JPH03146429A - Production of silica glass - Google Patents

Abstract

PURPOSE:To facilitate the release of silica glass from a porous base plate and to prevent the cracking of the face of the glass brought into contact with the base plate by drying silica gel obtd. by hydrolyzing silicon alkoxide and sintering the resulting dry gel on the base plate. CONSTITUTION:Water is added to silicon alkoxide to hydrolyze the alkoxide, the resulting silica sol is converted into gel and this gel is dried to obtain dry gel. This dry gel is sintered on a porous base plate having 0.1-1,000mum surface roughness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing silica glass used in optical applications, semiconductor industry, electronic industry, science and engineering, and the like.

[Prior Art] Silica glass has excellent heat resistance, corrosion resistance, and optical properties, so it is an important material indispensable for semiconductor manufacturing, and is also used as a photomask substrate for optical fiber and IC manufacturing, and TPT substrate. It is used for various purposes, and its applications are expanding more and more.

Conventional methods for producing silica glass include a method in which natural quartz is melted in an electric furnace or an oxyhydrogen flame, or a method in which silicon tetrachloride is oxidized and melted at high temperature in an oxyhydrogen flame or a plasma flame. Because the manufacturing process requires high temperatures of 2000°C or higher, it consumes a large amount of energy, and materials that can withstand such high temperatures are required during manufacturing, making it difficult to obtain high-purity materials, making it economical. There are some problems in terms of performance and quality.

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.

Add water to silicon alkoxide and hydrolyze it to produce silica hydrosil. At this time, an appropriate alcohol is usually added to the solvent so that the silicon alkoxide and water form a homogeneous system. This silica sol is gelled by standing still, raising the temperature, adding a gelling agent, etc. Thereafter, the gel is evaporated and dried to obtain a dry silica gel. This dried gel is usually prepared using mirror-polished quartz glass (surface roughness Ra).
0.05 μm or less) and sintered in an appropriate atmosphere to obtain silica glass.

[Problems to be Solved by the Invention] However, the above sol-gel method for producing silica has the following problems. That is, when the dry gel is sintered,
In many cases, silica glass adheres to the bottom plate, making it difficult to separate, and cracks are likely to occur in the silica glass on the surface in contact with the bottom plate.

The present invention provides a method in which silica glass can be easily peeled off and cracks do not occur on the surface in contact with the floor plate.

[Means for Solving the Problems] The present invention provides a method for producing silica glass in which silicon alkoxide is hydrolyzed to produce silica sol, this is gelled, dried to form a dry gel, and then sintered. In the sintering step, the dry gel is placed on a porous base plate or a base plate with a surface roughness (Ra) of 0.1 to 1,000 μm and sintered.

The floor plate used in the present invention has a thickness of 1 μm to 1 cm, preferably 1 μm to 1 cm.
When the porous plate has pores with a size of 0 μm to 5 mm with an open area or porosity of o, oi to 75%, or when the surface roughness is measured according to the method of J I 5BO 601, The plate has a roughness of 0.1 to i, ooo μm. If it is smaller than this range, the silica glass and the bottom plate may adhere to each other and be difficult to separate, or the silica glass is likely to crack. Moreover, if it is larger than this, excessive unevenness will occur on the surface of the sintered glass, which is not preferable.

The material for the bottom plate is preferably a material that does not contain impurities in the silica glass produced during sintering, and examples of these include silica glass, alumina, silicon carbide, mullite, and silicon nitride.

The shape of the bottom plate may be a plate with a flat surface and a uniform thickness to the extent that it does not break during operation.

There are various ways to obtain the porous floor plate as described above, but the simplest method is to drill holes.

In addition, as a method for obtaining a bottom plate with a surface roughness of 0.1 to 1,000 μm, for example, a commercially available plate called an opaque quartz glass plate may be obtained, or a plate made of the above material may be obtained. It can also be obtained by polishing with abrasive grains.

[Function] At the stage of sintering the dry gel, the dry gel is placed on a porous plate,
Alternatively, by placing it on a bottom plate with a surface roughness (Ra) of 0.1 to 1.000 μm, the substantial contact area between the dry gel and the bottom plate becomes smaller, so that when the dry gel is vitrified, the silica glass It is thought that adhesion between the silica glass and the floor plate can be avoided, and the silica glass can be easily peeled off from the floor plate. In addition, since there are many parts between the dry gel and the floor plate that are not substantially in contact with each other, it is thought that organic matter easily disperses from the dry gel without resistance, and cracks are less likely to occur in the silica glass.

[Example] (Example 1) Silicon tetramethoxide (S i (OCH3)
Weigh out 4) and methanol so that the molar ratio is 1=4, and add aqueous ammonia with a concentration of 0.01 mol to this solution so that the ratio of water to 11 mol of silicon tetramethoxy is 4 mol. A silica sol was obtained by mixing. The obtained sol was placed in a Teflon-coated glass Petri dish with a diameter of 200 mm to a depth of 10 mm, sealed, and gelatinized at room temperature.

After gelatinization, 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. This dried gel is 1mm in diameter.
It was placed on a 200 mm square silica glass plate with 100 uniformly perforated circular holes, and placed in a firing furnace under an air atmosphere.
Silica glass was obtained by heating to 1250°C at a heating rate of 100'C/hour. The obtained silica glass had weak adhesion to the floor plate, could be easily peeled off, and no cracks were observed.

(Example 2) Silica glass was produced in the same manner as in Example 1, except that a high-purity alumina plate with a surface roughness (Ra) of 0.7 μm was used as the base plate. The obtained silica glass could be easily peeled off from the floor plate, and no cracks were observed. Note that the surface roughness (Ra) was measured using a surface roughness measuring device (manufactured by Koita Research Institute, Model 5E-30D) manufactured in accordance with the JIS 80601 surface roughness standard.

(Comparative Example) Silica glass was produced in the same manner as in Example 1, except that a silica glass plate with a surface roughness (Ra) of 0.02 μm was used as the bottom plate. The obtained silica glass had a strong adhesion to the floor plate and broke when tried to forcefully peel it off. Also,
Cracks were also observed in some places in the silica glass.

[Effects of the Invention] According to the present invention, it is possible to easily separate the silica glass from the base plate, and to manufacture large-sized silica glass with few cracks by the sol-gel method.

Claims (1)

[Claims] 1. In a method for producing silica glass in which silicon alkoxide is hydrolyzed to obtain silica sol, which is gelled, dried to form a dry gel, and then sintered, in the step of sintering the dry gel, A method for producing silica glass characterized by placing dry gel on a porous plate and sintering it. 2. In the method for producing silica glass, in which silicon alkoxide is hydrolyzed to produce silica sol, this is gelled, dried to form a dry gel, and then sintered, the dry gel is sintered to improve its surface roughness. (Ra) is 0.1 to 1,
A method for producing silica glass, which comprises placing it on a base plate having a thickness of 0.000 μm and sintering it.