JPH0829958B2 - Method for producing porous quartz glass base material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a porous quartz glass base material by a gas phase reaction synthesis method.

[Prior Art] Conventionally, a silica glass is synthesized by a vapor phase reaction method by hydrolyzing a silicon compound in an oxyhydrogen flame to deposit silica fine particles on a seed rod and firing the same. There is.

Conventionally, in the case of producing such a porous quartz glass preform, if the reaction is carried out in the atmosphere, a problem occurs that impurities in the air are mixed into the quartz glass preform,
Normally, a seed rod is placed in a reactor made of Pyrex or the like having one exhaust port, and silica particles are sprayed and deposited on the seed rod, and the seed rod is gradually pulled up to form a porous quartz glass base material. The method of growing is adopted.

At this time, if the flame in the reactor is disturbed, the shape of the porous quartz glass base material is disturbed and the base material cannot be stably manufactured. Therefore, some proposals have been made to eliminate this disturbance.

The inventors of the present invention have previously proposed, as an improved apparatus for suppressing the above-mentioned turbulence in the reactor, in Japanese Utility Model Application No. 59-16732, a reaction is performed so as to surround a porous quartz glass base material and an oxyhydrogen flame. We devised a dual structure reactor with an inner cylinder installed inside the reactor.

In addition, in the manufacture of optical fiber preforms, etc.
As shown in No. 57-61641, in order to suppress the fluctuation of the burner flame due to downflow etc. in order to suppress the axial fluctuation of the outer diameter and the refractive index of the base material, in order to keep the fluctuation between the reactor and the exhaust equipment. A buffer tank filled with water is installed, and a bias gas is forcibly supplied from the middle of a pipe connecting the reaction container and the buffer tank, and a bias gas amount is adjusted by a pressure detection device. JP-A-56-32345 proposes a method of installing a rotor in the exhaust port to prevent soot from adhering to the exhaust port.

[Problems to be Solved by the Invention] When quartz glass is used as, for example, a substrate material for a photomask, the quartz glass material is required to have a large size. A quartz glass base material with a diameter of 28 to 30 cm and a length of 100 cm or more is required, but when manufacturing such a long base material with a large diameter, it is necessary to use a large reactor to It is necessary to drive for an hour (24 to 30 hours).

However, when it is attempted to manufacture the above-mentioned large-diameter long preform by a production method that has been conventionally proposed, silica fine particles that have adhered / grown on the inner wall of the reactor over time fall during the synthesis and the preform However, problems such as damage to the glass, turbulence of the flame flow in the reactor with the passage of time, and the inability to stably synthesize the porous quartz glass preform were found.

One of the causes of such a problem is that in the case of producing a large-diameter long base material in a large and long reactor, a large amount of heat due to an oxyhydrogen flame is generated in the reactor. A non-uniform gas flow is likely to occur in the reactor due to the draft action from the lower part of the reactor to the upper part caused by the temperature difference between the upper and lower positions of the inside of the reactor. It is considered that a scale of non-uniform thickness, which is structurally prone to collapse, adheres and grows, and when it reaches the critical thickness, it cannot withstand a slight pressure fluctuation in the vessel and falls off.

Furthermore, in order to produce a large-sized base material as described above, a considerable amount, for example, 1.8 to 2.5 kg / Hr of a silicon compound in terms of silicon tetrachloride will be reacted for a long time,
In the conventional method, it is considered that the pressure inside the vessel fluctuates greatly due to a short-term drop-off of the scale composed of silica fine particles that have been successively deposited and accumulated in the pipe.

The present invention prevents the occurrence of the above-mentioned problems.

[Means for Solving the Problems] The present invention solves the problems of the above-mentioned conventional techniques and provides a method for stably manufacturing a long base material having a large diameter, the gist of which is an exhaust device. A seed rod is placed in a reactor having an attached exhaust port, and a silicon compound is flame-hydrolyzed in an oxyhydrogen flame using a multi-tube burner to deposit silica fine particles on the seed rod.
In the method of growing to produce a large-diameter long base material,
The secondary air is introduced from a secondary air inlet having a predetermined opening provided in the central part of the upper part of the reactor whose diameter of the upper part of the reactor is D _{2, and} at a position L ₂ away from the upper end of the reactor, L ₂ / D ₂ = 0.9
The upper exhaust port is provided so as to satisfy ~ 1.1, and the lower exhaust port is also provided at the lower part so that the reaction exhaust gas and the flame flow containing silica particles flow from the lower part of the reactor to the upper exhaust port. The upper exhaust gas exhausted from the exhaust port and the lower exhaust gas exhausted from the lower exhaust port are passed through the same regulator, and the amount of gas supplied to the multi-tube burner is 8 to 15 due to the introduction of the secondary air. A method for producing a porous quartz glass preform characterized in that a reactor is used by setting exhaust conditions so that a double amount of exhaust gas is passed through a regulator and extracted.

As illustrated in FIG. 1, a suction / exhaust device such as a blower is installed in the post-process of the adjuster, and this suction / exhaust device reduces the amount of gas supplied to the multi-tube burner to 8%.
About 15 times the amount of exhaust gas is passed from the upper exhaust port and the lower exhaust port through pipes (indicated by a bar with an arrow), and then passed through a regulator to be withdrawn.

For example, 2H ₂ + O ₂ → 2H ₂ O, SiCl ₄ + 2H ₂ O → SiO ₂ + 4HCl
In the reaction example of, the supply gas (H ₂ 2 mol, O ₂ 1 mol, SiCl
_As can be seen from the fact that the supply gas and the reaction exhaust gas are generally in the same amount, as can be seen from the fact that the reaction exhaust gas (HCl 4 moles) is the same, the amount of gas supplied to the multi-tube burner is 4 8 to 15 times the amount of exhaust gas passing through the regulator and being withdrawn, the amount of exhaust gas passed through the regulator and withdrawn becomes about 8 to 15 times the amount of reaction exhaust gas.

Further, the amount of reaction exhaust gas is determined and fixed by the amount of gas supplied to the multi-tube burner, and the sum of the amount of air introduced from the secondary air inlet and the amount of reaction exhaust gas passes through the regulator and is extracted. Since it is the amount of exhaust gas leaving, the amount of air introduced from the secondary air inlet becomes about 7 to 14 times that of the reaction exhaust gas.

That is, using the regulator, a large amount of exhaust gas, which is about 7 to 14 times as much as the reaction exhaust gas, is taken in from the secondary air inlet, and the exhaust gas which is a mixed gas of these is sucked and discharged by a blower or the like via the regulator. Then, the exhaust conditions are set so that the reaction exhaust gas and the flame flow containing the silica fine particles flow from the lower part of the reactor toward the upper exhaust port.

By setting the exhaust conditions in this way, i.e., a flame flow containing rectified silica fine particles rising along the outer peripheral surface of the porous quartz glass base material in the reactor is formed, and internal pressure fluctuations in the lower part of the reactor are formed. The exhaust conditions are set so that the secondary air is introduced from the center of the upper part of the reactor and the introduced secondary air is mainly discharged from the exhaust port of the upper part of the reactor so that A flow is generated toward the upper part of the reactor to achieve the above object.

Moreover, the air is introduced from the secondary air inlet having a predetermined opening provided in the central part of the upper part of the reactor having the diameter D ₂ at the upper part of the reactor, and at a position L ₂ away from the upper end of the reactor, ₂ / D
_{Since the} upper exhaust port is provided so as to satisfy ₂ = 0.9 to 1.1, the discharge balance between the air flow rising from the lower part of the reactor and the secondary air introduced from the outside is stable, and porous quartz glass is provided inside the reactor. A flame flow containing rectified silica fine particles rising along the outer peripheral surface of the base material is formed.

That is, the method for producing a porous quartz glass base material of the present invention is to hydrolyze a silicon compound such as trichlorosilane, silicon tetrachloride, and silicon tetrabromide in an oxyhydrogen flame to deposit silica fine particles on a seed rod. In order to form a large-diameter and long porous quartz glass base material, part of the reaction exhaust gas that is the reaction product gas is discharged from the lower exhaust port at the bottom of the reactor, and secondary air is introduced from the upper center. Furthermore, by discharging the introduced secondary air and the rest of the reaction exhaust gas that has risen due to negative pressure from the upper exhaust port of the upper part of the reactor, fluctuations in the internal pressure of the lower part of the reactor are suppressed, and flames containing silica fine particles are suppressed. Is a method of forming a flow that smoothly rises along the outer peripheral surface of the base material to accelerate the hydrolysis reaction of the silicon compound.

FIG. 1 is an explanatory view showing an example of an apparatus for carrying out the present invention to obtain a porous quartz glass base material.

The present invention will be described with reference to the drawings. In FIG. 1, hydrogen and oxygen are supplied from a cylinder 1 and a cylinder 2 to a multi-tube burner 8 through a mass flow controller 5 to generate an oxyhydrogen flame.

A gas of a silicon compound such as silicon tetrachloride, trichlorosilane, silicon tetrabromide, etc. is supplied into the oxyhydrogen flame through the evaporator 7 and is hydrolyzed to generate silica fine particles having an average particle diameter of about 0.1 to 0.2 μm.

This hydrolysis reaction is represented by the following chemical formula when the silicon compound is silicon tetrachloride.

SiCl ₄ + 2H ₂ O → SiO ₂ + 4HCl And these silica particles are made by a Pyrex reactor
It adheres to a rotating seed rod 12 made of quartz and is grown in sequence to form a porous quartz glass base material 13. The exhaust gas containing HCl generated at this time is exhausted from the exhaust ports 14 and 15
It is discharged from a and 15b, guided to a detoxification tower 18 via a regulator 17, where it comes into countercurrent contact with caustic soda water 19 to remove HCl, and then released to the atmosphere by a blower 20.

In a preferred form of the present invention, the structure of the reactor 10 has a structure in which the diameter of the bottom squeezed slightly is thicker top, the dimensions as shown in FIG. 1, the diameter of the reactor bottom D _1, reactor When the diameter of the upper part is D ₂ , the length of the lower part of the reactor is H ₁ , and the length of the upper part of the reactor is H ₂ , D ₂ / D ₁ = 0.8 to 0.9, H ₂ / H ₁ = 1.6 to 2.0 Selected from the range, the burner is designed to be inserted from the bottom of the reactor.

Also, if the distance L ₂ away from the reactor upper provided an upper air outlet, the upper outlet is preferably placed at a position of L ₂ / D ₂ = 0.9~1.1.

On the other hand, when the positions of the upper exhaust ports 15a and 15b deviate from the above range, the discharge balance between the air flow rising from the lower part of the reactor and the secondary air introduced from the outside is disturbed, and the pressure fluctuation in the reactor becomes large.

Size D of upper exhaust ports 15a and 15b, and secondary air inlet 1
The size D _{3 of} 6 is preferably selected from the range of D / D ₁ = 0.18 to 0.22 and D ₃ / D ₁ = 0.16 to 0.18. By doing this, the amount of gas entering and leaving the reactor is kept balanced from beginning to end, and if the exhaust conditions are set using the regulator 17 at the beginning of the reaction, the internal atmospheric conditions will remain stable until the end of the synthesis. Kept in.

At this time, the amount of exhaust gas passing through the regulator 17 is the amount of gas supplied to the burner 8 in order to form a flame flow containing exhaust gas and silica fine particles directed from the lower part of the reactor toward the upper exhaust port as already described in detail. It is selected from the range of 8 to 15 times. In order to produce a porous quartz glass base material with a diameter of about 30 cm, it is necessary to supply a reaction gas of 5 to 6 Nm ³ / Hr, and therefore a gas of 40 to 100 Nm ³ is discharged to the regulator 17 per hour, and The exhaust gas is approximately equal to the sum of the amount of gas forcedly introduced by the burner 8 and the amount of gas introduced into the upper opening 16 by a natural flow.

The exhaust gas discharged from the exhaust ports 14, 15a, 15b is diluted 2 to 3 times with the dilution air introduced from the outside by the regulator 17, and this diluted gas is spilled into the detoxification tower 18. The first
What is provided above the regulator 17 in the figure is a bypass for introducing the aforementioned dilution air from the outside.

Here, for example, if adjustment is made so that the amount of dilution air from the bypass increases, the amount of exhaust gas from the exhaust ports 14, 15a, 15b decreases and the amount of secondary air decreases. on the other hand,
Adjusting to reduce the amount of dilution air from the bypass increases the amount of exhaust gas from the exhaust ports 14, 15a, 15b,
The amount of secondary air increases. In this case, the amount of dilution air from the bypass can be adjusted by providing a valve in the bypass and adjusting the opening.

Alternatively, as another method, there is a method of adjusting the exhaust gas amount and the secondary air amount by increasing or decreasing the suction force of the blower 20.

By thus diluting the exhaust gas from the reactor with a large amount of air, the dust concentration in the gas is reduced and the exhaust pipe is not blocked.

In the present invention, the temperature in the reactor should be kept in the range of 350 to 550 ° C, preferably 450 to 500 ° C. When synthesizing a large-diameter base metal, the temperature of the central part of the normal flame is set to 1150 to 1200
It is preferable to increase the temperature to ℃ (measured with an infrared thermometer), but if the temperature of the atmosphere in the reactor is lower than 350 ° C., it is necessary to supply a large amount of hydrogen gas to the burner in order to maintain this flame temperature. Under this condition, a stable flame suitable for synthesis cannot be obtained.

Further, at a temperature higher than 550 ° C., there is a risk that the material for sealing the lower burner insertion portion will deteriorate due to heat and impurities may be mixed into the porous quartz glass base material, which is not preferable.

According to a preferred embodiment of the present invention, the reactor 10 has its outer peripheral portion kept warm by a heat insulating material or the like, and the thickness of the heat insulating material is adjusted so that the ambient temperature is maintained.

In the present invention, it is preferable that the number of exhaust ports is one at the bottom and at least two at the top.

In the embodiment, the number of exhaust ports is one in the lower part and two in the upper part. The aforementioned size D in this case is the equivalent diameter of the upper exhaust ports 15a, 15b, that is, the area-converted diameter D corresponding to the total amount of exhaust gas from these upper exhaust ports 15a, 15b per unit time.

For example, by providing the blower in this way, the amount of the exhaust gas sucked by the blower becomes larger in the upper exhaust port than in the lower exhaust port, and the flame flow containing the reaction exhaust gas and silica fine particles flows from the lower part of the reactor toward the upper exhaust port. You can

In the case where one exhaust port is provided as in the conventional case, when exhausting from only the exhaust port, the reaction gas goes upward, so that the base material temperature is maintained at a high temperature and the deposition and growth of silica fine particles are efficient. On the other hand, silica fine particles contained in the reaction gas tend to adhere to the inner wall of the reactor too much, which is not preferable.

Further, when exhausting only from the lower exhaust port, silica fine particles contained in the reaction gas are less likely to adhere to the inner wall of the reactor, but the reaction gas does not go to the upper part, so the base material temperature cannot be maintained at a high temperature and the silica fine particles Inefficient deposition / growth.

In contrast to the conventional technique, as in the present invention, while exhausting from both the lower exhaust port and the upper exhaust port, the amount of exhaust gas sucked by the blower is set to be larger in the upper exhaust port than in the lower exhaust port. When a flame flow containing reactive exhaust gas and silica particles is made to flow from the lower part of the reactor to the upper exhaust port, the reaction gas goes to the upper part, so the base material temperature is kept high and the deposition and growth of silica particles occurs. Is effective, and the silica fine particles contained in the reaction gas are less likely to adhere to the inner wall of the reactor.

[Example] Using the apparatus shown in FIG. _{1 in} which the maximum diameter D _{1 of the} reactor was 800 mm, SiCl ₄ with H ₂ as a carrier gas was supplied at a rate of 1800 g / Hr to a multi-tube burner 8 having a diameter of 65 mm. And the total amount is H ₂ = 2.4
H ₂ gas, N ₂ gas, and O ₂ gas were supplied at a ratio of m ³ / Hr, N ₂ = 1.0 m ³ / Hr, and O ₂ = 2.8 m ³ / Hr to cause flame hydrolysis reaction. Silica fine particles were generated and deposited and grown on the tip of a seed rod which is a starting member for rotation. The diameter D ₃ of the secondary air inlet of this reactor was 140 mm.

During this reaction, the regulator 17 was set so that the total amount of exhaust gas exhausted from the exhaust ports 14, 15a, 15b was 70 m ³ / Hr.
Further, prior to this reaction, the outer circumference of the reactor was kept warm by using a heat insulating material (Fineflex: manufactured by Nichias) having a thickness of about 5 mm.

It takes about 24 hours to form a well-formed porous quartz glass preform with a diameter of 29 cm and a length of 1.2 m, and the average deposition yield at this time is
It was 91.5%. From the start to the end of the synthesis, a pressure sensor was inserted near the bottom of the base material in the reactor, and the internal pressure was measured.As a result, the pressure was extremely stable in the fluctuation range of -1.2 to -1.5 mmAq. . After the synthesis was completed, the scale adhering to the inner wall of the reactor was scraped off and the amount was measured. As a result, the total amount was about 180 gr, and the thickness of the scale was uniform.

In the case of the conventional method which does not carry out the present invention, the pressure in the reactor fluctuates to about -3.0 to +0.01 mmAq, which is larger than that in the case of the method of the present invention.

[Effects of the Invention] As described above, according to the present invention, secondary air is introduced from the center of the upper part of the reactor to suppress the fluctuation of the internal pressure of the lower part of the reactor, and is introduced from the exhaust port of the upper part of the reactor. Since the secondary air is mainly discharged, a flame flow containing rectified silica fine particles rising along the outer peripheral surface of the porous quartz glass base material is formed in the reactor, and the generated silica fine particles are efficiently produced. Well adhered and deposited on the surface of porous quartz glass base material.

That is, since the secondary air for pressure adjustment is introduced from the upper part of the reactor and is withdrawn from the adjacent outlet, the internal pressure fluctuation in the lower part of the reactor becomes extremely small.

Furthermore, since there is no turbulence of the air flow in the reactor, the adhesion of silica fine particles to the inner wall is significantly reduced, and the problem that the scale falls during synthesis and the pressure in the reactor fluctuates greatly is unlikely to occur.

Further, the introduced secondary air is controlled so as to be large in volume, and the exhaust gas containing hydrochloric acid vapor is prevented from rising along the seed rod. Therefore, the metal device is pulled up while rotating the seed rod. Can be prevented from corroding.

Moreover, since the reaction temperature in the reactor is increased to 350 to 550 ° C., the hydrolysis reaction of silicon compounds such as SiCl ₄ is promoted, and a large-diameter porous silica glass preform can be obtained with high yield.

Further, since the gas discharged from the reactor is diluted with a large amount of gas, it is difficult for the scale to adhere to the exhaust duct and to be clogged.

In particular, the present invention is suitable for producing a large-diameter porous quartz glass base material for a photomask or the like.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of an apparatus for obtaining a porous quartz glass base material embodying the present invention. 1 ... Hydrogen cylinder, 2 ... Oxygen cylinder, 3 ... Nitrogen cylinder, 4 ... Silicon tetrachloride tank, 5 ... Mass flow controller, 7 ... Evaporator, 8 ... Multi-tube burner, 9 ...
Flame containing silica, 12 …… Seed rod, 13 …… Porous quartz glass base material, 14 …… Lower exhaust port, 15a, 15b …… Upper exhaust port, 1
6 …… Secondary air inlet, 17 …… Regulator, 18 …… Harmful removal tower, 1
9 …… NaOH water, 20 …… Blower, 24 …… Lower exhaust pipe, 25
a, 25b …… Upper exhaust pipe

Claims (2)

[Claims] 1. A seed rod is arranged in a reactor having an exhaust port with an exhaust device, and a silicon compound is flame-hydrolyzed in an oxyhydrogen flame using a multi-tube burner to deposit silica fine particles on the seed rod. In the method for producing a large-diameter long base material by growing, a secondary air is introduced from a secondary air inlet having a predetermined opening provided in the central part of the upper part of the reactor where the diameter of the upper part of the reactor is D _2. as well as, the distance L ₂ away from the reactor upper, L ₂ / D ₂ = 0.9 to
An upper exhaust port is provided to satisfy 1.1, and a lower exhaust port is also provided in the lower part so that the reaction exhaust gas and the flame flow containing silica particles flow from the lower part of the reactor toward the upper exhaust port, and The upper exhaust gas exhausted from the exhaust port and the lower exhaust gas exhausted from the lower exhaust port are passed through the same regulator, and the amount of gas supplied to the multi-tube burner is 8 to 15 due to the introduction of the secondary air. A method for producing a porous quartz glass preform, comprising using a reactor by setting exhaust conditions so that a double amount of exhaust gas is passed through a regulator and removed. 2. The porous quartz glass preform according to claim 1, characterized in that the temperature of the atmosphere in the reactor is kept at 350 to 550 ° C. by keeping the reactor warm with a heat insulating material. Production method.