JP2003192364A - Synthetic quartz glass substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a synthetic quartz glass substrate having a high annealing point (a temperature at which the viscosity of the glass is equivalent to 10<SP>13</SP>poises), and excellent thermal resistance, and preventing optical fog form generating. <P>SOLUTION: In the synthetic quartz glass substrate the halogen content is less than 10 ppm, the OH group content is less than 100 ppm, the heavy metal and alkali metal content in total is less than 1 ppm, the annealing point is more than 1050°C and the double refraction within the substrate is less than 0.5 nm/cm. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a synthetic quartz glass substrate suitable for a high temperature process requiring heat resistance of 1000 ° C. or higher.

[0002]

Quartz glass has the highest heat resistance among transparent glass materials, has a very small coefficient of thermal expansion, is excellent in dimensional stability, and is excellent in chemical durability. In recent years, it has been used as a substrate material such as a high temperature polysilicon TFT substrate and a waveguide substrate. Particularly, as a liquid crystal display element for a viewfinder of a video camera, a high temperature polysilicon TFT substrate is mainly used.

Generally, the manufacturing method of these substrates depends on the manufacturing temperature level: (1) high temperature process method (maximum process temperature of about 1000 ° C.), (2) medium temperature process method (maximum process temperature of about 700 ° C.) ) And (3) low temperature process method (maximum process temperature of about 500 ° C.).

The problem with using the high temperature process method is the heat resistance of the substrate material, but in this respect, quartz glass that is relatively resistant to high temperatures is advantageous, and in particular, bubbles and foreign substances contained in the glass are In recent years, synthetic quartz glass substrates, which are few and excellent in quality, have been used.

[0005]

[Problems to be Solved by the Invention] However, in recent years, higher quality has been required for liquid crystal display elements and waveguides. When conventional synthetic quartz glass is used as a substrate material, It has been found that there are cases where sufficient quality cannot be obtained. Specifically, when a conventional synthetic quartz glass substrate is used, the optical quality is not sufficient, and there are cases where defects such as a decrease in yield occur.

The object of the present invention is to solve the above-mentioned problems,
Excellent heat resistance, suitable for liquid crystal display polysilicon TFT substrates and waveguide substrates used in viewfinders, etc.
It is to provide a high-quality synthetic quartz glass substrate.

[0007]

The present invention has been made to solve the above-mentioned problems, and is a synthetic quartz glass substrate having a halogen content of 10 ppm or less, an OH group content of 100 ppm or less, and a heavy metal. And a total content of alkali metals of 1 ppm or less, an annealing point of 1050 ° C. or more, and a birefringence in the substrate of 0.5 nm / cm or less. In particular, the substrate of the present invention has a low water vapor partial pressure in a temperature range below the temperature at which a porous quartz glass body obtained by depositing and growing quartz glass fine particles obtained by heating and hydrolyzing a glass forming raw material is made into transparent vitreous. After being kept in the atmosphere for a certain period of time, it is preferably composed of synthetic quartz glass obtained by raising the temperature to a transparent vitrification temperature and heating it to obtain a transparent vitrification.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION When the conventional synthetic quartz glass is used for a liquid crystal display polysilicon substrate or the like, the present inventors
In particular, the inventors have found that there is a portion having a large birefringence due to stress concentration near the end face of the substrate, which impairs the quality, particularly the optical quality, and has reached the present invention. That is, since the light transmitted through a portion having a large birefringence is anisotropically polarized, when an optical element is formed in such a portion, its optical characteristics are adversely affected.

The amount of halogen (chlorine, fluorine, etc.) contained in the synthetic quartz glass substrate of the present invention is 10 ppm or less, and when halogen exceeds 10 ppm, the heat resistance may decrease. . Preferably 5p
pm or less, particularly preferably 1 ppm or less.

The amount of OH groups contained in the synthetic quartz glass substrate of the present invention is 100 ppm or less. 100 pp
When the OH group exceeds m, sufficient heat resistance may not be obtained as in the case of halogen. It is preferably 50 ppm or less, particularly preferably 10 ppm or less.

Further, the annealing point of the synthetic quartz glass substrate of the present invention is 1050 ° C. or higher, and if there is an annealing point above this temperature, about 1000 ° C. should be adopted as the process temperature for producing the optical element. You can Here, the slow cooling point is a temperature at which the viscosity of glass shows 10 ¹³ poise.
The annealing point is preferably 1100 ° C or higher, particularly preferably 1150 ° C or higher.

Further, the synthetic quartz glass substrate of the present invention,
The total amount of heavy metal elements such as iron and nickel and alkali metals such as sodium and potassium is 1 ppm or less. If the content of these metals exceeds 1 ppm, impurities may diffuse into the functional portion such as the silicon film during high temperature treatment to deteriorate the portion. Preferably 100 pp
b or less, particularly preferably 10 ppb or less.

The birefringence value in the synthetic quartz glass substrate of the present invention is 0.5 nm / cm or less. 0.5 nm / c
If an optical element or the like is formed in a portion having a birefringence value exceeding m, the optical characteristics may be adversely affected. Preferably 0.3 nm / cm or less, particularly preferably 0.2 nm
/ Cm or less.

As a method of inspecting birefringence, there are two inspection sites.
It is sandwiched by a pair of polarizing plates, arranged so that the polarization directions of the respective polarizing plates are vertical, and allows light rays to pass through, and is observed on the substrate by the interference of passing light anisotropically polarized by birefringence. A method of determining whether there is a target cloud is used (this inspection method is hereinafter referred to as a cloudiness inspection). When a haze test is performed on a part having a birefringence value of more than 0.5 nm / cm, an optical haze is detected, and the color tone is impaired when such a part is actually formed, for example, a color liquid crystal display device.

As a method of manufacturing the synthetic quartz glass substrate of the present invention, the following method can be adopted.

The raw material for forming the synthetic quartz glass is not particularly limited as long as it is a gasifiable raw material.
l ₄ , SiHCl ₃ , SiH ₂ Cl ₂ , SiCH ₃ Cl
Chlorides such as ₃ , SiF ₄ , SiHF ₃ , SiH ₂ F ₂
Fluorides such _as, SiBr _4, SiHBr bromides such as _3, halogenated silicon compounds such as iodide such as SiI _4, or RnSi _{(OR) 4-n} (wherein R is an alkyl group having 1 to 4 carbon atoms, n represents 0-3 alkoxysilane or represented by an integer) of _{(CH 3) 3 Si-O} -Si (C
H ₃ ) ₃ and other halogen-free silicon compounds may be mentioned.

When a silicon halide compound is used as the glass forming raw material, halogen in the glass forming raw material may remain in the synthetic quartz glass. Therefore, a halogen-free organosilicon compound is preferable as the glass forming raw material. . However, an organosilicon compound containing no halogen is relatively expensive, and when this is used as a glass forming raw material, an increase in manufacturing cost cannot be avoided. Therefore, if heat resistance is obtained, it is preferable to use a silicon halide compound, particularly a silicon chloride compound, in order to suppress the production cost. The porous quartz glass body is formed by hydrolyzing these glass forming raw materials in a normal oxyhydrogen flame and depositing them on a substrate.

The porous quartz glass body thus obtained is then held for a certain period of time in a low water vapor partial pressure atmosphere to reduce the OH group content. That is, for example, a porous quartz glass body is mounted in an electric furnace whose atmosphere can be controlled, and then heated at a constant temperature rising rate. Then, after reaching a predetermined temperature, a dry gas is introduced into the atmosphere to replace the atmosphere in contact with the porous quartz glass body, thereby reducing the water vapor partial pressure in the atmosphere to a predetermined value or less. The water vapor partial pressure is preferably 0.26 Pa or less and the dew point temperature is −70 ° C. or less. If it exceeds this, it may be difficult to reduce the amount of OH groups in the glass finally obtained. is there.

In order to reduce the OH group content, the temperature for heating and holding is preferably in the range of 800 to 1250 ° C.,
At temperatures below this temperature range, substantial effects may not be obtained, and at temperatures above this temperature range, the transparent vitrification of the surface of the porous quartz glass body proceeds, so There is a possibility that the atmosphere may not be replaced or may be replaced with a desired low water vapor partial pressure atmosphere. Also, even in the case of transparent vitrification under reduced pressure, the desorption of water is not sufficiently performed, which is not preferable.

In this temperature range, the heat treatment may be carried out at a constant temperature, or may be carried out while raising the temperature within this temperature range for a predetermined time. Further, the holding time in this temperature range depends on the holding temperature and cannot be specified unconditionally, but it is preferably 1 to 10 hours or more, and if it is less than this, substantial effects may be lost, and Even when applied for a long period of time, the effect remains the same, which may reduce the productivity.

The atmosphere gas used for reducing the OH group content may be an inert gas such as nitrogen, helium, or argon, but is not limited to these gases.

Then, after such heat treatment, the porous quartz glass body is transparentized into a quartz glass body.
The transparent vitrification is performed by maintaining the porous quartz glass at a predetermined transparent vitrification temperature for a predetermined time. The transparent vitrification temperature is usually 1300 to 1600 ° C, and particularly preferably 1350 to 1500 ° C. As the atmosphere at this time, an atmosphere containing 100% by volume of an inert gas such as helium or nitrogen, or an atmosphere containing an inert gas such as helium or nitrogen as a main component can be used. The pressure may be reduced pressure or normal pressure. Helium gas can be used especially under normal pressure.
In the case of decompression, 13.3 kPa (100 Tor)
r) or less is preferable.

Further, the OH group reduction treatment and the transparent vitrification treatment may be performed by different heating devices, but it is preferable to take measures such as preventing moisture from being adsorbed during the delivery. . Therefore, it is preferable to perform the OH group reduction treatment and the vitrification treatment in the same equipment.

When the final vitrification is carried out under reduced pressure, the OH group content may be reduced under reduced pressure to effect vitrification at the same time. That is, after the porous quartz glass body was mounted in an electric furnace capable of controlling the atmosphere and pressure, the atmosphere was replaced with a dry gas, and the furnace was further depressurized in a depressurized atmosphere in which the degree of vacuum was kept constant. In, the OH group inside the porous quartz glass body is desorbed by heating and holding, so that the glass body becomes transparent. The degree of vacuum in the furnace is 133P
It is preferably a (1.0 Torr) or less. If it exceeds this, it may be difficult to reduce the OH group content in the finally obtained glass.

The quartz glass body thus obtained is heated to a temperature equal to or higher than the softening point and deformed by its own weight to be molded into a desired shape to produce a quartz glass ingot. The temperature range of the molding process is preferably selected from the range of 1650 to 1800 ° C. At a temperature of less than 1650 ° C., the viscosity of quartz glass is high, so that the self-weight deformation is not substantially performed,
Further, there is a possibility that so-called devitrification may occur due to the growth of cristobalite, which is a crystal phase of SiO ₂ , and
At a temperature higher than 0 ° C, the sublimation of SiO ₂ may not be ignored. The direction in which the quartz glass body is deformed by its own weight is not particularly limited, but it is preferably the same as the growth direction of the porous quartz glass body.

Next, the obtained quartz ingot is annealed to reduce birefringence. That is, in an electric furnace in which the atmosphere can be controlled, under a dry inert gas atmosphere such as nitrogen, helium, or argon, the temperature is raised to a temperature equal to or higher than the slow cooling point, approximately 1250 to 1800 ° C., and after holding for 1 to 10 hours
Slow cooling is performed at a temperature decrease rate of 5 ° C./hour or less. If the temperature rise is less than 1250 ° C, the effect of reducing birefringence is low.
If the temperature exceeds 800 ° C., the sublimation of SiO ₂ may not be ignored. When the rate of temperature decrease is 5 ° C./hour or more, a sufficient effect for relaxing the internal stress cannot be obtained, and the birefringence may remain as a large value in the quartz ingot. Further, if the temperature lowering rate is less than 1 ° C./hour, the effect of removing birefringence does not change, and there is a possibility that productivity will deteriorate.

The quartz ingot thus obtained is further subjected to grinding, slicing and polishing to obtain a synthetic quartz glass substrate. The sliced substrate may be heat-treated in an atmosphere containing hydrogen to improve the transmittance.

The synthetic quartz silica glass substrate obtained through the above steps has a halogen content of 10 ppm or less,
The OH group content is 100 ppm or less, the total content of heavy metals and alkali metals is 1 ppm or less, and the annealing point is 1050.
℃ or more, and the birefringence in the substrate is 0.5 nm / cm
Below, no optical haze is detected by the haze test.

[0029]

[Example 1] A porous quartz glass body having a diameter of 35 cm and a length of 100 cm formed by heating and hydrolyzing SiCl ₄ in an oxyhydrogen flame by a known method was placed in an electric furnace capable of controlling the atmosphere. did. Then, after replacing the atmosphere in the electric furnace with nitrogen gas having a dew point temperature of -70 ° C, the dew point temperature of -70 ° C
1 at a heating rate of 500 ° C / hour while flowing nitrogen gas
The temperature was raised to 000 ° C. Subsequently, the temperature was raised to 50 ° C./hour, the temperature was raised to 1250 ° C., and the temperature was maintained for 10 hours to subject the porous quartz glass body to OH group reduction treatment.

The heat-treated porous quartz glass body thus obtained has a maximum temperature of 145 in a furnace for transparent vitrification.
It is installed in an electric furnace capable of controlling the atmosphere and pressure controlled at 0 ° C., and after replacing the inside of the furnace with nitrogen gas having a dew point temperature of −70 ° C., the degree of vacuum in the furnace is 133 Pa (1.0 Torr) or less. It was evacuated and heated up to 1250 ° C. at a heating rate of 500 ° C./hour. Sequentially, the heating rate is set to 10 ° C./hour and 1
After the temperature was raised to 450 ° C., the temperature was maintained for 3 hours. In addition,
During a series of temperature operations, the degree of vacuum inside the furnace is always 133 Pa
The control was performed so as to maintain (1.0 Torr) or less.

The transparent quartz glass thus obtained was placed in an electric furnace having a heating element made of carbon and had a softening point of 1750 or higher.
170mmφ × 400
It was molded into a cylindrical ingot shape of mm.

OH group content is 170 mmφ × 400 m
A glass plate with a thickness of 2 mm was cut out from a m quartz glass ingot, and 3700c was obtained with an FTIR device manufactured by JASCO Corporation.
It was quantified by the absorption of m ^{- 1} . The Cl content was quantified by an ion chromatography method after melting the obtained quartz glass with an alkali. In the present embodiment, since Cl is the element most easily contained in halogen, the content of halogen can be represented by the content of Cl. Further, the annealing point was measured by cutting out a sample having a sample size of 2.4 mm × 5 mm × 60 mm and measuring the span of 52 mm by the beam pending method. The results are shown in Table 1.

Next, the quartz glass ingot was placed in an electric furnace capable of controlling the atmosphere for slow cooling. Then, the atmosphere inside the electric furnace was replaced with nitrogen gas having a dew point temperature of -70 ° C, and then 125 gas was supplied while flowing nitrogen gas having a dew point temperature of -70 ° C.
The temperature is raised to 0 ° C, then 400 at a cooling rate of 1 ° C / hour.
The temperature was lowered to ℃.

170 mmφ × 40 thus obtained
170mmφ × 2m from 0mm quartz glass ingot
A substrate sample of m thickness is cut out and the birefringence value is calculated by Hind.
It was measured at a span of 10 mm by an Exicor 150AT birefringence measuring device manufactured by s company. Table 2 shows the maximum value of the measured birefringence and the result of the presence or absence of haze when the haze test was performed on the sample.

[Example 2] The maximum birefringence value, cloudiness, of a 170 mmφ × 2 mm thick substrate sample cut from a quartz glass ingot produced by the same method as in Example 1 except that the temperature lowering rate during slow cooling was 3 ° C / hour. Table 2 shows the presence or absence of cloudiness during the inspection.

[Example 3] The maximum birefringence value, cloudiness, of a 170 mmφ × 2 mm thick substrate sample cut from a quartz glass ingot produced by the same method as in Example 1 except that the temperature lowering rate during slow cooling was 10 ° C / hour. Table 2 shows the presence or absence of cloudiness during the inspection.

Example 4 The maximum birefringence value, cloudiness, of a 170 mmφ × 2 mm thick substrate sample cut from a quartz glass ingot produced by the same method as in Example 1 except that the temperature lowering rate during slow cooling was 30 ° C./hour. Table 2 shows the presence or absence of cloudiness during the inspection.

[Example 5] The amount of OH groups, the distribution width, the Cl content, and the annealing point of the quartz glass ingot produced by the same method as in Example 1 except that no heat treatment was performed at 1250 ° C are shown in Table 1. Shown in.

Examples 1 and 2 are examples, and Examples 3 to 5 are comparative examples. In any of the examples, heavy metals (Fe, N) in the synthetic quartz glass measured by ICP mass spectrometry (SPQ9000 manufactured by Seiko Instruments Inc.)
The total amount of i, Cu, Zn, Ti) and alkali metal (Na, K) was 1 ppm or less.

[0040]

[Table 1]

[0041]

[Table 2]

[0042]

The synthetic quartz glass substrate of the present invention has a high annealing point, excellent heat resistance, and a small birefringence value in the substrate, so that optical fog does not occur.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinya Kikukawa             1-12-1 Yurakucho, Chiyoda-ku, Tokyo Asahi             Glass Co., Ltd. F-term (reference) 2H090 JB02 JD18 LA04 LA09                 2H092 JA24 NA25 PA01 PA11                 4G014 AH00

Claims (4)

[Claims] 1. A synthetic quartz glass substrate having a halogen content of 10 ppm or less, an OH group content of 100 ppm or less, and a total content of heavy metals and alkali metals of 1 ppm.
Hereinafter, a synthetic quartz glass substrate having an annealing point of 1050 ° C. or higher and birefringence in the substrate of 0.5 nm / cm or less. 2. A porous quartz glass body obtained by depositing and growing fine particles of quartz glass obtained by heating and hydrolyzing a glass-forming raw material is placed in an atmosphere having a low water vapor partial pressure in a temperature range lower than a temperature for vitrification. The synthetic quartz glass substrate according to claim 1, which is made of synthetic quartz glass obtained by heating the transparent vitrification temperature to a transparent vitrification temperature and heating the transparent vitrification after holding for a certain period of time. 3. The synthetic quartz glass substrate according to claim 1, which is used as a high temperature polysilicon TFT substrate. 4. The use as a waveguide substrate according to claim 1 or 2.
The synthetic quartz glass substrate described.