JPH0455331A - Production of silica glass - Google Patents

Abstract

PURPOSE:To obtain a silica glass without any crack at a low cost by interposing a fine silica powder between a porous silica body and a porous silica body at the time of sintering the porous silica body. CONSTITUTION:A fine silica powder 2 is laid over a bottom board 3, a porous silica body 1 is placed thereon, a fine silica powder 2 is placed thereon, a porous silica body 1 is further placed thereon, and the process is repeated. The laminated porous silica bodies 1,1,... with the fine silica powder 2 in between are sintered. Consequently, the volatilization of the gas in the body 1 is facilitated, the sintered glasses are not fused together, and the cracking of the silica glass is prevented. Furthermore, since the space in the sintering furnace is effectively utilized, the silica glass is produced at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing silica glass used for optics, semiconductor industry, electronic industry, physics and chemistry, etc.

[Conventional technology]

Because silica glass has excellent heat resistance, corrosion resistance, and optical properties, it is an important material indispensable for semiconductor manufacturing, and is also used for photomask substrates, plates, TPT substrates, etc. for optical fiber and IC manufacturing. and its uses are expanding more and more.

Silica glass can be produced by melting natural quartz in an electric furnace or oxyhydrogen flame, or by oxidizing and melting silicon tetrachloride at high temperature in an oxyhydrogen flame or plasma flame. The process requires high temperatures of 2000°C or higher, which consumes a large amount of energy.In addition, materials that can withstand such high temperatures are required during manufacturing, and it is difficult to obtain materials with even higher purity, resulting in economical and quality issues. It has some problems.

On the other hand, in recent years, a method of synthesizing silica glass at low temperature called the sol-gel method has been attracting attention.

The outline will be briefly described below.

Silicon alkoxide represented by the general formula Si (OR) 4 (R: alkyl group) or its polycondensate, such as (RO)! S i・(O81(OR)2)n・O8
i (OR)3 (n=o ~8, R: alkyl group)
Water (pH may be adjusted with an alkali or acid) is added to the solution to hydrolyze it to obtain silica hydrosil (referred to as silica sol in the present invention).

At this time, an appropriate organic solvent such as alcohol is generally added as a solvent so that the silicon alkoxide and water form a uniform system. Take this silica sol in a container, leave it still,
It is gelled by raising the temperature, adding a gelling agent, etc. Thereafter, the gel is evaporated to dryness to obtain a dry gel (silica porous material). Silica glass is obtained by sintering this dried gel in a suitable atmosphere.

Sintering methods include a method in which a heat-resistant material called a saya is made into a multi-stage structure, and dried gel is charged in each stage so as not to overlap, and then fired, or a method in which dried gel is stacked and fired (Japanese Patent Application Laid-Open No. 60-65731) No.) etc.

[Problem to be solved by the invention]

However, in the method of forming a multi-stage structure using a heat-resistant material called a pod, the dry gel cannot be fired efficiently because the pod occupies a large space. In addition, in the method of stacking dry gels and firing them, gas does not evaporate from the contact surface between the dry gels when the temperature rises, so the sintered silica glasses tend to fuse together, and cracks also occur. Cheap.

An object of the present invention is to provide a method for manufacturing silica glass at low cost.

[Means to solve the problem]

The present invention provides a method for producing silica glass by sintering porous silica bodies, in which porous silica bodies are stacked and sintered while fine silica powder is interposed between the porous silica bodies. The present invention relates to a method for producing silica glass characterized by the following.

A suitable porous silica material in the present invention is a dry gel prepared by a sol-gel method. However, instead of this, a porous silica prepared by gas-phase oxidation of silicon tetrachloride or the like, a porous silica prepared by leaching of a phase-divided glass such as silicon dioxide-boron trioxide, etc. can also be used.

The fine silica powder interposed between the porous silica bodies of the present invention has a high purity to the extent that it does not contaminate the sintered silica glass, and the particle size is 0.1 in consideration of operability.
~10 μm is preferred. Examples of such fine silica powder include Aerosil (Degussa), which is white carbon produced by gas phase oxidation.
Product name of Deggussa) and Carbosil (Ca
b-o-sil) (trade name of Cabot), silica fine powder produced from silicon alkoxide (tetramethoxysilane, tetraethoxysilane, etc.), and the like.

The thickness of the layer of fine silica powder interposed between the porous silica materials is determined by the ease of operation, economic efficiency,
Considering efficiency, 0.1 to 5 mm, preferably 0.5 to 3
1E11 is good.

[Effect]

By stacking and sintering the porous silica bodies while interposing fine powder between the porous silica bodies, the gas in the porous silica bodies can be easily volatilized, and the sintered glass can also be bonded. No fusion will occur. It is thought that this contributes to preventing the occurrence of cracks in silica glass.

〔Example〕

(Example 1) Tetramethoxysilane (S i (OCH3) 4)
Weigh out and methanol so that the molar ratio is 1=4,
Aqueous ammonia having a concentration of 0.01 mol/L was added to this solution in an amount of 4 mol of water per 1 mol of tetramethoxysilane, and the mixture was thoroughly mixed to obtain a silica sol. The obtained sol was placed in 10 stainless steel petri dishes, each 200 mm square and 20 mm deep, coated with polyfluoroethylene to a depth of 10 mm, sealed and gelatinized at room temperature.

After gelation, the gel was dried at 60° C. for 10 days using a lid with holes, and then heated to 150° C. at a rate of 30° C./day to obtain a dry gel. As shown in Figure 1, fine silica powder (0X-5 manufactured by Degussa)
0) was placed so that the thickness was about 1 mm, and 10 sheets of dry gel were stacked on top of each other and set in a firing furnace. First, it was heated to 700°C in air at a heating rate of 50°C/hour, then heated to 13°C.
When heated to 50°C in helium at a rate of 50°C/hour and sintered, transparent, crack-free silica glass becomes 10
I got one.

(Example 2) The same procedure as in Example 1 was carried out except that FFC manufactured from silicon alkoxide manufactured by Tama Kagaku ■ was used as the silica fine powder. Transparent and crack-free silica glass 10
I got one.

〔Effect of the invention〕

According to the present invention, the space in the firing furnace can be used effectively, so silica glass can be manufactured at low cost. Also,
The resulting silica glass is transparent and has no cracks, so it can be used not only as photomask substrates for IC manufacturing, optical materials, etc. that have been conventionally used, but also as substrates for liquid crystal displays.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the state of the porous silica body when it is set in a firing furnace. Explanation of symbols 1 Silica porous body 2 Silica fine powder 3 Floor plate

Claims (1)

[Claims] 1. A method for producing silica glass by sintering porous silica bodies, which is characterized by interposing fine silica powder between the porous silica bodies, stacking the porous silica bodies, and sintering the porous silica bodies. A method for producing silica glass.