JPH0829950B2 - Silica glass manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing silica glass used for optics, semiconductor industry, electronic industry, physics and chemistry, and the like.

(Conventional technology) Silica glass is an indispensable material for semiconductor manufacturing because of its excellent heat resistance, corrosion resistance and optical properties. In addition, silica glass, photomask substrates for IC manufacturing, TFT substrates, etc. And its applications are expanding.

Conventional methods for producing silica glass include a method of melting natural quartz with an electric furnace or an oxyhydrogen flame, or a method of oxidizing silicon tetrachloride at a high temperature in an oxyhydrogen flame or a plasma flame to dissolve it. Also requires a high temperature of 2000 ° C or higher in the manufacturing process, so a material that consumes a large amount of energy and that can withstand such a high temperature during manufacturing is needed, and it is difficult to obtain a high-purity product, which is economical, There are some problems in terms of quality.

On the other hand, in recent years, a method called sol-gel method for synthesizing silica glass at a low temperature has attracted attention. The outline is briefly described.

Silicon alkoxide represented by the general formula Si (OR) ₄ (R: alkyl group) (including, in the present invention, a polycondensate thereof. For example, (RO) ₃ Si. {OSi (OR) ₂ } _n. OSi (OR)
₃ , (n = 0 to 8, R: alkyl group)) is hydrolyzed by adding water (pH may be adjusted with alkali or acid) to silica hydrosol (referred to as silica sol in the present invention). And At this time, an appropriate alcohol is generally added as a solvent so that the silicon alkoxide and the water become a uniform system. This silica sol is allowed to gel by standing, heating, addition of a gelling agent, and the like. Thereafter, the gel is evaporated and dried to obtain a silica dry gel. The dried gel is sintered in an appropriate atmosphere to obtain silica glass.

(Problems to be Solved by the Invention) However, there are still unsolved problems in the production of silica glass by the sol-gel method. In particular, cracks and cracks are easily generated in the gel during the drying process, and it is difficult to produce a large monolithic dry gel without cracks and cracks with good yield.

The present invention provides a method for producing silica glass without cracks or cracks.

(Means for Solving Problems) In the present invention, in the method for producing silica glass by the sol-gel method, a solvent containing N, N-dimethylacetamide is used as a solvent for silicon alkicoside during sol preparation. In addition, hydroxyalkyl cellulose is added.

In the present invention, although there is no particular limitation on the alkyl group of the silicon alkoxide, it is preferable to use a silicon alkoxide having a methyl group, an ethyl group, a propyl group, or a butyl group in terms of ease of hydrolysis and gelation time. Is preferred. Further, it is also possible to use those obtained by partially polymerizing these silicon alkoxides.

The catalyst to be added together with water is not particularly limited, such as a base and an acid, but a base gives a preferable result from the viewpoint of gelation time and easiness of sintering of the obtained dry gel.

As the hydroxyalkyl cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxybutyl cellulose, hydroxybutyl methyl cellulose and the like can be used. The molecular weight of these hydroxyalkyl celluloses is not particularly limited in the present invention, but it is selected according to the solubility in water or solvent and the degree of growth of silica fine particles in the sol.

N, N- used as a solvent for silicon alkoxide
The amount of dimethylacetamide is not particularly limited in the present invention, but is selected according to the degree of growth of silica fine particles in the sol. As the solvent component used together with N, N-dimethylacetamide, methyl alcohol,
Alcohols such as ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, butyl alcohol,
At least one of ethers such as dimethyl ether, ketones such as acetone and ethyl methyl ketone, and esters such as ethyl acetate can be used.

Silica glass is transferred to a container such as a petri dish of Siligazol prepared as described above, gelled while being kept at room temperature to 70 ° C., and then dried at a temperature of room temperature or higher for several weeks to give a dry gel, which is a known method. , For example, 1000-1400 ℃ in air
It is obtained by raising the temperature to 0 and sintering.

(Function) The details of the reason why the cracking of the gel that occurs during the drying process is prevented by using a solvent containing N, N-dimethylacetamide is not clear, but N, N-dimethylacetamide, together with hydroxyalkyl cellulose, is Involved in the generation and control of growth of silica fine particles in the sol,
In addition, since the boiling point is 166 ° C, which is higher than that of other solvents such as alcohol and water, the evaporation rate in the drying process is slow, which contributes to the relaxation of the stress generated in the gel, allowing the gel to be made larger. It is thought that it has become.

Example 0.01M choline aqueous solution 47 g, methyl alcohol 67 g, N,
21 g of N-dimethylacetamide was mixed, and 2 g of hydroxypropyl cellulose (average molecular weight 300,000) was added and dissolved therein. The resulting solution is tetramethylsiloxane 99
Slowly added to g and mixed well to obtain silica sol. This was put in a petri dish coated with Teflon having a diameter of 200 mm, sealed with aluminum foil, and gelled at room temperature. Then open a small hole in the lid and dry in a thermostat at 60 ° C for 2 weeks, then 170
The temperature was raised to ℃ and dried for 1 day to obtain a dry gel. The dried gel thus obtained had no cracks or splits. When the obtained dried gel was heated to 1300 ° C. in air and sintered, a transparent silica glass without cracks and cracks was obtained.

(Effects of the Invention) According to the present invention, it is possible to easily manufacture a large-sized silica glass without cracks or cracks by the zorgel method. There is basically no restriction on the size, and the shape is plate, rod,
It can be manufactured in any shape such as tubular.

Further, according to the present invention, silica glass can be produced at a lower cost than before, so that the application can be expanded not only to the fields of photomask base materials for IC manufacture which have been conventionally used but also to liquid crystal display base materials and the like.

Claims (1)

[Claims] (1) hydrolyzing a silicon alkoxide into a silica sol, gelling this, and drying to form a dry gel;
Then, in a method for producing a silica glass to be sintered, in a step of hydrolyzing a silicon alkoxide into a silica sol,
A method for producing silica glass, which comprises using a solvent containing N, N-dimethylacetamide as a solvent for silicon alkoxide and adding hydroxyalkyl cellulose.