JPH0280329A - Production of synthetic quartz glass - Google Patents

Abstract

PURPOSE:To produce synthetic quarts glass having extremely small OH group content by producing silica having a particle size within a predetermined range by hydrolyzing methyl silicate dissolved in methanol with NH3 as hydrolyzing agent, concentrating and then drying the hydrolyzed product, oxidizing the product by heating, sealing the pores and vitrifying, followed by crushing, then pulverizing and melting by heating. CONSTITUTION:After separating solid from liquid, in the silica having 200-3000nm average particle size which has been obtd. by the above discribed sol-gel process, the solid is concentrated and dried then heated in O2 atmosphere at about 500 deg.C to remove org. matters. The pores of the silica freed of org. matters are sealed and vitrified by heating at about 1500 deg.C in vacuum, etc. Thus, transparent lamps having almost a same specific gravity as ordinary quartz glass is obtd. The lump of glass is pulverized with a ball mill, etc., and the particle size of the pulverized product is adjusted to 50-200 mesh average particle size, and the product is washed with acid and melted by heating at >=1700 deg.C in vacuum, etc. As the result synthetic quartz glass having, for example, <=1ppm OH group content, and for example, 1-4X10<10> poise viscosity at 1400 deg.C is obtd.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for producing synthetic quartz glass, and in particular to a crucible material for pulling silicon single crystals, since it has a low OH group content of less than ippm and high viscosity at high temperatures. This article relates to a method for manufacturing synthetic quartz glass by the sol-gel method, which is useful as a semiconductor material.6 (Prior technology and issues to be solved) Crucibles for pulling semiconductor materials, especially silicon single crystals, have high heat resistance at high temperatures. Products made of natural quartz glass are widely used due to their superior properties. However, since natural quartz glass contains impurities, a decrease in yield has become a problem due to the recent increase in the integration density of semiconductor memories. Purification is desired.

For this reason, it is being considered to make this crucible out of highly pure synthetic silica glass, but it is possible to: Hydrolyze silicon tetrachloride in an oxyhydrogen flame to produce fine silica particles, which are then melted to form silica glass. In this method, there is one OH group in the glass.
．． There is a problem that OOOppm also remains, the high temperature viscosity is low, and foaming occurs at high temperatures in a vacuum. For this, silica is produced by hydrolyzing alkoxysilane in an alcohol solvent.
This is melted to obtain synthetic quartz, a so-called sol.
The gel method is also being considered, and although this has the advantage of being able to obtain high-purity products at low cost, the OH
The base tends to remain.

It has the disadvantage that it takes a long time to produce, and it is difficult to obtain a product with particularly high viscosity at high temperatures.

(Means for Solving the Problems) The present invention relates to a method for producing synthetic quartz glass that overcomes these disadvantages, and this invention involves hydrolyzing methyl silicate in a methanol solvent using ammonia as a solvent to obtain particles with a particle size of 200 mm. After preparing silica of ~3,000 nm, concentrating it, drying it, heating and oxidizing it, closing the pores, vitrifying it, and crushing it to adjust the particle size.

1.It is characterized by melting at a temperature of 700°C or higher.

That is, the present inventors investigated various methods for producing synthetic quartz glass that can be used as a crucible material for pulling silicon single crystals, and found that when methyl silicate is hydrolyzed in a methanol solvent using ammonia as a catalyst, the particle size is 200 mm. ~3.00OnI11 silica is obtained;
This silica is concentrated, dried, heated and oxidized to further close the pores, and vitrified to obtain a quartz glass lump with few OH groups.
They discovered that synthetic quartz glass with high high temperature viscosity can be obtained by melting and vitrifying it at 700°C or higher, and completed research on each process to complete the present invention.

This will be explained in detail below.

Although the method of the present invention is based on a sol-gel method, methyl silicate is used as a starting material in the method of the present invention. That is, in the conventionally known sol-gel method, ethyl silicate is usually used as a starting material, and this is hydrolyzed in an ethanol solvent using ammonia or hydrochloric acid as a catalyst.
In this case too, it is 500nl! Silica with a particle size of about 1 is obtained, which is dried and sintered at 1,050°C, and further silica with a particle size of about 1,
Although transparent quartz glass can be obtained by melting and vitrifying it at 500° C., it has been found that this quartz glass has the disadvantages of having a high OH group content and low high-temperature viscosity.

However, if this ethyl silicate is replaced with methyl silicate, it is advantageous in terms of cost, and when this is hydrolyzed in a methanol solvent using ammonia as a catalyst, this hydrolysis reaction starts immediately after the methyl silicate is added, and the silica is instantly converted into methyl silicate. The advantage is that the generation of The particle size of the silica obtained by this hydrolysis can be controlled by the weight ratio of methanol, ammonia, and methyl silicate used for this N, reaction temperature, and stirring speed.
In order to produce silica powder with a low OH group content, it is necessary to have an average particle size of 200 nm or more, and in order to dry it into a lump, a certain degree of fineness is required. In the method of the present invention, the silica obtained by sawing has an average particle size of 200 to 3. OOOnm is required.

The silica thus obtained is subjected to solid-liquid separation using a centrifuge or filter press, concentrated and dried in a vacuum or nitrogen gas atmosphere, and then heated to about 500°C in air or an oxygen atmosphere to remove organic matter. When this is heated to about 1,500°C in vacuum, helium gas, or hydrogen gas, the silica becomes pore-closed and vitrified, making it transparent and normal quartz. The resulting silica has a specific gravity equivalent to that of glass, but since this silica has a particle size of 3 tO00n+a or less, the above-mentioned pore closure progresses easily, and a glass lump that does not contain bubbles can be easily obtained.

The glass lump obtained in this way is then ball milled.
Grind with a roll mill, rod mill, etc. to an average particle size of 50
After adjusting the particle size from 1 to 200 mesh, acid washing is performed and the particle size is reduced to 1,70 mesh in vacuum or in the presence of an inert gas.
If it is heated to 0°C or higher and melted, it can be made into synthetic quartz glass.

The synthetic quartz glass obtained in the second step has a low OH group content, for example less than ippm, and this is also because the silica made by the above method has an extremely regular structure, and even when heated and melted as described above. Since this structure does not become irregular, it has a high temperature viscosity of, for example, 1 to 4 x 10" poise at 1,400°C, so it is particularly useful as a crucible material for pulling silicon single crystals. It has an industrial advantage of being useful.

(Example) Next, examples using the method of the present invention will be given.

Example: Put 150 moles of methanol, 120 moles of pure water, and 50 moles of ammonia into a reaction vessel, keep it at 20°C, and drop 10 moles of methyl silicate into it over 120 minutes to cause a hydrolysis reaction. After the reaction, the produced silica After allowing it to settle naturally, the precipitate was taken out and dried by heating at 150° C. in a vacuum to obtain silica powder with an average particle size of 700 nm.

Next, this silica powder was heated to 500°C in air to oxidize and remove organic matter, and then heated to 1,500°C in vacuum.
This silica is heated to 4 closed pores.

When vitrified, transparent glass lumps having a particle size of 1 to 5+ m could be obtained with a yield of 98%.

Next, this transparent glass lump is crushed in a conical ball mill, sieved into 50 to 200 meshes, acid-treated with hydrochloric acid, calcined at 800℃, magnetically separated in a magnetic separator, and the powder is placed in argon gas. When melted at 1°950°C and molded, an opaque synthetic quartz glass plate of 30IIaφ x 5cm thick was obtained.The OH group content of this glass was examined using an infrared absorption spectrum. It was not detected, and chemical analysis revealed that the amount of this impurity was A.
l 60ppb, Fe 75ppb, Na 35
ppb, K was 20 ppb.

In addition, the powder obtained above was melted in a vacuum at a temperature of 1.80
When heated to 0°C for 15 minutes, a transparent synthetic quartz glass body was obtained, and no OH group content was detected.Furthermore, when this powder was arc melted and a crucible was formed from it, , the resulting crucible is opaque;
The OH group content of this product was 15 ppm, probably due to moisture absorption from the air before melting.

In addition, when the high-temperature viscosity of the synthetic quartz glass obtained above was investigated using the fiber dilongation method, the viscosity at 1,400°C of the product fused at normal pressure in argon gas was 2.5.
X 10" poise, the vacuum melted product had 3.7 X 10" poise, the 7'1 m melted product had 9 X 1010 poise, and all showed high high temperature viscosity.

Comparative Example 1 150 moles of methanol, 120 moles of pure water, and 1 mole of ammonia were placed in a reaction vessel and kept at 80°C, and 10 moles of methyl silicate was added dropwise to the reactor over 120 minutes to cause a hydrolysis reaction. After allowing the silica to settle naturally, the precipitate was taken out and dried by heating at 150° C. in a vacuum to obtain silica powder with an average particle size of 1100 nm.

Next, this silica powder was heated to 500°C in air to oxidize and remove organic matter, and then heated to 1,500°C in vacuum.
The silica was heated to close the pores and vitrified, but in this case it foamed and a satisfactory glass lump could not be obtained.

Comparative Example 2 150 moles of methanol, 120 moles of pure water, and 50 moles of ammonia were placed in a reaction vessel and kept at 0°C, and 10 moles of methyl silicate was added dropwise to the reactor over 120 minutes to cause a hydrolysis reaction. After allowing the silica to settle naturally, the precipitate was taken out and dried by heating at 150° C. in a vacuum to obtain silica powder with an average particle size of 3,200 nm.

Next, when this silica powder was heated to 500°C in air to oxidize and remove organic matter, it did not form lumps and was a better silica powder with a particle size of 3.2QQnm.
When this silica powder was heated to 1,500° C. in a vacuum to close the pores and vitrify the silica, it became an opaque synthetic quartz glass lump containing bubbles.

Next, this synthetic quartz block is crushed in a conical ball mill,
Sieve into 50 to 200 meshes and sieve in a vacuum to 1.8
When heated to 00°C and melted, a transparent glass body was obtained, but this contained large bubbles, and although this one had no OH group content, the size of the bubbles was 1.
Since the diameter was more than 1φ, there was a problem in practicality.

Claims (1)

[Claims] Methyl silicate is hydrolyzed in a methanol solvent using ammonia as a catalyst to obtain a particle size of 200 to 3,000 nm.
silica is prepared, concentrated, dried, heated and oxidized to close the pores,
After vitrification and pulverization to adjust the particle size, heat to 1,700℃
A method for producing synthetic quartz glass, characterized in that it is melted in the above manner.