JPH0825758B2 - 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 of synthesizing silica glass at a low temperature called a sol-gel method 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) The present invention relates to a method for producing silica glass by a sol-gel method, in which a solvent containing tetrahydrofurfuryl alcohol is used as a solvent for silicon alkicoside during sol preparation. It is characterized by adding polyvinyl acetate.

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.

The molecular weight of polyvinyl acetate is not particularly limited in the present invention, but solubility in water and a solvent and growth of silica fine particles in a sol are selected according to the degree.

The amount of tetrahydrofurfuryl alcohol used as a solvent for the silicon alkoxide is not particularly limited in the present invention, but it is selected according to the degree of growth of silica fine particles in the sol.

Solvent components used together with tetrahydrofurfuryl alcohol include alcohols such as methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol and butyl alcohol, ethers such as dimethyl ether, ketones such as acetone and ethyl methyl ketone. At least one ester such as ethyl acetate can be used.

The silicon alkoxide, the polyvinyl acetate, the solvent and the water are mixed well by using a stirrer or the like in order to make the produced sol as uniform as possible. Also, ultrasonic waves may be applied. Fine particles of silica may be added during the preparation of the sol.

The produced sol solution is quickly transferred to another container for gelation. At the time of gelation, the container is preferably sealed in order to prevent the solvent from escaping from the generated gel, and the temperature at the time of gelation is preferably 0 ° C. or higher.

In the step of drying, a dry gel is prepared by shrinking and shrinking and solidifying under a suitable atmosphere instead of using a lid having holes. Then gel
Silica glass is manufactured by sintering by the sol method.

For the step of gelling, the step of drying and the step of sintering, generally used conditions are used. For example, 0 ° C
Leave at ~ 100 ° C for several minutes to tens of days, room temperature to 200 ° C for several hours to several days
Leave for 10 days, in an appropriate atmosphere 1000 to 1400 ℃ to 50 to 400 ℃
/ Hour heating rate.

(Action) Although the action of tetrahydrofurfuryl alcohol and polyvinyl acetate is unknown, it contributes to the generation of silica fine particles in the sol, the control of growth, and the relaxation of the stress generated in the gel during the drying process. It is thought that it has become possible to make it larger.

Example 1 A molar ratio of silicon tetramethoxide: tetrahydrofurfuryl alcohol = 1: 1 was adjusted, methanol was added in the same amount as tetrahydrofurfuryl alcohol and stirred, and polyvinyl acetate was further added to silicon tetramethoxide 100. 10 parts by weight was added to parts by weight to obtain a uniform solution.
An aqueous choline solution having a concentration of 0.01 mol / mol was added to this solution in an amount of 4 mol with respect to 1 mol of silicon tetramethoxide and sufficiently mixed to obtain a silica sol. The obtained sol was put into a glass petri dish having a diameter of 200 mm and coated with Teflon to a depth of 10 mm, and the gel was sealed at room temperature. After gelling, it was dried at 60 ° C. for 14 days instead of the lid with holes, and then heated to 170 ° C. at 30 ° C./day and dried to obtain a dry gel without cracks or cracks. This dried gel was heated in air to 1300 ° C. at a heating rate of 60 ° C./hour to obtain silica glass free from cracks and foaming. This silica glass is of high quality without devitrification or bubbles. As a result of the analysis, this silica glass was in agreement with the properties of commercially available silica glass.

Example 2 A molar ratio of silicon tetramethoxide: tetrahydrofurfuryl alcohol = 1: 1 was adjusted, methanol was added with half the amount of tetrahydrofurfuryl alcohol, and the mixture was stirred. 10 parts by weight was added to each part to make a uniform solution.
An aqueous choline solution having a concentration of 0.01 mol / mol was added to this solution in an amount of 4 mol with respect to 1 mol of silicon tetramethoxide and sufficiently mixed to obtain a silica sol.

Thereafter, the same operation as in Example 1 was performed to obtain a silica glass. This silica glass is of high quality without devitrification or bubbles. As a result of the analysis, this silica glass was in agreement with the properties of commercially available silica glass.

Comparative Example As a result of performing the same operation as in Example 1 except that tetrahydrofurfuryl alcohol was not used as a solvent and only methanol was used, cracks and cracks were easily generated in the gel during drying.

(Effects of the Invention) According to the present invention, large-sized silica glass can be easily produced by the sol-gel method without generating cracks or cracks. The size is basically not limited, and the shape is not limited to the plate-shaped one, and rod-shaped or tubular-shaped ones can be manufactured, which can be manufactured at a lower cost than before.

In addition, since silica glass can be manufactured at a lower cost according to the present invention, it can be used not only in fields such as photomask base materials for IC manufacturing which have been conventionally used, but also in fields which have not been used because of its high price. Demand can be expanded.

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 tetrahydrofurfuryl alcohol as a solvent for silicon alkoxide and adding polyvinyl acetate.