JPH10114533A - Production of high purity transparent silica glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high purity transparent silica glass almost free from bubbles and a crystallized part and not undergoing a density change by heating or the penetration of gas by melting high purity amorphous silica powder obtd. from silicon alkoxide by heating in an atmosphere under reduced pressure, giving a pressurized state with inert gas and subjecting the resultant transparent silica glass to hot isostatic pressing. SOLUTION: High purity amorphous silica powder cong. An, K, Mg, Ca, Fe, Al and Ti by <=0.1ppm each obtd. from silicon alkoxide is used as starting material, heat-treated and pressurized to produce high purity silica glass. At this time, the starting material is held at a temp. at which the powder is meltable in an atmosphere under a reduced pressure of <=10mmHg, bubbles each having >=1mm diameter are diminished by gibing a pressurized state of >=2kgf/ cm<2> with inert gas and bubbles each having <1mm diameter and diminished by applying 100-200MPa pressure by inert gas at 1,200-1,350 deg.C with a hot isostatic press. Heat treatment at 1,000-1,300 deg.C and slow cooling are then carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing high-purity transparent silica glass with reduced bubbles. More specifically, the present invention relates to a method for producing a high-purity transparent silica glass that can be used as a material for various optical materials utilizing high light transmittance and a high-temperature liquid crystal substrate.

[0002]

2. Description of the Related Art Various synthetic silica powders are mixed under reduced pressure atmosphere.
A method for producing a transparent silica glass by heating to 800 to 1900 ° C. has been conventionally known. For example, JP
-37120, JP-A-3-5329, JP-A-2-229
In 735, silica powder obtained by calcining a gel obtained by hydrolyzing alkoxysilane is mixed under reduced pressure atmosphere for 150 minutes.
A method for producing a transparent silica glass by heating to 0 to 2200 ° C. is disclosed. In such a method, transparent silica glass with high purity can be obtained relatively easily,
The resulting glass contains air bubbles. The form of the bubble is 10
When small air bubbles of １００100 μm are scattered or 0.5 to 2 m
It varies depending on the production method, for example, when bubbles having a large m are scattered. When such a glass is kept at 1200 to 1500 ° C. for a long time, there is a disadvantage that the periphery of the bubbles is crystallized.

Further, Japanese Patent Publication No. 59-34660 and Japanese Patent Application Laid-Open
7-34031 discloses a method of applying a high-pressure gas in a temperature range of 1000 to 1500 ° C. as a method for reducing bubbles in silica glass. Although such a method is certainly effective in reducing bubbles, the resulting glass has a higher density than ordinary quartz glass, and if the silica glass having the higher density is used as it is, the silica glass expands. Had the disadvantage of doing so. Further, there is also a problem that when high pressure gas pressure is applied, gas enters the surface of the silica glass and foaming or the like may occur.
Furthermore, such silica glass is inferior in homogeneity (Δn) to ordinary silica glass.

[0004] Problems such as generation of bubbles, crystallization, density change, and gas infiltration are caused by various optical materials utilizing light transmissivity, applications such as high temperature type liquid crystal substrates, and semiconductor manufacturing which is used at high temperatures for a long time. Not suitable for applications such as jigs
Materials that do not have these problems have been desired.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned problems of the prior art and to use various optical materials utilizing light transmissivity, high temperature type liquid crystal substrates, etc. An object of the present invention is to provide a method for producing a high-purity transparent silica glass which has extremely few bubbles or crystallized portions applicable to applications such as a jig for a semiconductor manufacturing apparatus to be used, and has no change in density or intrusion of gas due to heating.

[0006]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have obtained a high-purity amorphous silica powder obtained from silicon alkoxide under high-pressure atmosphere. By heating and melting to a temperature at which the pure amorphous silica powder can be melted, and then pressurizing with an inert gas, and subjecting the obtained transparent silica glass to hot isostatic pressing, a diameter of 1 mm in the glass is obtained. The present inventors have found that bubbles less than less can be effectively reduced, and further, by reheating the high-purity transparent silica glass, the density can be returned and the invading gas can be removed, and the present invention has been completed.

That is, according to the present invention, Na, K, Mg, Ca, Fe, Al, Ti
Is a high-purity amorphous silica powder obtained from a silicon alkoxide having a content of 0.1 ppm or less, and a heat treatment and a pressure treatment to produce a high-purity transparent silica glass, wherein (a) the starting material is 10 mmHg Placing the starting material under a reduced pressure atmosphere at a temperature at which the starting material can be melted, and then applying a pressure of 2 kgf / cm ² or more with an inert gas to reduce bubbles having a diameter of 1 mm or more;
(B) Using a hot isostatic pressing device, from 1200 to 135
A step of applying a pressure of 100 to 200 MPa of inert gas in a temperature range of 0 ° C. to reduce bubbles having a diameter of less than 1 mm, and after steps (c) and (b), 1000 to 130
A method for producing a high-purity transparent silica glass, comprising a step of performing a heat treatment at 0 ° C. and then gradually cooling.

Hereinafter, the present invention will be described in more detail.

The high-purity amorphous silica powder used as a starting material in the present invention is an amorphous silica powder obtained from an alkoxide of silicon, and contains N, which is a metal impurity contained therein.
a, K, Mg, Ca, Fe, Al and Ti are all 0.1
ppm or less.

The alkoxide of silicon can be used without any particular limitation as long as it has a high purity as described above. Examples thereof include alkoxides of silicon such as methyl silicate and ethyl silicate. Can be.

As a method for converting silicon alkoxide into high-purity amorphous silica powder, a method obtained by contacting with an acid or an alkali to hydrolyze silicon alkoxide can be exemplified. Examples of the acid or alkali used for hydrolysis of the silicon alkoxide include organic acids such as hydrochloric acid and acetic acid and inorganic acids as the acid, and ammonia and the like as the alkali, but are not limited thereto. Absent.

Metal impurities that can be contained in the high-purity amorphous silica powder include Na, K, Mg, Ca, Fe, A
l, Ti, the content of all impurities is 0.1 ppm
It is as follows. If the alkali metals such as Na and K are contained as impurities in excess of 0.1 ppm, they are not preferable because they cause a problem that they are easily crystallized in the glass production process. Further, when Mg, Ca, Fe, Al, and Ti are contained in excess of 0.1 ppm as impurities, they have a problem of deteriorating the transmittance of high-purity transparent silica glass because they have an ultraviolet absorbing effect, and are thus preferable. Absent.

The high-purity amorphous silica powder is filled in a heat-resistant container, for example, a high-purity carbon crucible, and subjected to a heat treatment. When used, it is preferable to adjust the particle size of the powder, and the particle size range can be controlled by setting processing conditions such as hydrolysis and pulverization. As the particle size range of the high-purity amorphous silica powder, it is preferable to adjust the particle size range to 30 to 500 μm in order to adjust the particle size range and to facilitate the removal of bubbles in the manufacturing process of the high-purity transparent silica glass, Further, the thickness is preferably 30 to 200 μm.

In the method of the present invention, in the step of producing a high-purity transparent silica glass, the step (a) comprises charging a high-purity amorphous silica powder, which is a starting material, into a heat-resistant container.
Under a reduced pressure atmosphere of not more than mmHg, the starting material is heated to a temperature at which the starting material can be melted or more, and then the pressure is increased to 2 kgf / cm ² or more with a gage pressure using an inert gas such as Ar or nitrogen. This is for producing silica glass. The heat-resistant container used in this step (a) can be used without particular limitation as long as the object of the present invention can be achieved.
Examples include a bon container and a silicon carbide container.

The condition of the pressure reduction is 10 mmHg or less. When the pressure reduction condition exceeds 10 mmHg, it is not preferable because transparent silica glass cannot be obtained due to the gas generated by sublimation of silica at a high temperature.

The heating can be performed, for example, by using a carbon atmosphere heating method or a high frequency heating method in a vacuum atmosphere electric furnace. The heating temperature is a temperature higher than the temperature at which the starting materials can be melted. The temperature at which the starting material can be melted is a temperature at which the high-purity amorphous silica powder used in the present invention can be melted by heating, and is 1713 ° C. at normal pressure. If the heating temperature does not reach this temperature, the starting material is not melted, or cristobalite crystals cannot be completely melted in the melted starting material, and the remaining glass is easily broken. The time for melting and holding the starting material is not particularly limited as long as substantially all of the starting material can be dissolved and vitrified, but if it is low, a long time is required. For example, if the heating temperature is 1800-1
In the case of 850 ° C., this is achieved by holding for 5 minutes or more.

The inert gas used for pressurizing can be used without any particular limitation as long as it can produce the high-purity transparent silica glass which is the object of the present invention, and may be Ar, nitrogen, He or the like. The inert gas may be exemplified, but in consideration of economy, airtightness, thermal conductivity of the inert gas, and the like, Ar and nitrogen are preferable, and Ar is more preferable. Conditions for pressurizing with inert gas are 2
kgf / cm ² or more. Pressurizing condition is 2kgf / cm ²
If it is less than this, bubbles generated during the manufacturing process become large and removal thereof becomes difficult, which is not preferable. Pressurizing condition is 2k
gf / cm ² or more can be carried out without any particular problem.
For economy, avoiding operational troubles of the pressure device, gate - is preferably set to 2~20kgf / cm ² di pressure, and more preferably to 2~10kgf / cm ^2.

The transparent silica glass obtained in the step (a) reduces bubbles having a diameter of 1 mm or more when the starting material is dissolved. The reason for reducing the bubbles having a diameter of 1 mm or more is as follows. This is because there is a critical value in the bubble diameter that can be reduced by the hot isostatic pressing in b), and it is difficult to reduce bubbles having a diameter of 1 mm or more.

In the method of the present invention, in the step of producing a high-purity transparent silica glass, the step (b) is performed by using a hot isostatic pressing apparatus on the transparent silica glass to form a transparent silica glass of 1200 to 135.
A high-purity transparent silica glass is produced by applying a pressure of an inert gas of 100 to 200 MPa in a temperature range of 0 ° C.

The temperature condition in the step (b) is 1200
温度 1350 ° C. If the temperature is lower than 1200 ° C., the fluidity of the glass decreases and it becomes difficult to reduce bubbles having a diameter of less than 1 mm in step (b), which is not preferable. If the temperature exceeds 1350 ° C., the crystallization of the glass becomes remarkable, and it becomes impossible to obtain a homogeneous high-purity transparent silica glass.

The pressure condition when pressurizing with an inert gas is 100 to 200 MPa. Pressure condition is 100MP
If it is less than a, it is not preferable because it becomes difficult to remove bubbles having a diameter of less than 1 mm. When the pressure condition exceeds 200 MPa, it is not preferable because it is economical and avoids trouble in operation of the pressurizing device.

The inert gas used for pressurizing in the step (b) can be used without any particular limitation as long as it can produce the high-purity transparent silica glass which is the object of the present invention. , Nitrogen, and inert gas such as He, but Ar, nitrogen are preferable, and Ar is more preferable in consideration of economy, airtightness, and thermal conductivity of the inert gas.

Here, the meaning of reducing bubbles is as follows.
The high-purity transparent silica glass obtained by the method of the present invention can be applied to various optical materials utilizing light transmissivity, applications such as high-temperature liquid crystal substrates, and applications such as jigs for semiconductor production which are used at high temperatures for a long time. For this reason, the amount of bubbles is expressed as the number of bubbles per unit volume as seen in the examples. The specific numerical value is preferably less than 1 / cm ³ in the high-purity transparent silica glass, and it is more preferable that bubbles are not recognized by the measurement and disappear.

In the method of the present invention, among the steps for producing a high-purity transparent silica glass, the conditions for heat-treating the high-purity transparent silica glass in the step (c) are as follows: After being taken out, it is preferable to heat and hold in the air within a temperature range of 1000 to 1300 ° C. for 15 hours or less, and then gradually cool. Also, as for the rate of temperature increase or decrease, conditions for gradually increasing or decreasing the temperature are preferably used. When gradually lowering,
It is desirable to gradually cool at a rate of 3 ° C./min or less, and it is particularly important to gradually cool to about 700 ° C. after heating to 1000 to 1300 ° C. For example, the temperature is raised to 1200 ° C. in the air in about 6 hours, the temperature is maintained at 1200 ° C. for about 4 hours, the temperature is lowered from 1200 ° C. to 700 ° C. in about 8 hours, and the temperature is gradually cooled from 700 ° C. to room temperature. Conditions are preferably used. The reason for this is that by performing the reheating treatment under the conditions described above, the density can be returned to the density before the bubbles were removed, so that the distortion could be eliminated. This is because the inert gas existing on the surface portion of the high-purity transparent glass can be removed. Here, if the density is different from that before the air bubble removal treatment, it may expand and break when heated during use, which is not preferable. Also, if high-purity transparent silica glass is used while containing an inert gas, foaming or a change in the refractive index may be unfavorable as a jig for semiconductor production or a material for optical use. As described above, the reheating treatment in the step (c) is important in application of the obtained high-purity transparent silica glass.

The high purity transparent silica glass obtained by the method of the present invention preferably has a homogeneity (Δn) of less than 3 × 10 ⁻⁵ . Thereby, it can be used as various optical materials.

Further, the OH group content of the high-purity transparent silica glass obtained by the method of the present invention is desirably 10 ppm or less in order to reduce deterioration due to heating. This makes it possible to suppress deformation due to heat treatment that can occur when the substrate is used as a substrate material.

[0027]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. The analysis of impurities and the like were performed as follows.

Analysis of Impurities A commercially available amorphous silica powder obtained by hydrolyzing an alkoxide of silicon was analyzed by an ICP method which is a known method.

Average Particle Diameter The average particle diameter of the amorphous silica powder is determined by laser diffraction scattering method COULTER LS-130 (COULTER EL).
(Ectronics).

~ Bubble diameter and bubble amount ~ Silica glass was cut into 100 mm ×
It was mirror-polished to a size of 100 mm × 10 mm (thickness) to obtain a measurement sample. Using a polarization microscope (manufactured by Olympus Corporation, model: BH-2) having a graduated lens, the bubble diameter and bubble amount in the sample were measured. In addition,
About the amount of air bubbles, the number per 1 cm ³ (pieces / cm ³ )
Asked.

~ Density ~ Silica glass is cut into 100 mm ×
It was mirror-polished to a size of 100 mm × 10 mm (thickness) to obtain a measurement sample. The density was measured by the Archimedes method.

~ OH group content ~ Silica glass is cut into 100 mm ×
It was mirror-polished to a size of 100 mm × 10 mm (thickness) to obtain a measurement sample. Using an FT-IR apparatus (manufactured by Shimadzu Corporation, model: FT-IR-8100M), the sample was quantified by an OH group absorption spectrum at a wavelength of 3600 Kaiser of IR transmitted light of the sample.

-Surface Gas Analysis- A silica glass having a size of 10 mm x 10 mm and a thickness as produced was measured using a cutting machine as a sample for measurement. This sample was used for ESCA (Perkin
The gas amount was measured by Elmer, model 5400MC).

~ Measurement of homogeneity (Δn) ~ A silica glass was polished to a diameter of 165 mm x 25 m using a polishing machine.
m (thickness) was mirror-polished to a measurement sample.
The homogeneity (Δn: unit: cm · cm ⁻¹ ) was measured using an interferometer (manufactured by ZYGO, model: Mark IV).

Example 1 A commercially available amorphous silica powder obtained by hydrolyzing an alkoxide of silicon was used as a starting material. The average particle size of this amorphous silica powder was 151 μm as measured by a laser diffraction scattering method. The results of analyzing the impurities in this powder are shown in Table 1.

[0036]

[Table 1]

The mosquitoes were high purity process this powder - filling in Bonn container, Ca - installed in Bonn resistance heating furnace, a vacuum degree of 10 ^-3
mmHg, and at a heating rate of 300 ° C./hour, 18
After the temperature was raised to 50 ° C. and held for 5 minutes, the vacuum was released,
Nitrogen gas was introduced until the pressure became 4 kgf / cm ^2, and the temperature was further maintained for 10 minutes. The degree of vacuum during holding was 1 mmHg. Cooling was allowed to cool while applying gas pressure to obtain a transparent silica glass.

Next, the glass was put into a hot isostatic press, and heated to 1300 ° C. at a heating rate of 600 ° C./hour using Ar gas as a pressure medium, and kept at a pressure of 150 MPa for 1 hour. .

The diameter and amount of bubbles in the glass after the hot isostatic pressing and the density of the glass were measured by the methods described above. The results are shown in Table 2. From this result, it was found that air bubbles were eliminated by hot isostatic pressing. The amount of infiltration of Ar gas after the hot isostatic pressing was measured by the method described above, and was about 1%.

[0040]

[Table 2]

Next, after hot isostatic pressing, the temperature of the silica glass was raised to 1200 ° C. in the air for 6 hours to 1200 ° C.
After maintaining at 4 ° C. for 4 hours, a reheating treatment was performed in which the temperature was lowered from 1200 ° C. to 700 ° C. over 8 hours.
When the density of the reheated silica glass was measured, it was 2.210 g / cm ³ , and it was possible to return to the density before hot isostatic pressing. Ar was not detected.

Example 2 Using the same amorphous silica powder as used in Example 1,
This powder is filled in a highly purified carbon container,
The furnace was set in a Bonn resistance heating furnace, the degree of vacuum was reduced to 10 ⁻³ mmHg, the temperature was raised to 1850 ° C. at a rate of 300 ° C./hour, and the temperature was maintained for 5 minutes. It was introduced until the pressure became 0.5 kgf / cm ^2, and was further maintained for 10 minutes. The degree of vacuum during holding was 1 mmHg. Cooling was allowed to cool while applying gas pressure to obtain a transparent silica glass.

Next, the glass was put into a hot isostatic press, and heated to 1250 ° C. at a heating rate of 600 ° C./hour using Ar gas as a pressure medium, and maintained at a pressure of 150 MPa for 4 hours. .

After the hot isostatic pressing, the diameter and amount of bubbles in the glass, the density of the glass, and the OH group content in the glass were measured by the methods described above.
It was shown to. From this result, it was found that air bubbles were eliminated by hot isostatic pressing. The amount of infiltration of Ar gas after the hot isostatic pressing was measured by the method described above, and was about 1%.

[0045]

[Table 3]

Next, after the hot isostatic pressing, the silica glass was heated to 1200 ° C. in the air for 6 hours to 1200 ° C.
After being kept at a temperature of 4 ° C. for 4 hours, reheating was performed in which the temperature was lowered from 1200 ° C. to 700 ° C. over 8 hours. When the density of the reheated silica glass was measured, it was 2.205 g / cm ³ , which could be returned to the density before hot isostatic pressing. Ar was not detected.
In addition, the homogeneity (Δ
n) was measured by the method described above and found to be 1.9 × 10
^-5 .

Comparative Example 1 Using the same amorphous silica powder as used in Example 1,
This powder is filled in a highly purified carbon container,
The sample was placed in a Bonn resistance heating furnace, the degree of vacuum was reduced to 10 ⁻³ mmHg, the temperature was raised to 1850 ° C. at a rate of 300 ° C./hour, and the reduced pressure was maintained for 15 minutes. The degree of vacuum during the holding was 2 mmHg. Cooling was allowed to take place in a reduced pressure state to obtain a transparent silica glass. The bubble diameter and bubble amount in the obtained transparent silica glass were measured, and the results are shown in Table 4.

[0048]

[Table 4]

From this result, when the raw material powder is melted at a pressure of less than ² kgf / cm ² when melting it, 1 mm
It was found that many of the above bubbles existed.

[0050]

According to the production method of the present invention, it is possible to extremely reduce bubbles by applying high pressure when melting high purity powder and hot isostatic pressing silica glass obtained by melting and pressing. Further, the density can be returned to the density before the hot isostatic pressing by the reheating treatment, and the inert gas which has entered can be removed. Therefore, it can be used for applications requiring light transmittance which has not been conventionally available due to bubbles, for example, various optical materials such as high-temperature liquid crystal substrates, prisms, and lenses. It can also be used as a material that could not be used due to crystallization around bubbles and deformation due to heat treatment, for example, as a material for various jigs and tools for semiconductor manufacturing.

Claims (4)

[Claims] (1) Na, K, Mg, C
a, Fe, Al, and Ti are each independently high-purity amorphous silica powder obtained from a silicon alkoxide of 0.1 ppm or less as a starting material, and heat-treated and pressure-treated to produce high-purity transparent silica glass. (A) placing the starting material in a reduced-pressure atmosphere of 10 mmHg or less at a temperature at which the starting material can be melted, and then pressurizing with an inert gas at a pressure of 2 kgf / cm ² or more to form a starting material having a diameter of 1 mm
(B) using a hot isostatic pressing device to reduce the number of air bubbles;
A step of applying a pressure of an inert gas of 100 to 200 MPa in a temperature range of 0 ° C. to reduce bubbles having a diameter of less than 1 mm; and (c) after the step (b), heat-treating at 1000 to 1300 ° C. A method for producing a high-purity transparent silica glass, comprising a step of cooling. 2. The method for producing a high-purity transparent silica glass according to claim 1, wherein the pressurized state in the step (a) is 2-10.
A method for producing a high-purity transparent silica glass, which is kgf / cm ² and eliminates bubbles in steps (a) and (b). 3. A method for producing a high-purity transparent silica glass, wherein the homogeneity (Δn) of the high-purity transparent silica glass according to claim 1 or 2 is less than 3 × 10 ⁻⁵ . 4. The method for producing a high-purity transparent silica glass according to claim 1, wherein the OH group content of the high-purity transparent silica glass is 10 ppm or less.