JPH08165130A - Apparatus for producing synthetic quartz glass - Google Patents

Abstract

PURPOSE: To enable production most suitable for uniformity of refractive index and stabilized in discharge state by providing a gas introducing means as a discharge means in an apparatus for producing a synthetic quartz glass. CONSTITUTION: This closed type synthetic quartz glass producing apparatus is constituted by installing a burner 1 for synthesizing a quartz glass in a state in which the top part of the burner 1 is turned toward a target 2 for forming an ingot 3 from the upper part of a furnace and connectedly installing a discharge port, a poisonous gas-removing apparatus and a discharge fan 8 into a discharge gas line in a discharge means for discharging silica fine particles which were not deposited on a target. A gas introducing means 9 is provided in the discharge means and measured value of the flow rate measuring apparatus 10 and flow rate measuring apparatus 11 provided in the downstream, that is, an introduced gas amount and discharge gas amount data are treated by a computer 12 and an introduction gas flow amount of the gas introducing means 9 is controlled so as to keep discharge gas amount from the furnace constant and prevent adhesion of a substance produced in the discharged line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing quartz glass, and particularly in fields requiring a synthetic quartz glass member that requires high homogeneity, such as photolithography, high-precision spectroscope, and laser. The present invention relates to a highly homogeneous synthetic quartz glass for optics, which is useful for precision optical instruments.

[0002]

2. Description of the Related Art With the recent increase in the degree of integration of LSIs, fine patterning is progressing in an optical lithography exposure apparatus that exposes and transfers integrated circuits onto a silicon wafer. Therefore, the wavelength of the light source has been shortened, and quartz glass as an optical element for ultraviolet lithography is required to have high transmittance in the ultraviolet region and high homogeneity of the refractive index. In order to realize high transmittance in the ultraviolet region, it is necessary to suppress the impurity concentration in quartz glass. Therefore, a Si compound gas as a raw material of the quartz glass and a carrier gas (H ₂ or O ₂ gas, etc.) for sending the Si compound gas, and a combustion gas for heating flow out from the burner to remove the quartz glass in the flame. The flame hydrolysis method of depositing is commonly used.

An apparatus for producing synthetic quartz glass for synthesizing quartz glass by the flame hydrolysis method is roughly classified into
There are an open type manufacturing apparatus in which a part of the furnace is open to the atmosphere, and a closed type manufacturing apparatus in which the inside of the furnace is shut off from the atmosphere. These are properly used depending on the intended use. For example,
In the case where quartz glass is doped with toxic gas, a closed system manufacturing device is used so that the toxic gas does not flow out of the furnace. Further, in order to manufacture quartz glass for large-diameter optical members, the diameter of the ingot is also increased. In this case, however, an open-type manufacturing apparatus that can easily maintain a uniform atmosphere in the furnace is used.

FIG. 2 shows an example of an open system synthetic quartz glass manufacturing apparatus. Specifically, a furnace, a target for ingot formation installed inside the furnace, a burner for synthesizing quartz glass installed with its tip facing the target,
And an exhaust means for exhausting silica fine particles not deposited on the target. In addition, it is known that the flame hydrolysis method can obtain high-purity silica glass because it is easy to suppress impurities in the raw material and combustion gas, but this type of silica glass has a refractive index distribution. It is also known. The main cause of the non-uniform refractive index distribution of quartz glass is fluctuations in various conditions that occur when synthesizing quartz glass, such as changes in the temperature distribution on the synthetic surface due to flames.
This is because of changes in the diffusion state of impurities into the glass. These factors, that is, the thermal conditions, chemical reactions, diffusion of impurities, etc., that the quartz glass receives during synthesis may result in growth stripes called striae in the quartz glass and distribution in the radial refractive index. Are known.

[0005]

To solve these problems,
In Japanese Patent Application No. 5-022294 and Japanese Patent Application No. 5-022293, a method of measuring the temperature distribution of the composite surface, controlling the temperature distribution, and optimizing the temperature distribution is proposed, and the effect of homogenizing the refractive index is proposed. Has been obtained. However, in order to keep the temperature distribution on the synthetic surface constant, the diameter of the grown quartz glass becomes unstable due to fluctuations in control conditions, and in some cases, divergence causes uncontrollability. There were things.

In order to eliminate the fluctuation of the exhaust condition in the fluctuation of various conditions that occur when synthesizing quartz glass, Japanese Patent Application No. 5-255417 proposes a method of periodically improving the exhaust condition. ing. However, according to this method, the exhaust state is temporarily changed when stabilizing, so striae may remain under certain conditions, and as a result, the dispersion of the refractive index Δn = 1 × 10 ^−6. The following optically homogeneous quartz glass could not be manufactured without striations in the growth direction.

The object of the present invention is to solve these problems.

[0008]

[Means for Solving the Problems] In the synthesis of quartz glass in a flame, in the process of reacting raw materials and continuously depositing on an ingot, flame temperature, furnace temperature, ingot temperature, gas flow velocity near the deposition point, etc. There is a capture rate that depends on In general, the trapping rate cannot be 100%, so that the product substances that are not trapped adhere and deposit in the furnace. Further, contact with an ingot makes it difficult to manufacture under stable synthesis conditions.

Further, since the generated substance adheres to and deposits on the exhaust means of the furnace, the exhaust state of the atmospheric gas in the furnace changes, affecting the temperature distribution in the furnace, and by extension, the silica glass being synthesized. It has been confirmed that the effect on the homogeneity of the refractive index in the radial direction and the generation of striae in the growth direction are promoted. In other words, if the amount of exhaust gas is easily increased, the amount of deposits in the furnace can be reduced, but the amount of produced substances attached to exhaust means such as the exhaust line and the exclusion device is increased, resulting in This causes fluctuations in the exhaust state, and the homogeneity of the refractive index in the radial direction varies in the ingot. In addition, the refractive index fluctuates in the growth direction in the silica glass to be produced, so-called striae are generated.

Based on such a situation, the inventors of the present invention have conducted earnest researches on an exhaust condition optimal for the homogeneity of the refractive index, and as a result, changed the temperature distribution of the ingot by introducing gas. Therefore, it has been found that it is possible to suppress the adhesion to the exhaust line and the like, stabilize the exhaust state, and solve the above-mentioned problems, and have completed the present invention. Therefore, the present invention provides a synthetic quartz glass manufacturing apparatus that ejects Si compound gas, O ₂ gas, and H ₂ gas from a burner and burns them to deposit quartz glass on a target to form an ingot. The present invention provides an apparatus for producing synthetic quartz glass, which is provided with a gas introducing means. Further, in the manufacturing apparatus of the present invention, the total amount of exhaust gas at the downstream viewed from the gas flow of the gas introduction unit and the gas flow of the abatement device is measured, and the amount of introduced gas is controlled by a computer to remove the gas from the furnace. It is characterized in that the exhaust gas amount of is kept constant.

[0011]

In the synthetic quartz glass manufacturing apparatus, increasing the amount of exhaust gas lowers the temperature of the outer peripheral portion of the synthetic surface, resulting in a strong effect on the temperature distribution of the synthetic surface. This changes the atmosphere in the furnace, making it difficult to synthesize the ingot with a constant diameter. On the other hand, reducing the amount of exhaust gas makes it impossible to prevent the produced substance from adhering to the exhaust means, and thus creates an unstable exhaust state.

These contradictory problems of exhaust gas amount are solved by providing a gas introducing means in the exhaust means. In the present invention, the amount of exhaust gas is apparently increased by introducing the gas into the exhaust line without changing the amount of exhaust gas from the furnace. As a result, the flow velocity of exhaust gas in the exhaust line is increased, and adhesion of the produced substance is prevented. As a result, the exhausted state is stabilized, the atmosphere in the furnace can be kept uniform, and it is possible to perform stable synthesis that is optimal for the homogeneity of the refractive index.

The gas introducing means makes it possible to control the opening, and by controlling the amount of exhaust gas by feeding back the state of the exhaust means, the temperature distribution of the ingot can be kept good, and highly homogeneous quartz glass can be synthesized. . Even if the opening is fixed, a sufficient effect can be obtained with respect to adhesion in the exhaust line. Even if it is an open-type or closed-type manufacturing apparatus, the effect of increasing the exhaust gas flow rate can be obtained by providing the gas introduction means, but there is no outside air entering from the hearth and a closed system with a small amount of exhaust gas is better. The effect obtained is large.

In the quartz glass to be synthesized, H ₂ , F, Cl,
SF ₆ or the like is used to dope OH or the like, but in this case, the gas reacted in the furnace contains toxic gases such as HF and SO ₂ . It is necessary to remove all of this gas, but if a gas introduction means is provided, it is conceivable that the toxic gas will flow backward from this gas introduction means for some reason. In the case of the present invention, since the opening for introducing gas is controlled by the computer according to the measured value of the flow rate measuring device, the abnormality in the exhaust system can be promptly judged and the opening for introducing gas can be completely closed. In addition, assuming that the control will not work due to a power failure, we adopted a damper type control method for the opening and made it a normally closed structure.

The quartz glass synthesized by the synthetic quartz glass manufacturing apparatus of the present invention is mainly composed of lenses, prisms,
Used as a base material for optical elements such as reflectors. The outer peripheral portion of this base material is cut, cut and re-formed as necessary to be processed into an arbitrary shape. Then, after annealing (heat treatment) for the purpose of eliminating internal strain, polishing and coating steps are performed to obtain an optical element.

[0016]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. Example 1 A synthetic quartz glass manufacturing apparatus of the present invention is shown in FIG.
As shown in FIG. 1, the burner 1 is installed from the upper part of the furnace to the target 2 with its tip end portion, and the exhaust means is constituted by connecting the exhaust port, the abatement device 7, and the exhaust fan 8 in series in the exhaust line. ing.

The respective measured values of the flow rate measuring device 10 provided in the gas introducing means 9 and the flow rate measuring device 11 provided downstream from the gas flow of the abatement device, the introduced gas amount and the total exhaust gas amount are , Computer 12 for processing data
The exhaust gas amount V from the furnace is calculated.
The obtained V is determined by the frequency of the exhaust fan, but varies with the aging of the exhaust system (pressure loss due to adhesion in the exhaust pipe, etc.). In order to eliminate this fluctuation and maintain a stable amount of exhaust gas, the exhaust frequency was raised to keep the flow velocity of the gas flowing in the exhaust pipe high and suppress the adhesion to the exhaust pipe. When the exhaust frequency is increased, the amount of exhaust gas naturally increases, but the opening area of the secondary air introduction means was controlled in order to keep the exhaust gas flow rate from the furnace constant and to keep the exhaust flow velocity fast and to absorb fluctuations. .

In order to monitor the amount of exhaust gas from the furnace, it is desirable to install a flow rate measuring device in the exhaust line immediately after the exhaust port and measure directly, but since the exhaust gas is hot and corrosive, V is calculated from the difference between the amount and the total exhaust gas amount. All of these can be processed online. Further, since SF is doped in the synthetic quartz glass, SF ₆ is used as a carrier of SiCl _{4 as} a raw material. At this time, the exhaust gas is toxic gas such as HF and SO.
_{Although 2} etc. are included, it was possible to send all of these toxic gases to the abatement device because it is a closed manufacturing device. Furthermore, in order to eliminate the risk that the exhaust gas from the gas introduction means flows back to the outside air, the operating status of the exhaust fan and the exhaust status at each measurement point are constantly monitored by a computer, and when the exhaust means is abnormal (fan stop, In order to prevent the exhaust gas amount from abnormally decreasing due to clogging of the exhaust line and the like), a backflow preventing means for reducing the opening area of the gas introducing means to 0 is provided. By adopting a damper type as shown in 13 of FIG. 1, the gas introducing means has a structure in which the opening area becomes 0 due to its own weight even in the event of power failure.

An ingot was formed using the above synthetic quartz glass manufacturing apparatus. In this case, the frequency of the exhaust fan was around 50 Hz, and almost no deposition of the produced substance on the exhaust line was observed after the manufacturing was completed. In addition, the synthesized quartz glass keeps the diameter of the ingot constant, and the homogeneity of the refractive index in the radial direction is stable in the upper and lower parts of the ingot.
It was highly homogeneous and no striae in the growth direction was observed. [Comparative Example] In the above manufacturing apparatus, the opening area of the gas introduction means was set to 0 to form an ingot. In this case, the temperature of the exhaust fan is 20 to 25H in order to obtain a high temperature sufficient for synthesizing quartz glass without affecting the temperature distribution in the furnace.
It was as low as z, the exhaust flow rate was slower than that in Example 1, and a large amount of the produced substance was observed to be adhered to the exhaust line after the production was completed. In addition, the quartz glass synthesized by the manufacturing apparatus without the gas introduction means had an ingot with an unstable diameter, and a large number of striae which were considered to be due to fluctuations in the exhaust gas amount were detected.

[0020]

As described above, according to the synthetic quartz glass manufacturing apparatus of the present invention, the exhaust state can be controlled stably. Further, since it is possible to stabilize the temperature, pressure and gas concentration in the furnace, it is possible to stabilize the homogeneity of the refractive index of the silica glass. That is, the synthetic quartz glass manufacturing apparatus of the present invention makes it possible to obtain optimal synthetic quartz glass for an optical element.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a closed system synthetic quartz glass manufacturing apparatus of the present invention.

FIG. 2 is a conceptual diagram of a conventional open-type synthetic quartz glass manufacturing apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 burner 2 target 3 ingot 4 hearth 5 furnace frame 6 refractory 7 detoxification device 8 exhaust fan 9 gas introduction means 10 flow measuring device 11 flow measuring device 12 computer 13 damper

Claims (7)

[Claims] 1. A furnace, a target for forming an ingot installed inside the furnace, a burner for synthesizing quartz glass installed with its tip facing the target, and silica fine particles not deposited on the target. In a closed system synthetic quartz glass manufacturing apparatus consisting of exhaust means for exhausting
An apparatus for producing synthetic quartz glass, characterized in that a gas introduction means is provided in the exhaust means. 2. A furnace, a target for forming an ingot installed inside the furnace, a burner for synthesizing quartz glass installed with its tip facing the target, and silica fine particles not deposited on the target. In a closed system synthetic quartz glass manufacturing apparatus consisting of exhaust means for exhausting
An exhaust port provided with the exhaust means in the furnace, and an abatement device,
An apparatus for producing synthetic quartz glass, comprising an exhaust fan, which are connected to each other by an exhaust line, and which has a gas introducing means in the exhaust line between the exhaust port and the abatement device. 3. The synthetic quartz glass manufacturing apparatus according to claim 1 or ₂ , wherein a component other than SiO ₂ is introduced. 4. The synthetic quartz glass manufacturing apparatus according to claim 3, wherein components other than SiO ₂ are H ₂ or F or Cl.
Alternatively, it is OH, which is a synthetic quartz glass manufacturing apparatus. 5. The synthetic quartz glass manufacturing apparatus according to claim 2, wherein a flow rate measuring device is provided at the downstream of the abatement device as seen from the gas flow and at the gas introduction means. Manufacturing equipment. 6. The synthetic quartz glass manufacturing apparatus according to claim 2, wherein the gas introduction means is provided with a gas backflow prevention means. 7. The synthetic quartz glass manufacturing apparatus according to claim 2, wherein the gas introduced by the gas introducing means is air.