A method for producing a czochralski silicon single crystal
By combining regional solidification and the CUSP magnetic field, a solidified layer is formed to block oxygen release from the crucible and suppress silicon melt convection, thus solving the problem of preparing large-size ultra-low oxygen single crystals and achieving stable mass production of high-performance silicon single crystals.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA ELECTRONICS TECH GRP NO 46 RES INST
- Filing Date
- 2026-05-13
- Publication Date
- 2026-06-26
AI Technical Summary
Existing technologies struggle to achieve both large-size silicon single crystals with extremely low oxygen concentrations during Czochralski (CZ) growth. Traditional CZ methods have high oxygen content, while zone melting methods are costly and difficult to mass-produce stably.
By forming a solidified layer through zone solidification to block oxygen release from the crucible, and by combining this with a CUSP magnetic field to suppress silicon melt convection, large-size ultra-low oxygen single-crystal silicon can be prepared. The specific steps include material preparation, zone solidification, and single-crystal growth under a CUSP magnetic field.
Czochralski silicon single crystals with diameters of 200mm-300mm and oxygen content of <0.5E17atoms/cm3 were prepared to meet the requirements of high-performance power devices. The operation process is highly controllable and suitable for mass production.
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Figure CN122279731A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of single-crystal silicon preparation technology, and specifically discloses a method for preparing Czochralski-grown silicon single crystals. Background Technology
[0002] In the development of the semiconductor industry, monocrystalline silicon, as a core basic material, directly affects the reliability, carrier mobility, and electrical performance of devices due to its oxygen content. With the upgrading of power device technology, various devices relying on monocrystalline silicon substrates, such as insulated-gate bipolar transistors, are gradually developing towards higher performance. Low-oxygen monocrystalline silicon substrates can significantly reduce oxygen donor defects and avoid resistivity fluctuations and abnormal forward voltage drops after heat treatment. As the performance requirements for power devices continue to increase, the control of oxygen content in monocrystalline silicon becomes even more stringent.
[0003] Existing methods for preparing low-oxygen silicon single crystals are mainly divided into two categories: one is the zone melting method, which can produce silicon with an oxygen content of less than 1E17 atoms / cm³. 3 One method is the low-oxygen silicon single crystal method, but it is limited by the capabilities of high-frequency heating equipment and crystallization process, making it difficult to stably mass-produce silicon wafers of 200mm and above. Furthermore, the equipment cost is high and production efficiency is low. Another method is the Czochralski method, which can mass-produce silicon wafers of 200mm and above at low cost. However, the quartz crucible (mainly composed of SiO2) melts at temperatures above 1414℃, releasing oxygen atoms that convection into the single crystal growth interface with the molten silicon, resulting in an oxygen content between 4E17 atoms / cm³. 3 -10E17atoms / cm 3 It cannot meet the requirements for extremely low oxygen levels.
[0004] Therefore, the existing preparation methods have obvious defects, and how to prepare large-size, extremely low oxygen concentration Czochralski silicon single crystals has become a technical problem that urgently needs to be solved in this field. Summary of the Invention
[0005] To address the challenge of achieving both large-size and extremely low-oxygen single-crystal silicon in existing technologies, this invention provides a method for preparing Czochralski silicon single crystals. This method involves preparing ultra-low-oxygen single-crystal silicon through chemical preparation, zone solidification, and single-crystal growth under a CUSP magnetic field. The solidified layer blocks oxygen released during high-temperature melting in the crucible, while the CUSP magnetic field suppresses silicon melt convection, reducing oxygen migration to the growth interface, thus enabling the preparation of large-size ultra-low-oxygen single-crystal silicon. Through the synergistic effect of various steps and parameters, the Czochralski silicon single-crystal preparation method provided by this invention can produce silicon with a diameter of 200mm-300mm and an oxygen content <0.5E17 atoms / cm². 3 The Czochralski-grown silicon single crystal combines the requirements of large size and extremely low oxygen, meeting the development needs of power devices for high-performance silicon single crystal substrates.
[0006] This invention provides a method for preparing Czochralski-grown silicon single crystals, comprising the following steps: S1. Load the polycrystalline silicon material into a quartz crucible, start the upper and lower heaters to melt the material, so that the polycrystalline silicon material is completely melted to form a silicon melt; S2. Reduce the power of the lower heater, increase the power of the upper heater, and adjust the position of the heater so that the silicon melt at the bottom of the crucible solidifies to form a solidified layer, while the silicon melt at the top of the crucible remains in a molten state. S3. Apply a CUSP magnetic field so that the zero magnetic force surface of the CUSP is located above the surface of the silicon melt, and the magnetic field strength at the interface between the solidified layer and the silicon melt is equal to the CUSP magnetic field strength. Then perform crystal pulling, shoulder formation, constant diameter growth, and tailing to obtain Czochralski silicon single crystal.
[0007] In this invention, reducing the power of the lower heater and increasing the power of the upper heater in step S2 creates a temperature gradient between the low-temperature zone at the bottom of the crucible and the high-temperature zone at the top. This causes the temperature of the silicon melt at the bottom of the crucible to drop below its solidification point, forming a solidified layer, while simultaneously maintaining the upper silicon melt in a molten state, achieving regional solidification. Furthermore, adjusting the heater position further adjusts the heat distribution, allowing the bottom melt to crystallize at a certain rate. The solidified layer formed adheres tightly to the inner wall of the quartz crucible, acting as a physical barrier to effectively prevent oxygen atoms released from the melting of the quartz crucible from entering the upper molten silicon melt. This avoids oxygen contamination caused by oxygen atoms mixing into the melt, thereby reducing the oxygen content in the silicon melt and solving the problem of high oxygen content in single crystals caused by oxygen released from the quartz crucible directly entering the melt in the traditional Czochralski method.
[0008] In this invention, a CUSP magnetic field is applied in S3 and the zero magnetic force surface of the magnetic field is controlled to be above the surface of the silicon melt. At the same time, the magnetic field strength at the interface between the solidified layer and the silicon melt is equal to the CUSP magnetic field strength. This allows the magnetic field to concentrate the constraint effect of the silicon melt on the single crystal growth region. By suppressing the convection movement of the silicon melt, the migration of residual oxygen atoms in the melt to the solid-liquid growth interface is reduced, and oxygen atoms are prevented from embedding into the growing single crystal lattice, thereby reducing the oxygen content of the single crystal.
[0009] In this invention, the equal diameter stage of S3 increases the power of the lower heater to slowly melt the solidified layer. On the one hand, it can continuously provide sufficient silicon melt for equal diameter growth and prevent single crystal diameter fluctuations caused by insufficient melt. On the other hand, the slow melting rate can avoid disturbance of the melt due to sudden temperature changes and maintain the stability of the solid-liquid interface.
[0010] This invention achieves a dual oxygen-blocking synergistic effect by using a solidified layer to block oxygen release from the crucible and CUSP magnetic field confinement to reduce oxygen entering the melt. The synergistic effect of these two factors ensures the preparation of Czochralski silicon single crystals with larger diameters.
[0011] Preferably, in S1, during the process of loading the polycrystalline silicon material into the quartz crucible, blocky silicon material with a particle size of 45-100mm is placed at the bottom of the crucible, granular silicon material with a particle size of 30-45mm is placed in the middle layer, and fine silicon material with a particle size of 5-30mm is placed on the surface layer.
[0012] Preferably, in S1, the power of the upper heater is 48-52kW and the power of the lower heater is 43-47kW.
[0013] In this invention, the power difference between the upper and lower heaters in S1 can suppress the violent convection of the silicon melt during the melting process, reduce the mixing of impurities caused by melt disturbance, and ensure the purity of the silicon melt.
[0014] More preferably, the mass ratio of the blocky silicon material, granular silicon material and fine silicon material is (50-60):(25-35):(10-15).
[0015] In this invention, S1, by limiting the particle size of polycrystalline silicon, can prevent metallic impurities (such as iron, copper, etc.) and non-metallic impurities (such as carbon, boron, etc.) from embedding into the single crystal lattice during the crystallization process to form carrier recombination centers or structural defects.
[0016] Preferably, in S2, the power of the upper heater is increased to 70-75kW, and the power of the lower heater is reduced to 5-10kW.
[0017] Preferably, in S2, the specific operation of adjusting the position of the heater is to move the upper heater up by 12-18mm and the lower heater down by 9-11mm.
[0018] Preferably, in S2, the temperature at the bottom of the crucible is 1400-1412℃.
[0019] Preferably, in S2, the surface temperature of the silicon melt is 1420-1450℃.
[0020] In this invention, S2 limits the power of the upper and lower heaters and the temperature at the bottom of the crucible, ensuring that the temperature at the bottom of the crucible is below the melting point of silicon. This satisfies the requirement for solidification of the silicon melt at the bottom of the crucible. Simultaneously, the temperature range has a small difference from the melting point, preventing excessively rapid solidification due to excessively low temperatures. This, in turn, prevents structural defects such as pores and cracks from forming in the solidified layer due to stress concentration during crystallization. Furthermore, the solidified layer formed by the solidification of the silicon melt effectively blocks the migration of oxygen atoms to the molten silicon melt at the top of the crucible, thereby reducing the oxygen content of the silicon melt.
[0021] Preferably, in S3, the zero magnetic field surface of the CUSP is located 10-40 mm above the surface of the molten silicon.
[0022] Preferably, in S3, the current ratio of the upper and lower coils of the CUSP magnetic field device is 1:1, and the magnetic field strength of the CUSP magnetic field is 1000-1200 Gs.
[0023] In this invention, by limiting the strength of the CUSP magnetic field in S3, the suppression effect of melt convection can cover the entire solid-liquid interface. At the same time, it can avoid the magnetic field strength being too low, which would not be able to effectively prevent the residual oxygen atoms in the silicon melt from migrating to the solid-liquid growth interface and causing oxygen atoms to embed into the single crystal lattice. It can also avoid the magnetic field strength being too high, which would cause defects such as resistivity fluctuations and dislocations in the single crystal.
[0024] Preferably, in S3, the crystal pulling rate during the crystal pulling process is 250-300 mm / h.
[0025] Preferably, in S3, during the shoulder formation process, the crystal pulling rate is 200-220 mm / h, and the crystal diameter increase rate is 0.05-0.1 mm / min.
[0026] Preferably, in S3, during the constant diameter growth process, the crystal pulling rate is 40-70 mm / h, the upper heater power reduction rate is 0.3-0.5 kW / h, and the lower heater power increase rate is 0.1-0.3 kW / h.
[0027] In this invention, S3, by limiting the rate of increase of the heater power, enables the solidified layer to melt at a uniform rate, avoiding the problem of rapid melting of the solidified layer due to excessively rapid increase of the rate, which would lead to a sudden increase in the volume of the silicon melt and intensified convection. This would disrupt the inhibitory effect of the CUSP magnetic field on melt convection, causing residual oxygen atoms in the melt to migrate back to the solid-liquid growth interface. At the same time, it can avoid the problem of uneven melt composition and temperature distribution caused by rapid melting, which would generate dislocations during single crystal crystallization.
[0028] In this invention, S3, by limiting the crystal pulling rate of constant diameter growth, can avoid both excessively high crystal pulling rates, which would prevent single crystal atoms from arranging themselves in an orderly manner due to the rapid crystallization rate, resulting in structural defects such as dislocations and vacancies in the crystal, and excessively fast growth rates would also disrupt the stability of the solid-liquid interface, making it easier for residual oxygen atoms in the silicon melt to be carried into the single crystal lattice; and excessively low crystal pulling rates, which would lead to prolonged contact time between the quartz crucible and the silicon melt at high temperatures, increasing the risk of additional oxygen release from the crucible, and prolonged static placement of the melt could easily cause uneven solute distribution, resulting in deviations in the electrical properties of the center and edges of large-size single crystals, affecting the uniformity of the entire substrate.
[0029] Preferably, in S3, after equal diameter growth, the current ratio of the upper and lower coils of the CUSP magnetic field device is 1:1-1.5, and the magnetic field strength of the CUSP magnetic field is 1450-1550 Gs.
[0030] More preferably, in S3, after equal diameter growth, the current ratio of the upper and lower coils of the CUSP magnetic field device is 1:1.3.
[0031] In this invention, uniformly increasing the current in the lower coil compensates for the weakening of the magnetic field caused by the descent of the melt during constant-diameter growth. This ensures that the zero magnetic field plane of the CUSP magnetic field remains stable near the solid-liquid interface, allowing oxygen to volatilize through SiO under the influence of the zero magnetic field plane. Simultaneously, the strong edge magnetic field suppresses the migration of oxygen atoms to the growth interface, thereby reducing the oxygen content of the prepared single crystal. Furthermore, uniformly adjusting the current avoids sudden changes in the magnetic field, which could lead to turbulent melt convection. This maintains a smooth solid-liquid interface, ensuring that the single crystal diameter fluctuation meets requirements and reducing dislocation problems. Additionally, by enhancing the suppression effect of the magnetic field at the crucible edge, this invention prevents the migration of newly released oxygen atoms from the crucible after the solidified layer melts in the later stages of constant-diameter growth, thus ensuring a consistently low oxygen content in the prepared single crystal.
[0032] Preferably, in S3, the crystal pulling rate is 15-25 mm / h during the finishing process.
[0033] In this invention, S3 can effectively shorten the contact time between the top of the single crystal and the high-temperature silicon melt by limiting the crystal pulling rate at the end, and avoid the oxygen atoms released by the continuous high-temperature dissolution of the quartz crucible during the end process from further penetrating into the top of the single crystal.
[0034] In summary, this invention provides a method for preparing Czochralski-grown silicon single crystals. By using a solidified layer formed through zone solidification to physically isolate the silicon and prevent high oxygen content due to crucible oxygen release, and by employing the zero-magnetic-force surface of the CUSP magnetic field to facilitate oxygen volatilization and the strong edge magnetic field to suppress oxygen atom migration to the growth interface, large-size, extremely low-oxygen-content single-crystal silicon can be prepared. This solves the problem of the existing zone melting method's difficulty in stably mass-producing large-size, low-oxygen-content single-crystal silicon. The preparation method provided by this invention does not require special high-frequency heating equipment, offers strong controllability of parameters during operation, and can stably meet the dual requirements of large size and extremely low oxygen content, making it suitable for large-scale production and satisfying the development needs of power devices for high-performance silicon single-crystal substrates. Attached Figure Description
[0035] Figure 1 This is a comparison chart of the oxygen content of the Czochralski silicon single crystal obtained in Example 1 and the ordinary single crystal. Detailed Implementation
[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0037] Example 1 This embodiment provides a method for preparing Czochralski-grown silicon single crystals, specifically including the following: The method for preparing the Czochralski silicon single crystal includes the following steps: S1. Equip the Czochralski single crystal furnace with an upper heater, a lower heater, and a CUSP magnetic field device. Place 100kg of block silicon material with a particle size of 45-100mm at the bottom of the quartz crucible, fill the middle layer with 50kg of granular silicon material with a particle size of 30-45mm, and lay 20kg of fine silicon material with a particle size of 5-30mm on the surface. Start the upper heater and the lower heater to melt the material, so that the power of the upper heater is 48kW and the power of the lower heater is 43kW, so that the polycrystalline silicon material is completely melted. S2. Increase the power of the upper heater to 70kW and decrease the power of the lower heater to 5kW. Adjust the position of the heaters, move the upper heater up by 15mm and the lower heater down by 10mm, so that the temperature of the bottom of the crucible is 1400℃, so that the silicon melt at the bottom of the crucible solidifies to form a solidified layer, so that the temperature of the silicon melt surface is 1420℃, and so that the silicon melt in the upper part of the crucible remains in a molten state. S3. Apply a CUSP magnetic field so that the zero magnetic force plane of the CUSP magnetic field is 10mm above the surface of the molten silicon. Simultaneously, set the current ratio of the upper and lower coils of the CUSP magnetic field device to 1:1, and the magnetic field strength of the CUSP magnetic field to 1000 Gs. Ensure the magnetic field strength at the interface between the solidified layer and the molten silicon is equal to the CUSP magnetic field strength. Then, perform crystal pulling at a rate of 250mm / h. When the crystal pulling length is ≥250mm and the crystal neck diameter is 8mm, perform shoulder formation at a pulling rate of 200mm / h, with a crystal diameter increase rate of 0.05mm / min. When the single crystal diameter is 2... At 00mm, constant diameter growth is performed at a crystal pulling rate of 40mm / h. The power of the upper heater decreases at a rate of 0.3kW / h, and the power of the lower heater increases at a rate of 0.1kW / h. This increases the power of the lower heater during the constant diameter stage to slowly melt the solidified layer. During constant diameter growth, the current of the lower coil is increased at a uniform rate. When constant diameter growth ends, the current ratio of the upper and lower coils of the CUSP magnetic field device is set to 1:1.3, and the magnetic field strength of the CUSP magnetic field is set to 1450Gs. When the single crystal length is 1.5m, the crystal pulling process is completed at a rate of 15mm / h, yielding a Czochralski silicon single crystal.
[0038] Example 2 This embodiment provides a method for preparing Czochralski-grown silicon single crystals, specifically including the following: The method for preparing the Czochralski silicon single crystal includes the following steps: S1. Equip the Czochralski single crystal furnace with an upper heater, a lower heater, and a CUSP magnetic field device. Place 120kg of block silicon material with a particle size of 45-100mm at the bottom of the quartz crucible, fill the middle layer with 60kg of granular silicon material with a particle size of 30-45mm, and lay 20kg of fine silicon material with a particle size of 5-30mm on the surface. Start the upper heater and the lower heater to melt the material, so that the power of the upper heater is 52kW and the power of the lower heater is 47kW, so that the polycrystalline silicon material is completely melted. S2. Increase the power of the upper heater to 75kW and decrease the power of the lower heater to 10kW. Adjust the position of the heaters, move the upper heater up by 15mm and the lower heater down by 10mm, so that the temperature of the bottom of the crucible is 1412℃, so that the silicon melt at the bottom of the crucible solidifies to form a solidified layer, so that the temperature of the silicon melt surface is 1450℃, and so that the silicon melt in the upper part of the crucible remains in a molten state. S3. Apply a CUSP magnetic field so that the zero magnetic force plane of the CUSP magnetic field is 40mm above the surface of the molten silicon. Simultaneously, set the current ratio of the upper and lower coils of the CUSP magnetic field device to 1:1, and the magnetic field strength of the CUSP magnetic field to 1200 Gs. The magnetic field strength at the interface between the solidified layer and the molten silicon is equal to the CUSP magnetic field strength. Then, perform crystal pulling at a rate of 300 mm / h. When the crystal pulling length is ≥250mm and the crystal neck diameter is 10mm, perform shoulder formation at a pulling rate of 220mm / h, with a crystal diameter increase rate of 0.1mm / min. When the single crystal diameter is... At 300mm, constant diameter growth is performed at a crystal pulling rate of 70mm / h. The power of the upper heater decreases at a rate of 0.5kW / h, and the power of the lower heater increases at a rate of 0.3kW / h. This increases the power of the lower heater during the constant diameter stage to slowly melt the solidified layer. During constant diameter growth, the current of the lower coil is increased at a uniform rate. When constant diameter growth ends, the current ratio of the upper and lower coils of the CUSP magnetic field device is set to 1:1.3, and the magnetic field strength of the CUSP magnetic field is set to 1550Gs. When the single crystal length is 2m, the crystal pulling process is completed at a rate of 25mm / h, yielding a Czochralski silicon single crystal.
[0039] Example 3 This embodiment provides a method for preparing Czochralski-grown silicon single crystals, specifically including the following: The method for preparing the Czochralski silicon single crystal includes the following steps: S1. Equip the Czochralski single crystal furnace with an upper heater, a lower heater, and a CUSP magnetic field device. Place 110kg of block silicon material with a particle size of 45-100mm at the bottom of the quartz crucible, fill the middle layer with 60kg of granular silicon material with a particle size of 30-45mm, and lay 30kg of fine silicon material with a particle size of 5-30mm on the surface. Start the upper heater and the lower heater to melt the material, so that the power of the upper heater is 50kW and the power of the lower heater is 45kW, so that the polycrystalline silicon material is completely melted. S2. Increase the power of the upper heater to 73kW and decrease the power of the lower heater to 7kW. Adjust the position of the heaters, move the upper heater up by 15mm and the lower heater down by 10mm, so that the temperature of the bottom of the crucible is 1407℃, so that the silicon melt at the bottom of the crucible solidifies to form a solidified layer, so that the temperature of the silicon melt surface is 1435℃, and so that the silicon melt in the upper part of the crucible remains in a molten state. S3. Apply a CUSP magnetic field so that the zero magnetic force plane of the CUSP magnetic field is 25mm above the surface of the molten silicon. Simultaneously, set the current ratio of the upper and lower coils of the CUSP magnetic field device to 1:1, and the magnetic field strength of the CUSP magnetic field to 1100 Gs. The magnetic field strength at the interface between the solidified layer and the molten silicon is equal to the CUSP magnetic field strength. Then, perform crystal pulling at a rate of 270 mm / h. When the crystal pulling length is ≥250 mm and the crystal neck diameter is 9 mm, perform shoulder formation at a pulling rate of 210 mm / h, with a crystal diameter increase rate of 0.07 mm / min. When the single crystal diameter is 2... At 50mm, constant diameter growth is performed at a crystal pulling rate of 55mm / h. The power of the upper heater decreases at a rate of 0.4kW / h, and the power of the lower heater increases at a rate of 0.2kW / h. This increases the power of the lower heater during the constant diameter stage to slowly melt the solidified layer. During constant diameter growth, the current of the lower coil is increased at a uniform rate. When constant diameter growth ends, the current ratio of the upper and lower coils of the CUSP magnetic field device is set to 1:1.3, and the magnetic field strength of the CUSP magnetic field is set to 1500Gs. When the single crystal length is 1.7m, the crystal pulling process is completed at a rate of 20mm / h, yielding a Czochralski silicon single crystal.
[0040] Comparative Example 1 This comparative example provides a method for preparing silicon single crystals, specifically including the following: The method for preparing the Czochralski silicon single crystal includes the following steps: S1. Equip a heater and a CUSP magnetic field device in the Czochralski single crystal furnace. Place 110kg of block silicon material with a particle size of 45-100mm at the bottom of the quartz crucible, fill the middle layer with 60kg of granular silicon material with a particle size of 30-45mm, and lay 30kg of fine silicon material with a particle size of 5-30mm on the surface. Start the heater to melt the material, so that the heater power is 50kW, and the polycrystalline silicon material is completely melted. S2. Apply a CUSP magnetic field so that the zero magnetic force plane of the CUSP magnetic field is located at the surface of the silicon melt, and then perform crystal pulling at a rate of 270 mm / h. When the crystal pulling length is ≥250 mm and the crystal neck diameter is 9 mm, shoulder formation is performed at a rate of 210 mm / h, with the crystal diameter increasing at a rate of 0.07 mm / min. When the single crystal diameter is 250 mm, constant diameter growth is performed at a rate of 55 mm / h. During constant diameter growth, the current of the lower coil is increased at a uniform rate. When constant diameter growth ends, the ratio of the upper and lower coil currents of the CUSP magnetic field device is set to 1:1.3, and the magnetic field strength of the CUSP magnetic field is set to 1500 Gs. When the single crystal length is 1.7 m, the crystal pulling is completed at a rate of 20 mm / h, resulting in a Czochralski silicon single crystal.
[0041] Comparative Example 2 This comparative example provides a method for preparing Czochralski-grown silicon single crystals, specifically including the following: The method for preparing the Czochralski silicon single crystal includes the following steps: S1. Equip an upper heater and a lower heater in a Czochralski single crystal furnace. Place 110kg of blocky silicon material with a particle size of 45-100mm at the bottom of the quartz crucible, fill the middle layer with 60kg of granular silicon material with a particle size of 30-45mm, and lay 30kg of fine silicon material with a particle size of 5-30mm on the surface. Start the upper heater and the lower heater to melt the material, so that the power of the upper heater is 50kW and the power of the lower heater is 45kW, so that the polycrystalline silicon material is completely melted. S2. Increase the power of the upper heater to 73kW and decrease the power of the lower heater to 7kW. Adjust the position of the heaters, move the upper heater up by 15mm and the lower heater down by 10mm, so that the temperature of the bottom of the crucible is 1407℃, so that the silicon melt at the bottom of the crucible solidifies to form a solidified layer, so that the temperature of the silicon melt surface is 1435℃, and so that the silicon melt in the upper part of the crucible remains in a molten state. S3. Perform crystal pulling at a rate of 270 mm / h. When the crystal length is ≥250 mm and the neck diameter is 9 mm, perform shoulder formation at a rate of 210 mm / h. The crystal diameter increases at a rate of 0.07 mm / min. When the single crystal diameter is 250 mm, perform constant diameter growth at a rate of 55 mm / h. The upper heater power decreases at a rate of 0.4 kW / h, and the lower heater power increases at a rate of 0.2 kW / h. This increases the power of the lower heater during the constant diameter stage to slowly melt the solidified layer. When the single crystal length is 1.7 m, perform finishing at a rate of 20 mm / h to obtain a Czochralski silicon single crystal.
[0042] To further verify the technical effect of the present invention, the oxygen content of the Czochralski silicon single crystals in Examples 1-3 and Comparative Examples 1-2 was detected according to GB / T 35306-2023 "Determination of Carbon and Oxygen Content in Silicon Single Crystals - Low Temperature Fourier Transform Infrared Spectroscopy". The detection results are shown in Table 1.
[0043] Table 1 Oxygen content detection results
[0044] The present invention also compares the Czochralski silicon single crystal obtained in Example 1 with ordinary single crystals prepared by existing techniques, and the results are shown in Table 2 and... Figure 1 As shown.
[0045] Table 2. Oxygen content detection results for normal single crystal and Czochralski silicon single crystal.
[0046] According to Table 2 and Figure 1 It can be seen that the Czochralski silicon single crystals prepared by the method of the present invention have extremely low oxygen content, with the lowest oxygen content reaching 0.31E17 atoms / cm. 3 More than half of the single crystals in the entire crystal have an oxygen content of less than 0.5E17 atoms / cm². 3 The oxygen content only rises rapidly at the tail of the single crystal, but it is still lower than the normal level of ordinary Czochralski single crystal. The reason for the rapid rise in oxygen content at the tail of the single crystal is mainly that there is very little melt in the quartz crucible at the tail of the single crystal, and regional melting cannot be achieved. At this time, the silicon in the crucible is completely melted and there is no solid layer, so the oxygen content of the single crystal increases.
[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing Czochralski-grown silicon single crystals, characterized in that, Includes the following steps: S1. Load the polycrystalline silicon material into a quartz crucible, start the upper and lower heaters to melt the material, so that the polycrystalline silicon material is completely melted to form a silicon melt; S2. Reduce the power of the lower heater, increase the power of the upper heater, and adjust the position of the heater so that the silicon melt at the bottom of the crucible solidifies to form a solidified layer, while the silicon melt at the top of the crucible remains in a molten state. S3. Apply a CUSP magnetic field so that the zero magnetic force surface of the CUSP is located above the surface of the silicon melt, and the magnetic field strength at the interface between the solidified layer and the silicon melt is equal to the CUSP magnetic field strength. Then perform crystal pulling, shoulder formation, constant diameter growth, and tailing to obtain Czochralski silicon single crystal.
2. The method for preparing Czochralski-grown silicon single crystals according to claim 1, characterized in that, In S1, during the process of loading the polycrystalline silicon material into the quartz crucible, blocky silicon material with a particle size of 45-100mm is placed at the bottom of the crucible, granular silicon material with a particle size of 30-45mm is placed in the middle layer, and fine silicon material with a particle size of 5-30mm is placed on the surface layer. In S1, the power of the upper heater is 48-52kW, and the power of the lower heater is 43-47kW.
3. The method for preparing Czochralski-grown silicon single crystals according to claim 2, characterized in that, The mass ratio of the blocky silicon material, granular silicon material and fine silicon material is (50-60):(25-35):(10-15).
4. The method for preparing Czochralski-grown silicon single crystals according to claim 1, characterized in that, In S2, the power of the upper heater is increased to 70-75kW, and the power of the lower heater is reduced to 5-10kW; In S2, the specific operation for adjusting the position of the heater is to move the upper heater up by 12-18mm and the lower heater down by 9-11mm. In S2, the temperature at the bottom of the crucible is 1400-1412℃; In S2, the surface temperature of the silicon melt is 1420-1450℃.
5. The method for preparing Czochralski-grown silicon single crystals according to claim 1, characterized in that, In S3, the zero magnetic force surface of the CUSP is positioned 10-40 mm above the surface of the molten silicon. In S3, the current ratio of the upper and lower coils of the CUSP magnetic field device is 1:1, and the magnetic field strength of the CUSP magnetic field is 1000-1200Gs.
6. The method for preparing Czochralski-grown silicon single crystals according to claim 1, characterized in that, In S3, during the crystal pulling process, the crystal pulling rate is 250-300 mm / h.
7. The method for preparing Czochralski-grown silicon single crystals according to claim 1, characterized in that, In S3, during the shoulder formation process, the crystal pulling rate is 200-220 mm / h, and the crystal diameter increase rate is 0.05-0.1 mm / min.
8. The method for preparing Czochralski-grown silicon single crystals according to claim 1, characterized in that, In S3, during the constant diameter growth process, the crystal pulling rate is 40-70 mm / h, the upper heater power reduction rate is 0.3-0.5 kW / h, and the lower heater power increase rate is 0.1-0.3 kW / h.
9. The method for preparing Czochralski-grown silicon single crystals according to claim 1, characterized in that, In S3, after equal diameter growth, the current ratio of the upper and lower coils of the CUSP magnetic field device is 1:1-1.5, and the magnetic field strength of the CUSP magnetic field is 1450-1550 Gs.
10. The method for preparing Czochralski-grown silicon single crystals according to claim 1, characterized in that, In S3, during the finishing process, the crystal pulling rate is 15-25 mm / h.