JP7128156B2 - Synthetic silica glass manufacturing apparatus and synthetic silica glass manufacturing method using this apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to a synthetic silica glass manufacturing apparatus and a synthetic silica glass manufacturing method, and more particularly, to a synthetic silica glass manufacturing apparatus in which silica glass fine particles are less likely to adhere to the inner wall of a furnace, and to manufacture synthetic silica glass using this apparatus. Regarding the method.

Synthetic silica glass ingots for optical applications have long been made by ejecting silica raw materials such as silicon tetrachloride from a quartz burner into a refractory furnace, hydrolyzing them, and producing silica glass fine particles as targets. It has been manufactured by depositing on

In such a manufacturing apparatus, silica glass fine particles that have not been used to form an ingot adhere to the vicinity of the burner or to the inner wall of the furnace. We had problems with quality deterioration of ingots and deterioration of durability of production equipment.

As a solution to the above problem, for example, Patent Document 1 proposes a manufacturing apparatus for quartz glass. FIG. 7 shows a schematic configuration of this quartz glass manufacturing apparatus 20, and the schematic configuration will be described based on FIG.
In FIG. 7, this quartz glass manufacturing apparatus 20 has a melting furnace 21 with a diameter of about 40 cm and a wall thickness of about 10 cm.
A connecting member 24 is provided on the upper part of the furnace wall of the melting furnace 21 , and a synthesizing burner 23 is attached to an insertion hole of the connecting member 24 so that the tip of the synthesis burner 23 faces the interior of the melting furnace 1 .
The center line average roughness (Ra) of the inner wall surface of this connection member 24 is set to 2×10 ⁻¹¹ m or less, and inside this connection member 24, the temperature of the outer peripheral region of the synthesis burner 23 is set to 750 A heating means 26 is provided to maintain the temperature above 0°C.

The connecting member 24 is made of synthetic quartz glass, and is a disk-shaped member having a diameter of about 20 cm and a thickness of about 2 cm, which constitutes the upper portion of the furnace wall of the melting furnace 21 . The connecting member 24 is installed so as to close the upper part of the furnace wall of the melting furnace 1 .
A rotary ingot forming target 25 is provided in the melting furnace 21 so as to face the synthesizing burner 23 . By depositing and melting glass particles on the rotary ingot forming target 25, a transparent glass ingot I having a hemispherical tip is produced.

In this quartz glass manufacturing apparatus 20, the flame hydrolysis means includes the upper wall surface in the melting furnace 21 (the area where the synthesis burner 23 opens), in other words, the melting furnace 21 and the synthesis burner 23. The surface roughness of the inner wall surface of the connection member 24 between and the temperature of the connection member (connection region) between the melting furnace 21 and the synthesis burner 23 are appropriately controlled.
As a result, deposition and adhesion of silica glass particles in this region are restricted and controlled, and deposition and adhesion of silica glass particles can be effectively prevented.

As a solution to the above problem, for example, Patent Document 2 proposes an apparatus for producing synthetic silica glass. FIG. 8 shows a schematic configuration of this quartz glass manufacturing apparatus 30, and the schematic configuration will be described.

As shown in FIG. 8, this synthetic silica glass manufacturing apparatus 30 includes a refractory furnace 31, an ingot forming target (not shown) installed in the furnace, and raw material gas in the furnace. It is equipped with a burner 32 for synthesizing silica glass that draws out a combustion-supporting gas and a combustible gas to form a flame stream.
The burner 32 for synthesizing silica glass includes a burner inner cylindrical tube 32a for leading out at least raw material gas, and a burner outer cylindrical tube 32b for leading out at least combustible or combustion-supporting gas.

A first flame flow F1 directed downward along the outer peripheral surface of the burner inner cylindrical tube 32a is formed by the discharge of the gas from the burner outer cylindrical tube 32b.
The furnace 31 is composed of a refractory cylindrical side wall 31a and a refractory ceiling 31b closing the upper part of the side wall 31a.
A plurality of gas outlet holes 31b1 are provided in the ceiling portion 31b, and the gas is led out from the gas outlet holes 31b1 to form a second flame flow F2 directed vertically downward from the gas outlet holes 31b1.

In this manner, the synthesizing burner 32 forms the first flame flow F1 directed downward in the furnace, and the plurality of gas outlet holes 31b1 in the ceiling portion 31b form the second flame flow directed vertically downward in the furnace. Since the flow F2 is formed, silica fine particles are suppressed from adhering to the side wall 31a, the ceiling 31b, the synthesis burner 32, and the like of the furnace.
As a result, the adhesion of the suspended silica fine particles to the ingot synthesis surface (fused silica adhesion surface) is suppressed, and synthetic silica glass in which striae and internal defects are suppressed can be produced.

Japanese Patent Application Laid-Open No. 2002-201031 JP 2012-41231 A

By the way, in the quartz glass manufacturing apparatus disclosed in Patent Document 1, it is necessary to provide a heating means in the connection member, and in the quartz glass manufacturing apparatus disclosed in Patent Document 2, the ceiling It was necessary to provide a plurality of gas outlet holes in the part. As a result, the cost of manufacturing the quartz glass manufacturing apparatus disclosed in Patent Documents 1 and 2 is high, which has been a factor in increasing the manufacturing cost of synthetic silica glass ingots.

The present inventors diligently studied a synthetic silica glass manufacturing apparatus which has a simple structure and which makes it more difficult for silica glass fine particles to adhere to the vicinity of the burner or the inner wall of the furnace.
Then, by making the upper end of the side wall (muffle) of the cylindrical furnace and the ceiling that closes the upper part of the side wall in a specific configuration, The present inventors have found that the silica glass fine particles generated by the method can be further suppressed, and have conceived the present invention.

SUMMARY OF THE INVENTION The present invention has been made under the circumstances described above, and provides a synthetic silica glass manufacturing apparatus capable of obtaining a silica glass ingot of high quality with a simple structure, and a synthetic silica glass using this synthetic silica glass manufacturing apparatus. It aims at providing the manufacturing method of.

A synthetic silica glass manufacturing apparatus according to the present invention includes a furnace body, a silica glass synthesis burner installed in the upper part of the furnace body, and an ingot forming target installed in the furnace body, The furnace body has a cylindrical muffle and a top plate made of silica glass, which is placed on the upper end surface of the muffle and provided with a through hole into which the burner is inserted, and the muffle is the top plate. and a base portion made of a refractory material on which the annular portion is provided at the upper end, and the boundary between the annular portion and the base portion in the furnace body is the top plate and the boundary is in the range of 10 mm or more and 60 mm or less from the upper end surface of the annular portion downward in the vertical direction of the furnace body .

With such a configuration, silica glass fine particles are less likely to adhere to the entire top plate, and adhered silica glass fine particles and the like are less likely to fall into the ingot. Synthetic silica glass can be manufactured.

Moreover, it is desirable that the synthetic silica glass manufacturing method uses the synthetic silica glass manufacturing apparatus.

INDUSTRIAL APPLICABILITY The present invention provides a synthetic silica glass manufacturing apparatus capable of obtaining high-quality silica glass ingots with a simple structure, and a synthetic silica glass manufacturing method using this synthetic silica glass manufacturing apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS The schematic diagram which shows one Embodiment of the synthetic silica glass manufacturing apparatus concerning this invention. Schematic diagram for explaining the thickness of an annular portion. The schematic diagram which shows the modification of the synthetic silica glass manufacturing apparatus concerning this invention. The cross-sectional schematic diagram which shows the 1st comparative example of a synthetic silica glass manufacturing apparatus. The cross-sectional schematic diagram which shows the 2nd comparative example of a synthetic silica glass manufacturing apparatus. The cross-sectional schematic diagram which shows the 3rd comparative example of a synthetic silica glass manufacturing apparatus. The schematic diagram which shows the conventional synthetic silica glass manufacturing apparatus. The schematic diagram which shows the conventional synthetic silica glass manufacturing apparatus.

An embodiment according to the present invention will be described below with reference to FIG. The drawings schematically show the shape for explanation, and the present invention is not limited to the illustrated shape, dimensions, and the like. Also, other devices and members that are not necessary for explaining the present invention are not shown.

FIG. 1 is a schematic cross-sectional view showing one embodiment of a synthetic silica glass manufacturing apparatus according to the present invention. This synthetic silica glass manufacturing apparatus 1 includes a burner 2 for synthesizing silica glass, a cylindrical muffle 4 and a top plate 3 .
Further, the cylindrical muffle 4 and the top plate 3 constitute a furnace body of the synthetic silica glass manufacturing apparatus 1 . A target 5 is arranged in the furnace body 4 . The top plate 3 is made of silica glass and is provided with a through hole 3a into which the burner 2 is inserted, and the burner 2 is fitted into the through hole 3a. It should be noted that the ingot I is deposited on the target 5 .

The present invention is characterized by the configuration of the contact portion between the top plate 3 and the muffle 4, but other components and other members (not shown) are widely known without particular limitations. can be implemented in

The muffle 4 includes an annular portion 4b made of silica glass that contacts the top plate 3, and a cylindrical base portion 4a made of a refractory and having the annular portion 4b provided at its upper end.
The muffle 4 is made of a refractory except for the annular portion 4b, and known materials used in general synthetic silica glass manufacturing equipment can be widely applied to the refractory. One example is alumina or ceramics containing alumina as a main component.

The muffle 4 is also characterized in that the area (location) that contacts the top plate 3 is an annular (ring-shaped) annular portion 4b made of silica glass.
By using silica glass of the same material as the top plate 3 instead of a refractory material for the area (location) Y that contacts the top plate 3, materials having the same thermal expansion coefficient can be brought into contact with each other.
As a result, since there is almost no difference between the thermal expansion coefficients of the two, it is possible to prevent silica glass particles adhering to the boundary region Y between the top plate 3 and the annular portion 4b from falling.

The annular portion 4b is provided on the upper end face portion of the cylindrical base portion 4a.
The annular portion 4b preferably has an annular shape so as to hold the entire top plate 3 evenly and substantially horizontally and to prevent the inflow of outside air from the outside of the furnace body.

The outer diameter and inner diameter of the annular portion 4b can be appropriately designed according to the specifications of the synthetic silica glass manufacturing apparatus 1 and the shape of the muffle 4, but the thickness thereof has a preferable range as described later.
Further, the annular portion 4b is preferably an annular integral body, but may be an annular body formed by combining a plurality of divided bodies.

In this synthetic silica glass manufacturing apparatus 1 , the boundary X between the annular portion 4 b and the base portion 4 a in the furnace body is positioned on the side wall of the muffle 4 that does not contact the top plate 3 .
Thus, the boundary X is formed not on the horizontal plane like the top plate 3 but on the vertical plane of the side wall 4a1 of the muffle 4. As shown in FIG.
On the other hand, the air current inside the furnace flows along the side wall 4a1. Therefore, it is possible to suppress the silica glass particles from adhering to the boundary X and its vicinity, and to suppress the adhering silica glass particles from becoming clumps.
Even if agglomerated silica glass particles are formed on the side wall 4a1 and peeled off, most of them fall along the wall, and the degree of mixing into the ingot I depends on the degree of adhering to the top plate 3 (horizontal surface), It is relatively small compared to when it falls from there.

The vertical plane of the side wall 4a1 of the muffle 4a may also be slightly inclined with respect to the vertical direction perpendicular to the horizontal plane, and a maximum inclination of about 20° is allowed.

Further, the boundary X is preferably within a range of 10 mm or more and 60 mm or less from the upper end surface of the annular portion 4b downward in the vertical direction of the furnace body.
The range of 10 mm or more and 60 mm or less, that is, the value of the dimension L "vertical direction downward of the furnace body 10 from the upper end surface of the annular part 21" is, as shown in FIG. The length dimension is from the area (location) Y where the contact area (location) is to the area (location) X where the annular portion 4b and the base portion 4a contact each other. Specifically, the value of the dimension L "from the upper end surface of the annular portion 21 to the vertical direction downward of the furnace body 10" is the thickness dimension of the annular portion 4b. It can be expressed as an average value measured at four selected locations.

Here, if the dimension L is smaller than 10 mm, the boundary X is too close to the corner (boundary Y), so that the boundary X is also affected by the turbulent flow generated at the corner, and the effect of the present invention is not sufficiently exhibited. .
If the dimension L is larger than 60 mm, the annular portion 4b made of silica glass is exposed to the high-temperature region of the furnace body below the top plate 3. As shown in FIG. Therefore, there is concern that the annular portion 4b will be softened by high heat, causing the top plate 3 to wobble, disturbing the flame flow from the burner 2, or damaging the top plate 3 or the muffle 4 around it.

Note that the dimension L may be such that the surface exposed to the inside of the furnace body 10 has the thickness described above. Therefore, as shown in FIG. 2, it is not necessary to completely form the annular portion 4b up to the outside (peripheral portion) of the muffle 4. FIG.

As for the boundary X, there is a step of about 1 to 2 mm in the radial direction between the annular portion 4b and the muffle 4 (between the inner peripheral surface of the annular portion 4b and the inner peripheral surface of the muffle 4). Also, the effects of the present invention can be obtained.
However, if the step is too large, turbulence will be generated in the vicinity of the step, which is not very desirable.

Although the top plate 3 is shown as a plane in FIG. 1, the top plate 3 does not necessarily have to be a plane, and may have a curved shape as shown in FIG. Further, even if the top plate 3 has joints between silica glass sheets, there is no particular problem in the present invention.

Next, as an unfavorable example, FIG. 4 shows a case where the contact portion (boundary X) between the top plate 3 and the muffle 4 is exposed on the horizontal surface of the top plate 3 .
In the synthetic silica glass manufacturing apparatus 1, silica glass particles generated inside the furnace body are swirled up by the flame flow or the like from the burner 2 and adhere to the entire inner surface of the furnace body. In addition, the muffle 4 has a high frequency of cracking and chipping due to thermal shock and deterioration. The silica glass that has been coated becomes easy to peel off.

In particular, as shown in FIG. 4, if the boundary X is positioned on the horizontal plane of the top plate portion, the rising air current generated in the furnace body hits the top plate 3 substantially perpendicularly. Therefore, the amount of adhered silica glass particles and the amount of peeled off silica glass particles are relatively large compared to the case where the airflow contacts the surface horizontally.
Moreover, at the boundary X where the refractory and silica glass having different coefficients of thermal expansion are in contact with each other, the brittle refractory falls in the form of a relatively large lump accompanying the peeled silica glass particles. This mixes into the ingot 2 and significantly impairs its quality.

Thus, if the boundary X exists in the upper horizontal plane within the furnace body 10, the adhering silica glass particles and the muffle 4 (refractory material) may come together and fall.
These falling objects are larger than aggregates consisting of only silica glass particles, and when mixed with the ingot 2, the quality thereof is significantly impaired.

The phenomenon described above is the same when the boundary X is located at the corner where the top plate 3 and the muffle 4 intersect perpendicularly or at an angle close to it, as shown in FIGS.
In particular, the corners are not preferable because the airflow is greatly disturbed and there is concern that the silica glass powder will adhere to the corners.

In addition, by the synthetic silica glass manufacturing method using the synthetic silica glass manufacturing apparatus 1 of the present invention, an ingot with less foreign matter than conventional ingots can be obtained, and furthermore, high-quality synthesis with less foreign matter mixed in can be obtained. A silica glass substrate can be obtained.

EXAMPLES The present invention will be described below based on examples, but the present invention is not limited to the following examples.
(Example 1)
A synthetic silica glass manufacturing apparatus shown in FIG. 1 was used. A counterbore having a width of 50 mm and a depth of 30 mm is formed along the opening of the upper end of the base portion 4a of the muffle 4, and a ring made of silica glass having an outer diameter of 270 mm, an inner diameter of 170 mm, and a thickness of 30 mm is formed in the counterbore. (annular portion 4b) was fitted.
A through hole was provided in the center of the top plate 3 and the burner 2 was attached. The top plate 3 thus formed was placed on the annular portion 4b of the muffle 4 to form a furnace body, and an ingot I was manufactured.
The burner had a general multi-tube structure made of silica glass, and the muffle was made of alumina with a height of 800 mm and a straight body of 700 mm.

In addition, as ingot manufacturing conditions, the temperature during ingot formation was adjusted to be around 1400°C. As for the gas conditions, 50 g/min of SiCl ₄ +10 liter/min of O ₂ gas, 150 liter/min of O ₂ gas, and 300 liter/min of H ₂ gas were introduced into the furnace. The O ₂ gas/H ₂ gas ratio was set to 0.5. Then, an ingot having an outer diameter of φ500 mm and a weight of 1000 kg was manufactured.

(Example 2)
The same procedure as in Example 1 was performed except that the depth of the counterbore and the thickness of the ring (thickness dimension L of the annular portion 3) were set to 10 mm.

(Example 3)
The same procedure as in Example 1 was carried out except that the depth of the counterbore and the thickness of the ring (thickness dimension L of the annular portion 3) were set to 60 mm.

(Comparative example 1)
A synthetic silica glass manufacturing apparatus shown in FIG. 4 was used. The opening at the upper end of the muffle 4 had a diameter of 170 mm, and a refractory material having a thickness of 5 mm was provided with a flange of 5 mm in the center direction of the opening so that the opening had a diameter of 160 mm.
Then, a counterbore of 5 mm was provided on one side of a top plate made of silica glass with a diameter of 170 mm, and was engaged with the brim portion. A burner 2 was attached to the center of the top plate 3 by providing a through hole. The top plate 3 made in this way was placed on the opening of the upper end face of the muffle 4 to manufacture the ingot 2 . Other conditions were the same as in Example 1.

(Comparative example 2)
A synthetic silica glass manufacturing apparatus shown in FIG. 6 was used. A top plate made of silica glass with a diameter of 200 mm and having a burner installed through the center thereof was placed on the opening of the upper end face of the muffle to produce an ingot. Other conditions were the same as in Example 1.

(Comparative Example 3)
The same procedure as in Example 1 was performed except that the depth of the counterbore and the thickness of the ring (thickness dimension L of the annular portion 3) were set to 5 mm.

(Comparative Example 4)
The same procedure as in Example 1 was performed except that the depth of the counterbore and the thickness of the ring (thickness dimension L of the annular portion 3) were set to 70 mm.

(Evaluation - Confirmation of mixed foreign matter)
The obtained ingot was sliced and then surface ground to obtain 100 substrates per ingot. Foreign matter was observed on these substrates by visual inspection using natural light and camera observation using laser light.
When a foreign substance having a size of 30 μm or more was observed, it was regarded as defective. Table 1 shows the above results.

As is clear from the results in Table 1, the samples to which the present invention was applied clearly contained less foreign matter than the samples to which the present invention was not applied.
From this, it was found that according to the present invention, it is possible to greatly reduce the contamination of the ingot with foreign matter caused by the exfoliated material generated from the boundary X between the top plate and the muffle.

For reference, the acceptable products of the substrates of each example and each comparative example are, for example, the transmittance of light of a predetermined wavelength, the concentration of various metal elements, the presence or absence of UV fluorescence generation, the OH concentration, the hydrogen concentration, etc. Each characteristic required for the mask substrate was good with no significant difference.

Further, after the ingot synthesis was completed, the furnace body was opened and observed from below. was not seen. On the other hand, in Comparative Examples 1 to 4, a part of the refractory constituting the muffle was chipped in several places.

REFERENCE SIGNS LIST 1 synthetic silica glass manufacturing apparatus 2 burner for silica glass synthesis 3 top plate 4 muffle 4a base portion 4b annular portion 5 target I ingot X boundary

Claims (2)

A furnace body, a silica glass synthesis burner installed in the upper part of the furnace body, an ingot forming target installed in the furnace body,
with
The furnace body includes a cylindrical muffle, a silica glass top plate placed on the upper end surface of the muffle and provided with a through hole into which the burner is inserted,
has
The muffle includes an annular portion made of silica glass in contact with the top plate, and a base portion made of a refractory material, the annular portion being provided at the upper end,
a boundary between the annular portion and the base portion in the furnace body is on a side wall of the muffle that does not contact the top plate;
Further, the synthetic silica glass manufacturing apparatus is characterized in that the boundary is in the range of 10 mm or more and 60 mm or less from the upper end surface of the annular portion downward in the vertical direction of the furnace body . A method for producing synthetic silica glass using the apparatus for producing synthetic silica glass according to claim 1 .

Images