JPH05301733A - Silica glass and its production - Google Patents

Abstract

PURPOSE:To improve the uniformity, purity and heat resistance of silica glass by heat-treating a silica porous body in specific conditions and vitrifying the porous body. CONSTITUTION:Glass fine particles obtained by hydrolyzing a raw material such as SiCl4 with flame are deposited to afford a silica porous body. The silica porous body is subjected to the first heat treatment in an oxidative or inert gas atomsphere containing no water content at 600-1400 deg.C for 1-8hr and then subjected to the second heat treatment in an inert gas atmosphere containing >=1vol% nitrogen compound at 600-1400 deg.C for 1-10hr. Then the treated silica porous body is subjected to the third heat treatment in an inert gas atmosphere containing >=1vol% oxygen at 600-1400 deg.C for 1-10hr and sintered to provide the objective vitribed transparent silica glass having <=10ppm OH group concentration, <=50ppm halogen element concentration, each <=10ppb of all metal impurity elements and having >=11.80 (pa.sec) viscosity (log eta) at 120 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to silica glass and a method for producing the same, and more specifically, it is a porous body composed of silica glass and silica fine particles having high purity, high heat resistance and no UV absorption at high temperature. The present invention relates to a method for producing silica glass, which comprises performing pretreatment heating, heat treatment in a gas atmosphere containing a nitrogen compound to dehydrate (deOH), and then subjecting to oxidation treatment, followed by vitrification.

[0002]

2. Description of the Related Art In recent years, demands for improving the physical properties of silica glass have been increasing. Silica glass has a wide variety of applications, and in particular, when it is used for jigs and tools used in semiconductor manufacturing and for liquid crystal display substrates, improvement in purity and heat resistance is strongly required.

Conventionally, for applications requiring heat resistance such as semiconductor manufacturing jigs and tools and substrates for liquid crystal displays,
A glass (fused silica glass) obtained by melting a naturally occurring crystal at a temperature exceeding 2000 ° C. has been used.

However, since this fused silica glass is made from natural quartz, the presence of a small amount of metallic impurities is unavoidable. For this reason, most of fused silica glass has been used for semiconductor manufacturing jigs and tools, but in recent years, the degree of integration of semiconductors has improved dramatically, with the result that slight contamination from jigs and tools has occurred. Has become a problem. Further, although fused silica glass has been conventionally used for liquid crystal display substrates, semiconductor elements have come to be incorporated with the recent trend of colorization and higher image quality. There has been a strong demand for improved purity. As a result, silica glass that can be used in these fields is being converted from fused silica glass to high-purity synthetic silica glass.

As a conventional method for obtaining a high-purity synthetic silica glass, 1) a synthesized high-purity raw material such as silicon tetrachloride is hydrolyzed in an oxyhydrogen flame, and this is heated at 2000 ° C.
Direct method of heating to high temperature around and depositing and vitrifying 2)
There is a vapor phase method in which a high-purity synthetic raw material such as silicon tetrachloride is hydrolyzed to generate and deposit glass fine particles into a silica porous material, and the porous material is sintered to form silica glass.

The silica glass obtained by these manufacturing methods has a high purity and metal impurities are ppb or ppt.
At virtually no level.

[0007]

However, when silica glass is used in jigs and tools for semiconductor manufacturing, liquid crystal display substrates, etc., high purity and heat resistance are required. There is a problem with sex.

That is, the silica glass produced by the direct method always contains about 1000 ppm of OH groups. If the silica glass contains OH groups, the heat resistance of the glass will deteriorate. The OH groups contained in the silica glass produced by the direct method are very difficult to remove from the glass by post-treatment.

The silica glass obtained by vitrifying the porous silica material produced by the vapor phase method also basically contains OH groups. This silica porous body is then vitrified by sintering. Therefore, even in the case of silica glass by the vapor phase method, since the glass fine particles are generated by hydrolysis, if the silica porous body is directly sintered and vitrified without any treatment, it will be slightly different depending on the sintering conditions. ,
The silica glass obtained usually has several tens to several hundreds of ppm.
OH groups are included. For this reason, the heat resistance is inferior to that of fused silica glass by the direct method, but inferior to that of fused silica glass, and is not sufficient for some applications.

The difference between the vapor phase method and the direct method is that the direct method vitrifies the raw material immediately after hydrolysis, whereas the vapor phase method can go through a state of a porous body once. Various treatments such as dehydration treatment and dope treatment can be performed in the state of the porous body. For example, when it is desired to remove OH groups that impair heat resistance from the glass, dehydration treatment is performed in the state of the porous silica material. The dehydration treatment is a treatment in which the porous silica material is heated at about 1000 ° C. in a gas atmosphere containing a halogen element such as chlorine gas. By the dehydration treatment, the silica porous body has no OH group, and the glass obtained by subsequent sintering does not contain any OH group.

However, the glass obtained by the dehydration treatment usually contains several hundred to several thousand ppm of the halogen element used in the dehydration treatment. The vapor phase method was originally developed for the purpose of manufacturing optical fibers, and we hate the existence of OH groups that increase transmission loss, but halogen elements such as chlorine and fluorine do not cause loss, so their existence Hasn't been a big issue so far. On the other hand, when silica glass is used for jigs and tools for semiconductor manufacturing and liquid crystal display substrates, the presence of halogen elements impairs the heat resistance of the glass, which is not preferable. Further, in the case of a halogen element present in silica glass, when exposed to a high temperature, it becomes a halogen gas and is released from the glass into the atmosphere, so that there is a problem that peripheral devices are corroded by this gas. ..

Therefore, when manufacturing silica glass used for semiconductor manufacturing jigs and liquid crystal display substrates, it is necessary to use a gas containing no halogen element as the gas used for the dehydration treatment. As such a gas, a nitrogen compound gas, in particular, ammonia gas is known because of its economical efficiency, availability and handling. In the case of ammonia, as in the case of a halogen-containing gas such as chlorine, the silica porous base material is heat-treated in an ammonia gas atmosphere.
Silica glass containing neither OH group nor halogen element can be obtained by vitrification after dehydration treatment with ammonia. In this case, nitrogen is taken into the glass.
The effect of nitrogen in silica glass on the heat resistance of the glass brings about a good result that the heat resistance of the glass is improved unlike the OH group and the halogen element. In fact, the silica glass obtained by vitrification after dehydration treatment with ammonia gas was observed to have a marked improvement in heat resistance (viscosity at high temperature as a guideline).

However, in the silica glass obtained by vitrification after subjecting to dehydration treatment with ammonia gas, when ultraviolet transmittance is examined, absorption occurs near 240 nm. This absorption may have an adverse effect on defocus etc. in the lithography step in the semiconductor manufacturing process.

Further, the silica porous material obtained by the vapor phase method is
It is obtained by depositing glass particles generated by flame hydrolysis of the raw material.The glass particles have a temperature distribution in the flame, which is the reaction field, so the heat generated during the generation depends on the reaction location in the flame. History is different.
Therefore, the silica porous body, which is a deposited body of glass fine particles, has different physical properties at its site, for example, at the center and outside, due to the difference in thermal history of the fine particles. When glass is obtained by subjecting this porous silica material to a dehydration treatment (a gas containing a halogen element such as chlorine, ammonia gas, etc.) without any treatment, this difference in physical properties is inherited by the obtained glass. Regarding the viscosity at high temperature, which is one of them, it means that the viscosity at the same temperature is different between the center part of the glass and the outside, which means that when the glass is processed, the diameter when drawn into a pipe or fiber shape. Is not stable and becomes a big problem.

The present invention has been made in view of the above problems, and its purpose is not only metal impurities but also OH.
It is an object of the present invention to provide a silica glass that does not contain a group or a halogen element, has high purity and high heat resistance, is homogeneous in the same glass lump without different physical properties, and does not absorb ultraviolet light at high temperature, and a method for producing the same.

[0016]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors have found that silica glass having high purity, high heat resistance, homogeneity and no absorption of ultraviolet rays is a metal impurity. In addition to elements, it is a glass that does not have OH groups and halogen elements, which have not been a problem in the past, and in order to obtain such silica glass, a porous body composed of silica fine particles is dried in a dry atmosphere. After heat treatment,
The inventors have found that it is sufficient to perform a dehydration treatment using a nitrogen compound gas as a dehydrating agent, then heat-treat it in an oxygen gas atmosphere, and then vitrify it, thereby completing the present invention.

That is, according to the present invention, the concentration of OH groups contained in the glass is 10 ppm or less and the concentration of halogen elements is 50.
ppm or less, all metal impurity elements are 10 ppb or less, and the viscosity at 1200 ° C. is logη =
A silica glass of 11.80 (Pa · sec) or more and a method for producing the same.

The present invention will be described in more detail below.

The silica glass in the present invention has an OH group concentration of 10 ppm or less and a halogen element concentration of 50 ppm or less contained in the glass. OH group concentration is 10
When the concentration of the halogen element is 50 ppm or less and the halogen element concentration is 50 ppm or less, the heat resistance is high, and further, in order to improve the heat resistance, the OH group concentration is preferably 1 ppm or less.

In the silica glass of the present invention, all metal impurity elements are 10 ppb or less. Therefore, the amount of metal impurities is small and the purity is high.

The silica glass in the present invention is 1200
The viscosity at ° C is log η = 11.80 (Pa · se
c) or more. Here, as an indication of the heat resistance of the glass, there is a method of measuring the viscosity of the glass,
This is to measure the viscosity of glass at 1200 ° C. by a beam bending method or the like. In the conventional fused silica glass, the viscosity at 1200 ° C. is logη =
It is about 11.70 (Pa · sec). Therefore, the silica glass of the present invention has higher heat resistance than the conventional fused silica glass.

In the production method of the present invention, the silica porous material obtained by the vapor phase method or the like is heat-treated in a dry atmosphere as a first heat treatment, and then a nitrogen compound is used as a second heat treatment. The dehydration treatment is performed in a gas atmosphere containing oxygen, and the third heat treatment is heat treatment in a gas atmosphere containing oxygen, followed by vitrification.

The method for obtaining the silica porous material is not particularly limited, but for example, raw materials such as silicon tetrachloride are subjected to flame hydrolysis to generate glass fine particles, and the glass fine particles are deposited to form the silica porous material. A vapor phase method for obtaining a substance is given, for example, an external CVD method, an internal C method.
There are a VD method, a vapor phase axis attaching method (VAD method) and the like.

The first heat treatment is not limited to any atmosphere such as an oxidizing atmosphere, a reducing atmosphere, an inert atmosphere or a vacuum atmosphere as long as the atmosphere does not contain water.
In order to avoid generation of H, Si—O radicals, etc., an oxidizing or inert atmosphere is preferable. The first heat treatment is pre-sintering for improving the homogeneity of the obtained silica glass, and the temperature is 600 to 140.
It is necessary to carry out at 0 ° C. If the temperature is lower than 600 ° C, the effect of pre-sintering cannot be obtained, and 1400 ° C
If it exceeds, the sintering will proceed and the pores of the porous body will be closed, making it impossible to perform the subsequent treatment. It should be noted that the sintering of the glass particles progresses to some extent, but the porous state is still maintained, so that it is more preferable to perform the sintering in the range of 1000 to 1 ° C and 50 ° C. The first heat treatment temperature is the second,
It may be higher than the third heat treatment temperature. The treatment time varies depending on the diameter of the silica porous matrix,
For example, when the diameter is 500 mm or less, it is preferably 1 to 8 hours in consideration of effects and productivity.

The second heat treatment is a dehydration step using a nitrogen compound gas, and if the atmosphere contains the nitrogen compound gas, the atmosphere is either 100% nitrogen compound gas or diluted nitrogen compound gas atmosphere. is not. When diluting the nitrogen compound gas, the diluent gas is not particularly limited as long as it does not interfere with the dehydration action of the nitrogen compound gas, and examples thereof include an inert gas such as N ₂ or He. Be done. Moreover, the dilution ratio is not particularly limited, but the nitrogen compound gas 1 vol. % Or more is preferable. If the temperature is lower than 600 ° C., the dehydration reaction does not proceed sufficiently, and OH groups remain 10 ppm or more in the obtained glass.
Further, at a temperature higher than 1400 ° C., the silica porous matrix undergoes sintering from a porous state to a closed state, and bubbles remain in the resulting glass, so that the dehydration reaction proceeds sufficiently. And, it remains porous 60
It is necessary to carry out at 0 to 1400 ° C. The treatment time depends on the diameter of the silica porous matrix, but for example,
When the diameter is 500 mm or less, it is preferably 1 to 10 hours in consideration of effects and productivity.

Since the third heat treatment is an oxidation step, it is not particularly limited to an atmosphere containing 100% oxygen or diluted oxygen as long as it is an atmosphere containing oxygen. When diluting oxygen, the diluting gas is not particularly limited as long as it does not interfere with the oxidizing action of oxygen. For example, N ₂
And an inert gas such as He. In addition, the ratio in the case of diluting is not particularly limited, but oxygen 1 vol. % Or more is preferable. As for the temperature, the oxidation reaction proceeds sufficiently, and
Silica porous matrix remains porous 60
It needs to be performed within the range of 0 to 1400 ° C. If the temperature is lower than 600 ° C., the oxidation reaction does not proceed sufficiently, and if it exceeds 1400 ° C., the sintering proceeds and the pores of the porous body are closed, so that the treatment thereafter cannot be performed.
Note that the third heat treatment temperature is preferably higher than or equal to the treatment temperature in the second heat treatment in order to compensate for defects that may occur in the second heat treatment. The treatment time varies depending on the diameter of the porous silica base material. For example, when the diameter is 500 mm or less, it is preferably 1 to 10 hours in consideration of effects and productivity.

Silica glass can be obtained by sintering and vitrifying the silica porous base material which has been treated by the above method, and the vitrification may be carried out by a commonly used method.

[0028]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Example 1 Silicon tetrachloride was subjected to flame hydrolysis with an oxyhydrogen flame burner to generate glass fine particles, which were axially deposited on a target to obtain a porous silica preform of about 400 mm × 1000 mm. .. This silica porous base material was inserted into a furnace core tube provided in a uniform heating type electric furnace, and a first heat treatment was performed at a temperature of 1000 ° C. for 2 hours in a 100% N ₂ atmosphere.
Then, 10 vol. % NH ₃ -90vol. A second heat treatment (dehydration treatment) was performed at a temperature of 600 ° C. for 2 hours in a% N ₂ atmosphere. After the second heat treatment, after purging the inside of the furnace core tube with N ₂ gas, 5 vol. % O ₂ -95 vol. % N
_A third heat treatment was performed in a ₂ atmosphere at a temperature of 1000 ° C. for 2 hours.

After completion of the treatment, the silica porous base material was inserted into a furnace core tube provided in an electric furnace of zone heating system, and 100%
It was gradually pulled down to a heating zone at 1500 ° C. in a He atmosphere, and was transparentized from the lower end to obtain silica glass. A part of the obtained glass was cut, and quantitative analysis of OH groups, Cl, and all metal elements contained in the glass was carried out. The results were 7 ppm, less than 50 ppm, and 10 ppb, respectively.
Was less than.

When the transmittance of ultraviolet rays was measured, no peculiar absorption was observed and good transmittance was exhibited as shown in FIG. Further, a test piece for high temperature viscosity measurement was cut out from the center at 10 points, and the viscosity of each glass at 1200 ° C. was measured by a beam bending method. Log η = 12.07 ± 0.01 (Pa · s
ec).

Comparative Example 1 By the same method as in Example 1, a silica porous matrix having substantially the same size was obtained. This silica porous base material was inserted into a furnace core tube provided in a uniform heating type electric furnace, and a first heat treatment was performed at a temperature of 1000 ° C. for 2 hours in a 100% N ₂ atmosphere. Then 10 vol. % NH ₃ -90vol. % N ₂
A second heat treatment (dehydration treatment) was performed at a temperature of 500 ° C. for 2 hours in the atmosphere. After the second heat treatment, after purging the inside of the furnace core tube with N ₂ gas, 5 vol. % O ₂ -95 vol. % N
_A third heat treatment was performed in a ₂ atmosphere at a temperature of 1000 ° C. for 2 hours.

After the completion of the treatment, the silica porous base material was inserted into a furnace core tube provided in an electric furnace of zone heating system, and 100% was added.
It was gradually pulled down to a heating zone at 1500 ° C. in a He atmosphere, and was transparentized from the lower end to obtain silica glass. A part of the obtained glass was cut, and quantitative analysis of OH groups, Cl, and total metal elements contained in the glass was carried out. The results were 20 ppm, less than 50 ppm, and 10 pp, respectively.
It was less than b.

When the transmittance of ultraviolet rays was measured, no peculiar absorption was observed and good transmittance was exhibited as shown in FIG. Further, a test piece for high temperature viscosity measurement was cut out from the center at 10 points, and the viscosity of each glass at 1200 ° C. was measured by a beam bending method. Log η = 11.65 ± 0.01 (Pa · s
ec).

Comparative Example 2 By the same method as in Example 1, a silica porous matrix having substantially the same size was obtained. This silica porous base material was inserted into a furnace core tube provided in a uniform heating type electric furnace, and a first heat treatment was performed at a temperature of 1000 ° C. for 2 hours in a 100% N ₂ atmosphere. Then 10 vol. % NH ₃ -90vol. % N ₂
A second heat treatment (dehydration treatment) was performed at a temperature of 600 ° C. for 2 hours in the atmosphere. After completion of the treatment, the third porous heat treatment was not performed, and the porous silica preform was inserted into the furnace core tube provided in the electric furnace of the zone heating system, and the silica was heated in the 100% He atmosphere at 150%.
Gradually pulled down to a heating zone of 0 ° C., and transparentized glass was obtained from the lower end to obtain silica glass. A part of the obtained glass was cut, and quantitative analysis of OH groups, Cl, and all metal elements contained in the glass was carried out.
m, less than 50 ppm, less than 10 ppb.

When the transmittance of ultraviolet rays was measured, as shown in FIG. 2, absorption estimated to be caused by oxygen defects was observed near a wavelength of 240 nm. Further, a test piece for high temperature viscosity measurement was cut out from the center at 10 points, and the viscosity of each glass at 1200 ° C. was measured by a beam bending method. Log η = 12.09 ±
It was 0.03 (Pa · sec).

Example 2 By the same method as in Example 1, a silica porous matrix having substantially the same size was obtained. This silica porous base material was inserted into a furnace core tube provided in an electric furnace of uniform heating system, and the temperature was set to 1000 in a 100% N ₂ atmosphere.
The first heat treatment was carried out at 0 ° C. for 2 hours. Then 10vο
l. % NH ₃ -90vol. % N ₂ atmosphere, temperature 70
A second heat treatment (dehydration treatment) was performed at 0 ° C. for 2 hours. After the second heat treatment, after purging the inside of the furnace core tube with N ₂ gas, 5
vol. % O ₂ -95 vol. % N ₂ atmosphere, temperature 1
A third heat treatment was performed at 000 ° C for 2 hours.

After the completion of the treatment, the silica porous base material was inserted into a furnace core tube provided in a zone heating type electric furnace, and 100% was added.
It was gradually pulled down to a heating zone at 1530 ° C. in a He atmosphere, and transparent glass was formed from the lower end to obtain silica glass. Part of the obtained glass was cut, and quantitative analysis of OH groups, Cl, and all metal elements contained in the glass was performed.
It was less than pb.

When the transmittance of ultraviolet rays was measured, no specific absorption was observed and it was the same as in Example 1. Further, the test piece for high temperature viscosity measurement is moved from the center to the outside by 10
The points were cut out, and the viscosity of each glass at 1200 ° C. was measured by the beam bending method.
It was gη = 12.35 ± 0.01 (Pa · sec).

Comparative Example 3 By the same method as in Example 1, a silica porous matrix having substantially the same size was obtained. This silica porous base material was inserted into a furnace core tube provided in an electric furnace of uniform heating system, and 10 vol. % NH ₃ -90vol. % N
_{A second} heat treatment (dehydration treatment) was performed at a temperature of 700 ° C. for 2 hours in _two atmospheres. After the second heat treatment, without performing the third heat treatment, the silica porous base material was inserted into a furnace core tube provided in an electric furnace of a zone heating system, and was heated in a heating zone at 1530 ° C. in a 100% He atmosphere. The silica glass was obtained by gradually pulling it down and turning it into a transparent glass from the lower end. A part of the obtained glass is cut, and OH groups and C contained in the glass are cut.
Quantitative analysis of 1 and all metal elements revealed that they were less than 1 ppm, less than 50 ppm and less than 10 ppb, respectively.

When the transmittance of ultraviolet rays was measured, Comparative Example 1
In the same manner as above, absorption supposed to be caused by oxygen defects was observed near the wavelength of 240 nm. Further, a test piece for high temperature viscosity measurement was cut out from the center at 10 points, and the viscosity of each glass at 1200 ° C. was measured by a beam bending method. Log η = 12.43
It was ± 0.04 (Pa · sec).

Comparative Example 4 By the same method as in Example 1, a silica porous matrix having substantially the same size was obtained. This silica porous base material was inserted into a furnace core tube provided in an electric furnace of uniform heating system, and 10 vol. % Cl ₂ -90 vol. % N
_{A second} heat treatment (dehydration treatment) was performed at a temperature of 800 ° C. for 2 hours in _two atmospheres. After the second heat treatment, without performing the third heat treatment, the porous silica preform was inserted into a furnace core tube provided in an electric furnace of a zone heating system, and heated in a heating zone at 1500 ° C. in a 100% He atmosphere. The silica glass was obtained by gradually pulling it down and turning it into a transparent glass from the lower end. A part of the obtained glass is cut, and OH groups and C contained in the glass are cut.
Quantitative analysis of 1 and all metal elements showed less than 1 ppm, 1500 ppm and less than 10 ppb, respectively.

When the transmittance of ultraviolet rays was measured, Comparative Example 1
In the same manner as above, absorption supposed to be caused by oxygen defects was observed near the wavelength of 240 nm. Further, a test piece for high temperature viscosity measurement was cut out from the center at 10 points, and the viscosity of each glass at 1200 ° C. was measured by a beam bending method. Log η = 11.28
It was ± 0.04 (Pa · sec).

Example 3 By the same method as in Example 1, a silica porous matrix having substantially the same size was obtained. This silica porous base material was inserted into a furnace core tube provided in a uniform heating type electric furnace, and a first heat treatment was performed at a temperature of 1000 ° C. for 2 hours in a 100% N ₂ atmosphere. Then 10 vol. % NH ₃ -90vol. % N ₂
A second heat treatment (dehydration treatment) was performed at a temperature of 1000 ° C. for 2 hours in the atmosphere. After the second heat treatment, after purging the inside of the furnace core tube with N ₂ gas, 5 vol. % O ₂ -95 vol. %
A third heat treatment was performed at a temperature of 1000 ° C. for 2 hours in an N ₂ atmosphere.

After completion of the treatment, the silica porous base material was inserted into a furnace core tube provided in an electric furnace of zone heating system, and 100% was added.
Gradually pulling it down to a heating zone of 1550 ° C. in He atmosphere, and transparent glass was obtained from the lower end to obtain silica glass. Part of the obtained glass was cut, and quantitative analysis of OH groups, Cl, and all metal elements contained in the glass was performed.
It was less than pb.

When the transmittance of ultraviolet rays was measured, no specific absorption was observed and it was the same as in Example 1. Further, the test piece for high temperature viscosity measurement is moved from the center to the outside by 10
The points were cut out, and the viscosity of each glass at 1200 ° C. was measured by the beam bending method.
It was gη = 12.43 ± 0.01 (Pa · sec).

Example 4 By the same method as in Example 1, a silica porous matrix having substantially the same size was obtained. This silica porous base material was inserted into a furnace core tube provided in an electric furnace of uniform heating system, and first heat treatment was carried out at a temperature of 1300 ° C. for 4 hours in a 100% N ₂ atmosphere. Then 10 vol. % NH ₃ -90vol. % N ₂
A second heat treatment (dehydration treatment) was performed at a temperature of 1000 ° C. for 2 hours in the atmosphere. After the second heat treatment, after purging the inside of the furnace core tube with N ₂ gas, 5 vol. % O ₂ -95 vol. %
A third heat treatment was performed at a temperature of 1000 ° C. for 2 hours in an N ₂ atmosphere.

After completion of the treatment, the silica porous base material was inserted into a furnace core tube provided in a zone heating type electric furnace, and 100% was added.
Gradually pulling it down to a heating zone of 1550 ° C. in He atmosphere, and transparent glass was obtained from the lower end to obtain silica glass. Part of the obtained glass was cut, and quantitative analysis of OH groups, Cl, and all metal elements contained in the glass was performed.
It was less than pb.

When the transmittance of ultraviolet rays was measured, no specific absorption was observed and it was the same as in Example 1. Further, the test piece for high temperature viscosity measurement is moved from the center to the outside by 10
The points were cut out, and the viscosity of each glass at 1200 ° C. was measured by the beam bending method.
gη = 12.40 ± 0.01 (Pa · sec).

Comparative Example 5 By the same method as in Example 1, a silica porous base material having substantially the same size was obtained. This silica porous base material was inserted into a furnace core tube provided in a uniform heating type electric furnace, and a first heat treatment was performed at a temperature of 1000 ° C. for 2 hours in a 100% N ₂ atmosphere. Then 10 vol. % Cl ₂ · 90 vol. % N ₂
A second heat treatment (dehydration treatment) was performed at a temperature of 800 ° C. for 2 hours in the atmosphere. After completion of the treatment, the third porous heat treatment was not performed, and the porous silica preform was inserted into the furnace core tube provided in the electric furnace of the zone heating system, and the silica was heated in the 100% He atmosphere at 150%.
Gradually pulled down to a heating zone of 0 ° C., and transparentized glass was obtained from the lower end to obtain silica glass. A part of the obtained glass was cut, and quantitative analysis of OH groups, Cl, and all metal elements contained in the glass was carried out.
It was less than m, less than 500 ppm, and less than 10 ppb.

When the transmittance of ultraviolet rays was measured, Comparative Example 1
Similarly to the above, absorption presumed to be caused by oxygen defects was observed near the wavelength of 240 nm. Further, a test piece for high temperature viscosity measurement was cut out from the center at 10 points, and the viscosity of each glass at 1200 ° C. was measured by a beam bending method, and log η = 11.46 ±
It was 0.02 (Pa · sec).

[0052]

As is apparent from the above description, according to the present invention, it is possible to obtain a silica glass having high purity, high heat resistance, homogeneity, and no ultraviolet absorption at high temperature. is there. Therefore, this silica glass is preferably used as a material for semiconductor manufacturing jigs and tools, liquid crystal display substrates, and the like, which must have both high purity and high heat resistance.

[Brief description of drawings]

FIG. 1 is a diagram showing the transmittance of ultraviolet rays.

FIG. 2 is a diagram showing the transmittance of ultraviolet rays.

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[Procedure amendment]

[Submission date] May 21, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction content]

[0001]

BACKGROUND OF THE INVENTION This invention relates to silica glass and a manufacturing method thereof, particularly, high purity, high heat resistance, the porous body consisting of ultraviolet absorbing no silica glass and silica particles The present invention relates to a method for producing silica glass, which comprises performing pretreatment heating, heat treatment in a gas atmosphere containing a nitrogen compound to dehydrate (deOH), then oxidizing treatment, and then vitrifying.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction content]

The present invention has been made in view of the above problems, and its purpose is not only metal impurities but also OH.
It is to provide a silica glass which does not contain a group or a halogen element, has high purity and high heat resistance, is homogeneous in the same glass lump without different physical properties , and has no ultraviolet ray absorption, and a method for producing the same. ..

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0052

[Correction method] Change

[Correction content]

[0052]

As apparent from the above description, by the present invention Repa, high purity, high heat resistance, homogeneous and has an advantage of being able to obtain the ultraviolet absorption is not silica glass .. Therefore, this silica glass is preferably used as a material for semiconductor manufacturing jigs and tools, liquid crystal display substrates, and the like, which must have both high purity and high heat resistance.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshiyuki Taga 1264 276 Osaki, Hofu, Yamaguchi Prefecture (72) Inventor Koji Tsukuma 1-18-7 Fujisaki, Tsuchiura City, Ibaraki (72) Inventor Tomoyuki Akiyama 1-18-7 Fujisaki, Tsuchiura City, Ibaraki Prefecture

Claims (2)

[Claims] 1. The concentration of OH groups contained in glass is 10 p.
pm or less, halogen element concentration is 50 ppm or less, all metal impurity elements are 10 ppb or less, and 1
The viscosity at 200 ° C. is log η = 11.80 (Pa ·
sec) or more, which is a silica glass. 2. A porous silica material is subjected to a first heat treatment at a temperature of 600 to 1400 ° C. in an atmosphere containing no water, and then 600 in a gas atmosphere containing a nitrogen compound.
Perform a second heat treatment at a temperature of ~ 1400 ° C, and
The method for producing silica glass according to claim 1, wherein vitrification is performed after the third heat treatment is performed at a temperature of 600 to 1400 ° C. in a gas atmosphere containing oxygen.