Quartz crucible for continuously drawing crystalline silicon and preparation method thereof

Abstract

The invention provides a quartz crucible for continuously drawing crystalline silicon and a preparation method of the quartz crucible, and belongs to the technical field of crucible manufacturing. Comprising the following steps: S1, performing electric arc melting on quartz sand to obtain a blank quartz crucible with a smooth inner surface and a rough outer surface; s2, the blank quartz crucible is sequentially subjected to outer surface sand blasting, outer surface grinding, height cutting, first cleaning, outer surface fire machining polishing, second cleaning and drying procedures, and the inner surface roughness Rlt is obtained; the thickness is 5 microns, and the roughness of the outer surface is Ralt; the invention discloses a 5-micron quartz crucible. Therefore, the quartz crucible can reduce oxygen brought into silicon liquid in the process of drawing crystalline silicon, the oxygen content of the crystalline silicon is reduced, and the quality of the crystalline silicon is improved.

Description

Technical Field

[0001] The invention relates to the technical field of crucible manufacturing, and in particular to a quartz crucible for continuously pulling crystalline silicon and a preparation method thereof. Background Art

[0002] The continuous feeding direct silicon pulling method (CCZ for short) is a method of feeding silicon material into the furnace and melting it into silicon liquid while pulling crystalline silicon. The silicon material used is usually granular silicon with a certain particle size. The quartz crucible used is usually composed of an outer quartz crucible and an inner quartz crucible. The outer diameter of the inner quartz crucible is smaller than the inner diameter of the outer quartz crucible. The inner quartz crucible is placed inside the outer quartz crucible. The hollow part between the outer quartz crucible and the inner quartz crucible is used for feeding and melting silicon material. The melted silicon liquid flows into the inner quartz crucible through a specific hole set in the inner quartz crucible. The inner quartz crucible forms a space for accommodating silicon liquid and crystal growth. This process can realize feeding and pulling crystalline silicon at the same time, achieving high-efficiency production of crystalline silicon and uniform resistivity distribution of crystalline silicon. However, the crystalline silicon pulled by the continuous feeding direct silicon pulling method has a high oxygen content, which affects the quality of crystalline silicon.

[0003] In the prior art, for example, the Chinese patent application number 202311172947.6 specifically discloses a continuous straight-pulling single crystal feeding crucible and a single crystal furnace, and specifically discloses that by designing a quartz ring to replace the inner quartz crucible, the area of ​​the inner crucible submerged in the liquid surface can be reduced, thereby reducing the quartz crucible material from dissolving oxygen ions in the melt and reducing the oxygen content of the pulled crystal. However, the crucible structure of the patent is complex, which makes the pulling process complicated and reduces the efficiency of crystalline silicon pulling. Summary of the invention

[0004] In view of this, the present invention provides a quartz crucible for continuously pulling crystalline silicon and a preparation method thereof, so as to solve the technical problems of the complex crucible structure and reduced crystalline silicon pulling efficiency in the prior art.

[0005] The technical solution adopted by the present invention to solve its technical problem is: A method for preparing a quartz crucible for continuously pulling crystalline silicon comprises the following steps: S1. Arc melting quartz sand to obtain a rough quartz crucible with a smooth inner surface and a rough outer surface; S2. The rough quartz crucible is sequentially subjected to outer surface sandblasting, outer surface grinding, height cutting, first cleaning, outer surface fire processing and polishing, second cleaning, and drying steps to obtain a quartz crucible with an inner surface roughness Ra<5 microns and an outer surface roughness Ra<5 microns.

[0006] Preferably, in step S1, arc melting of quartz sand to obtain a rough quartz crucible with a smooth inner surface and a rough outer surface is performed by the following steps: S11, stacking high-purity quartz sand on the inner wall of the mold, and applying power to the graphite electrode, so that the graphite electrode ionizes the gas to generate plasma to heat and melt the quartz sand; S12, using a vacuum device to remove bubbles in the gaps between quartz sand particles during the melting process; S13, turning off the power and stopping heating to obtain a rough quartz crucible with an inner surface roughness Ra<5 microns and an outer surface roughness Ra>30 microns.

[0007] Preferably, in step S2, sandblasting the outer surface of the blank quartz crucible comprises: sandblasting the outer surface of the blank quartz crucible with a 20-100 mesh sandblasting material to obtain a blank quartz crucible with an outer surface roughness Ra>15 microns.

[0008] Preferably, in step S2, grinding the outer surface of the blank quartz crucible comprises: grinding the outer surface of the blank quartz crucible with a 50-200 mesh polishing sheet to obtain a blank quartz crucible with an outer surface roughness Ra>5 microns.

[0009] Preferably, in step S2, cutting the rough quartz crucible to a height comprises: using a cutting machine to cut the burrs of the rough quartz crucible port at a specified height to obtain a quartz crucible with a port flatness less than 5 mm.

[0010] Preferably, in step S2, performing a first cleaning on the blank quartz crucible comprises: chemically cleaning the inner and outer surfaces of the blank quartz crucible, and then rinsing with high-pressure pure water after the chemical cleaning.

[0011] Preferably, the chemical cleaning adopts any one of hydrofluoric acid, sulfuric acid, hydrochloric acid, mixed acid, and sodium hydroxide solution.

[0012] Preferably, in step S2, performing fire processing and polishing on the outer surface of the blank quartz crucible comprises: performing fire processing and polishing on the outer surface of the blank quartz crucible using a flame polisher to obtain a blank quartz crucible with an outer surface roughness Ra<5 μm.

[0013] Preferably, in step S2, the process of drying the blank quartz crucible comprises: drying the blank quartz crucible in an environment of 50-150°C.

[0014] A quartz crucible for continuously pulling crystalline silicon is prepared by the method for preparing the quartz crucible for continuously pulling crystalline silicon as described above.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention reduces the roughness of the outer surface of the quartz crucible through the outer surface sandblasting, outer surface grinding, height cutting, first cleaning, outer surface fire processing polishing, second cleaning, and drying processes, so that the inner and outer surfaces of the obtained quartz crucible are both smooth mirror surfaces, and the inner and outer surface roughness are relatively low. When pulling crystalline silicon, the oxygen brought into the silicon liquid by the quartz crucible can be reduced, the oxygen content in the silicon liquid can be reduced, and the oxygen content of the crystalline silicon can be reduced, thereby improving the quality of the crystalline silicon. In addition, the present invention only processes the outer surface of the quartz crucible, so the structure of the quartz crucible of the present invention is the same as the structure of the quartz crucible used in the traditional continuous feeding direct pulling crystalline silicon method, the pulling process is simple, and the crystalline silicon pulling efficiency is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of a quartz crucible of the present invention.

[0017] Figure 2 Schematic diagram of fire processing and polishing of the outer surface of quartz crucible In the figure: outer surface of quartz crucible 1, inner surface of quartz crucible 2, hydrogen 3, oxygen 4. DETAILED DESCRIPTION

[0018] The technical solutions and technical effects of the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings of the present invention.

[0019] A method for preparing a quartz crucible for continuously pulling crystalline silicon comprises the following steps: S1. Arc melting quartz sand to obtain a rough quartz crucible with a smooth inner surface and a rough outer surface; S2. The rough quartz crucible is sequentially subjected to outer surface sandblasting, outer surface grinding, height cutting, first cleaning, outer surface fire processing and polishing, second cleaning, and drying steps to obtain a quartz crucible with an inner surface roughness Ra<5 microns and an outer surface roughness Ra<5 microns.

[0020] The inventors discovered during the production process that the actual reason for the high oxygen content of crystalline silicon pulled by the continuous feeding direct silicon pulling method is that the continuous feeding direct silicon pulling method uses inner and outer quartz crucibles, and the smooth inner surface of the outer quartz crucible is in contact with the silicon liquid, so less oxygen is brought into the silicon liquid. However, the inner surface and outer surface of the inner quartz crucible are in contact with the silicon liquid, and the inner surface of the inner quartz crucible is also a smooth surface, so less oxygen is brought into the silicon liquid. The outer surface of the inner quartz crucible processed by conventional technology is a rough surface containing microbubbles, and more oxygen is brought into the silicon liquid by the reaction, resulting in a higher oxygen content in the overall silicon liquid. The high oxygen content of the produced crystalline silicon affects the quality of the crystalline silicon. Therefore, the present invention reduces the roughness of the outer surface of the quartz crucible through the steps of outer surface sandblasting, outer surface grinding, height cutting, first cleaning, outer surface fire processing and polishing, second cleaning, and drying, so that the obtained quartz crucible is as follows Figure 1As shown, the inner and outer surface roughness Ra is less than 5 microns, and the inner and outer surfaces are both smooth mirror surfaces. When pulling crystalline silicon, the oxygen brought into the silicon liquid by the quartz crucible can be reduced, the oxygen content in the silicon liquid can be reduced, and then the oxygen content of the crystalline silicon can be reduced, thereby improving the quality of the crystalline silicon. In addition, the present invention only processes the outer surface of the quartz crucible. Therefore, the structure of the quartz crucible of the present invention is the same as the structure of the quartz crucible used in the traditional continuous feeding direct pulling crystalline silicon method, the pulling process is simple, and the crystalline silicon pulling efficiency is high.

[0021] In the specific implementation process, in step S1, arc melting of quartz sand is performed to obtain a rough quartz crucible with a smooth inner surface and a rough outer surface by the following steps: S11, stacking high-purity quartz sand on the inner wall of the mold, and applying power to the graphite electrode, so that the graphite electrode ionizes the gas to generate plasma to heat and melt the quartz sand; S12, using a vacuum device to remove bubbles in the gaps between quartz sand particles during the melting process; S13, turning off the power and stopping heating to obtain a rough quartz crucible with an inner surface roughness Ra<5 microns and an outer surface roughness Ra>30 microns.

[0022] Specifically, high-purity quartz sand is piled up on the inner wall of a mold, the mold has a straight wall, a bottom and a curved portion connecting the straight wall and the bottom, and has air holes running through the inner and outer surfaces, a conductive graphite electrode is arranged above the mold, and power is applied to the graphite electrode so that an arc is generated in the graphite electrode to convert electrical energy into thermal energy to heat and melt the quartz sand, and at the same time, during the melting process, an exhaust device is used to remove bubbles in the gaps between the quartz sand particles to obtain a quartz crucible with a smooth inner surface, and residual heat still exists on the outer surface of the quartz crucible after the power is turned off and the heating is stopped, which will cause the incompletely melted quartz sand to adhere to the outer surface, resulting in a certain rough surface of the outer surface with quartz sand attached, thereby obtaining a rough quartz crucible with a smooth and transparent inner surface and a rough outer surface. Among them, when the quartz crucible is arc-melted, the current of the graphite electrode is 1200A-6000A, the voltage is 100V-500V, and the relative vacuum degree generated by the exhaust device is <-0.04Mpa, thereby obtaining a rough quartz crucible with an inner surface roughness Ra<5 microns and an outer surface roughness Ra>30 microns.

[0023] In the specific implementation process, in step S2, sandblasting the outer surface of the blank quartz crucible includes: using 20-100 mesh sandblasting material to sandblast the outer surface of the blank quartz crucible to obtain a blank quartz crucible with an outer surface roughness Ra>15 microns. Specifically, the sandblasting material is transported and sprayed to the outer surface of the blank quartz crucible by high-pressure gas with a pressure greater than 1Mpa, and the outer surface of the blank quartz crucible is impacted to remove the quartz sand that is not firmly adhered to the outer surface, thereby reducing the roughness of the outer surface of the blank quartz crucible, and obtaining a blank quartz crucible with an outer surface roughness Ra>15 microns. The sandblasting material includes any one of pomegranate sand, quartz sand, corundum sand, etc.

[0024] In the specific implementation process, in step S2, grinding the outer surface of the blank quartz crucible includes: grinding the outer surface of the blank quartz crucible with a 50-200 mesh polishing sheet to obtain a blank quartz crucible with an outer surface roughness Ra>5 microns. The polishing sheet includes any one of an oil stone, a grinding wheel, etc., so that the outer surface of the blank quartz crucible is polished by using a polishing sheet with a certain roughness to further reduce the roughness of the outer surface, and obtain a blank quartz crucible with an outer surface roughness Ra>5 microns.

[0025] After the quartz crucible is made by arc melting, quartz sand is still attached to the outer surface of the quartz crucible, so it is not easy to clamp the quartz crucible. At the same time, the presence of quartz sand will affect the accuracy of height cutting on the one hand, and will damage the cutting tool on the other hand. Therefore, in the present invention, the outer surface is first sandblasted and ground to remove the quartz sand on the outer surface of the blank quartz crucible, and then the blank quartz crucible is height cut. In the specific implementation process, in step S2, the height cutting of the blank quartz crucible includes: using a cutting machine tool to cut the burrs of the blank quartz crucible port according to a specified height to obtain a quartz crucible with a port flatness of less than 5 mm.

[0026] In the specific implementation process, in step S2, the first cleaning of the blank quartz crucible includes: chemically cleaning the inner and outer surfaces of the blank quartz crucible, and then rinsing with high-pressure pure water after chemical cleaning. Specifically, the inner and outer surfaces of the quartz crucible are chemically cleaned by single acid or mixed acid of hydrofluoric acid, sulfuric acid, and hydrochloric acid, or alkaline cleaning is performed with sodium hydroxide solution, and then rinsing is performed with 0.1Mpa-5Mpa high-pressure pure water after chemical cleaning, so that on the one hand, the dirt on the inner and outer surfaces of the quartz crucible is removed, and on the other hand, the mechanical damage layer on the surface of the quartz crucible is removed, and the roughness of the surface of the quartz crucible is further reduced.

[0027] In the specific implementation process, in step S2, the outer surface of the blank quartz crucible is subjected to fire processing and polishing, including: using a flame polisher to perform fire processing and polishing on the outer surface of the blank quartz crucible to obtain a blank quartz crucible with an outer surface roughness Ra<5 microns. Specifically, the flame polisher uses the high-speed airflow and high-temperature gas generated during the combustion of a mixed gas of hydrogen and oxygen at high temperature to treat the surface of the material. During the combustion process, hydrogen will undergo an oxidation reaction, releasing a large amount of heat and water vapor. At the same time, the high-speed airflow and high-temperature gas generated can clean the impurities and oxide layer on the outer surface of the quartz crucible, thereby making the outer surface of the quartz crucible smoother, and the roughness of the outer surface of the quartz crucible is less than 5 microns. At the same time, the hardness of the outer surface of the quartz crucible can be increased by fire processing and polishing, making the quartz crucible more stable and durable, and increasing the service life of the quartz crucible. Among them, the hydrogen combustion heating temperature is greater than 1200°C.

[0028] In some embodiments, after the outer surface of the rough quartz crucible is subjected to fire processing and polishing, the rough quartz crucible needs to be second cleaned to further wash away the impurities generated by the fire processing and polishing. The second cleaning includes chemically cleaning the inner and outer surfaces of the quartz crucible with a single acid or a mixed acid of hydrofluoric acid, sulfuric acid, and hydrochloric acid, or alkaline cleaning with a sodium hydroxide solution, and then washing with 0.1Mpa-5Mpa high-pressure pure water after chemical cleaning. After washing, the impurity content of the inner and outer surfaces of the quartz crucible is less than 0.01ng / CM 2 , thereby reducing the impurities entering the silicon liquid and further improving the quality of crystalline silicon.

[0029] In the specific implementation process, in step S2, the process of drying the blank quartz crucible includes: drying the blank quartz crucible in an environment of 50-150°C.

[0030] A quartz crucible for continuously pulling crystalline silicon is prepared by the method for preparing the quartz crucible for continuously pulling crystalline silicon as described above. Example

[0031] Taking a quartz crucible with an outer diameter of 24 inches as an example, high-purity quartz sand is molded on the inner surface of the mold to form a quartz crucible shape. The current passed through the graphite electrode is 2100-2400A, and the voltage is 300-380V. The graphite electrode ionizes the gas to generate plasma to heat and melt the quartz sand. At the same time, during the melting process, a vacuum device is used to form a negative pressure zone of -0.06Mpa between the quartz sand particles to absorb the bubbles in the sand. After 12 minutes of melting, the power is turned off to obtain a rough quartz crucible with an inner surface roughness Ra less than 5 microns and an outer surface roughness Ra greater than 30 microns.

[0032] The outer surface of the blank quartz crucible is sandblasted, and the sandblasting medium is 20-100 mesh corundum sand. The corundum sand is transported and sprayed onto the outer surface of the quartz crucible by high-pressure gas with a pressure of 1.5Mpa, so as to obtain a quartz crucible with an outer surface roughness Ra of 15 microns to 30 microns. The outer surface of the quartz crucible is then ground with a 70-mesh oilstone to obtain a quartz crucible with an outer surface roughness Ra of 5 microns to 15 microns.

[0033] Furthermore, the quartz crucible is subjected to a height cutting process, and the rough edges of the port of the blank quartz crucible are cut by a cutting machine according to a height of 260 mm, so as to obtain a quartz crucible with a port flatness of 2-3 mm. After the cutting is completed, the quartz crucible is subjected to a first cleaning process, and the inner and outer surfaces of the quartz crucible are chemically cleaned for 15 minutes using 10% hydrofluoric acid, and then rinsed with 0.5Mpa high-pressure pure water after chemical cleaning. Then the outer surface of the quartz crucible is subjected to fire processing and polishing, such as Figure 2 As shown, the outer surface of the quartz crucible is fire-polished by spraying a mixture of hydrogen and oxygen in a pipeline to generate high heat, wherein the hydrogen combustion heating temperature is 1200-1700°C, and the outer surface roughness Ra of the quartz crucible after fire processing and polishing is less than 5 microns.

[0034] Finally, the quartz crucible is cleaned and dried for the second time. The inner and outer surfaces of the quartz crucible are chemically cleaned for 15 minutes using 10% hydrofluoric acid, and then rinsed with 0.5Mpa high-pressure pure water. After rinsing, the impurity content of the inner and outer surfaces of the quartz crucible is less than 0.01ng / CM 2 . After the second cleaning, the quartz crucible is placed in an environment of 105°C for drying to obtain a quartz crucible of the present invention with inner and outer surface roughness less than 5 microns and smooth mirror surfaces on both the inner and outer surfaces. When continuously pulling crystalline silicon, the quartz crucible prepared by the present invention is used as an inner quartz crucible, thereby reducing the oxygen brought into the silicon liquid by the quartz crucible during the pulling of crystalline silicon, reducing the oxygen content in the silicon liquid, and further reducing the oxygen content of the crystalline silicon, thereby improving the quality of the crystalline silicon.

[0035] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for preparing a quartz crucible for continuously pulling crystalline silicon, characterized in that: The following steps are involved: S1, arc melting quartz sand to obtain a rough quartz crucible with a smooth inner surface and a rough outer surface; S2. The rough quartz crucible is sequentially subjected to outer surface sandblasting, outer surface grinding, height cutting, first cleaning, outer surface fire processing and polishing, second cleaning, and drying steps to obtain a quartz crucible with an inner surface roughness Ra<5 microns and an outer surface roughness Ra<5 microns.

2. The method for preparing a quartz crucible for continuously pulling crystalline silicon according to claim 1, characterized in that: In step S1, arc melting is performed on quartz sand to obtain a rough quartz crucible with a smooth inner surface and a rough outer surface by the following steps: S11, stacking high-purity quartz sand on the inner wall of the mold, and applying power to the graphite electrode, so that the graphite electrode ionizes the gas to generate plasma to heat and melt the quartz sand; S12, using a vacuum device to remove bubbles in the gaps between quartz sand particles during the melting process; S13, turning off the power and stopping heating to obtain a rough quartz crucible with an inner surface roughness Ra<5 microns and an outer surface roughness Ra>30 microns.

3. The method for preparing a quartz crucible for continuously pulling crystalline silicon according to claim 1, characterized in that: In step S2, sandblasting the outer surface of the blank quartz crucible includes: sandblasting the outer surface of the blank quartz crucible with a 20-100 mesh sandblasting material to obtain a blank quartz crucible with an outer surface roughness Ra>15 microns.

4. The method for preparing a quartz crucible for continuously pulling crystalline silicon according to claim 1, characterized in that: In step S2, grinding the outer surface of the blank quartz crucible includes: grinding the outer surface of the blank quartz crucible with a 50-200 mesh polishing sheet to obtain a blank quartz crucible with an outer surface roughness Ra>5 microns.

5. The method for preparing a quartz crucible for continuously pulling crystalline silicon according to claim 1, characterized in that: In step S2, cutting the rough quartz crucible to a height comprises: using a cutting machine to cut the burrs of the rough quartz crucible port according to a specified height to obtain a quartz crucible with a port flatness less than 5 mm.

6. The method for preparing a quartz crucible for continuously pulling crystalline silicon according to claim 1, characterized in that: In step S2, the first cleaning of the blank quartz crucible includes: chemically cleaning the inner and outer surfaces of the blank quartz crucible, and then rinsing with high-pressure pure water after the chemical cleaning.

7. The method for preparing a quartz crucible for continuously pulling crystalline silicon according to claim 6, characterized in that: Chemical cleaning uses any one of hydrofluoric acid, sulfuric acid, hydrochloric acid, mixed acid, and sodium hydroxide solution.

8. The method for preparing a quartz crucible for continuously pulling crystalline silicon according to claim 1, characterized in that: In step S2, performing fire processing and polishing on the outer surface of the blank quartz crucible includes: performing fire processing and polishing on the outer surface of the blank quartz crucible using a flame polisher to obtain a blank quartz crucible with an outer surface roughness Ra<5 microns.

9. The method for preparing a quartz crucible for continuously pulling crystalline silicon according to any one of claims 1 to 7, characterized in that: In step S2, the process of drying the blank quartz crucible includes: drying the blank quartz crucible in an environment of 50-150°C.

10. A quartz crucible for continuously pulling crystalline silicon, characterized in that: The quartz crucible is prepared by the method for preparing a quartz crucible for continuously pulling crystalline silicon as described in any one of claims 1 to 9.

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