JPS6272536A - Production of high-purity quartz glass - Google Patents

Abstract

PURPOSE:To obtain the titled large-sized glass without generating any cracks and droppings by gradually heating a porous quartz glass base material formed by gas-phase reaction synthesis from the upper part to prebake the material and then heating the material from the lower end to vitrify the material. CONSTITUTION:A silicon compd. (e.g., silicon tetrachloride and trichlorosilane) is hydrolyzed in an oxyhydrogen flame in a reactor 9 and the formed line silica particles are deposited and accumulated on a starting member 10 to form the porous quartz glass base material 11. Then the base material 11 is gradually pulled up from the lower end of a heating furnace 20, heated by a heater 21 and prebaked. Then the prebaked base material 12 is lowered from the upper part of a heating furnace 30 and heated by a heater 31. Consequently, the prebaked base material 12 is gradually vitrified from the lower end part and the large-sized quartz glass 13 for a photomask substrate, etc., is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing high-purity quartz glass, in which a porous quartz glass base material is formed by a gas phase reaction synthesis method, and the same is fired in a heating furnace to produce transparent glass. be.

[Prior Art] Conventionally, one of the methods for manufacturing quartz glass has been to form a porous quartz glass base material by a vapor phase reaction synthesis method, and then heat this base material to vitrify it. There is.

That is, a silicon compound such as silicon tetrachloride is hydrolyzed in an oxyhydrogen flame, and silica fine particles are attached and deposited on the lower end of a starting member, a quartz seed rod (hereinafter referred to as starting member or seed rod). Form a porous quartz glass matrix. Then, this porous quartz glass base material is placed in a heating furnace and heated with a heater to sinter the base material, thereby vitrifying it.

When manufacturing optical fibers and the like, a silica glass manufacturing method called the VAD method is employed. This method is
Fine silica particles are attached and deposited on the lower end of the seed rod using the gas phase reaction synthesis method to form a porous quartz glass base material, which is then gradually pulled up and passed through a heater to gradually vitrify the base material starting from the top. It's a method. This method has the advantage that the formation of a porous quartz glass base material and the vitrification of this base material can be performed continuously.

[Problems to be solved by the invention] However, when trying to manufacture large quartz glass such as a photomask substrate, porous quartz glass f
It is necessary to make the fJ material large in diameter and long, and its weight is equivalent to about 14 kg per piece in the case of a base material with a diameter of 30 cm and a length In, for example. When vitrifying such a large porous quartz glass base material, the above VA
When method D is used, the base material is heated from the top and vitrified, so the area near the bottom end of the seed rod softens first, making it impossible to support the base material that connects downward, and the base material below. As a way to prevent the material from separating from the vicinity of the lower end of the seed rod and falling, it is possible to increase the diameter of the quartz seed rod, but it is possible to support the L base material under a temperature condition of 1400℃. In order to do so, the cost of seed rods becomes considerably high and it is difficult in practice.

On the other hand, as a method to solve the above problem, a porous quartz glass base material is inserted from the upper part of the heating furnace, and the base material is gradually turned into transparent glass from the bottom, and the base material is lowered and the lower end of the seed rod is lowered. There is a method of stopping the descent when the temperature reaches the 1400°C temperature range. However, the porous quartz glass base material generally manufactured by the above-mentioned method does not have sufficient strength, and such a base material is inserted from the top of the furnace in a single step to produce transparent glass. However, the porous quartz glass base material collapsed during heat forming due to the turbulence of the air flow in the furnace, making it impossible to produce large-diameter quartz glass.

An object of the present invention is to solve the above-mentioned problems and provide a method for manufacturing large-sized high-purity quartz glass for use in photomasks and plates.

[Means for Solving the Problems] The present invention has been made in order to solve the above-mentioned problems, and it involves attaching and depositing silica particles produced by hydrolyzing a silicon compound in an oxyhydrogen flame to a starting member. The first step is to form a porous quartz glass base material, and the second step is to pre-fire the base material by gradually pulling it up from the lower end of the heating furnace.
In addition, the pre-fired porous quartz glass base material (hereinafter referred to as "F pre-fired base material") is lowered from a part of the heating furnace to gradually form transparent glass from the lower end of the pre-fired base material. The present invention provides a method for producing high-purity quartz glass, which is characterized by comprising a third step of converting the quartz glass into a quartz glass.

In the present invention, the porous quartz glass material is, for example, the first
Manufactured by the equipment shown in the figure (first step)
, that is, hydrogen and # from pombe l and pombe 2
The raw material is supplied to a multi-tube burner 5 through mass flow controllers 3 and 4. In addition, gases of silicon compounds such as silicon tetrachloride, trichlorosilane, and silicon tetrabromide are preheated from the tank 6 by the pump 7 through the heat exchanger 8 and sent to the multiple pipes.
5. The multi-tube burner 5 forms an oxyhydrogen flame in the 15-sided chamber 9, and hydrolyzes the silicon compound to form silica fine particles. Although not shown, an inert gas such as nitrogen or argon is also supplied to the burner 5 and used as a carrier gas for these silicon compounds or as an air curtain in an oxyhydrogen flame. The chemical formula for this hydrolysis reaction when the silicon compound is silicon tetrachloride is as follows.

2H2÷02→2H20---(1)2H20÷
5iC14→S i02◆4HC:I --------
(2) The silica fine particles adhere to and accumulate on the lower end of the quartz seed rod 10 suspended vertically as a starting member in the reaction chamber 9 and grow sequentially, forming a large-diameter porous quartz glass base material 11. be done. In addition, 1 muic acid generated by the reaction is 1,?
It is brought into contact with the sodium chloride water in a countercurrent flow in the washing tower 13 and is absorbed and removed.

The first step, second step, and third step in undeveloped IJ+ are illustrated in FIG. 2. That is, as shown in FIG. 2, t?
The porous quartz glass FF member 11 manufactured in the first step according to the method described in ii is inserted into the lower part of the auxiliary firing furnace 20, and moved to the L direction of the heating furnace 20 while rotating the seed rod 10. After the porous quartz glass base material is pre-fired gradually from the upper part, the pre-fired base material 11 is extracted from the upper part of the heating furnace 20.After the pre-fired base material is finished, the pre-fired base material 11 is removed immediately or after some time. Said pre-fired material I
I (11) is moved above the vitrification heating furnace 30,
The base material 11 is inserted from the top of the heating furnace 30 and moved toward the bottom of the heating furnace 30 while being rotated, thereby gradually turning the base material into transparent glass from the lower end, thereby manufacturing high-purity quartz glass. do. In addition, when the vicinity of the lower end of the seed rod of the base material reaches the high temperature range of 1400° C. or more of the heating furnace 30, the movement in the lower direction is stopped to prevent the base material from falling from the seed rod. .

In this way, after inserting the porous quartz glass base material from the bottom of the heating furnace and pre-firing it, the temperature in the transparent vitrification area was raised to 14.
Since the glass is moved downward from the top of the heating furnace, which is maintained at 00 to 1,500℃, the base material may be broken during the firing process, or the seed rod may be thermally deformed and the base material may be damaged during vitrification. will no longer fall. Furthermore, the bubbles or the gas in the bubbles that flow out during vitrification can escape upward through the porous layer above the base material that has not yet been vitrified. can be prevented from being contained.

According to a preferred embodiment of the present invention, the heating furnace used for pre-firing the porous quartz glass base material is provided with a heater so as to have a temperature gradient increasing from the bottom to the top. In this way, when inserting the porous quartz glass base material into the heating furnace, it is possible to gradually increase the temperature of the 11 materials, thereby preventing cracks from occurring in the base material due to sudden heating. can do. As for the temperature gradient, since the temperature at which the porous quartz glass DJ material can be inserted is 600°C or lower, the lower part of the furnace is set at around 500°C, and the sintering temperature of the 1ξI material is 1100°C or higher, and the sintering temperature is 1400°C or higher. At this temperature, the quartz seed rod will be thermally deformed and will no longer be able to withstand the stress of the material. Furthermore, the heating furnace used for the preliminary firing is provided with a uniform temperature area in the upper part of the heating furnace where the temperature is almost uniform in the 7F direction, and the temperature decreases from the lower part of the uniform temperature area toward the lower part of the heating furnace. In this case, there is an advantage that the degree of freedom in selecting the working conditions for pre-firing increases.

The porous quartz glass base material is gradually pulled up into a heating furnace having the temperature distribution shown in L for pre-firing, but it is preferable that the atmosphere at this time is clean, with air that has been conserved with a filter or the like as necessary. The pulling speed is carried out while introducing nitrogen gas or other inert gas upward from the bottom of the furnace.The rate of pulling varies depending on the temperature level in the middle stage of the heating furnace and the length of the equal temperature zone, but for example, when the temperature is 1300℃ and the temperature is equalized, When using a furnace with a temperature range of 20 cm, a temperature of around 250 m/Hr is appropriate.

After performing such preliminary firing, the base material is transported to the upper part of the adjacent heating furnace and moved downward from the top of the furnace, thereby gradually turning the base material into transparent glass. At this time, the atmosphere in the furnace has a He concentration. 70z or more, preferably 80 to 90%, and the heating furnace used to gradually transform the base material into transparent vitrification is preferably provided with a temperature gradient that increases from the J: part to the lower part. The temperature gradient at this time is such that the vitrification temperature of the porous quartz glass base material is 1400
℃ or above, it is appropriate to set the temperature of the upper part of the heating furnace to around 1200℃ and the lower part of the furnace to 1400 to 1500℃.
It is appropriate to stop the descent when the temperature reaches a high temperature range of C or higher. Furthermore, the heating furnace used for transparent vitrification is provided with a uniform temperature area in the lower part of the heating furnace where the temperature is almost uniform in the vertical direction, and the temperature decreases from the upper part of the uniform temperature area toward the upper part of the heating furnace. In this case, there is an advantage that the degree of freedom in selecting the working conditions for transparent vitrification is increased.

[Example]: Figure 52 (A), (B), (C), (D)
shows the equipment and process for manufacturing everything from porous base materials to transparent quartz glass rods. Embodiments of the present invention will be described below with reference to the drawings.

As shown in Fig. i2 (A), silicon tetrachloride is hydrolyzed in a hydrogen-resistant flame, and fine particles of silica are deposited and grown on a quartz seed rod to form a porous material with a diameter of approximately 30 cm and a length of 100 cm. A quartz glass base material 11 was formed. This base material is synthesized 2
19, the seed rod is cut from the joint portion 15 and inserted from the lower part of the heating furnace 20 installed at an adjacent location. The heating furnace 20 has a temperature gradient that increases from the bottom to the top, and the temperature at the bottom of the furnace is approximately 500°C;
The temperature at the upper part of the furnace is controlled to be approximately 1300'C. As shown in Figure 2 (B), the seed rod 10 is slowly rotated in the direction of the arrow, l/hour.

The porous quartz glass base material 11 was gradually inserted into the heater by pulling upward at a speed of ~50 c layers, and preliminary firing was performed. Therefore, the porous quartz vitrification temperature is gradually heated from the upper part, and the air bubbles in the porous quartz glass 111 material move toward the outer periphery or to the lower low temperature part, and the air bubbles inside are defoamed and the porous quartz glass 111 is heated. The glass base material shrunk in the radial and axial directions with open bores remaining, resulting in a pre-fired base material 12 that can be easily transformed into transparent glass in the first step.

After the preliminary firing is completed, the base material is placed in the heating furnace 20.
As a result of measuring the dimensions of the base material extracted from the top of the
It was 1 cm and the length was 80 cm.

As shown in FIG. 2(C), the pre-fired base material 12 is moved above the adjacent heating furnace 30, and the heating furnace 3 is moved at a rate of about 10 c layers per hour while slowly rotating the seed rod IO.
By gradually moving the porous quartz glass base material downward from the top and inserting it into the heater 31, the lower part of the porous quartz glass base material was turned into transparent vitrification.

The heating furnace 31 is large enough to allow the pre-fired base material 12 to be inserted therein, and has a temperature gradient that increases from the top to the bottom. This temperature gradient is controlled so that the upper part of the heating furnace is approximately 1200°C and the lower part is approximately 1430°C.Helium gas is supplied from the lower part of the furnace at a rate of 1.3 m3/Hr by a device not shown. The helium atmosphere inside the furnace is maintained at 80-90%. In the furnace, the porous quartz glass base material 12 is gradually heated and melted from the lower end to be degassed, and becomes a transparent quartz glass 13 having a smaller diameter than the base material 12. At this time, the air bubbles escape to the outside through the upper porous glass layer that has not yet become transparent vitrified, so that the air bubbles do not get mixed into the formed quartz glass.

As shown in FIG. 2(D), when the vicinity of the lower end of the seed rod 10 reaches the upper end of the heater 31, the descent stops and transparent vitrification is completed. Therefore, the vicinity of the lower end of the seed rod 10 is prevented from being heated and deformed, and the quartz glass 13 connected below can be supported without falling. Further, thermal deformation of the lower end of the seed rod 10 can be prevented.

[Effects of the Invention] As explained above, according to the present invention, a two-stage firing method is employed in which a porous quartz glass base material is heated from the L part to gradually pre-fire it, and then heated from the lower end to make it transparent vitrified. Because of the rapid thermal contraction when firing large-diameter base materials,
It is possible to prevent the base material from cracking, the seed rod from being exposed to high temperatures of 1400° C. or higher and being thermally deformed, and the RI material from falling from the lower end of the seed rod.

Furthermore, as the base material diameter increases, the temperature difference in the radial direction during firing increases, but in the present invention, the porous quartz glass base material is pre-fired under conditions that do not form closed bores to shrink the diameter. As a result, the temperature difference in the radial direction (outer periphery and center) during transparent vitrification is reduced, and degassing proceeds uniformly, preventing air bubbles from entering the quartz glass even when vitrifying it at high speed. It can be prevented.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of an apparatus for obtaining a porous quartz glass base material, and FIG. 2 is an explanatory diagram showing an example of the transparent quartz glass manufacturing method according to the present invention. FIG. 2 is an explanatory diagram showing an apparatus and process for obtaining a quartz glass base material, (B) an apparatus and process for pre-firing, and (G) and (D) an apparatus φ process for forming a transparent glass. 9-----Porous quartz glass Iri material synthesis reactor 1
0-------1 Starting member Class 1 rod 11-----1 Porous quartz glass IJ material 12----
-Ikkobi fired porous quartz glass LN1 material 13---
---1 Transparent quartz glass 15--11-11 Joint 20.30----1 Heating furnace 21.31---Change to the clean side of the heater frame 2 Procedures-? 111 Official Book (Method) February 1st, 1985

Claims (8)

[Claims] (1) A first step in which silica fine particles produced by hydrolyzing a silicon compound in an oxyhydrogen flame are attached and deposited on a starting member to form a porous quartz glass base material, and the base material is placed in a heating furnace. a second step of pre-firing the pre-fired base material by gradually pulling it up from the lower end; and a second step of gradually turning the pre-fired base material into transparent vitrification from the lower end of the furnace by lowering the pre-fired base material from the upper part of the heating furnace. A method for manufacturing high-purity quartz glass, characterized by comprising the steps of 3. (2) The method for manufacturing high-purity quartz glass according to claim 1, characterized in that in the second step, the porous quartz glass base material is pre-fired at a temperature range of 1150 to 1350°C. (3) The method for manufacturing high-purity quartz glass according to claim 1, characterized in that in the third step, the pre-fired base material is gradually turned into transparent vitrification at a temperature range of 1400 to 1500°C. . (4) The method for manufacturing high-purity quartz glass according to claim 1, wherein the porous quartz glass base material is rotated in the first step and the second step. (5) The method for manufacturing high-purity quartz glass according to claim 1, wherein the heating furnace in the second step has a temperature gradient that increases from the bottom to the top of the furnace. (6) The method for manufacturing high-purity quartz glass according to claim 1, wherein the heating furnace in the third step has a temperature gradient that increases from the top to the bottom of the furnace. (7) The heating furnace of the second step has a uniform temperature area in the upper part of the heating furnace where the temperature is almost equal in the vertical direction, and the temperature decreases from the lower part of the uniform temperature area toward the lower part of the heating furnace. 2. The method for producing high-purity quartz glass according to claim 1, wherein the method has a temperature gradient of: (8) The heating furnace of the third step has a uniform temperature area in the lower part of the heating furnace where the temperature is almost uniform in the vertical direction, and the temperature decreases from the upper part of the uniform temperature area toward the upper part of the heating furnace. 2. The method for producing high-purity quartz glass according to claim 1, wherein the method has a temperature gradient of: