JPH0567575B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for producing synthetic quartz glass, particularly as a member for semiconductor heat treatment such as a crucible material for pulling silicon single crystals due to its high purity and high temperature viscosity. The present invention relates to a method for producing synthetic quartz glass, which is considered to be useful, by a sol-gel method.

[Prior art] Synthetic quartz glass is produced by hydrolyzing silicon compounds such as silicon tetrachloride in an oxyhydrogen flame to produce silica particles, which are then melted to produce silica glass. A method of converting a flame into a plasma flame, by hydrolyzing alkoxysilane with an acid catalyst in an alcohol solvent to produce silica.
A so-called sol-gel method is known in which this is sintered to form quartz glass.

However, this method using an oxyhydrogen flame leaves as much as 1000 ppm of OH groups in the quartz glass, has low high-temperature viscosity, and has the problem of foaming at high temperatures in a vacuum.The plasma method is expensive and mass-produced. Although the sol-gel method has the advantage of being able to obtain products with high viscosity at low cost, it tends to leave OH groups, takes a long time to produce, and produces products with high viscosity at high temperatures. The disadvantage is that it is difficult to obtain.

However, since this sol-gel method yields a glass that is very close to amorphous, it is being considered for use in optical fibers, IC photomasks, lenses, etc. A method in which fine silica particles are produced by hydrolysis with and mixed with a sol obtained by hydrolyzing an alkyl silicate under an acid catalyst (see Japanese Patent Application Laid-Open No. 62-241837), SiCl ₄
A method in which SiO ₂ particles obtained by oxidation of
Scheere & J.C.Luong, J.Non−Cryst.Solids, 63
(1984) 163-172]. In addition, the sol-gel method is being considered for heat-resistant parts such as crucibles and jigs, and for this purpose, silica obtained by hydrolysis using an acid catalyst in the presence of an alkaline component such as Na is converted into α-cristobalite. The method of transferring and then dissolving (see JP-A-63-166730) and the method of monodisperse and polydisperse obtained by hydrolyzing methyl silicate with an ammonia catalyst in a methanol solvent, which the present inventors previously applied There are methods to obtain it by sintering silica.

[Problems to be solved] However, methods for obtaining monodisperse and polydisperse silica particles, such as this sol-gel method, have the disadvantages of poor productivity and the need for a large amount of energy consumption to remove the solvent. However, with the method of mixing the hydrolyzate under a basic catalyst and the hydrolyzate under an acidic catalyst, it was not possible to obtain a product with high high temperature viscosity such as natural quartz. However, quartz glass has the disadvantage that it cannot be used as a semiconductor heat treatment member, and although the method of converting α-cristobalite in the presence of Na can yield quartz glass with high viscosity, it is difficult to remove alkaline components. Therefore, this also has the disadvantage that it cannot be used as a member for semiconductor heat treatment.

[Means for Solving the Problems] The present invention relates to a method for producing synthetic quartz glass by a sol-gel method that overcomes these disadvantages. Hydrolyzed and polymerized without using a solvent to achieve a particle size of 100-500n
m primary silica particles are made into silica aggregates with a particle size of 10 to 100 μm, and after separating the solvent by solid-liquid separation, heating is performed to oxidize and remove unreacted organic matter, and then this silica powder is heated in a vacuum for 1500 μm. It is characterized by being sintered by heating to a temperature of 1700°C or higher, followed by pulverization, acid treatment, drying, and then melt-forming at a temperature of 1700°C or higher.

That is, the present inventors conducted various studies on a method for inexpensively producing synthetic quartz glass with high purity and high temperature viscosity using the sol-gel method. When polymerization is carried out in the presence of ammonia, the silica obtained as primary particles with a particle size of 100 to 500 nm becomes agglomerated, and the particle size becomes 10 nm.
Since it becomes ~100 μm silica particles, it can be separated from the solution by simple solid-liquid separation methods such as centrifugation, and after removing unreacted organic matter by oxidation, it is heated and sintered at 1500°C or higher, crushed, The present invention was completed by discovering that synthetic quartz glass with high high temperature viscosity can be obtained easily and inexpensively by acid treatment, drying, and then melt-forming at a temperature of 1700° C. or higher.

This will be explained in more detail below.

[Function] The synthetic quartz glass composition according to the present invention
Since this is carried out by a gel method, the starting material is methyl silicate as an alkyl silicate, but this hydrolysis must be carried out in the presence of ammonia. When methyl silicate is hydrolyzed in the presence of ammonia, primary silica particles having a particle size of 100 to 500 nm are produced by this hydrolysis. This reaction has an apparent particle size of 10 to 10% in this methanol-free system.
It becomes a 100μm silica aggregate. These primary particles are spherical and contain almost no OH groups inside, and OH groups exist only on the surface.When these particles are filled, there are large gaps between them, and even when heated The pores do not become closed, the OH groups on the surface can be easily removed, there are no OH groups that reduce viscosity, and the above three-dimensional condensation polymerization occurs regularly, resulting in a dense structure. Synthetic quartz glass has the advantage of being highly viscous at high temperatures. It has been discovered that this three-dimensional condensation polymerization of silica progresses reliably at ammonia concentrations above a certain level, and that the particles can maintain their shape and structure up to temperatures of about 1400°C. Therefore, the concentration of ammonia should be at least 0.8 times the molar amount of methyl silicate, but this hydrolysis will occur in the presence of ammonia.
It is sufficient to add more than double the molar amount of water and conduct the reaction at a temperature of 50°C or less.

The silica aggregates obtained in this way must then be separated from the solution, but since the silica aggregates have a large apparent particle size, they can be separated by a simple solid-liquid separation method. For example, this can be done by dehydration using a centrifugal dehydrator using a filter cloth of about 800 mesh, or separation by vacuum filtration or decantation. This solves the disadvantage of large energy consumption.

In addition, the silica aggregates obtained in this way are dried, heated, sintered, crushed, and then melted and formed into synthetic silica glass.
It may be heated at 100 to 200°C for 5 to 10 hours, and in order to remove the remaining organic matter, heat it to 300 to 1200°C in air or oxygen gas to oxidize and remove this organic matter. Bye. The silica aggregates treated in this way are then placed in, for example, a carbon crucible, heated to 1500°C or higher to sinter, pulverized, and acid-treated with HCl, HF, etc.
The synthetic quartz glass obtained in this way has a content of metal impurities such as Al, Fe, Na, K, and Ca of 0.2. It has a high purity of less than ppm, and its high-temperature viscosity is, for example, 10 ¹⁰ poise or more at 1400°C, making it advantageous as it is useful as a member for semiconductor heat treatment.

[Example] Next, examples of the present invention and comparative examples are given. The metal impurity content is the value measured by Zeeman atomic absorption spectrometry, and the high temperature viscosity is the value measured by fiber elongation method.

Example 1 Put 130% of semiconductor grade 29% ammonia water and 30% of ultrapure water into a 500mm glass-lined reactor, cool it to 0°C, and add methylene silicate (distilled product) to it while stirring with a Teflon-coated stirring rod.
When 265 kg of silica was added and dehydrated using a centrifugal dehydrator after the application was completed, silica aggregates 105 were polydispersed particles with a primary particle size of 100 to 500 nm and a particle size of 10 to 100 μm.
Kg was obtained.

Next, this was dried at 150°C in nitrogen air, and the dried product was packed into a quartz furnace tube and heated in oxygen gas from room temperature to 1200°C in 10 hours.
Thereafter, 25 kg of the material was packed in a high-purity graphite case, and the temperature was raised from room temperature to 1500°C over 2 hours and from 1500°C to 1700°C over 10 hours in a vacuum to sinter it.

Next, this sintered product is crushed into 50 to 80 meshes, washed with HCl and HF, dried and passed through a magnetic separator, then packed into a rotating crucible-shaped mold and heated with an arc
When melted by heating to 2400-2600℃, the resulting crucible was relatively transparent and contained Al, Fe,
The content of metal impurities such as Na, K, and Ca was 0.1 ppm or less, and the viscosity at 1400°C was 3.8×10 ¹⁰ poise.

Example 2 The silica powder calcined at 1200°C in Example 1 was packed into a quartz crucible, heated to 1500°C in a vacuum for 3 hours, crushed and sieved, and a powder with an average particle size of 50 μm was obtained. Now that I have a body,
After acid treatment with HCl and HF, it is repacked into a high-purity graphite case and heated from room temperature to 1800℃ in a vacuum of 10 ^-3 Torr.
By raising the temperature over 20 hours, a synthetic quartz ingot with a diameter of 300 mm and a length of 600 mm was produced.

This material is transparent and has high purity with metal impurity content such as Al, Fe, Na, K, and Ca of 0.2 ppm or less, and its viscosity at 1400°C is 7.5.
×10 It was ¹⁰ poise.

Comparative Example: Semiconductor grade 29% by weight ammonia water 50% and ultrapure water 50% in a glass-lined reactor
Add 120% methanol and dry ice.
The temperature was maintained at 0°C with methanol, and a mixture of 76 methyl silicate and 100 methanol was dropped therein. After the dropwise addition, the produced silica particles were sampled and observed with an electron microscope, and the diameter was 700 nm. It was a monodisperse of spherical particles.

This material was then subjected to solid-liquid separation, but since filtration was impossible, it was heated at 100 Torr and 100°C for 20 hours to remove water, methanol, and ammonia, and 29 kg of silica was obtained. This was packed into a quartz furnace core tube and heated in oxygen gas from room temperature to 1200°C over 10 hours, then packed back into a high-purity graphite case and heated to 1500°C in vacuum for 3 hours to sinter. .

Next, this sintered product was crushed, sieved into 50 to 80 meshes, washed with HCl and HF, dried, passed through a magnetic separator, packed into a rotating crucible-shaped mold, and arc-fused. Al, Fe, and
Metal impurity content such as Na, K, Ca etc. is 0.20 ~
Concentration of impurities in the solvent and contamination during drying were observed at 0.1 ppm, and the high temperature viscosity of this material was 1400℃.
It was 3.8×10 ¹⁰ poise.

[Effects of the Invention] As described above, synthetic quartz glass according to the present invention is produced by hydrolyzing and polymerizing methyl silicate in the presence of ammonia to produce silica aggregates with a particle size of 10 to 100 μm, which are separated into solid and liquid. Later, sintering,
Synthetic quartz glass is obtained by crushing and melting, but according to this method, silica obtained by hydrolyzing methyl silicate is obtained as aggregates, and this solid-liquid separation is performed using filtration, centrifugal dehydrators, etc. It can be carried out using a simple and inexpensive method, and since the process is short, contamination is minimized, and the synthetic silica glass obtained by sintering, crushing, and melting the silica aggregates obtained here is of high purity. , since the high temperature viscosity is high,
This provides the advantage that synthetic quartz glass, which is useful as semiconductor heat treatment parts, can be produced industrially in large quantities at low cost by the sol-gel method.

Claims (1)

[Claims] 1 Methyl silicate was hydrolyzed in the presence of ammonia and polymerized to form silica as primary particles with a particle size of 100 to 500 nm into silica aggregates with a particle size of 10 to 100 μm, and the solvent was removed by solid-liquid separation. After that, the silica powder is heated to oxidize and remove unreacted organic matter, and then the silica powder is sintered by heating to 1500℃ or higher in vacuum, followed by pulverization, acid treatment, drying, and then sintering at a temperature of 1700℃ or higher. A method for producing synthetic quartz glass, characterized by melting and forming it.