Bubble-free long-life quartz crucible and preparation method thereof

Abstract

The invention provides a bubble-free long-life quartz crucible and a preparation method thereof, and belongs to the technical field of quartz crucible production. Comprising the following steps: S1, pouring quartz sand into a mold, and manufacturing a bubble layer of a quartz crucible; s2, spraying high-purity quartz sand to the bubble layer of the quartz crucible through a sand blasting device, and heating the high-purity quartz sand while spraying, so that the high-purity quartz sand is converted into high-jet silicon dioxide molten drops which are uniformly attached to the bubble layer of the quartz crucible; s3, carrying out secondary arcing on the mold so as to carry out secondary heating on the inner surface of the quartz crucible; and S4, after heating for a preset time, stopping heating, and taking out the mold to obtain the bubble-free long-life quartz crucible. According to the method, the bubble layer is firstly manufactured, and then the transparent layer is manufactured in a thermal spraying melting coating mode, so that microbubbles and impurities in the quartz sand can be effectively removed, the quality of a crystal bar can be improved, the thermal stability of the quartz crucible can be improved, the service life of the quartz crucible can be prolonged, and the crystal pulling cost can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of quartz crucible production, and particularly relates to a bubble-free long-life quartz crucible and a preparation method thereof. Background Art

[0002] In the field of semiconductor wafer manufacturing, the quartz crucible is the core container for single crystal silicon growth (CZ method) and is used to hold molten silicon material. Its high purity (extremely low impurity content) can avoid silicon crystal contamination and ensure the electrochemical performance of semiconductor-grade silicon wafers. Similarly, in the field of photovoltaic manufacturing, the production of solar cells is inseparable from the production of polysilicon ingots and single crystal silicon rods. As a key tool for the production of photovoltaic-grade polysilicon ingots and single crystal silicon rods, due to its characteristics of chemical stability and low coefficient of thermal expansion, the quartz crucible can reduce the risk of impurity introduction and thermal stress cracking during the solidification of silicon material, and has gradually attracted the attention of the industry.

[0003] During the semiconductor and photovoltaic crystal pulling processes, the quartz crucible needs to withstand a high temperature of over 1450°C. Under such high temperature conditions, the quartz glass will soften and the microbubbles inside it will also expand due to heat. When maintained at a high temperature for a long time, the microbubbles on the inner surface of the quartz crucible may overflow from the inner surface due to expansion, driving impurities to migrate into the silicon solution, thereby affecting the impurity concentration of the single crystal silicon rod and causing a series of defects, reducing the quality of the crystal rod. Summary of the Invention

[0004] In view of this, the present invention provides a bubble-free long-life quartz crucible and a preparation method thereof to solve the technical problem that the microbubbles on the inner surface of the existing quartz crucible overflow at high temperature, driving impurities to migrate into the silicon melt and affecting the quality of the crystal rod.

[0005] The technical solution adopted by the present invention to solve its technical problems is as follows: A preparation method of a bubble-free long-life quartz crucible, comprising the following steps: S1. Pour quartz sand into a mold to make a bubble layer of the quartz crucible; S2. Spray high-purity quartz sand onto the bubble layer of the quartz crucible through a sandblasting device, and heat the high-purity quartz sand while spraying, so that the high-purity quartz sand is converted into high-velocity silica melt droplets and uniformly adheres to the bubble layer of the quartz crucible; S3. Perform secondary arcing on the mold to perform secondary heating on the inner surface of the quartz crucible, so that the inner surface of the quartz crucible is smooth; S4. After heating for a preset time, stop heating, take out the mold, and obtain a bubble-free long-life quartz crucible.

[0006] Preferably, in step S1, making the bubble layer of the quartz crucible specifically includes the following steps: S11. Form the quartz sand by centrifugal molding method; S12. Use the arc method to perform high-temperature melting on the formed quartz sand for a period of time to form the bubble layer of the quartz crucible.

[0007] Preferably, the parameters of the centrifugal forming method include a rotation speed of 2500 - 3500 revolutions per minute and a centrifugal time of 25 - 35 minutes.

[0008] Preferably, the parameters of the arc method include a current of 100 - 120 A, a voltage of 200 - 220 V, a melting temperature of 1500 - 2000 °C, and a melting time of 0.8 - 1.2 hours.

[0009] Preferably, after step S1 and before step S2, it further includes: taking the mold out of the arc melting furnace and tilting it to a preset angle so that the high-velocity silica melt droplets can be evenly sprayed onto the bubble layer of the quartz crucible; wherein, the preset angle is 40 - 60°.

[0010] Preferably, in step S2, the pressure of the sandblasting device is 0.3 - 0.7 MPa, and the sandblasting particle size is 15 - 20 mesh.

[0011] Preferably, in step S2, the heating temperature is 1000 - 1200 °C, and the heating time is 10 - 15 minutes.

[0012] Preferably, in step S2, a flame spray gun is used to heat the ejected high-purity quartz sand, wherein the gas flow rate of the flame spray gun is 0.9 - 1.1 L / min, and the oxygen flow rate is 0.4 - 0.6 L / min.

[0013] Preferably, in step S3, the parameters of the secondary arcing include a current of 140 - 160 A, a voltage of 300 - 330 V, a heating temperature of 1600 - 1800 °C, and a heating time of 15 - 25 minutes.

[0014] The present invention also provides a bubble-free long-life quartz crucible prepared by using the preparation method of the bubble-free long-life quartz crucible as described above.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: By adopting the method of thermal spraying and melting coating, the present invention can effectively remove microbubbles and impurities in quartz sand. On the one hand, there are no microbubbles in the transparent layer of the quartz crucible, thus avoiding the problem that microbubbles expand under high-temperature conditions and drive the migration of impurities; on the other hand, the purity of the inner surface of the quartz crucible is further improved, thus avoiding the problem of local crystallization on the inner surface of the quartz crucible caused by impurity elements, which is beneficial to improving the quality of the crystal bar. In addition, removing microbubbles and impurities in quartz sand can further improve the thermal stability of the quartz crucible, significantly extend the service life of the quartz crucible during the crystal pulling process, improve the production efficiency of wafer manufacturing enterprises, and reduce the crystal pulling cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a process flow chart of a method for preparing a bubble-free long-life quartz crucible according to the present invention.

[0017] Figure 2 It is a cross-sectional view of a quartz crucible prepared by using the preparation method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] The following further elaborates in detail the technical solutions and technical effects of the embodiments of the present invention in conjunction with the drawings of the present invention.

[0019] Please refer to Figure 1 , a method for preparing a bubble-free long-life quartz crucible, comprising the following steps: S1. Pour quartz sand into a mold to make the bubble layer of the quartz crucible; S2. Spray high-purity quartz sand onto the bubble layer of the quartz crucible through a sandblasting device, and heat the high-purity quartz sand while spraying, so that the high-purity quartz sand is converted into high-velocity silica melt droplets and uniformly adheres to the bubble layer of the quartz crucible; S3. Perform secondary arcing on the mold to perform secondary heating on the inner surface of the quartz crucible to make the inner surface of the quartz crucible smooth; S4. After heating for a preset time, stop heating, take out the mold, and obtain a bubble-free long-life quartz crucible.

[0020] In the present invention, the bubble layer of the quartz crucible is first fabricated, and then high-purity quartz sand is sprayed onto the bubble layer of the quartz crucible by a sandblasting device. While being sprayed, the high-purity quartz sand is heated. After the high-purity quartz sand is ejected by the sandblasting device, during the movement process, it is transformed into high-jet silica droplets via a high-energy flame heating zone, and the high-jet silica droplets uniformly adhere to the bubble layer. Finally, arc striking heating is performed again to provide sufficient and uniform heat for the quartz crucible in the mold, so that the bubble layer and the transparent layer are integrated, and a long-life quartz crucible with no microbubbles in the inner surface transparent layer is ultimately prepared. By adopting the method of thermal spraying and melting coating, the present invention can effectively remove microbubbles and impurities in the quartz sand. On the one hand, there are no microbubbles in the transparent layer part of the quartz crucible, thus avoiding the problem that microbubbles expand under high-temperature conditions and drive the migration of impurities. On the other hand, the purity of the inner surface of the quartz crucible is further improved, thus avoiding the problem of local crystallization on the inner surface of the quartz crucible caused by impurity elements, which is beneficial to improving the quality of the ingot. In addition, removing microbubbles and impurities in the quartz sand can further improve the thermal stability of the quartz crucible, significantly extend the service life of the quartz crucible during the crystal pulling process, improve the production efficiency of wafer manufacturing enterprises, and reduce the crystal pulling cost.

[0021] Existing quartz crucibles are generally formed in one step by the arc method, that is, high-purity quartz powder is loaded into a rotatable forming mold with an arbitrarily tiltable angle, formed by centrifugal force, the rotating device in the shape of a crucible is moved to the electrode rod, then the electrode is powered on to strike an arc, and at the same time the vacuum system is started, melting while evacuating, so that it is quickly melted into a molten quartz in the shape of a crucible, and after cooling, it is taken out, and thus the melting of one quartz crucible is completed. There are three ways to form microbubbles: one is the air between quartz particles; one is the gas-liquid inclusions in quartz; and one is that hydroxyl groups combine into water at high temperature. If the crucible melting process is relatively good, the air between quartz gaps can be pumped out, but if the content of gas-liquid inclusions and hydroxyl groups in the quartz itself is relatively high, since these inclusions are usually located inside the quartz crystal and most of their volumes are small (micrometer level), it is difficult to achieve a very good effect in the melting process.

[0022] The present invention uses the thermal spraying method to transform high-purity quartz sand into high-jet silica droplets. On the one hand, when the droplets are injected into the mold, the droplets will naturally fuse together, thus avoiding the generation of gaps, and removing the microbubbles generated by the gaps. On the other hand, during the process of the high-purity quartz sand being ejected by the sandblasting device, it is heated, so that the high-purity quartz sand can be fully heated and be under high-temperature conditions. Then, a large pressure difference will be generated at the interface between the high-purity quartz sand and the gas-liquid inclusions therein, and this pressure difference will cause the gas-liquid inclusions in the quartz sand to burst, thereby removing the gas-liquid inclusions in the quartz sand. Therefore, the microbubbles in the inner surface transparent layer of the quartz crucible can be well removed by the thermal spraying method.

[0023] Further, in step S1, the specific steps for fabricating the bubble layer of the quartz crucible are as follows: S11. Molding the quartz sand by the centrifugal molding method; S12. High-temperature melting the molded quartz sand by the arc method for a period of time to form the bubble layer of the quartz crucible.

[0024] The bubble layer of the present invention is fabricated by an existing method, that is, by the high-speed centrifugal molding method. The centrifugal force generated by high-speed rotation makes the quartz sand evenly arranged to form a dense green body, and the arc method is used for heating to prepare the matrix of the bubble layer of the quartz crucible. Specifically, quartz sand with appropriate purity is selected and screened and cleaned to remove impurities and quartz particles with uneven particles. The quartz sand and additives are mixed evenly according to a certain formula ratio. The mixed quartz sand is poured into the mold of the centrifugal molding machine, and the centrifugal molding machine is started. The centrifugal force generated by high-speed rotation makes the quartz sand evenly arranged to form a dense green body. Among them, the rotation speed of the centrifugal molding machine is 2500 - 3500 revolutions per minute, and the centrifugation time is 25 - 35 minutes. Then the centrifugally molded quartz sand is put into the arc melting furnace, and the quartz sand is high-temperature melted by the arc method to form the micro-bubble layer of the quartz crucible. Among them, the current of the arc method is 100 - 120 A, the voltage is 200 - 220 V, the melting temperature is 1500 - 2000 °C, and the melting time is 0.8 - 1.2 hours.

[0025] Further, after step S1 and before step S2, it further includes: taking out the mold from the arc melting furnace and tilting it to a preset angle so that the high-velocity jet silica droplets can be evenly sprayed onto the bubble layer of the quartz crucible; wherein, the preset angle is 40 - 60°. After the bubble layer of the quartz crucible is fabricated in the arc melting furnace, the mold is taken out of the arc melting furnace and moved to the position where the sandblasting device and the flame spray gun are located, and the mold is tilted to the preset angle to facilitate spraying the high-velocity jet silica droplets into the mold. At the same time, after the mold is tilted, the quartz sand ejected by the sandblasting device can cover a larger area of the inner surface of the quartz crucible instead of accumulating at one point, so that the high-velocity jet silica droplets can be more evenly sprayed onto the bubble layer of the quartz crucible. The sandblasting device and the flame spray gun are turned on, and at the same time, the rotation of the mold is controlled. After the high-purity quartz sand is ejected by the sandblasting device, it is converted into high-velocity jet silica droplets in the process of movement through the high-energy flame heating area. During the rotation of the mold, the high-velocity jet silica droplets are evenly attached to the inner surface of the quartz crucible enriched with micro-bubbles, that is, the bubble layer of the quartz crucible. Among them, the preset angle is 40 - 60°.

[0026] Further, in step S2, the pressure of the sandblasting device is 0.3 - 0.7 MPa, and the sandblasting particle size is 15 - 20 mesh.

[0027] Further, in step S2, the heating temperature is 1000 - 1200 °C, and the heating time is 10 - 15 minutes.

[0028] Further, in step S2, a flame gun is used to heat the ejected high-purity quartz sand. Among them, the gas flow rate of the flame gun is 0.9 - 1.1 L / min, and the oxygen flow rate is 0.4 - 0.6 L / min. Specifically, the high-purity quartz sand is poured into the sandblasting device, the sandblasting device is started, and the high-purity quartz sand is ejected. At the same time, the flame gun is started, and the ejected high-purity quartz sand is heated by the flame gun to convert the high-purity quartz sand into high-jet silica droplets, which are uniformly attached to the bubble layer of the quartz crucible.

[0029] In some embodiments, a sandblasting device and a flame gun are arranged outside the arc melting furnace. The flame gun and the sandblasting device are arranged on one side of the mold moving route, and the flame direction of the flame gun intersects with the sandblasting direction of the sandblasting device. When the bubble layer of the quartz crucible is made, after the mold is taken out of the arc melting furnace, it is moved to the opposite side of the sandblasting device, and the mold is tilted at a preset angle. The intersection point of the flame direction and the sandblasting direction is located between the mold and the sandblasting device. When the sandblasting device ejects the quartz sand, the quartz sand is heated by the flame ejected by the flame gun to be converted into high-jet silica droplets when passing through the intersection point, but the moving direction of the quartz sand remains unchanged. After passing through the high-energy flame heating area, it is injected into the mold. During the rotation of the mold, the high-jet silica droplets are uniformly attached to the bubble layer of the quartz crucible. It should be noted that the installation position of the flame gun should ensure that its flame direction does not intersect with the mold, so as to avoid heating the mold by the flame of the flame gun.

[0030] In some embodiments, the sandblasting device and the flame gun can be arranged in one device. The sandblasting direction of the sandblasting device overlaps with the flame direction of the flame gun, and the sandblasting device is arranged behind the flame gun, so that the quartz sand ejected by the sandblasting device passes through the high-energy flame heating area during the movement process, ensuring that the quartz sand can be completely heated and converted into high-jet silica droplets, and then sprayed into the mold and uniformly attached to the bubble layer of the quartz crucible. As an example, a flame spraying device can be used. The flame spraying device uses a special powder feeder hose for powder supply and a flame spraying gun, generates heat by means of an oxygen-acetylene flame, and uses compressed air as a protective gas jet flame to heat the sprayed quartz sand to the molten droplet state and spray it onto the inner surface of the mold to form a uniform and pore-free transparent layer of the quartz crucible. It can be understood that the above two installation positions of the sandblasting device and the flame gun are only examples, and the specific structures and positions of the sandblasting device and the flame gun are not limited herein and can be adjusted according to the actual situation.

[0031] Further, in step S3, the parameters for the secondary arc starting include a current of 140 - 160 A, a voltage of 300 - 330 V, a heating temperature of 1600 - 1800 °C, and a heating time of 15 - 25 minutes. After the high-purity quartz sand of the required quality is transformed by thermal spraying and completely adheres to the inner surface of the crucible, the mold is then inserted into the melting machine for secondary arc starting to perform secondary heating on the fine sand on the inner surface of the crucible. After a period of time, the fine material layer on the inner surface of the quartz crucible is fully melted. Then, the heating is stopped, and the mold is taken out. The fine material layer on the inner surface of the quartz crucible will merge with the bubble enrichment layer and form the transparent layer of the high-purity quartz crucible. As an example, the quartz crucible coated with high-purity quartz sand by the thermal spraying method is placed in a melting furnace, and the mold is heated by providing uniform heat through secondary arc starting. The heating temperature is 1600 °C, and the heating time is 20 minutes. After 20 minutes, the heating is stopped, and the mold is taken out from the secondary heating furnace. At this time, the fine material layer on the inner surface of the quartz crucible will merge with the bubble enrichment layer to form a transparent layer.

[0032] When the transparent layer is fabricated by the thermal spraying method, the high-purity quartz sand is transformed into high-velocity silica melt droplets and injected into the mold, coating the inner surface of the quartz crucible. The high-velocity silica melt droplets overlap to form the transparent layer of the quartz crucible. Although the transparent layer appears smooth overall, locally, the surface of the transparent layer has undulations. By performing secondary arc starting on the mold, the high-velocity silica melt droplets can be further fused and homogenized, thus ensuring the uniform smoothness of the inner surface of the quartz crucible. Additionally, during the secondary arc starting process, a purification treatment can be performed on the inner surface of the quartz crucible to further reduce the impurities in the quartz crucible and improve the purity of the inner surface of the quartz crucible.

[0033] Further, since the existing method for preparing quartz crucibles generates a large thermal shock to the quartz sand during the melting process, some of the quartz sand on the inner surface of the quartz crucible will directly sublime and be removed by the vacuum system, resulting in the loss of quartz sand in the quartz crucible. Moreover, currently, when preparing quartz crucibles, there are generally three layers. Among them, the purity of the quartz sand in the three layers is different, and the requirements for the quartz sand in the inner layer of the quartz crucible are higher. However, with the preparation method of the present invention, on the one hand, the transparent layer of the quartz crucible uses the thermal spraying method to heat the quartz sand, and the heating temperature is lower than that in the electric arc melting furnace. Therefore, it only causes the quartz sand to be transformed into high-velocity silica melt droplets, avoiding the sublimation of the quartz sand due to the thermal shock generated by high temperature, thereby reducing the loss of quartz sand and lowering the raw material cost. On the other hand, the quartz crucible prepared by the method of the present invention has only two layers. The outermost bubble layer can use quartz sand with relatively poor purity, and the transparent layer on the inner surface uses high-purity quartz sand. Without the middle layer, the usage amount of high-purity quartz sand is reduced, further lowering the raw material cost of the quartz crucible.

[0034] In addition, the quartz crucibles prepared by the existing methods have at least three layers. Some quartz crucibles will add a high-alumina layer to the outermost layer to improve the strength. However, it can be understood that the more layers there are, the worse the homogenization of the product and the lower the strength of the product. This is because the expansion rates of different layers are different. During the process of temperature increase or decrease, delamination will occur, thus reducing the strength of the product. The quartz crucible prepared by the present invention has only two layers, namely the bubble layer and the transparent layer. Compared with the existing quartz crucibles, the number of layers is less. Therefore, the strength of the quartz crucible can be effectively improved. Moreover, the bubble layer of the quartz crucible plays a role in providing strength support. The thickness of the bubble layer of the quartz crucible prepared by the present invention is greater than that of the existing quartz crucibles. Therefore, the strength of the quartz crucible can be further improved. In summary, the preparation method of the present invention can also reduce the raw material cost of the quartz crucible and improve the strength of the quartz crucible, thereby obtaining a long-life quartz crucible.

[0035] The present invention also provides a bubble-free long-life quartz crucible, which is prepared by using the preparation method of the bubble-free long-life quartz crucible as described above. Please refer to Figure 2 , Figure 2 FIG. is a cross-sectional view of the quartz crucible prepared by using the preparation method of the present invention. It can be seen from the cross-sectional view that there are many white spots in the bubble layer of the quartz crucible, and these white spots are bubbles; while there are almost no white spots in the transparent layer of the quartz crucible, that is, there are no bubbles in the transparent layer of the quartz crucible. Therefore, by adopting the production method combining the arc method and the thermal spraying method, the present invention can obtain an inner surface transparent layer without microbubbles, thereby avoiding the expansion of partial microbubbles in the transparent layer, effectively reducing the migration of impurity elements on the inner surface of the crucible and the local crystallization caused thereby. In addition, under the high-temperature conditions of the thermal spraying method, the impurity elements on the inner surface of the crucible are secondarily purified, effectively reducing the content of impurity elements on the inner surface, which is beneficial to the drawing of high-quality crystal rods. Through the above preparation method, a quartz crucible with a transparent layer without microbubbles can be obtained. The quartz crucible has the advantages of high inner surface purity and long service life, and is applicable to the photovoltaic crystal pulling industry and the semiconductor-grade wafer manufacturing industry.

[0036] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A preparation method of a bubble-free long-life quartz crucible, characterized in that, It includes the following steps: S1. Pour quartz sand into the mold to make the bubble layer of the quartz crucible; S2. Spray high-purity quartz sand onto the bubble layer of the quartz crucible through a sandblasting device, and heat the high-purity quartz sand while spraying, so that the high-purity quartz sand is transformed into high-jet silica melt droplets and evenly adheres to the bubble layer of the quartz crucible; S3. Perform secondary arcing on the mold to perform secondary heating on the inner surface of the quartz crucible, so that the inner surface of the quartz crucible is smooth; S4. After heating for a preset time, stop heating, take out the mold, and obtain a bubble-free long-life quartz crucible.

2. The preparation method of the bubble-free long-life quartz crucible according to claim 1, characterized in that, In step S1, making the bubble layer of the quartz crucible specifically includes the following steps: S11. Form the quartz sand by centrifugal molding method; S12. Perform high-temperature melting on the formed quartz sand by arc method for a period of time to form the bubble layer of the quartz crucible.

3. The preparation method of the bubble-free long-life quartz crucible according to claim 2, characterized in that, The parameters of the centrifugal molding method include a rotation speed of 2500 - 3500 revolutions per minute and a centrifugal time of 25 - 35 minutes.

4. The preparation method of the bubble-free long-life quartz crucible according to claim 3, characterized in that, The parameters of the arc method include a current of 100 - 120A, a voltage of 200 - 220V, a melting temperature of 1500 - 2000 °C, and a melting time of 0.8 - 1.2 hours.

5. The preparation method of the bubble-free long-life quartz crucible according to any one of claims 1-4, characterized in that, After step S1 and before step S2, it further includes: taking the mold out of the arc melting furnace and tilting it to a preset angle so that the high-jet silica melt droplets can be evenly sprayed onto the bubble layer of the quartz crucible; wherein, the preset angle is 40 - 60°.

6. The preparation method of the bubble-free long-life quartz crucible according to claim 5, characterized in that, In step S2, the pressure of the sandblasting device is 0.3 - 0.7 MPa, and the sandblasting particle size is 15 - 20 mesh.

7. The preparation method of the bubble-free long-life quartz crucible according to claim 6, characterized in that, In step S2, the heating temperature is 1000 - 1200 °C, and the heating time is 10 - 15 minutes.

8. The preparation method of the bubble-free long-life quartz crucible according to claim 7, characterized in that, In step S2, a flame spray gun is used to heat the sprayed high-purity quartz sand, wherein the gas flow rate of the flame spray gun is 0.9 - 1.1 L / min, and the oxygen flow rate is 0.4 - 0.6 L / min.

9. The method for preparing a bubble-free long-life quartz crucible according to claim 1, characterized in that, In step S3, the parameters of the secondary arcing include a current of 140 - 160A, a voltage of 300 - 330V, a heating temperature of 1600 - 1800 °C, and a heating time of 15 - 25 minutes.

10. A bubble-free long-life quartz crucible, characterized in that, It is prepared by using the preparation method of the bubble-free long-life quartz crucible according to any one of claims 1 - 9.

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