JPH01160834A - Quartz glass and production thereof - Google Patents

Abstract

PURPOSE:To produce quartz glass without striae in three directions, by dispersing silica fine particles in a hydrolyzate solution of an alkyl silicate, drying the resultant gel, heating the dried gel and vitrifying the formed glass (precursor) body. CONSTITUTION:An acidic catalyst is added to hydrolyze an alkyl silicate (e.g., ethyl silicate) and silica fine powder is then added to the resultant hydrolyzate solution obtained by the hydrolysis, sufficiently stirred and dispersed to form a sol. Aqueous ammonia is added to adjust the sol to pH3-6 and the resultant gel is dried to provide a dry gel, which is then heated in an atmosphere of O2/N2 and heated under reduced pressure of <=1Torr or in an He atmosphere at 1300-1500 deg.C to close pores and afford a glass (precursor) body. The obtained glass (precursor) body is subsequently heated at 1500-2200 deg.C and kept for a constant time.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to lenses of projection exposure apparatuses for integrated circuits, TPT substrates for liquid crystal displays, prisms, beam splitters, etc.
This invention relates to quartz glass that can be applied to optical components such as spectrometers, and a method for manufacturing the same.

[Conventional technology]

Quartz glass is classified into type I, type ■, type ■, and type ■, as shown in Table 1, depending on the melting method and the raw materials used.

Table 1 ■Type and ■type are used for semiconductor furnace core tubes and jigs.

The ■ type is used for IC mask substrates, optical prisms, lenses, cells, etc., and the ■ type is used for some optical applications.

[Problem that the invention seeks to solve]

However, all four conventional methods are basically melting methods, and are manufacturing methods that essentially generate striae. Therefore, when used for optical purposes, local areas without striae have been selected and used. However, when it comes to large lens applications, it is currently unavoidable to use quartz glass, which requires no unidirectional striae.

Due to its high purity and heat resistance, quartz glass has been used in semiconductor furnace core tubes and jigs. Also, since it has no absorption in the ultraviolet region, it has been used for IC mask substrates. Furthermore, it has been dehydrated and applied to optical fibers for communication, etc. What all of the above uses have in common is that striae do not pose much of a problem. The only optical parts that were required to be striae-free were small in quantity, so quartz glass, selected as mentioned above, was offered at nearly 10 times the normal price.

In the future, the demand for striae-free quartz glass will increase.0For example, projection lenses used to print patterns of integrated circuits such as IC1LSI onto silicon wafers using projection exposure equipment are required to use a light source with a wavelength of 150nm to 400r+n. With the advent of the use of quartz glass, projection lenses that could only use quartz glass and some crystals and required extremely high resolution had to be free of striae and also required a large size of 150 mm x 30 nm. ing. In addition, since the TPT substrate for liquid crystal display is also displayed through a polarizing plate,
There should be no striae. As expected, 3001WI x 300
There is a demand for large substrates such as city boards. Optical components such as beam splitters are predicted to become a large market in the future.

Until now, large quartz glass without three-way striae has not existed. Furthermore, a method for producing quartz glass that does not generate striae has not yet been established.

Therefore, an object of the present invention is to provide a quartz glass without three-way striae that can be applied to lenses of projection exposure devices for integrated circuits, TPT substrates for liquid crystal displays, and various optical components, and a method for producing the quartz glass. The purpose is to provide

[Means for solving problems]

To achieve the flush objective, the quartz glass of the present invention is characterized by the absence of three-way striae.

Further, the method for manufacturing quartz glass of the present invention is characterized in that it includes at least one or more of the steps shown below.

a) A step of hydrolyzing an alkyl silicate using an acidic catalyst.

b) A step of dispersing silica fine particles in the hydrolysis solution.

C) A step of adjusting the silica dispersion to a pH range of 3 to -6.

d) A step of gelling and drying the sol to form a dry gel.

e) A step of heating the dry gel to close the pores under reduced pressure or in a helium atmosphere to form a glass body or glass precursor.

f) The glass body or glass precursor is heated to 1500
A process of heating to a temperature between ℃ and 2200℃ and holding it for a certain period of time.

[For production]

Generally, striae are formed when the meltability of raw materials is poor, when refractories are eroded and dissolved into the melt, or when non-uniform temperatures occur during molding. The striae caused by the above causes are called soluble streaks, refractory streaks, and formed streaks, respectively.

The material of quartz glass is silicon dioxide, which has a melting point of over 1,700°C, and is difficult to melt and has a high viscosity, so it is unavoidable that liquefied streaks will occur. Furthermore, since it is difficult to obtain a high-temperature state in a high-purity atmosphere, the occurrence of refractory streaks is also difficult to avoid. Furthermore, since quartz glass is degassed by a manufacturing method that stacks a molten phase on top of a solid phase, non-uniform temperatures cannot be avoided. This is the reason why striae essentially occur in normal manufacturing methods.

On the other hand, in the sol-gel method, a homogeneous sol state is fixed by gelation, and then it is vitrified by uniform heating, so striae does not occur. The purity of the atmosphere is manageable. As described above, the sol-gel method is a manufacturing method that essentially does not generate striae, but unless a large glass body can be obtained, its applications are extremely limited, and even the measurement of striae is difficult. Even if it is just a few papers, the size of the standard striae sample is 50x50x20.

When fine silica particles are dispersed in a solution obtained by hydrolyzing an alkyl silicate using an acidic catalyst, a porous dry gel that does not crack during drying or sintering can be produced. When the pH of the sol is adjusted to a range of 3 to 6, the polymerization rate of tetrahydroxysilane, which is a hydrolysis product, is accelerated, the network structure is strengthened, and a strong structure that is difficult to crack is formed.

When dry gel, which is a porous material, is closed in pores under reduced pressure or in a helium atmosphere, the closed pores disappear by sintering and no bubbles remain.Furthermore, when heated to 1500-2200°C and held for a certain period of time, grain boundaries, Crystals, bubbles, and foreign matter can be completely removed, resulting in extremely high optical quality.

〔Example〕

Example 1゜0.0 to ethyl silicate at a weight ratio of 1:1
A hydrolysis solution was prepared by adding 2N hydrochloric acid and stirring for about 2 hours while cooling with water.

There, ultrafine powdered silica (Aerosil 0X-50
) was gradually added to the ethyl silicate in a molar ratio of 1:1, and the mixture was thoroughly stirred.

While keeping this sol at 20℃, 28kHz ultrasonic waves were applied for 2 hours.
After irradiation for a period of time, a centrifugal force of 1500 G was applied for 10 minutes, and the mixture was passed through a 1 μm filter.

The pH value of this sol was adjusted to 4.5 using 0.4N aqueous ammonia, and gelatinized over about 2 hours.

This gel body is transferred to a drying container with an open area ratio of approximately 0.3%, and dried in a constant temperature dryer kept at approximately 60°C in approximately 2 weeks, resulting in a porous structure that does not crack even when left in the air. A dry gel was obtained.

This porous body was once heated to 1000° C. in an oxygen/nitrogen atmosphere, and various treatments such as promotion of condensation reaction, dehydration, and removal of organic matter were performed. Vitrification was performed by heating to a maximum of 1400° C. while maintaining the degree of vacuum at ITorr or less using a vacuum furnace.

The glass body obtained in this way is a highly transparent colorless soul-like body, and the size can be increased to 300 x 30 OX 50 +
It was possible to produce an ingot of about n+.

To measure striae, a sample of 50 x 50 x 20 + m was cut out and polished parallel to each other, and striae were measured in three directions using the method specified in the Japan Optical Glass Industry Association standards, but no striae were observed. It was grade 1 in terms of direction.

I also tried polishing it to a size of 300x300x5+m+ and rotating the polarizing plates sandwiched in parallel while shining a backlight, but no streak-like or layer-like non-uniform parts could be detected.

Example 2゜Ethyl silicate, ethanol, water, ammonia water (2
9%) at a molar ratio of 6:4:0°08, stirred for about 5 hours, aged at room temperature for several days, and concentrated under reduced pressure to obtain a mixture with good dispersibility. A silica fine particle solution was prepared.

Next, prepare twice the amount of ethyl silicate as the previous ethyl silicate, add 0.02 N hydrochloric acid so that the weight ratio is 1:1, and stir for about 2 hours while cooling with water to form a hydrolyzed solution. was prepared.

The pH value of the silica fine particle solution was adjusted to 4.0 using 2N hydrochloric acid.
5, the hydrolyzate was mixed and sufficiently stirred until a homogeneous solution was obtained. Then, the pH value of this solution was adjusted to 0.
Adjust to 5.0 using 4-normal ammonia water, about 50
It took several minutes to gel.

This gel body is dried in a polypropylene drying container (with an opening ratio of 0.
3%) and dried in a constant temperature dryer kept at about 60°C for about 2 weeks to obtain a porous gel body that does not crack even when left in the air.

This gel body is heated to 800°C in an oxygen/nitrogen atmosphere, and after various treatments such as promotion of condensation reaction, dehydration, and removal of organophilic substances, the inside of the furnace is changed to a helium atmosphere,
It was heated to 0°C to vitrify it. Further, the temperature was raised to 1750°C in a nitrogen atmosphere, held for 10 minutes, and then rapidly cooled.
Strain removal was performed in an annealing furnace.

The glass body thus obtained was a colorless block with high transparency, and it was possible to produce an ingot of about 300 x 300 x 50 m in size.

Striae were measured in the same manner as in Example 1, but no striae were detected in all three directions.

Example 3 First, a silica fine particle solution was prepared in the same manner as in Example 2. Next, a hydrolyzed solution was prepared in the same manner from 4 times the amount of ethyl silicate.

Thereafter, the sol was mixed, pH value adjusted, gelled, and dried in exactly the same manner as in Example 2 to obtain a porous gel body that would not break even when left in the air.

This gel body was once heated to 800° C. in an oxygen/nitrogen atmosphere, and then set in a vacuum furnace equipped with a quartz glass jig to prevent contamination from the furnace. Reduce the degree of pressure reduction to 0. IT
When heated up to a maximum of 1300° C. while maintaining the temperature below orr, a milky white glass precursor was obtained which was not completely transparent but had completed pore closure. Next, the temperature was raised to 1720° C. in a nitrogen atmosphere, held for 30 minutes, and rapidly cooled to obtain a highly transparent glass body. Furthermore, sufficient strain was removed in an annealing furnace.

The glass body thus obtained was examined using the striae measurement method shown in Example 1, but striae were not detected in all three directions.

〔Effect of the invention〕

As described above, according to the present invention, quartz glass can be applied to lenses of projection exposure apparatuses for integrated circuits, TPT substrates for liquid crystal displays, and various optical components due to the absence of three-way striae.

Furthermore, by including at least one or more of the steps shown below, it was possible to provide a method for producing quartz glass free of three-way striae that satisfies the above conditions.

a) A step of hydrolyzing an alkyl silicate using an acidic catalyst.

b) A step of dispersing silica fine particles in the hydrolysis liquid.

C) A step of adjusting the pH of the silica dispersion to a range of 3 to 6.

d) A step of gelling and drying the sol to form a dry gel.

e) A step of heating the dry gel to close the pores under reduced pressure or a helium atmosphere to form a glass body or glass precursor.

f) The glass body or glass precursor is heated to 1500
A process of heating to a temperature between ℃ and 2200℃ and holding it for a certain period of time.

that's all Applicant: Seiko Epson Corporation

Claims (2)

[Claims] (1) Quartz glass characterized by the absence of three-way striae. (2) A method for producing quartz glass, which includes at least one or more of the following steps. a) A step of hydrolyzing an alkyl silicate using an acidic catalyst. b) A step of dispersing silica fine particles in the hydrolysis liquid. c) A step of adjusting the pH of the silica dispersion to a range of 3 to 6. d) A step of gelling and drying the sol to form a dry gel. e) A step of heating the dry gel to close the pores under reduced pressure or a helium atmosphere to form a glass body or a glass precursor. f) The glass body or glass precursor is heated to 1500°C.
A process of heating to ~2200°C and holding for a certain period of time.