JP3847819B2 - Method for producing synthetic quartz glass powder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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. or higher. 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 based on alkoxysilane 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, it has been found that when the operation is continuously performed on a mounting production line having a large scale, a large amount of black foreign matter with carbon remaining after firing is mixed 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 This causes problems such as dimensional stability at the time of high temperature use, bubbles popping when the single crystal is pulled up, liquid level fluctuation, 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. In addition, from the viewpoint of safety, it is not preferable that toxic alkoxysilane remains, and it is desired to proceed the hydrolysis reaction completely.
[0003]
[Means for Solving the Problems]
In order to obtain a synthetic quartz glass powder having no disadvantages as described above, the present inventors have intensively studied. As a result, in the hydrolysis process, if the time from the completion of raw material charging to the gelation is short, firing is performed. Later, it was found that a large number of black foreign matters were generated, and the present invention was reached. That is, according to the present invention, when the silica gel powder obtained by hydrolysis of alkoxysilane is baked to produce synthetic quartz glass powder, in the hydrolysis step, at least after alkoxysilane and water are charged, it is gelled. And a method for producing synthetic quartz glass powder, wherein a reactor with a jacket is used as a reaction vessel .
[0004]
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.
[0005]
As the alkoxysilane used as a raw material, Cl to C4 lower alkoxysilanes such as tetramethoxysilane and tetraethoxysilane or oligomers thereof are preferable because black foreign matters are not generated in the resulting synthetic quartz glass powder.
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. .
[0006]
In the present invention, in this hydrolysis step, at least 10 minutes from the completion of charging both alkoxysilane and water to gelation, and using a jacketed reactor as a reaction vessel It has been found that the amount of black foreign matter contained in the product after firing is reduced. The mechanism for obtaining such an effect is not clear, but is considered to be due to the following mechanism.
[0007]
If the time from the completion of the raw material charging to the gelation is short, the alkoxysilane hydrolysis reaction will not proceed sufficiently and gelation will occur. For this reason, it is considered that a wet gel having the intended composition cannot be obtained, or that unreacted organic groups remain in the wet gel. Such a gel that has absorbed unreacted raw materials or a gel that has unreacted organic groups is considered to carbonize the organic groups and become black foreign matter after firing. In order to suppress the formation of this black foreign matter, special operations such as extending the firing time or increasing the oxygen concentration during firing are required to completely burn the residual carbon of the organic group. Will significantly reduce the performance.
[0008]
In addition, the toxic alkoxysilane remains unreacted and is taken into the wet gel and discharged as it is. In particular, tetramethoxysilane is known to cause damage to the human body when exposed to its vapor, such as corneal detachment and bronchitis. Even if such unreacted material remains in such a small amount, it is preferable for safety. There is nothing.
[0009]
In addition, the time from the completion of preparation to gelation is not particularly limited as long as it is 10 minutes or longer, and even if a long time is required, the physical properties of the obtained gel and the synthetic quartz powder obtained by firing the gel are reduced. Absent. Therefore, in consideration of productivity, it is practical to set the time within several hours from the preparation, and particularly preferably within one hour.
Regarding the means to control the time from the completion of raw material charging to gelation, the liquid temperature in the reaction vessel is kept low until the raw material charging is completed, the method of slowing the hydrolysis reaction rate and the raw material charging time are shortened, A method of gaining time until gelation can be appropriately employed.
[0010]
In addition, the time when the contents are gelled can be easily confirmed visually. In general, immediately before gelation, the liquid is in a bumping state, and when the bubbles move around, the viscosity suddenly increases and the behavior of the bubbles stops and gels can be observed.
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.
[0011]
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.
When the raw material is charged and the hydrolysis reaction is performed according to the method described above, the amount of black foreign matter contained in the fired product can be suppressed, and the safety is improved.
[0012]
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.
[0013]
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, and 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.
[0014]
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 a very small amount of black foreign matter contained in the product, and when such synthetic quartz glass powder is melt-molded, ingots and crucibles with very few bubbles can be produced. .
[0015]
Hereinafter, the present invention will be described more specifically with reference to examples.
[0016]
【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 temperature of the hot water flowing through the jacket was 45 ° C. Thereafter, the stirring was stopped when the sol became uniform, and the contents were allowed to stand for 30 minutes. When the change of the contents was visually observed from the glass window of the reaction vessel, it gelled 40 minutes after the completion of the preparation. After that, the rotation of the stirring blade was started again, the valve installed at the bottom of the reactor was opened, and the fist-sized massive gel was taken out from the reactor.
[0017]
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.
[0018]
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 or five black foreign matters were detected respectively.
Example 2
In the same apparatus as in Example 1, 15 kg of ultrapure water was charged, 25 kg of tetramethoxysilane was charged for 25 minutes, and then stirring was started at 20 rpm. The temperature of the hot water flowing through the jacket was 45 ° C. When uniform sol was obtained, stirring was stopped and the contents were allowed to stand for 30 minutes. Gelation occurred 25 minutes after the completion of the preparation.
[0019]
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 and 25 kg of tetramethoxysilane was charged for 15 minutes, and then stirring was started. The jacket temperature was 65 ° C. When uniform sol was obtained, stirring was stopped and the contents were allowed to stand for 30 minutes. Gelation occurred 13 minutes after the completion of the preparation.
[0020]
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, 25 kg of tetramethoxysilane was charged for 3 minutes, and stirring was started at 20 rpm. The temperature of warm water flowing through the jacket was 65 ° C. When uniform sol was obtained, stirring was stopped and the contents were allowed to stand for 30 minutes. Gelation occurred 15 minutes after the completion of the preparation.
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 at 20 rpm. Thereafter, 25 kg of tetramethoxysilane was charged in 25 minutes. The temperature of warm water flowing through the jacket was 40 ° C. When uniform sol was obtained, stirring was stopped and the contents were allowed to stand for 30 minutes. Gelation occurred 5 minutes after the completion of the preparation.
[0021]
Subsequent operations were the same as in Example 1.
As a result, 26 black foreign objects were detected in 50 g of the product. In addition, as a result of repeating the operation after 15 kg of ultrapure water was charged, 34 black foreign objects were detected.
[0022]
【The invention's effect】
According to the present invention, synthetic quartz glass powder suitable for a raw material for high-purity quartz glass products can be obtained.

Claims (6)

In the production of synthetic quartz glass powder by firing the silica gel powder obtained by hydrolysis of alkoxysilane, the time from the completion of charging at least alkoxysilane and water to the gelation in the hydrolysis step is 10 minutes. A method for producing synthetic quartz glass powder characterized by using a reactor with a jacket as a reaction vessel . The method for producing synthetic quartz glass powder according to claim 1, wherein the reaction vessel used in the hydrolysis step has a physical stirring means inside thereof. 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 used in the hydrolysis step is 150 liters or more. The method for producing synthetic quartz glass powder according to any one of claims 1 to 4, wherein tetraalkoxysilane is used as the alkoxysilane. The method for producing synthetic quartz glass powder according to claim 5, wherein tetramethoxysilane is used as the tetraalkoxysilane.