A method for synthesizing large-size quartz glass by multi-burner CVD

Abstract

The present invention discloses a method for synthesizing large-sized quartz glass by multi-torch CVD, comprising the following steps: igniting the torches to preheat the furnace; introducing hydrogen, oxygen and silicon tetrachloride into each torch until the temperature and pressure in the furnace are in a stable state; increasing the flow rate of hydrogen, oxygen and silicon tetrachloride introduced into each torch, driving the carrier to rotate and lift to the reference point to start deposition to 90% of the carrier depth; stopping the introduction of silicon tetrachloride into the outer ring torch, and continuing to deposit on the surface of the deposition lump to the target height; stopping the introduction of raw materials, and unloading the lump after natural cooling. The present invention adopts multiple groups of torches arranged in inner rings, middle rings and outer rings, and the torch flames do not interfere with each other, and the furnace temperature distribution can be accurately controlled, thereby improving the uniformity of large-sized synthetic quartz lumps, and at the same time improving the preheating efficiency and deposition efficiency; controlling the raw material supply of different ring torches in the two stages of stable deposition, and realizing uniform and stable deposition of large-sized synthetic quartz lumps.

Description

Technical Field

[0001] The invention relates to the technical field of large-size quartz glass preparation, and in particular to a method for synthesizing large-size quartz glass by multi-burner CVD. Background Art

[0002] Quartz materials are widely used in semiconductor, photovoltaic, optics, aerospace and other fields due to their excellent physical and chemical properties, such as good light transmittance, low expansion coefficient, high temperature resistance and good chemical stability. At present, the main processes for preparing high-purity synthetic quartz glass in the industry include CVD, VAD and PCVD, among which the preparation method of large-size high-purity synthetic quartz glass is mainly vertical CVD (chemical vapor deposition) process.

[0003] The CVD process is to split hydrogen and oxygen in the blowtorch burner and then spray out the end face of the burner, burning to produce high-temperature water vapor. After the gaseous silicon-containing materials (such as silicon tetrachloride, D4, silane, etc.) are sprayed out of the discharge pipe, they react with the high-temperature water vapor to produce nano-scale silicon dioxide molecules. The silicon dioxide collides and agglomerates into particles that are directly deposited on the rotating target surface and gradually accumulate to form a quartz glass ingot. During the deposition process of the quartz glass ingot, the high-temperature molten quartz glass ingot is under the action of centrifugal force and gravity, and the quartz glass deposited in the center gradually diffuses to the edge and grows to form a quartz glass ingot with a larger diameter.

[0004] There are two methods for preparing large-diameter quartz lumps using CVD technology in the industry. Method 1: A quartz substrate is fixed horizontally at the upper end of a support rod, and a blowtorch fixed on the top of the kiln sprays silicon-containing raw materials and oxyhydrogen flames onto the substrate. The produced silicon dioxide particles accumulate layer by layer and the support rod is slowly controlled to descend, eventually forming a round rod-shaped quartz lump; Method 2: A high-temperature resistant crucible or vessel is fixed at the upper end of the support rod as a quartz glass carrier, and a blowtorch fixed above the carrier sprays silicon-containing raw materials and oxyhydrogen flames into the crucible or vessel. The produced silicon dioxide particles accumulate and the support rod is slowly controlled to descend, gradually depositing inside the carrier until the carrier is full, eventually forming a quartz lump inside the carrier, and the shape of the quartz lump is determined by the shape and size of the crucible or vessel.

[0005] In order to ensure the stable forming of the quartz glass ingot, the above-mentioned method 1 requires that the furnace be preheated for a long time before deposition (generally more than 12 hours) and a certain temperature gradient must exist on the ingot surface during the deposition process, otherwise the quartz glass ingot will not be formed due to the low viscosity of the material surface. Therefore, the temperature gradient of the deposition surface is required to be around 15-30°C when depositing synthetic quartz glass using this method. However, the temperature gradient of the deposition surface will cause a large difference in the structure from the center to the edge of the quartz glass ingot, resulting in uneven distribution of the refractive index and density of the quartz glass, which in turn affects the structural uniformity of the quartz glass in the deposition surface direction. Method 2 uses a single blowtorch and uses a high-temperature resistant crucible or vessel as a carrier for high-temperature molten quartz glass, which can reduce the temperature gradient inside and outside the ingot and thus improve the structural uniformity of the quartz glass, but the deposition size (height) is limited by the carrier, and large-size and heavy quartz ingots cannot be deposited. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for synthesizing large-sized quartz glass by multi-torch CVD. The method adopts multi-torch distributed in an inner ring, a middle ring and an outer ring, improves the preheating efficiency in the baking furnace stage, improves the temperature uniformity in the direction of the material surface in the deposition stage, and solves the problems of long preheating time in the existing CVD process, difficulty in controlling the material surface temperature in the initial deposition stage, and poor uniformity of the deposition block due to large temperature difference of the material surface during the deposition process. At the same time, the deposition is carried out in sections by controlling the flow rate of the torch, and deposition continues on the surface of the deposition block after the carrier is fully deposited, thereby avoiding the problem that the product size is limited by the carrier in the process of preparing synthetic quartz glass using the carrier in the prior art.

[0007] In order to solve the above technical problems, the present invention provides a method for synthesizing large-size quartz glass by multi-burner CVD, wherein the burners are arranged in an inner ring, a middle ring and an outer ring, and the method comprises the following steps:

[0008] S1, ignition and baking furnace stage: hydrogen and oxygen are introduced into each blowtorch, and the blowtorch is ignited to preheat the furnace of the deposition furnace;

[0009] S2, pre-deposition stage: hydrogen, oxygen and silicon tetrachloride are introduced into each blowtorch until the temperature and pressure in the furnace are stable;

[0010] S3, the first stage of stable deposition: increase the flow rate of hydrogen, oxygen and silicon tetrachloride into each blowtorch, drive the carrier to rotate and lift it to the reference point to start deposition, and continue deposition in the carrier to 90% of the depth of the carrier;

[0011] S4, the second stage of stable deposition: stop the silicon tetrachloride injection from the outer ring burner, and reduce the silicon tetrachloride injection flow rate from the inner and middle ring burners, continue to deposit in the carrier until the carrier is full, and then continue to deposit on the surface of the deposition lump to the target height;

[0012] S5, insulation and unloading stage: stop the introduction of silicon tetrachloride from the inner ring and middle ring blowtorches, and stop the introduction of oxygen and hydrogen from each blowtorch. The deposited mass is unloaded after it is naturally cooled in the furnace.

[0013] The present invention arranges multiple groups of blowtorches on the top of the CVD furnace to improve the preheating efficiency in the baking stage, and can achieve a temperature increase to 800°C within 5 hours, avoiding the preheating time of more than 12 hours required in the prior art, and at the same time improving the deposition rate. The multiple groups of blowtorches are distributed in three circles: inner ring, middle ring and outer ring, which improves the uniformity of the temperature, thereby improving the uniformity of the deposition mass, avoiding the difficulty in controlling the temperature of the material surface in the initial deposition stage in the prior art, and the large temperature difference in the direction of the material surface during the deposition process, which leads to poor uniformity of the deposition mass; at the same time, the three circles of blowtorches are controlled to control the raw material supply and the retreat speed at different stages. In the first stage of stable deposition, the three circles of blowtorches all feed the material at a large flow rate, and the deposition is rapid in the carrier. Since the shape of the quartz glass mass is limited by the carrier, there is no It is necessary to precisely control the temperature difference and morphology of the material surface to improve the deposition qualification rate of large-sized synthetic quartz ingots. In the second stage of stable deposition, the quartz ingot is used as the substrate, and only the inner and middle ring blowtorches are used to introduce silicon source deposition, and the silicon source flow rate is reduced and the retracting speed is reduced. The temperature field is controlled by three circles of blowtorches to improve the uniformity of the quartz ingot, avoid the problem of poor uniformity of the refractive index and density of the quartz ingot caused by excessive temperature difference, and avoid the problem of stripes on the quartz ingot, thus solving the problem that the size of the quartz ingot is limited by the height of the carrier.

[0014] Furthermore, the number of the blowtorches in the inner ring is one, and the number of the blowtorches in the middle ring and the outer ring is two. The blowtorches in the inner ring are located at the center of the middle ring and the outer ring, and the line connecting the two blowtorches in the middle ring is perpendicular to the line connecting the two blowtorches in the outer ring. Multiple groups of blowtorches are arranged in three circles, and the line connecting the two blowtorches in the middle ring is perpendicular to the line connecting the two blowtorches in the outer ring. The blowtorches are independent of each other and do not affect each other. By accurately controlling the flow of the blowtorches, the problem of flame interference in the multi-blowtorch structure is solved, the uniformity and stability of the high-temperature field are achieved, and the problem of poor uniformity of the quartz lump caused by the large temperature difference between the inside and outside of the lump surface in the single-blowtorch design is improved.

[0015] Furthermore, the radius of the middle ring is 250-350 mm, and the radius of the outer ring is 250-350 mm larger than the radius of the middle ring. The three circles of blowtorches are reserved with appropriate spacing, do not affect each other, and can accurately control the temperature field.

[0016] Furthermore, the carrier is a "U"-shaped structure, the inner diameter of the bottom end of the carrier is 800-1000mm, and the inner diameter of the top end is 150-250mm larger than the inner diameter of the bottom end, and the depth of the carrier is 400-500mm.

[0017] Furthermore, in S1, the preheating temperature raising condition is: the temperature is raised to above 800° C. within 5 hours, and the preheating efficiency is high.

[0018] Furthermore, in S2, the flow rate of hydrogen is 500-700 L / min, the flow rate of oxygen is 250-350 L / min, and the flow rate of silicon tetrachloride is 50-75 g / min. By controlling the flow rates of hydrogen, oxygen and silicon tetrachloride, the system is stabilized to avoid defects such as bubbles caused by system fluctuations during deposition. At this stage, the carrier is in a non-deposition stage at the lower end.

[0019] Furthermore, in S2, the stable state condition is: the temperature fluctuation in the furnace is less than 0.5°C, and the pressure fluctuation is less than 0.5psi.

[0020] Furthermore, in S3, the flow rate of hydrogen is 1500-2000 L / min, the flow rate of oxygen is 750-1000 L / min, and the flow rate of silicon tetrachloride is 150-200 g / min; in S4, the flow rate of silicon tetrachloride of the inner ring and middle ring blowtorches is 90-150 g / min.

[0021] Furthermore, in S3, the carrier is rotated and lifted at a speed of 3-8 rpm.

[0022] Furthermore, in S3 and S4, the carrier rotates and retracts synchronously during the deposition process.

[0023] Furthermore, in S3 and S4, during deposition, the distance between the discharge end face of the inner ring blowtorch and the deposition surface is maintained at 300±5 mm.

[0024] Furthermore, in S3, the retraction rate of the carrier during the deposition process is 0.5-0.75 mm / min, and in S4, the retraction rate of the carrier during the deposition process is 0.2-0.5 mm / min, and the retraction speed is controlled to keep the material surface of equal diameter.

[0025] Beneficial effects of the present invention:

[0026] The present invention adopts multiple groups of blowtorches arranged in inner ring, middle ring and outer ring, and the flames of the blowtorches do not interfere with each other, so the furnace temperature distribution can be accurately controlled, the uniformity of large-sized synthetic quartz lumps is improved, and the preheating efficiency and deposition efficiency are improved at the same time.

[0027] The present invention accurately controls the raw material supply of different ring burners in the two stages of stable deposition. In the first stage, the carrier is used as the substrate, and a large amount of material is deposited simultaneously in the inner ring, the middle ring and the outer ring. In the second stage, the deposition ingot is used as the substrate, the silicon source supply of the outer ring burner is stopped, and the silicon source flow rates of the inner ring and the middle ring are reduced. The temperature field is controlled by the three-ring burners to achieve uniform and stable deposition of large-sized synthetic quartz ingots. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the structure of the device for synthesizing large-size quartz glass by multi-burner CVD of the present invention;

[0029] Figure 2 It is a schematic diagram of the distribution of the burners in the device for synthesizing large-size quartz glass by multi-burner CVD of the present invention;

[0030] Figure 3 This is a schematic diagram of the stable deposition process of synthesizing large-size quartz glass by multi-burner CVD of the present invention. Figure 1 ;

[0031] Figure 4 This is a schematic diagram of the stable deposition process of synthesizing large-size quartz glass by multi-burner CVD of the present invention. Figure 2 ;

[0032] Explanation of the numbers in the figure: 1. furnace top, 2. blowtorch, 21. inner ring, 22. middle ring, 23. outer ring, 3. support rod, 4. carrier. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention. Example 1

[0034] The present embodiment relates to a method for synthesizing large-size quartz glass by multi-torch CVD. A plurality of torches 2 are arranged on the top 1 of the CVD furnace. The torches 2 are arranged in an inner ring 21, a middle ring 22 and an outer ring 23. The lifting and rotation of the top carrier 4 are supported and controlled by a support rod 3. The device and the torch distribution diagram are shown in FIG. Figure 1 and Figure 2 As shown, the inner diameter of the lower part of the carrier 4 is 800 mm, the inner diameter of the upper part is 1000 mm, the depth is 400 mm, the radius of the middle ring is 250 mm, and the radius of the outer ring is 250 mm larger than the radius of the middle ring.

[0035] The method for synthesizing large-size quartz glass by multi-burner CVD in this embodiment comprises the following steps:

[0036] (1) Ignition and furnace baking stage: hydrogen and oxygen are introduced into each blowtorch, the blowtorch is ignited, and the furnace temperature is raised to 800°C and maintained for 4 hours;

[0037] (2) Pre-deposition stage: Each torch is fed with a hydrogen flow rate of 500 L / min, oxygen 250 L / min, and silicon tetrachloride 50 g / min until the temperature fluctuation in the furnace is less than 0.5 °C and the pressure fluctuation is less than 0.5 psi.

[0038] (3) Stable deposition, first stage: increase the flow rates of hydrogen, oxygen and silicon tetrachloride of each burner. Each burner is fed with a flow rate of 1500 L / min of hydrogen, 750 L / min of oxygen and 150 g / min of silicon tetrachloride. Drive the carrier to rotate at a speed of 3 rpm and lift it to the reference point to start deposition. During deposition, the distance between the discharge end face of the inner ring burner and the deposition surface is maintained at 300 mm. Figure 3 As shown, the deposition continues in the carrier body to 90% of the depth of the carrier body, that is, the carrier body is retracted 360 mm;

[0039] (4) The second stage of stable deposition: the flow rate of silicon tetrachloride in the outer ring burner is reduced to zero, such as Figure 4 As shown, the flow rate of silicon tetrachloride of the inner ring and middle ring torches is reduced to 90 g / min, and the deposition is continued with the surface of the deposition ball as the substrate. During the deposition, the distance between the discharge end face of the inner ring torch and the deposition surface is maintained at 300 mm until the ball grows to the target height;

[0040] (5) Stop feeding and keep warm: After the deposition reaches the target height, stop the supply of silicon tetrachloride to the middle ring and inner ring, then turn off the supply of hydrogen and oxygen to the middle ring, inner ring and outer ring blowtorches, and let the furnace stand and cool naturally;

[0041] (6) Unloading stage: The lump is unloaded after the surface temperature of the lump drops below 100°C.

[0042] After the deposition is completed, the uniformity of the deposited quartz blank material is tested and the uniformity is less than <15ppm. Example 2

[0043] The present embodiment relates to a method for synthesizing large-sized quartz glass by multi-torch CVD. The torches are arranged in an inner ring, a middle ring and an outer ring. The structure of the deposition furnace is the same as that of Example 1, except that the inner diameter of the lower part of the carrier is 1000 mm, the inner diameter of the upper part is 1200 mm, the depth is 500 mm, the radius of the middle ring is 350 mm, and the radius of the outer ring is 350 mm larger than the radius of the middle ring.

[0044] The method for synthesizing large-size quartz glass by multi-burner CVD in this embodiment comprises the following steps:

[0045] (1) Ignition and furnace baking stage: hydrogen and oxygen are introduced into each blowtorch, the blowtorch is ignited, and the furnace temperature is raised to 800°C and maintained for 5 hours;

[0046] (2) Pre-deposition stage: Each blowtorch is fed with a small flow rate of 600 L / min of hydrogen, 300 L / min of oxygen, and 60 g / min of silicon tetrachloride until the temperature fluctuation in the furnace is less than 0.5 °C and the pressure fluctuation is less than 0.5 psi.

[0047] (3) The first stage of stable deposition: the flow rates of hydrogen, oxygen and silicon tetrachloride of each torch were increased. Each torch was fed with a flow rate of 1750 L / min of hydrogen, 875 L / min of oxygen and 175 g / min of silicon tetrachloride. The carrier was driven to rotate at a speed of 5 rpm and lifted to the reference point to start deposition. During deposition, the distance between the discharge end face of the inner ring torch and the deposition surface was maintained at 300 mm. Deposition continued in the carrier until the depth of the carrier reached 90%, that is, the carrier was retracted 450 mm.

[0048] (4) The second stage of stable deposition: the flow rate of silicon tetrachloride of the outer ring burner is reduced to zero, and the flow rate of silicon tetrachloride of the inner ring and middle ring burners is reduced to 120 g / min, and deposition is continued with the surface of the deposition ball as the substrate. During deposition, the distance between the discharge end face of the inner ring burner and the deposition surface is maintained at 300 mm until the ball grows to the target height;

[0049] (5) Stop feeding and keep warm: After the deposition reaches the target height, stop the supply of silicon tetrachloride to the middle ring and inner ring, then turn off the supply of hydrogen and oxygen to the middle ring, inner ring and outer ring blowtorches, and let the furnace stand and cool naturally;

[0050] (6) Unloading stage: The lump is unloaded after the surface temperature of the lump drops below 100°C.

[0051] After the deposition is completed, the uniformity of the deposited quartz blank material is tested and the uniformity is less than <20ppm.

[0052] In summary, the present invention uses multiple groups of torches arranged in an inner ring, a middle ring, and an outer ring. The flames of the torches do not interfere with each other, and the furnace temperature distribution can be accurately controlled, thereby improving the uniformity of large-sized synthetic quartz lumps. The uniformity of the quartz lumps is controlled within 20ppm, and the preheating efficiency and deposition efficiency are improved at the same time. The present invention accurately controls the supply of raw materials of different ring torches in two stages of stable deposition. In the first stage, the carrier is used as the substrate, and the inner ring, the middle ring, and the outer ring are simultaneously deposited in large quantities. In the second stage, the deposition lumps are used as the substrate, the silicon source of the outer ring torch is stopped, and the silicon source flow of the inner ring and the middle ring is reduced at the same time. The temperature field is controlled by the three-ring torches to achieve uniform and stable deposition of large-sized synthetic quartz lumps.

[0053] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A method for synthesizing large-size quartz glass by multi-burner CVD, characterized in that: The distribution of the blowtorches is arranged in an inner ring, a middle ring and an outer ring, and the method comprises the following steps: S1, ignition and baking furnace stage: hydrogen and oxygen are introduced into each blowtorch, and the blowtorch is ignited to preheat the furnace of the deposition furnace; S2, pre-deposition stage: hydrogen, oxygen and silicon tetrachloride are introduced into each blowtorch until the temperature and pressure in the furnace are stable; S3, the first stage of stable deposition: increase the flow rate of hydrogen, oxygen and silicon tetrachloride into each torch, drive the carrier to rotate and lift it to the reference point to start deposition, and continue deposition in the carrier to 90% of the depth of the carrier; S4, the second stage of stable deposition: stop the silicon tetrachloride injection from the outer ring burner, and reduce the silicon tetrachloride injection flow rate from the inner and middle ring burners, continue to deposit in the carrier until the carrier is full, and then continue to deposit on the surface of the deposition lump to the target height; S5, insulation and unloading stage: stop the introduction of silicon tetrachloride from the inner ring and middle ring blowtorches, and stop the introduction of oxygen and hydrogen from each blowtorch. The deposited mass is unloaded after it is naturally cooled in the furnace.

2. The method for synthesizing large-size quartz glass by multi-burner CVD according to claim 1, characterized in that: The number of the blowtorches in the inner ring is one, the number of the blowtorches in the middle ring and the outer ring are both two, the blowtorches in the inner ring are located at the centers of the middle ring and the outer ring, and the line connecting the two blowtorches in the middle ring is perpendicular to the line connecting the two blowtorches in the outer ring.

3. The method for synthesizing large-size quartz glass by multi-burner CVD as claimed in claim 2, characterized in that: The radius of the middle ring is 250-350 mm, and the radius of the outer ring is 250-350 mm larger than the radius of the middle ring.

4. The method for synthesizing large-size quartz glass by multi-burner CVD as claimed in claim 1, characterized in that: The inner diameter of the bottom end of the carrier is 800-1000 mm, and the inner diameter of the top end is 150-250 mm larger than the inner diameter of the bottom end. The depth of the carrier is 400-500 mm.

5. The method for synthesizing large-size quartz glass by multi-burner CVD as claimed in claim 1, characterized in that: In S1, the preheating condition is: heating to above 800°C within 5 hours.

6. The method for synthesizing large-size quartz glass by multi-burner CVD as claimed in claim 1, characterized in that: In S2, the flow rate of hydrogen is 500-700 L / min, the flow rate of oxygen is 250-350 L / min, and the flow rate of silicon tetrachloride is 50-75 g / min.

7. The method for synthesizing large-size quartz glass by multi-burner CVD as claimed in claim 1, characterized in that: In S2, the stable state condition is: the temperature fluctuation in the furnace is less than 0.5°C, and the pressure fluctuation is less than 0.5psi.

8. The method for synthesizing large-size quartz glass by multi-burner CVD as claimed in claim 1, characterized in that: In S3, the flow rate of hydrogen is 1500-2000 L / min, the flow rate of oxygen is 750-1000 L / min, and the flow rate of silicon tetrachloride is 150-200 g / min; in S4, the flow rate of silicon tetrachloride of the inner ring and middle ring blowtorches is 90-150 g / min.

9. The method for synthesizing large-size quartz glass by multi-burner CVD as claimed in claim 1, characterized in that: In S3 and S4, during deposition, the distance between the discharge end face of the inner ring burner and the deposition surface is maintained at 300±5 mm.

10. The method for synthesizing large-size quartz glass by multi-burner CVD according to claim 9, characterized in that: In S3, the withdrawal rate of the carrier during the deposition process is 0.5-0.75 mm / min, and in S4, the withdrawal rate of the carrier during the deposition process is 0.2-0.5 mm / min.

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