, synthetic silica glass powder of high purity has been required.

In recent years, silica glass produced by a sol-gel method using alkoxysilane as a raw material has been introduced as a highly pure silicic acid. For example, JP-A-62-1769
Japanese Patent Publication No. 28 discloses a method of producing a silica glass powder by hydrolyzing an alkoxysilane in the presence of an acid or an alkali to prepare a gel, crushing and drying the gel, and then firing the silica glass powder.

[0004]

SUMMARY OF THE INVENTION Synthetic quartz glass powder is
It is obtained by baking a dry gel obtained by hydrolyzing, drying and crushing an alkoxysilane to 1,000 to 1,300 ° C. The dry gel before firing is a porous body having a specific surface area of 600 to 700 m ² / g and pores having an average of 1 to 5 nm. Many OH groups on this surface,
It has an unreacted alkoxy group. When this dry gel is baked, a combustion reaction of unreacted alkoxy groups and by-produced alcohol occurs at 400 to 600 ° C.,
At around 00 to 800 ° C, dehydration condensation of surface OH groups starts and pores begin to shrink, and completely disappear at 1,000 to 1100 ° C. However, at this time, not all the OH groups have been eliminated, and the silanol groups are left behind inside the non-porous glass. The presence of silanol groups in the glass causes a decrease in the viscosity of the crucible, core tube and the like during high temperature use. Therefore, the silanol group content should be as low as possible.

However, the dry gel is 1,000 to 1,
When it becomes non-porous at 100 ° C., the silanol groups inside can no longer be eliminated except for diffusing into the glass surface inside the SiO ₂ network structure in the solid. This solid diffusion rate is very slow, and it takes a high temperature and a long time to reduce the silanol concentration after making it non-porous.

[0006]

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, and as a result, in the production of synthetic quartz glass powder by the sol-gel method, hydrolysis was performed. In the step, 1 to 10 mol%, preferably 3 to 8 mol% based on tetraalkoxysilane
Particle size of 0.01 to 100 μm (preferably 0.05 to 8)
0 μm) by the presence of finely divided silica,
The inventors have found that it is possible to obtain a synthetic silica glass powder having a low silanol concentration in a shorter firing time as compared with the case of not present, and have reached the present invention.

A method of adding finely divided silica during the hydrolysis of tetraalkoxysilane is, for example, as described in JP-A-59-92924, to prevent cracking or cracking of a dry gel at the time of forming a molded body. However, the purpose of the present invention is to reduce the silanol concentration in the silica powder by adding the finely divided silica to the crushed synthetic quartz glass powder instead of the compact. . Therefore, the present invention is completely different from the above method in both object and configuration.

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.

Fine silica powder is present in the system in which the alkoxysilane is reacted with water. The particle size of the finely divided silica to coexist is 0.01 to 100 μm, preferably 0.1 to 80 μm. This particle size
If it is too small, the effect of reducing the concentration of silanol is hardly seen, and if it is too large, the dispersibility of particles during hydrolysis deteriorates, or cracks occur inside the particles when the gel shrinks during drying and baking. This is not preferable because it causes problems such as a decrease in the yield of a certain product grain size. The amount of finely divided silica added is 1 to 10 mol with respect to the alkoxysilane.
% (Preferably 3 to 8 mol%) is preferable. If this addition amount is too small, almost no effect of reducing the silanol concentration can be seen, and if it is too large, the gel strength becomes weak, it easily collapses, and there is a problem that the yield of a certain product particle size decreases, which is not preferable. . As the fine powder silica used in the present invention, spherical silica produced by a monodispersion method by a sol-gel method, silica glass powder pulverized by a jet mill or the like, or when producing silica glass powder having a constant particle size Examples thereof include recycling of undersized products that have been classified, but are not limited thereto. The fine silica powder may be in the form of a porous gel or in the non-porous state, but it is preferable to use a calcined product.

In addition, as a matter of course, in order to obtain high-purity silica glass powder, the raw materials used in this reaction such as alkoxysilane, water, solvent, and finely divided silica are all highly pure. Is preferred. In order 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 obtained gel may be subdivided and then dried, or may be dried and subdivided. The particle size of the dried silica gel powder is 60 to 900 μm,
It is preferably 80 to 800 μm.

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. . At this time, it is desirable that the carbon content after the drying treatment be 0.2% or less in order to prevent black foreign matter from remaining in the silica glass powder due to unburned carbon as a result of firing.

The dried silica gel powder produced as described above is fired in the temperature range of 1,000 to 1,400 ° C. to be non-porous to obtain a synthetic quartz glass powder. At this time, normally, when no finely divided silica is added, the porosity becomes remarkable at about 800 ° C., and the porosity becomes almost completely at about 1000 ° C. However, when the finely powdered silica as shown in the above conditions is added, the porosity-free temperature rises by about 100 to 200 ° C., although there is a difference depending on the particle size of the fine powder. As a result, since the porous state is maintained up to a higher temperature, silanol inside the particles is easily released, and as a result, silica glass powder having a low silanol concentration is obtained. It is considered that the reason why the non-porous temperature rises is that the presence of the fine particles hinders the contraction of the gel.

The thus-obtained synthetic quartz glass powder can significantly improve the firing process of the dry gel required for reducing the silanol concentration, and can be used in a diffusion furnace tube or a diffusion furnace tube that requires high-temperature strength. It becomes possible to inexpensively manufacture various ultra-high-purity silica glass products used in the semiconductor manufacturing field such as jigs and crucibles for pulling a single crystal.

[0015]

EXAMPLES The present invention will be described in detail with reference to the following examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Example 1 Tetramethoxysilane 1690 g and water 1000 in a stirring tank
Then, 54 g (8 mol% with respect to tetramethoxysilane) of spherical silica having a diameter of 0.1 μm (“ESQUATS 2001” manufactured by Nippon Steel Chemical Co., Ltd.) was charged, and the mixture was stirred at a temperature of 30 ° C. for about 2 hours. After the viscosity of the sol in the stirring tank increased and the stirring blade stopped, the sol was allowed to stand for about 1 hour for complete gelation. This gel was dried for 10 hours using a vacuum dryer at 200 ° C., and then the particle size was adjusted to a particle size of 100 to 500 μm. This dry silica gel powder 100
g was charged into a cylindrical quartz container of 80 mmφ × 60 mmH and set in an electric furnace. Then, while supplying air having a dew point of -50 ° C at a rate of 1 liter / min, the temperature was raised to 1220 ° C at a rate of 200 ° C / Hr, and the temperature was maintained at 1220 ° C for 10 hours for firing. 200 after natural cooling
The particle size was adjusted to ˜300 μm, and the silanol concentration in the particles was measured by the infrared absorption method. As a result, it was 16 ppm.

Example 2 In Example 1, the addition amount of spherical silica having a diameter of 0.1 μm (“Esquires 2001”, manufactured by Nippon Steel Chemical Co., Ltd.) was 34.
The silanol concentration in the particles having a particle diameter of 200 to 300 μm was 44 ppm when g (5 mol% relative to tetramethoxysilane) was used.

Example 3 In Example 1, 54 g of unburned dry gel fine powder having a particle size of 10 to 100 μm (average particle size of 60 μm) (based on tetramethoxysilane) was used in place of the spherical silica having a diameter of 0.1 μm. Particle size of 200 to 8 mol%)
The silanol concentration in the 300 μm particles was 28 ppm.

Comparative Example 1 Particle size of 2 in Example 1 in the case where the reaction was carried out in a system containing only tetramethoxysilane and water without adding finely divided silica.
The silanol concentration in the particles of 00 to 300 μm is 98 p
It was pm.

From the above results, the presence of finely divided silica during hydrolysis has a great effect on reducing the silanol concentration, which leads to a significant increase in the efficiency of the firing process during the production of the synthetic quartz glass powder, and the high temperature strength. It is possible to provide an ultra-high-purity silica glass product used in the semiconductor manufacturing field, which is required, at low cost.

[0021]

[Table 1]

[0022]

Industrial Applicability According to the present invention, it is possible to obtain quartz glass powder suitable as a raw material for high-purity quartz glass products.

Claims (1)

[Claims] 1. When producing a synthetic quartz glass powder by calcining silica powder obtained by hydrolyzing tetraalkoxysilane, a particle size of 1 to 10 mol% based on tetraalkoxysilane is used in the hydrolysis step. .01-10
A method for producing a synthetic quartz glass powder, characterized in that fine silica powder of 0 μm is present.