KR20080074256A - A manufacturing method for high-purify quartz glass with low oh content - Google Patents

Abstract

A manufacturing method of highly pure quartz glass is provided to prevent the deterioration of definition in a dust proof glass having similar thermal expansion coefficient with the substrate quartz glass by removing OH group in a heat-treatment of silica in dry gas atmosphere. A manufacturing method of highly pure quartz glass having less OH contents comprises a step of heat-treatment using He gas having dew pot temperature less than -100°C at a temperature of at least 1,150°C in dry gas atmosphere for more than 10 hours. The dry gas atmosphere is in a state having moisture of 1ppm under the control of dew pot temperature less than -20°C. After the heat-treatment in dry gas atmosphere, an annealing treatment is carried out at virtual temperature of 950-1,000°C. An anti-dust glass for projection display is prepared by a process comprising steps of: drying silica soot; preparing quartz glass ingot by heat-treatment of the dried silica for making a glass state; slicing the quartz glass ingot in a form of wafer by means of wire saw; lapping the slices to quartz glass wafer and polishing the wafer; and preparing anti-dust glass by means of dicing saw. A high-temperature poly-silicone TFT substrate or an opposed substrate is manufactured by a process comprising steps of: drying silica soot; preparing quartz glass ingot by heat-treatment of the dried silica for making a glass state; slicing the quartz glass ingot in a form of wafer by means of wire saw; and lapping the slices to quartz glass wafer and polishing the wafer.

Description

A manufacturing method for high-purify quartz glass with low OH content}

1 is a graph measuring the change in OH content according to the dew point temperature change (used gas: He, heat treatment temperature: 1200 ℃, heat treatment time: 20hr).

2 is a graph showing the relationship between dew point temperature and moisture content.

Figure 3 is a graph showing the OH content when the use gas is changed to He and Ar (dew point temperature: -196 ℃, heat treatment temperature: 1200 ℃, heat treatment time: 20hr).

4 is a graph measuring the effect of the heat treatment temperature on the OH content (using gas: He, dew point temperature: -196 ℃, heat treatment time: 20hr).

5 is a graph measuring the effect of the change in heat treatment time on the OH content (use gas: He, dew point temperature: -196 ℃, heat treatment temperature: 1200 ℃).

6 is a flowchart illustrating a process of manufacturing a dustproof glass or a high temperature polysilicon TFT substrate for a projection display device and an opposing substrate.

7 shows a measuring point for controlling the OH concentration distribution on the quartz glass.

FIG. 8 shows OH concentration distribution before and after the slow cooling treatment measured at the measurement point of FIG. 7.

Figure 9 shows the results of measuring the coefficient of thermal expansion of the samples of the OH content of 18, 87, 174ppm, respectively.

Figure 10 shows the viscosity change according to the OH content for the case where the viscosity measurement temperature is 1100, 1200, 1300 ℃, respectively.

11 is a schematic diagram illustrating a dry gas trap.

The present invention relates to a method for manufacturing high heat-resistant quartz glass, and more particularly, to heat-proof silica in a dry gas atmosphere in order to improve the heat resistance of dustproof glass or high temperature polysilicon TFT substrate and counter substrate used in a projection display device. It relates to a method for removing the OH group.

High-purity quartz glass is made of SiO ₂ only and has high chemical stability because it is a high-purity glass with very low content of other metal impurities. It is applied to display industry parts including photomask substrate for substrate and wafer for high temperature poly-Si TFT-LCD which is a core component of projection display, and is used for precision optical materials (UV grade lens, prism, mirror, filter, etc.), It is also used as a variety of equipment related to semiconductor / LCD manufacturing (baths, chambers, boats), and is also widely used in high-tech industries such as the display industry and the semiconductor industry.

In addition, quartz glass having excellent transmittance in the ultraviolet region is synthetic silica glass that strictly controls the purity of metal impurities in the manufacturing method, and synthetic quartz glass is an OH group (hydroxyl group) inside the quartz glass due to the nature of the manufacturing method. It contains a lot of). Since OH present in the glass breaks the [SiO ₄ ] tetrahedron network structure, it causes a decrease in heat resistance, which is one of the excellent properties of quartz glass.

The level of quartz glass industry used in display industry and semiconductor industry in Korea is processed low-purity quartz glass which is used as transportation tool, container and vacuum chamber in semiconductor manufacturing process. High purity quartz glass, such as quartz glass substrates for photomasks and quartz glass for precision optics, is imported and used as a finished product.

Considering the manufacturing status of quartz glass in Japan and the United States, which are leading technologies in the manufacturing of synthetic quartz glass, quartz glass was originally manufactured by melting quartz at a high temperature of 2000 ° C or higher. However, as the industry develops, its use and requirements are diversified. As they become more stringent, several manufacturing methods have been developed. The two types of quartz glass are largely divided into molten quartz glass prepared by melting the powder of natural crystal and synthetic quartz glass manufactured by chemical synthesis. According to the present invention, there are an electric melting method, a plasma melting method, an oxyhydrogen salt melting method, and a method of manufacturing synthetic quartz glass includes a direct method, a chemical vapor deposition method, a sol-gel method, and the like.

Since the electrofusion method is a method of melting the crystal powder with electricity, almost no moisture is contained in the quartz glass. The plasma melting method uses a plasma torch instead of an oxyhydrogen burner. Like the electrofusion method, it contains almost no OH group. Oxyhydrogen flame melting method is a method using a flame using a reaction of oxygen and hydrogen. When oxygen and hydrogen react, water is generated. At this time, a large amount of energy is generated to become a high temperature. This heat is used to melt the crystal powder. Because of the reaction between oxygen and hydrogen, quartz crystals are melted and a large amount of moisture is generated, which causes many defects in quartz glass. As a characteristic of molten quartz glass, it is heat resistant, but there are relatively many disadvantages of metal impurities.

There are many methods for producing synthetic quartz glass, but most of them are synthesized by reacting (hydrolysis) silicon tetrachloride (SiCl ₄ ) with water molecules produced by the reaction of oxygen and hydrogen in a burner that burns oxygen and hydrogen. At this time, since the compound with few impurities is used as a starting material, very high purity quartz glass is made. Molten quartz glass contains a metallic impurity in the crystal powder as a raw material and thus has a limited purity. Therefore, when high purity is required, chemically synthesized quartz glass is used. Direct synthetic quartz glass is made by hydrolyzing silicon tetrachloride in a hot oxyhydrogen flame. Since quartz glass synthesized by the direct method is synthesized in an oxyhydrogen flame, OH remains. The amount of OH is about 10 times higher than that of molten quartz glass melted in an oxyhydrogen salt. In addition, since silicon tetrachloride (SiCl ₄ ) is used as a raw material, since Cl is contained, it is easier to deform than molten quartz glass at a high temperature.

Chemical Vapor Deposition Synthetic quartz glass is prepared by heat treatment after preparing agglomerates made of fine particles of silica. VAD (Vapor-phase Axial Deposition) method, one of the typical manufacturing methods, was devised and put into practice in Japan. First, porous silica agglomerates were synthesized at a temperature of about 1100 ° C. lower than the direct method, and then sintered to about 1500 ° C. It is a method of making transparent quartz glass. This quartz glass is characterized by a very small amount of metal impurities compared to molten quartz glass.

The plasma method is a method for producing quartz glass containing no OH. This is also a direct method of synthesizing quartz glass, but instead of oxyhydrogen flames, silicon tetrachloride and oxygen are reacted using induction plasma such as argon (Ar) or oxygen (O ₂ ). This quartz glass has a disadvantage of being weak in radiation or ultraviolet rays due to residual oxygen or chlorine. The sol-gel method is a method of synthesizing a porous body in a solution, drying it, and heating and vitrifying. Research has been carried out in the hopes of several researchers because the glass can be manufactured with high efficiency (yield) by drying the solution to form a rough form and heat treatment.

Projection-type display devices include liquid crystal projectors and projection TVs, which are rapidly increasing in demand, and are expected to continue to grow in the future. Quartz glass for projection display is applied to dustproof glass, high temperature poly-Si TFT-LCD substrate, color filter substrate, etc., and the quality level is higher in order of dustproof glass, color filter substrate, TFT-LCD substrate. However, even in Korea, even the lowest quality dust-proof glass relies on imports, and if it cannot be localized, technology dependency is concerned.

Dust Proof Glass is located on the front and back of the high-temperature poly-Si TFT-LCD substrate and the color filter substrate to prevent deterioration of image quality caused by dust or foreign matter adhering to the substrate surface. In addition, it has a function of preventing mechanical damage to the substrate glass.

In addition, since the projection display device uses a halogen lamp as a light source, high heat is generated. Therefore, when the heat resistance of the quartz glass is different, the adhesion decreases due to the difference in the thermal expansion coefficient of the substrate / dustproof glass, leading to deterioration of image quality. do. Therefore, it is necessary to develop dust-proof glass at the same level as the coefficient of thermal expansion of the quartz glass for substrate. To this end, it is necessary to control the concentration of OH groups in the quartz glass that have the greatest influence on the coefficient of thermal expansion, thereby improving heat resistance. .

Since the research and development of quartz glass in Japanese manufacturing companies that dominate the world market is not disclosed at all except patents, the trend of heat resistance enhancement technology was investigated in the JPO data. Shown in

Table 1 summarizes the patent literature related to the heat resistance improvement of Sumitomo metal.

Application number Applicant Contents JP2002-160936 住友 金屬 Heat treatment at high temperature with oxygen gas reduced to 100 Pa to reduce OH concentration to 80 ppm JP2002-053338 住友 金屬 It is reduced to 12ppm by heat treatment at high temperature with He gas reduced to 20Pa. JP2002-087833 住友 金屬 Reduced to 18ppm by heat treatment at high temperature under ultra low pressure of 2 * 10E4 Pa JP1999-228160 住友 金屬 Reduced to 50ppm by heat treatment at high temperature under reduced pressure of 1-3Pa

Table 2 summarizes the contents of patent documents related to improving heat resistance of Asahi Glass.

Application number Applicant Contents JP2002-316123 Asahi Glass Heat treatment at 1200 ℃ with oxygen gas reduced to 0.1 atm to reduce OH concentration to 18 ppm JP2002-318049 Asahi Glass He gas reduced to 0.1 atm, and reduced to 9.4 ppm by heat treatment at 1250 ° C. JP2001-180962 Asahi Glass Heat treatment at high temperature in ultra low pressure at 0.1 Torr and drop to 7.8 ppm JP2000-239031 Asahi Glass Heat reduced at 4.2ppm after depressurizing to 1Torr

As can be seen from the table, a Japanese manufacturer is investigating that the concentration of OH is reduced by heat treatment under reduced pressure, and recently, a patent for heat treatment in a SiF ₄ gas atmosphere is also disclosed. However, the heat treatment in the SiF ₄ gas atmosphere is for the purpose of presenting fluorine (F) in the quartz glass in addition to the purpose of lowering the OH, and the fluorine-containing quartz glass is a product for use in optical fibers. In addition, fluorine serves to break the network structure in the quartz glass to lower the heat resistance. The present applicant has also obtained a domestic patent for a technology for removing OH from quartz glass by rapid heat treatment under reduced pressure, and is currently under international patent application (PCT). However, the removal of OH under reduced pressure requires a relatively long time, so the industrial utility is inferior, and thus, more efficient technology development is required.

The method of using dry gas has the advantage that the process is not added because there is no influx of unnecessary elements, but it is expected that it will take a very long time to reach the target OH concentration. Therefore, it is an object of the present invention to provide a method for producing high heat-resistant quartz glass with excellent productivity while lowering production cost through process optimization.

In order to achieve the above object, the present inventors have found the most suitable conditions by adjusting the dew point temperature, used gas, heat treatment temperature, time, and the like, as well as producing quartz glass having high heat resistance by slow cooling after heat treatment.

The present invention relates to a method for producing high purity quartz glass having a low OH content by heat treatment in a dry gas atmosphere under a dew point temperature of -100 ° C. or less, use gas He, heat treatment temperature of 1150 ° C. or more, and heat treatment time of 10 hr or more.

In addition, the heat treatment temperature in the present invention is characterized in that 1200 ~ 1500 ℃.

In addition, the heat treatment time in the present invention is characterized in that 10 to 50 hours.

In addition, the dew point temperature in the present invention is characterized in that -150 ~ -300 ℃.

In addition, the present invention is characterized in that the slow cooling heat treatment to the virtual temperature 950 ~ 1100 ℃ after the dry gas atmosphere heat treatment.

The condition range is the most suitable range for lowering the OH concentration of the quartz glass.

In order to remove OH of quartz glass, the dew point temperature, gas used, heat treatment temperature, and heat treatment time were controlled by drying atmosphere heat treatment test, and hypothetical temperature was controlled by slow temperature heat treatment to control OH concentration distribution. The OH concentration distribution of the quartz glass wafer was 65 when the GH was removed by dry gas atmosphere heat treatment under the condition of dew point temperature -196 ℃, used gas He, heat treatment temperature 1200 ℃ and heat treatment time 20hr, and virtual temperature was 1000 ℃. ± 3 ppm.

After removing OH by dry gas atmosphere heat treatment, a slow cooling heat treatment for uniform OH concentration distribution control is required. The OH concentration distribution was 65 ± 3 ppm when the slow cooling was performed such that the virtual temperature was 1000 ° C.

The OH concentration was analyzed by FT-IR, the viscosity was evaluated by the beam bending method, and the coefficient of thermal expansion was measured by TDA. As the OH content increased, the viscosity decreased and the coefficient of thermal expansion increased. When the OH content was 87 ppm, the average coefficient of thermal expansion was 4.5 × 10 ⁻⁷ / K.

Removing the OH group of the quartz glass using a dry gas can be represented by the following chemical reaction formula.

-Si-OH + HO-Si- → -Si-O-Si- + H ₂ O _(g)

The use of dry gas has the advantage that no additional process is required for the removal of other elements since there is no influx of other elements. In the present invention, the dry gas atmosphere refers to a condition in which the water vapor concentration is about 1 ppm, that is, 10 ⁻⁶ kg / kg under a dew point temperature of −20 ° C. or less.

The present inventors fabricated a dry gas trap for OH removal and concentration distribution control experiment by dry gas atmosphere heat treatment. If the working gas passes through a cryogenic dry gas trap before entering the chamber, it becomes a dry gas with a very low dew point temperature. When the liquid nitrogen is added to the dry gas trap, the dew point temperature of the dry gas is -196 ° C, and when the dry ice and ethanol are mixed, the dew point temperature of the dry gas is -78.5 ° C.

Experimental variables for the dry gas atmosphere heat treatment test for OH removal in quartz glass were set to dew point temperature, used gas, heat treatment temperature, heat treatment time, and the like. The dew point temperature was −196 ° C., −78.5 ° C., the used gas was He, Ar, the heat treatment temperature was 1000 to 1300 ° C., and the heat treatment time was 1 to 40 hours.

In order to measure the concentration of OH in the quartz glass, the transmittance was measured at 2600 nm and 2730 nm using FT-IR, and the following formula was obtained.

OH content [ppm] = 910 × (1 / t) log ₁₀ (Ta / Tb)

Where t is the thickness of the sample (mm), Ta is the transmittance (%) at 2600 nm wavelength, and Tb is the transmittance (%) at 2730 nm wavelength. In addition, the constant 910 is calculated by the following equation. MW is 17g at the molecular weight of (OH) ^- , E is 85liters / mol.cm at the extinction coefficient of (OH) ^- , and ρ is 2.21g / cm ^{3 at} the density of SiO ₂ .

910 = (MW × 10 ⁴ ) / (E × ρ)

* Viscosity evaluation

Unlike ordinary glass, quartz glass has high melting point and high temperature viscosity, making it difficult to measure viscosity at high temperature. Viscosity measurement methods include beam bending method, cantilever beam bending method, torsion method, and falling ball method. The beam bending method and the cantilever beam method can measure the viscosity of 10 ⁹ ~ 10 ¹⁶ Pa.s at 1100 ~ 1500 ℃, and the Torsion method can measure the viscosity of 10 ⁵ ~ 10 ⁸ Pa · s at 1500 ~ 2200 ℃. , Falling ball method can measure the viscosity of more than 10 ⁴ Pa · s above 2300 ℃. Only the beam bending method and the cantilever beam bending method are available for measuring the viscosity to check the heat resistance of quartz glass used at high temperature. Among them, in the present invention, the viscosity of the quartz glass was measured using a cantilever beam bending method which can be easily measured.

The viscosity (η) of the quartz glass can be obtained by the following equation by measuring the deformed length while keeping the measurement at a desired temperature for a certain time.

η = (ρ g L ⁴ Δt) / (2 a ² h)

Where ρ is the glass density, g is the acceleration of the specimen, L is the length of the specimen, Δt is the holding time at the measurement temperature, a is the thickness of the specimen, and h is the deformation of the specimen.

The test for the measurement of the viscosity of the quartz glass was carried out by fixing the holding time to 10 hours at a temperature of 1100 ~ 1300 ℃ using a high-temperature reactor capable of controlling the atmosphere, samples with different OH content produced under each heat treatment condition Was used for the experiment.

The viscosity of the quartz glass decreases with increasing OH content. The low viscosity when the OH concentration is high is considered to be because the network structure of the glass is cut at various places by the OH group, and impurities other than OH may affect the viscosity, but in the present invention, a sample having a constant purity is used. The influence of purity was excluded on the assumption that the system was used. In the present invention, by adjusting the parameters of the various experimental conditions it was possible to manufacture a quartz glass having an OH content of 20 ~ 200ppm range, it was also possible to calculate the range of viscosity value of the quartz glass according to each OH content.

* Coefficient of thermal expansion

The coefficient of thermal expansion of the quartz glass was measured using a TDA (Thermal Dilatometric Analyzer). The specimen for measuring the coefficient of thermal expansion was produced in the form of a rod 5 mm in diameter x 50 mm in length. The measurement temperature was in the range of room temperature to 500 ° C., and the temperature increase rate was 5 ° C./min. In order to investigate the relationship between the coefficient of thermal expansion and the OH content, specimens of OH content of 18, 87 and 174ppm were selected among the samples obtained above.

Figure 9 shows the results of measuring the coefficient of thermal expansion of the samples of the OH content of 18, 87, 174ppm, respectively. In the temperature range up to 500 ℃, when the OH content is 18ppm, the average coefficient of thermal expansion is 0.42x10 ^-6 / K, and when the OH content is 87ppm, the mean coefficient of thermal expansion is 0.45x10 ^-6 / K and 174ppm The mean coefficient of thermal expansion was 0.55x10 ^-6 / K. As the OH content increases, the coefficient of thermal expansion increases.

Anti Dust Glass (ADG) for a projection display is manufactured by the process as shown in FIG. Silica glass ingots are made by vitrification heat treatment after preparing the silica dried body. The quartz glass ingot is cut into a wafer using a wire saw and wrapped to form a quartz glass wafer. A quartz glass abrasive wafer prepared by polishing a wafer is manufactured using a dice saw to produce an antidust glass (mixed with "ADG" in the description and drawings of the invention). On the other hand, in the case of a high temperature polysilicon TFT substrate or a counter substrate, after manufacturing a silica dried body, a quartz glass ingot is formed by vitrification heat treatment, and a quartz glass wafer is made by cutting and lapping using a wire saw. It is produced by polishing a wafer.

Since the dust-proof glass is cut from a single wafer and dozens are manufactured, it is also important to control the OH concentration distribution in the wafer form. If the OH content in the wafer has a large deviation depending on the position, a problem occurs because it brings about a deviation of the dustproof glass heat resistance.

Nine points were measured and analyzed as shown in FIG. 7 for OH content distribution analysis. Among the samples subjected to the dry gas atmosphere heat treatment test, the OH content was measured at the measurement point of FIG. 7 with respect to test samples with dew point temperature of -196 ° C, used gas He, heat treatment temperature of 1200 ° C, and heat treatment time of 20hr. The same result was obtained. The average value was 66ppm, the maximum value was 82ppm, the minimum value was 48ppm, and the range value was 34ppm.

Slow cooling is required to reduce the variation in OH concentration distribution after OH removal by dry gas atmosphere heat treatment. It is possible to control the fictive temperature by the slow cooling heat treatment, thereby controlling the OH concentration distribution.

The hypothetical temperature is defined as the temperature of the glass in equilibrium when it is allowed to reach a certain temperature rapidly in a certain state [Ref. A. Q. Tool, J. Am. Ceram. Soc., 29 (1946) 240]. When the glass is heat treated at a constant temperature for a sufficient time, the virtual temperature of the glass approaches that temperature. The virtual temperature of the heat-treated and quenched glass at a constant temperature for a long enough time to reach the quasi-equilibrium state is that temperature. If you do not quench and slow cool, the virtual temperature of the glass will change according to the cooling rate. Virtual temperature can be an excellent tool in evaluating slow cooling processes to remove residual stress and produce homogeneous glass. In general glass, the virtual temperature can be measured by DSC (Differential Scanning Calorimetry). In the case of quartz glass, the virtual temperature cannot be measured by DSC because there is very little specific heat change before and after the glass transition temperature. The virtual temperature of quartz glass was measured by IR spectroscopic method (Anand Agrwal, Kenneth M. Davis, Minoru Tomozawa, Journal of Non-Crystalline Solids 185 (1995) 191-198).

The inventors conducted a dry gas atmosphere heat treatment experiment to remove OH groups in the quartz glass. Experiments were performed to find the optimum conditions by varying the dew point temperature, used gas, heat treatment temperature, and heat treatment time. Hereinafter, the configuration of the present invention will be described in detail through specific embodiments. However, it is apparent to those skilled in the art that the scope of the present invention is not limited only to the description of the following examples.

< Example  1: dew point temperature change>

Basic experimental methods applied to Examples 1 to 4 are as follows.

Put the bulk of silica into a hermetic chamber furnace, first increase the degree of vacuum to about 10 mTorr using a vacuum pump, and pass the gas through the dry gas trap (liquid nitrogen trap, dry ice / ethanol trap, etc.) He, Ar, etc.) was injected until reaching atmospheric pressure. In addition, the vacuum pump was used to increase the degree of vacuum and inject gas passed through the dry gas strap, and this process was repeated at least three times. Finally, the gas passed through the dry gas strap was flowed to raise the temperature of the furnace to a desired heat treatment temperature (1200 ° C.), maintained at that temperature for a desired heat treatment time (20 hr), and cooled.

First, the experiment was carried out by setting the dew point temperature of the dry gas to -196 ℃ and -78.5 ℃. A dew point temperature of -196 ° C was implemented using a liquid nitrogen trap and a dew point temperature of -78.5 ° C using a dry ice / ethanol trap. In order to examine the effect of the dew point temperature on the OH removal, the other conditions were the same as the used gas helium (He), heat treatment temperature 1200 ° C, and heat treatment time 20hr. Figure 1 shows the experimental results.

When the dew point temperature was -196 ° C, the average OH content was 65 ppm, and when the dew point temperature was -78.5 ° C, the average OH content was 97 ppm. As shown in FIG. 2, the relationship between the dew point temperature and the moisture content decreases exponentially as the dew point temperature decreases. If the dew point temperature is -196 ℃, the moisture content is less than 0.001ppm, and if the dew point temperature is -78.5 ℃, the moisture content is about 1 ppm. Lower dew point temperatures result in lower moisture content and are believed to be more effective at removing OH in the quartz glass.

< Example  2: change of used gas>

In order to examine the effect of used gas on OH removal by dry gas heat treatment, helium (He) gas and argon (Ar) gas were tested. The dew point temperature was fixed at −196 ° C., the heat treatment temperature at 1200 ° C., and the heat treatment time at 20 hr. 3 shows the experimental results.

The average OH content was 65 ppm when He gas was used, whereas the average OH content was 128 ppm when Ar gas was used. He gas has been shown to be more effective at removing OH than Ar gas. The molar mass of He is 4.003 g / mol, whereas the molar mass of Ar is 39.948 g / mol, so it is thought that He penetrates deeply inside the sample and the OH removal reaction is active.

< Example  3: heat treatment temperature change>

In order to examine the effect of the heat treatment temperature on the OH removal by dry gas heat treatment, the heat treatment temperature was set to 1000 ° C, 1100 ° C, 1200 ° C, and 1300 ° C, respectively, and other conditions (gas: He, dew point temperature: -196 ° C, Holding time: 20hr) was the same. 4 shows the experimental results.

The average OH content was 174 ppm when the heat treatment temperature was 1000 ° C, 125 ppm when the heat treatment temperature was 1100 ° C, 65 ppm when the heat treatment temperature was 1200 ° C, and 65 ppm when the heat treatment temperature was 1300 ° C. As the heat treatment temperature increases, the OH content decreases, but it was found that there was almost no change above 1200 ° C. As the heat treatment temperature is higher, more energy is required and production cost is increased, so the optimum heat treatment temperature is 1200 ° C.

< Example  4: heat treatment time change>

In order to examine the effect of heat treatment time on OH content in OH removal by dry gas heat treatment, the heat treatment time was 1hr, 5hr, 20hr, and 40hr, respectively, and the different conditions (gas: He, dew point temperature: -196 ℃) were maintained. Time: 20 hr) was the same. 5 shows the experimental results.

The average OH content when the heat treatment time was 1 hr was 103 ppm, when the heat treatment time was 5 hr, 86 ppm, when the heat treatment time was 20 hr, 65 ppm, and when the heat treatment time was 40 hr, 61 ppm. As the heat treatment time increases, the OH content decreases, but almost no change occurs over 20hr. The longer the heat treatment time, the more energy is needed and the production cost increases, so the optimal heat treatment time is 20hr.

In the OH removal experiment by dry gas atmosphere heat treatment, the optimum conditions found by changing dew point temperature, used gas, heat treatment temperature, heat treatment time, etc. were dew point temperature -196 ℃, used gas He, heat treatment temperature 1200 ℃, and heat treatment time 20hr. At this time, the OH content was 65 ppm.

< Example  5: by dry gas atmosphere heat treatment OH  Concentration Distribution Control>

The virtual temperature of the sample which performed the dry gas atmosphere heat treatment test, ie, the sample before a slow cooling heat treatment, was 1230 degreeC. This sample was subjected to cold heat treatment at a virtual temperature of 1100 ° C. and 1000 ° C., respectively. The slow cooling heat treatment is performed at a rate of 10 ° C./min up to 1100 ° C. in an Ar atmosphere, maintained at 1100 ° C. for 20 hours, and cooled to 5 ° C./min up to room temperature. In addition, the method of slow cooling heat treatment so that the virtual temperature is 1000 ℃ is heated at a rate of 10 ℃ / min to 1000 ℃ in an Ar atmosphere, maintained at 1000 ℃ heat treatment for 20 hours, and cooled to 5 ℃ / min at room temperature do.

The average OH concentration was 66ppm, the maximum value was 73ppm, the minimum value was 57ppm, and the range value was 16ppm when the slow cooling was performed such that the virtual temperature was 1100 ° C. The maximum value was 68 ppm, the minimum value was 62 ppm and the range value was 6 ppm.

In conclusion, after removing OH by dry gas atmosphere heat treatment under the condition of dew point temperature -196 ℃, used gas He, heat treatment temperature 1200 ℃ and heat treatment time 20hr, the slow cooling heat treatment was performed at a virtual temperature of 1000 ℃. The OH concentration distribution was 65 ± 3ppm, showing a very uniform value.

Dust Proof Glass is located on the front and back of the high-temperature poly-Si TFT-LCD substrate and the color filter substrate to prevent deterioration of image quality caused by dust or foreign matter adhering to the substrate surface. It also functions to prevent mechanical damage of the substrate glass. In addition, since the projection display device uses a halogen lamp as a light source, high heat is generated. Therefore, when the heat resistance of the quartz glass is different, the adhesion decreases due to the difference in the thermal expansion coefficient of the substrate / dustproof glass, leading to deterioration of image quality. do. Accordingly, the present invention prevents deterioration of image quality by providing a dustproof glass at a level similar to the thermal expansion coefficient of the quartz glass for a substrate.

In addition, the method of the present invention can be applied to dust-proof glass, optical engine components, photomask substrates, stepper lenses, and the like of liquid crystal projector optical engines, which are rapidly increasing in demand.

In addition, the method of the present invention can be utilized as a base technology for manufacturing substrate glass for high temperature poly-Si TFT-LCD, and can be applied to other technologies for manufacturing quartz glass for display, semiconductor, and precision optics.

Claims (5)

A method for producing high purity quartz glass having a low OH content by heat treatment in a dry gas atmosphere under a dew point temperature of -100 ° C. or lower, a used gas He, a heat treatment temperature of 1150 ° C. or higher, and a heat treatment time of 10 hr or more. The method of producing a high purity quartz glass having a low OH content according to claim 1, wherein the heat treatment temperature is 1200 to 1500 ° C. The method of manufacturing a high purity quartz glass having a low OH content according to claim 1, wherein the heat treatment time is 10 to 50 hours. The method of claim 1, wherein the dew point temperature is -150 ~ -300 ℃ method for producing high purity quartz glass with low OH content. The method of claim 1, wherein the low-OH content is high purity quartz glass, characterized in that the slow cooling heat treatment to a virtual temperature 950 ~ 1100 ℃ after the dry gas atmosphere heat treatment.

Images