JP2002037637A - Manufacturing method of fused silica glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an efficient manufacturing method of a large size silica glass ingot which has a good fusion of siliceous powder and homogeneous quality without blister. SOLUTION: Siliceous powder is dropped from a furnace ceiling 2 and accumulated/piled on the bottom of a rotating furnace 1 which has an inclined outer periphery wall 11. Then heated and piled fused silica glass flows toward the outer periphery wall and form a silica glass ingot whose outer diameter has inclination. The outer periphery wall 11 is moved to a horizontal position. The inclined outer diameter of the ingot is heated/melted and the upward lamination of the outer diameter area of the ingot is adjusted approximately horizontally. Thus silica glass ingot of slab shape of high homogeneity is manufactured.

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 a slab-shaped quartz glass ingot in which a silica powder is melted by heating to form a flat plate.

[0002]

2. Description of the Related Art There are various methods for producing quartz glass by heating and melting silica-based powder such as quartz or quartzite. An electric furnace such as a high frequency, arc, plasma, vacuum, or nitrogen atmosphere is used as a heat source. . Further, as a method using a flame, as described in Japanese Patent Publication No. 46-42111, a silica-based powder heated and melted by an oxyhydrogen gas flame or a propane-oxygen gas flame is deposited on a rotating target, and the deposition portion is formed. In general, a method of lowering, cooling and laminating at a constant speed to produce a shell-shaped column-shaped quartz glass ingot is used.

[0003]

SUMMARY OF THE INVENTION Quartz glass obtained by heating and melting siliceous powder is more frequently used in semiconductor manufacturing equipment and the like because of its superior heat resistance than synthetic quartz glass. In recent years, semiconductor wafers have been increased in size from 5 inches and 6 inches to 8 inches and 12 inches in diameter.
Quartz glass members used in the manufacture of semiconductor wafers, wafer holding and storage jigs for holding and heat treating semiconductor wafers, furnace core tubes, and various substrates are inevitably shifting to larger ones. A larger quartz glass ingot, which is the basis of the glass member, is also required.

[0004] However, in the quartz glass ingot manufactured by the conventional manufacturing method, the generation of bubbles is difficult to avoid in the electro-melted product, and the flame-melted product has a long column shape, a small cross section, and a small diameter. It could not handle large quartz glass products. For this reason, the method of re-melting the column-shaped ingot and secondary forming it into a large flat ingot has been adopted, but the method of melting and deforming the column into a flat plate has a large degree of deformation, so it is formed in several stages. As the ingot becomes large, it becomes inefficient as the size of the ingot increases. There was a problem of decline.

An object of the present invention is to directly produce a large slab-like ingot by fusing a siliceous powder, and to produce a quartz glass ingot having few bubbles and excellent homogeneity.

[0006]

Means for Solving the Problems Silica powder is dropped from the upper part of a rotating furnace in which the outer peripheral side wall is inclined, heated and melted, laminated at the center of the furnace bottom, and further heated and melted, and the outer peripheral direction of the furnace is melted. The resulting ingot was heated and melted and allowed to flow to obtain a large and highly uniform quartz glass ingot. In addition, a quartz glass ingot is manufactured with the furnace outer peripheral side wall having the same inclination angle as the striae rising shape when the outer peripheral side wall is vertical, the outer peripheral side wall is tilted horizontally, and the ingot outer peripheral portion is heated and fluidized, A quartz glass ingot having a uniform stria was obtained by flowing and extending horizontally. By determining the inclination angle of the outer peripheral side wall according to the number of rotations of the furnace, by making the rotation of the furnace high-speed rotation,
The stacking direction was made closer to a plane perpendicular to the growth axis of the ingot by promoting fluidization of the ingot, and the stacking direction was made closer to the horizontal by setting the bottom shape of the furnace to a distribution shape opposite to the stacking direction of the ingot.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Silica powder, silica powder, quartz powder or the like is used. In the case of producing a high-purity product, one kind of a high-purity silicon oxide source such as α-quartz or cristobalite or a mixture thereof is used. For example,
Purified high-purity quartz powder, baked silica obtained by hydrolyzing silicon alkoxide under hydrochloric acid or ammonia catalyst, or purified silica obtained by reacting alkali metal silicic acid aqueous solution with acid and calcination And the like, such as synthesized silica powder and the like.

[0008] A certain amount of the siliceous powder filled in the hopper is guided to a heating source oxyhydrogen burner mounted on the furnace ceiling 2 through a quartz glass tube by a supply device. The particle size of the silica powder is preferably in the range of 40 to 250 mesh, more preferably 80 to 100 mesh. The supply rate is set to 1.0 to 10 Kg / Hr depending on the use and shape of the quartz glass to be produced, such as whether it is a transparent material or an opaque material. In the case of using an opaque material, a mixed powder obtained by adding silicon nitride powder as a foaming agent to silica powder may be used.

As shown in FIG. 1, in a furnace 1, alumina bricks are spread on a frame which is driven to rotate by a motor, and a side wall 11 has silicon carbide bricks arranged in accordance with the outer shape of an ingot to be manufactured. . Alumina porous bricks and alumina bricks are double-laid on the outside of the side wall 11 for heat insulation. The upper part of the furnace is open, and the furnace ceiling 2 is arranged with a gap S therebetween so as to be independent of the rotation of the furnace 1. The furnace ceiling 2 is an array of heat-resistant bricks such as alumina bricks, porous bricks, or zirconia-based bricks. The furnace ceilings 2 have holes for mounting burners 6 and windows for monitoring the inside of the furnace. I have.

[0010] The material of the bricks constituting the furnace 1 is M
Magnesia bricks such as gO and MgO-Al ₂ O ₃ and C
Basic refractories such as aO cannot be used because they cannot withstand the high temperature of fused quartz glass and react violently with fused quartz glass.

A neutral refractory of Al ₂ O ₃ has sufficient heat resistance, but is not preferable because it reacts with fused silica glass.
It cannot be used for parts that are in direct contact with fused silica glass. Silicon carbide refractories have high heat resistance, good peelability of quartz glass, and sufficient strength, and thus are suitable as side wall materials that come into direct contact with fused quartz glass. Among them, silicon oxide (SiO ₂ ) or silicon nitride (Si ₃ N)
₄ ) Preferable is silicon carbide brick using binder as a binder.
More preferably, silicon nitride-bonded silicon carbide brick (SiC 80%, Si ₃ N ₄ 20
%).

Prior to use, the surface of the brick used in the furnace 1 is fired to remove metal impurities adhering to the surface of the brick which is to be in contact with the fused silica glass. Further, the fine fragments of the brick have a function as a foaming agent, and generate fine bubbles in the contacted fused silica glass to cause devitrification. Therefore, the fine fragments on the surface are removed by firing.

Since the furnace bottom directly receives the heat from the burner, it is desirable to use a ZrO ₂ —SiO ₂ zircon brick having higher heat resistance than alumina brick for the portion facing the inside of the furnace. However, similar to alumina bricks, zircon bricks react when they come into direct contact with quartz glass, causing problems such as cracking of the product and difficulty in taking it out of the furnace. Spread thinly over the brick.

By making the particles into particles, the influence of the difference in thermal expansion from the quartz glass during heating and cooling can be reduced. The zirconia particles are spread about 10 mm to prevent direct contact between the brick at the furnace bottom and the fused silica glass.
The reaction between the brick at the hearth and the quartz glass causes cracks. Therefore, the spread thickness is adjusted according to the state of the hearth.

The burner is a burner made of quartz glass and has a supply pipe for hydrogen and oxygen and a supply pipe for siliceous powder. This burner is attached to a hole provided in the heat-resistant brick of the furnace ceiling 2 so that the tip of the burner protrudes from the furnace ceiling 2.

As shown in FIG. 2, depending on the size of the ingot to be manufactured, that is, the size of the furnace, in addition to the main burner 61 having a silica powder supply device, an auxiliary burner 6 is provided.
One or a plurality of furnaces 2 are provided on the furnace ceiling 2. Heat is supplied into the furnace by the auxiliary burner 62 and the main burner 61
The quartz glass melted and laminated in step is further heated to raise the temperature and flow, and is extended in the outer peripheral direction of the furnace.

The auxiliary burner 62 is inclined not only in the vertical direction but also in an appropriate direction so that the entire furnace has a uniform temperature distribution. The auxiliary burner 62 is preferably inclined at an angle of 5 to 15 degrees in the rotation direction of the furnace in order to prevent disturbance and interference of the combustion gas.

A hydrogen and oxygen supply pipe is connected to the burner, and a supply pipe from a supply hopper is connected to the silica powder supply section of the main burner 61. A vibrating device is appropriately added to the supply system to prevent the siliceous powder from being clogged.

Main burner 61 and auxiliary burner 62
And the furnace 1 is rotated at 1 to 10 rpm. The fused quartz glass extends and reaches the side wall 11 of the furnace 1,
Of silicon carbide-based bricks. Therefore, the side walls are arranged on all sides, for example, 1000
A square or 300 mm thick square ingot, or a polygonal or round slab-like ingot can be manufactured by changing the arrangement of the bricks on the side wall 11.

As shown in FIG. 3, in the generated slab-like ingot, curved stria may be often observed on the outer peripheral portion. This is thought to be because the fused quartz glass extends, reaches the side wall 11 of the furnace 1 and rises along the side wall 11, so that a curved striae are formed on the outer periphery of the ingot. In fact, in order to see how the distribution of stria changes during the growth of the ingot, the introduction of the siliceous powder was divided into five stages, and at each stage the injection was stopped and the stria was observed. Until the fused quartz glass comes into contact with the side wall 11, the striae are relatively straight, and almost no rise at the outer periphery is recognized. However, it is recognized that the striae comes into contact with the side wall 11 and rises up.

The rise of striae around the ingot is a problem from the viewpoint of homogeneity of quartz glass.
It is necessary to flatten the stria to expand the effective homogeneous area. Therefore, in order to make the striae around the ingot as horizontal as the central part, the furnace outer peripheral side wall was inclined so as to be the same as the lamination direction of the produced ingot.

That is, the side wall 11 at the outer peripheral portion of the furnace which comes into contact with the produced ingot is inclined at an angle equal to the stacking direction of the ingot when the side wall 11 shown in FIG. 3 is vertical, and the ingot is produced. After removing 11, the outer periphery of the ingot was further heated and melted and allowed to flow as shown in FIG. 5 to make the striae horizontal.

More specifically, as shown in FIG. 4, the frame formed by cutting out the silicon nitride brick has the same inclination angle as the striae rising shape predicted in advance, and the frame is formed from the outside of the furnace by a silicon carbide rod 13. To support the side wall 11. If the roughened quartz glass 12 is pasted on the side wall surface to have a sealing property in advance, the moldability and peelability in a later process are improved, and contamination due to furnace wall contact can be prevented.
While rotating the furnace 1 having the inclined side walls 11, the siliceous powder is melted and dropped from the burner 6 installed on the ceiling,
Manufacture quartz glass ingots. After producing the ingot of the quartz glass having the inclined outer periphery, the frame is tilted horizontally to expose the inclined outer periphery of the ingot, and the outer periphery of the ingot is further heated and allowed to flow, as shown in FIG. Is horizontally flow-stretched to obtain a quartz glass ingot in which the stria is corrected to a horizontal state.

Further, an ingot is manufactured by setting the furnace side wall frame to the same inclination angle as the striae rising shape, and the ingot is taken out of the furnace and separately heated by an electric furnace or the like to perform secondary forming to form an inclined outer peripheral portion. May be horizontal, and the stria of the outer periphery of the ingot may be horizontal like the central portion.

By inclining the side wall of the furnace and heating and melting the inclined surface at the outer periphery of the ingot, the rise of the striae at the outer periphery of the ingot is improved to be horizontal, and the uniformity Δn
Was improved to 10 ^-6 throughout.

Further, it has been found that the distribution state of the stria, particularly the rising shape of the stria, changes according to the rotation speed of the furnace. The number of rotations of the furnace is 2 rpm, 10 rpm, 15 rpm
The striae state was compared at m, 20 rpm, and 25 rpm. When the rotation speed of the furnace was increased, the stria became more horizontal near the side wall, became more linear even in the central critical area where the stria was not affected, and the intensity of the stria became weaker. However, the rising angle of the stria near the center tends to be sharper as the rotation speed decreases, whereas the rising angle of the stria at the outer periphery increases when the rotation speed increases. Tended to be acute.

This is achieved by rotating the furnace body at high speed.
While promoting the flow of the fused silica glass to the outer peripheral part due to centrifugal force, and making the flow direction of the melt as close as possible to a plane perpendicular to the growth axis of the ingot, striae can be flattened near the central part, Conversely, it is considered that the rising angle of the stria became sharp because the outer peripheral portion collides with the side wall.

Therefore, it is effective to accelerate the fluidization of the fused silica glass by rotating the furnace at a high speed of 10 rpm or more so that the laminating direction approaches a plane perpendicular to the growth axis of the ingot. Since the rise angle of the furnace becomes large, it is necessary to determine the furnace wall inclination angle according to the number of rotations of the furnace.

If the rotation speed of the furnace exceeds 25 rpm, the distribution state including the striae intensity and the rising angle does not change, and conversely, there is a danger that foreign matter is mixed in by increasing the rotation speed. It is not particularly necessary to set the inclination angle of the furnace side wall at a higher rotation speed.

In anticipation of the striae rising at the outer periphery from the beginning, the shape of the bottom of the furnace is set to a distribution shape opposite to the stacking direction of the ingot, that is, the bottom of the furnace is provided with a slope so as to have a convex shape. It is also possible to prevent rising.
However, the rise of the striae is less than half the angle of the conventional case where the furnace bottom is flat, but the shape remains problematic, so that secondary forming is required.

A process of manufacturing a quartz glass ingot using the inclined side wall of FIG. 4 will be described. A main burner 61 and, if necessary, an auxiliary burner 62 are attached to a hole provided in the furnace ceiling 2 in advance, and hydrogen and oxygen supply pipes are connected to the main burner 61. A supply pipe from a hopper (not shown) is connected. In the supply system of the silica powder, a vibration device is added at an appropriate position to prevent the silica powder from being clogged.

A frame of a heat-resistant plate formed by cutting silicon nitride bricks is provided on the outer peripheral side wall of the furnace 1, and the frame is inclined in parallel with a predicted striae rising angle. For example, it was installed as a frame structure having the same inclination angle as the striae rising shape at a furnace rotation speed of 10 rpm shown in FIG.

Main burner 61 and auxiliary burner 62
And the furnace 1 is rotated at 10 rpm. The furnace 1 is preheated for 1 to 3 hours as needed to remove impurities and fine debris on the brick surface as described above.

By operating a powder supply device (not shown), the siliceous powder is supplied to the main burner 61 and melting is started. The siliceous powder falls from the furnace ceiling 2 to the center of the furnace bottom, is melted by the heat from the burner or the heat capacity of the fused quartz glass, and is laminated while flowing and extending. In the center of the furnace, the main burner 61 and the auxiliary burner 6
In Step 2, the temperature is maintained at about 2000 ° C., which is higher than the melting temperature of the quartz glass, and the furnace 1 is rotating and extends toward the outer periphery of the furnace as the fused quartz glass is laminated.

When a set amount of silica powder is supplied to the furnace 1,
The powder supply device is stopped, heating is continued, and when the raised portion at the center of the generated ingot flows and expands and becomes almost flat, the supply of hydrogen and oxygen is stopped to extinguish the fire. Tilt the frame installed incline to make it horizontal, and further heat and flow the outer periphery of the ingot formed by inclining with the oxyhydrogen gas burner, and make the outer periphery of the ingot flow and extend to make the oxyhydrogen gas burner horizontal. Extinguish and end heating. After the fire is extinguished, the rotation of the furnace 1 is stopped, and the quartz glass ingot generated inside the furnace is taken out.

FIG. 5 shows the distribution of striae of the obtained ingot. In this way, the striae was leveled over a wide range, and a large slab-like ingot with improved homogeneity was obtained. Also, a quartz glass ingot with very few bubbles can be manufactured because it is flowed and stretched. Originally, the flame melting method continuously drops silica powder and melts the silica powder with the heat capacity of the fused quartz glass at the drop point, so it can produce quartz glass with less bubbles compared to the electric melting method. Although there is an advantage, in the conventional method of obtaining a column-shaped ingot, when the heat capacity is insufficient, the particles of the individual silica powder are fused and do not unite, and the probability that the space between the particles remains as bubbles as it is However, in the case where the fused silica glass is extended toward the outer periphery of the furnace as in the present invention, the space is filled during the extension, so that the generation of bubbles is extremely reduced.

When the ingot is annealed with the oxyhydrogen flame of the main burner 61 and the auxiliary burner 62 for several hours after the completion of the melting, the stria at the center of the ingot is thinned, the distortion is reduced as a whole, and the homogeneity is reduced. The value of n is further improved.

According to the present invention, the fused quartz glass is stretched in a furnace to form a slab, so that an ingot having a desired size and having few bubbles can be obtained. In addition, since the side wall of the outer peripheral portion of the furnace is inclined at the same angle as the ingot laminating direction and the generated quartz glass ingot inclined outer peripheral portion is heated and melted, the striae of the ingot can be made uniform and horizontal. .

Since the furnace wall inclination angle is changed in accordance with the rotation speed of the furnace, the distribution of the stria near the center and the stria near the periphery can be stabilized, and the homogeneity can be further improved. . Silicon carbide brick is used for the side wall of the furnace outer periphery that comes in contact with the fused quartz glass, so it does not react with quartz glass at high temperatures, and it has good peelability, so a large slab-shaped ingot of any shape can be manufactured. it can.

According to the present invention, a quartz glass ingot of a desired size can be manufactured, so that it can be used for a large wafer holding device, a transfer device, a cleaning jig, a semiconductor manufacturing device such as a furnace core tube, a large substrate, and the like. can do.
In addition, it is suitable as various large-sized optical materials because it has few bubbles and excellent homogeneity.

[Brief description of the drawings]

FIG. 1 is a front sectional view of a rotary furnace.

FIG. 2 is a front sectional view of a furnace provided with an auxiliary burner.

FIG. 3 is a sectional view of an ingot showing a striae generation state.

FIG. 4 is a front sectional view of a furnace having inclined side walls.

FIG. 5 is a partial cross-sectional view showing a work for correcting striae on the outer peripheral portion of the ingot.

FIG. 6 is an ingot sectional view showing a corrected striae state.

[Explanation of symbols]

 Reference Signs List 1 furnace 11 furnace outer peripheral side wall 2 furnace ceiling 61 main burner 62 auxiliary burner

Claims (7)

[Claims] 1. A method in which siliceous powder is dropped and melted by heating from the upper part of a rotating furnace having a slanted outer peripheral side wall, and is laminated at the central part of the furnace bottom. A method for producing fused silica glass that is expanded into ingots. 2. A method for producing fused silica glass according to claim 1, wherein the outer peripheral side wall is inclined at an angle equal to the stacking direction of the ingot when the outer peripheral side wall of the furnace is vertical. 3. The method for producing fused quartz glass according to claim 1, wherein the produced ingot is further heated and melted to flow. 4. The outer peripheral side wall according to claim 1, wherein the outer peripheral side wall can be tilted, and after manufacturing the ingot, the outer peripheral side wall is horizontally inclined, and the ingot outer peripheral part is heated to flow and extend horizontally. A method for producing fused silica glass. 5. The method for producing fused silica glass according to claim 1, wherein the inclination of the furnace wall is determined according to the number of revolutions of the furnace. 6. The method according to claim 1, wherein the rotation of the furnace is performed at a high speed of 10 rpm or more to promote fluidization of the ingot and bring the laminating direction closer to a plane perpendicular to the growth axis of the ingot. Method for producing fused silica glass. 7. The method for producing fused quartz glass according to claim 1, wherein the bottom of the furnace has a convex shape opposite to the direction of lamination of the ingot.