JP3847818B2 - Method for producing synthetic quartz glass powder - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a synthetic quartz glass powder suitable for use as a raw material for a synthetic quartz glass powder used in the field of semiconductors and optical cables and the like, particularly an ultra-high purity quartz glass product for semiconductor production used in a high temperature region of 1000 ° C. It is to provide.
Conventionally, crucibles and jigs for manufacturing semiconductor single crystals have been manufactured by melting natural quartz powder obtained by pulverizing natural quartz. It was not satisfactory from the viewpoint of purity. In particular, high-purity single crystals required for higher performance in the semiconductor industry will adversely affect the performance of semiconductors when mixed with metal impurities. Etc. cannot be used. For this reason, recently, high-purity quartz glass powder by synthesis has become necessary. In recent years, silica glass based on a sol-gel method using alkoxysilane as a raw material has been introduced as a highly pure silicic acid source. For example, in JP-A-62-176928, alkoxysilane is hydrolyzed in the presence of an acid or alkali to prepare a gel, which is pulverized, dried and then fired to produce a synthetic quartz glass powder. The method is shown.
[0002]
[Problems to be solved by the invention]
In the production of synthetic quartz glass powder by the sol-gel method, first, alkoxysilane is used as a raw material, which is hydrolyzed and polycondensed to form a wet gel, and by-produced alcohol and water are removed by drying to obtain a dry gel. This is fired to produce synthetic quartz glass powder. However, when actually operating on a large-scale mounting production line, we faced the problem that a large amount of black foreign matter was generated in the synthetic quartz powder product. When this black foreign substance is mixed in a synthetic quartz powder product, when it is melted to form a crucible or ingot, it becomes CO or CO ₂ gas, causing foaming. Foamed quartz crucibles and furnace core tubes are It is known to cause problems such as dimensional stability when used at high temperatures, and bubbles that bounce when the single crystal is pulled up, causing liquid surface fluctuations and crystal defects. However, since the mechanism that suppresses the generation of this black foreign substance has not been sufficiently elucidated, it has reached today without being able to elucidate what is the control point in manufacturing. Especially in a large scale production line, unlike the lab scale, it is difficult to control the temperature and hydrolysis reaction, and because large equipment is used, there is contamination from shaft seals, valves, etc. This is not easy, and has been a major obstacle to mass production of synthetic quartz powder.
[0003]
[Means for Solving the Problems]
In order to efficiently obtain a synthetic quartz glass powder having no disadvantages as described above, the present inventors have conducted intensive studies, and as a result, at least until alkoxysilane and water are completely charged in the raw material preparation in the hydrolysis step. The synthetic quartz glass powder that keeps the liquid temperature of the raw material charged in the reaction vessel at 50 ° C. or lower, preferably 40 ° C. or lower, and suppresses the generation of bubbles during melt molding by using a reactor with a jacket as the reaction vessel. The present invention was reached.
[0004]
That is, in the present invention, when a silica gel powder obtained by hydrolysis of an alkoxysilane by hydrolysis of a hydrolyzable silicon compound is baked to produce a synthetic quartz glass powder, at least in the raw material preparation in the hydrolysis step, Until the preparation of silane and water is completed, the liquid temperature of the raw material charged in the reaction vessel is kept at 50 ° C. or lower, and a jacketed reactor is used as the reaction vessel, a method for producing synthetic quartz glass powder, Exist.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail. The synthetic quartz glass powder of the present invention is obtained by drying and firing a silica gel obtained by hydrolyzing an alkoxysilane. Hydrolysis of alkoxysilane by the sol-gel method is performed by reacting alkoxysilane with water.
[0006]
The alkoxysilane used as a raw material is preferably a C4 to C4 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 alkoxy groups in alkoxysilane.
Under the present circumstances, you may mix organic solvents, such as alcohol and ethers, as needed. Examples of the alcohol include methanol, ethanol, propanol, and butanol, and examples of the ether include acetones. Further, an acid such as hydrochloric acid or acetic acid or an alkali such as ammonia may be used as a catalyst. In order to obtain high-purity synthetic quartz glass powder, it is preferable that all the materials used, such as raw material alkoxysilane, water, solvent, etc., have high purity. Although the gel can be obtained immediately by heating the hydrolysis product, it gels in several hours even if it is left at room temperature, so the gelation time can be adjusted by adjusting the degree of heating. .
[0007]
In order to increase productivity, it is effective to shorten the hydrolysis reaction time. Conventionally, it is common to finish the preparation of raw materials at a normal liquid temperature, but this tends to increase the reaction time because the initial temperature of the reaction decreases. Naturally, the higher the temperature at the end of the raw material charging, the shorter the reaction time and the higher the production efficiency. However, as will be described later, it has been newly found out by the present inventors that finishing the raw material at a certain temperature or more leads to a reduction in the reaction time, but worsens the product quality. Specifically, the temperature at the end of the raw material charging is 50 ° C. or less, preferably 40 ° C. or less, usually 20 ° C. or more, and more preferably 30 to 40 ° C. When the raw material liquid temperature is too low, the hydrolysis reaction time becomes long and the productivity is lowered. On the other hand, if it is too high, a large amount of black foreign matter is generated in the product, making it unsuitable as a raw material for quartz glass products. The mechanism by which black foreign matter is likely to be generated when the temperature at the end of raw material charging is too high is not clear, but is presumed to be due to the following mechanism. When the temperature at the end of raw material charging is increased, the hydrolysis reaction proceeds rapidly and a non-uniform gel is generated. In the non-uniform gel, hydrolysis reaction does not proceed sufficiently, and a large amount of unreacted organic groups remain. This cannot be removed during firing, and becomes unburned carbon. It is thought that it remains in the powder and becomes a black foreign substance. In addition, when the temperature at the end of the raw material charging is increased, volatile components such as alcohol and alkoxysilane may evaporate during the hydrolysis reaction, which may have some influence on the gel composition.
[0008]
Control of the temperature at the end of raw material charging can be performed by adjusting the jacket temperature of the reaction vessel being charged or the temperature of the raw material before charging, but by using the heat of reaction by controlling the raw material charging speed. The temperature of the charged raw material can also be adjusted.
Thus, by controlling the temperature at the end of raw material charging to 50 ° C. or less, preferably 40 ° C. or less, usually 20 ° C. or more, more preferably 30 to 40 ° C., it is included in the product after firing. Synthetic quartz glass powder with an extremely small amount of black foreign matter can be obtained.
[0009]
The reaction vessel used in the hydrolysis step is not particularly limited, but a vessel having physical stirring means such as a stirring blade and a stirring blade is preferable because stirring is easy and a uniform gel can be easily obtained. The shape and the like of these physical stirring means are not particularly limited as long as the contents can be stirred. Moreover, since it is easy to discharge | emit the obtained gel, what is called a ribbon type stirring blade is especially preferable.
[0010]
Further, the volume of the reaction vessel is not particularly limited, but the present invention is particularly effective when a large-capacity vessel of 150 liters or more is used.
The gel thus obtained is a wet gel containing a large amount of liquid components such as moisture and solvent. The wet gel is preliminarily dried or pulverized as it is to prepare an arbitrary particle size. Since the particle size distribution in the gel governs the particle size of the synthetic quartz glass powder obtained by firing the silica gel, the particle size distribution of the target synthetic quartz glass powder is expected, and the shrinkage of the particles due to drying and firing is taken into consideration. What is necessary is just to determine the optimal particle size of.
[0011]
Usually, a wet gel of 1000 microns or less, preferably 900 microns or less, is heated at 100 ° C. or more to remove moisture and organic components such as alcohol generated by the hydrolysis reaction, and a moisture content of 30 wt. % Or less, preferably 20% by weight or less, more preferably about 1 to 10% by weight. Prior to this heating or classification after heating, if the particle size distribution of the dry gel is set to about 100 to 500 microns, the particle size distribution of the synthetic quartz glass powder obtained by firing the gel is easily controlled to a desired range. be able to.
[0012]
The dry gel thus obtained is further baked to remove residual carbon and silanol and close the pores to obtain synthetic quartz glass powder.
The synthetic quartz glass powder obtained by the present invention has an extremely small amount of black foreign matter contained in the product, and when such synthetic quartz glass powder is melt-molded, an ingot or crucible with very few bubbles can be produced. .
[0013]
Hereinafter, the present invention will be described more specifically with reference to examples.
[0014]
【Example】
Example 1
After charging 15 kg of ultrapure water into a jacketed horizontal cylindrical reactor having a ribbon type stirring blade, stirring was started at 20 rpm. Thereafter, 25 kg of tetramethoxysilane was charged in 3 minutes. The liquid temperature after preparation was 32 ° C. Hot water of 45 ° C. was passed through the jacket, and when the mixture became uniform sol, stirring was stopped and the contents were allowed to stand for 30 minutes. Thereafter, the rotation of the stirring blade was started again, the valve provided at the bottom of the reactor was opened, and the massive gel was taken out from the reactor.
[0015]
This massive gel was pulverized with a SUS304 corn mill type pulverizer, and the resulting powdered gel was dried at 200 ° C. for 5 hours using a vacuum dryer to obtain a dry gel. Subsequently, this dry gel was classified and adjusted to a particle size of 106 to 500 μm. 100 g of this dry gel classified product was charged in a quartz glass container, heated in air to 1000 ° C. over 2 hours, held at 1000 ° C. for 10 minutes, then taken out and rapidly cooled. The number of black foreign substances in the fired product was visually examined.
As a result, two black foreign objects were detected in 50 g of the product (about 5 million particles). Further, when the same operation was further repeated twice, three and five black foreign matters were detected, respectively.
Example 2
In the same apparatus as in Example 1, 15 kg of ultrapure water was charged, then 25 kg of tetramethoxysilane was charged for 25 minutes, and stirring was started at 20 rpm. The liquid temperature after preparation was 42 ° C. Hot water of 45 ° C. was passed through the jacket, and when the mixture became uniform sol, stirring was stopped and the contents were allowed to stand for 30 minutes. Subsequent operations were performed in the same manner as in Example 1. As a result, four black foreign objects were detected in 50 g of the product.
Example 3
In the same apparatus as in Example 1, 15 kg of ultrapure water was charged, then 25 kg of tetramethoxysilane was charged for 15 minutes, and stirring was started at 20 rpm. The liquid temperature after preparation was 38 ° C. The jacket temperature was 65 ° C. Then, when it became uniform sol, stirring was stopped and the contents were left still for 30 minutes. Subsequent operations were performed in the same manner as in Example 1. As a result, six black foreign objects were detected in 50 g of the product.
Example 4
In the same apparatus as in Example 1, 15 kg of ultrapure water was charged and 25 kg of tetramethoxysilane was charged for 3 minutes, and then stirring was started. The liquid temperature after preparation was 36 ° C. Hot water of 45 ° C. was passed through the jacket, and when the mixture became uniform sol, stirring was stopped and the contents were allowed to stand for 30 minutes. Subsequent operations were performed in the same manner as in Example 1. As a result, three black foreign objects were detected in 50 g of the product.
Comparative Example 1
In the same apparatus as in Example 1, 15 kg of ultrapure water was charged and stirring was started. Thereafter, 25 kg of tetramethoxysilane was charged in 25 minutes. The liquid temperature after preparation was 55 ° C. The jacket temperature was 40 ° C. When uniform sol was obtained, stirring was stopped and the contents were allowed to stand for 30 minutes. Subsequent operations were performed in the same manner as in Example 1. As a result, 26 black foreign objects were detected in 50 g of the product. As a result of repeating the same operation, 34 black foreign objects were detected.
[0016]
【The invention's effect】
According to the present invention, a synthetic quartz glass powder suitable for a raw material of a high purity quartz glass product can be obtained.

Claims (6)

When the silica gel powder obtained by hydrolysis of alkoxysilane was baked to produce synthetic quartz glass powder, it was charged into the reaction vessel until at least the alkoxysilane and water were charged in the raw material preparation in the hydrolysis step. A method for producing synthetic quartz glass powder, characterized in that the liquid temperature of the raw material is kept at 50 ° C. or lower and a reactor with a jacket is used as a reaction vessel . The method for producing synthetic quartz glass powder according to claim 1, wherein the reaction vessel used for the hydrolysis has a physical stirring means inside. The method for producing synthetic quartz glass powder according to claim 2, wherein the physical stirring means is a ribbon type stirring blade. The method for producing synthetic quartz glass powder according to any one of claims 1 to 3, wherein the internal volume of the reaction vessel is 150 liters or more. The method for producing synthetic quartz glass powder according to any one of claims 1 to 4, wherein the alkoxysilane is tetraalkoxysilane. The method for producing synthetic quartz glass powder according to claim 5, wherein the tetraalkoxysilane is tetramethoxysilane.