Method for preparing monocrystalline silicon ingot by recovering seed crystal
By optimizing the cutting and laying method of recovered seed crystals, the defect density and metal pollution problems of seed crystal recovery methods in the prior art are solved, the quality and production efficiency of cast single crystal silicon ingots are improved, and high-efficiency and low-cost single crystal silicon production is achieved.
Patent Information
- Application Number
- CN202510363348.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-26
- Publication Date
- 2025-07-04
AI Technical Summary
The existing seed crystal recovery methods have problems such as high defect density, metal pollution and poor performance, resulting in poor quality of cast single crystal silicon ingots, affecting production yield and electrical performance.
By accurately controlling the cutting direction and laying method of recovered seed crystals, select the growth surface crystal direction as <110> and the side crystal direction is <100> or <110>, and cut and recover the seed crystals away from the splicing seam. Combined with the temperature control of 1350-1500℃ and the cutting distance of 10-50mm, the casting process is optimized to form a new cast single crystal silicon ingot.
Significantly reduce defect density, reduce metal pollution, improve the electrical performance and production yield of cast single crystal silicon ingots, improve the conversion efficiency of solar cells, and reduce production costs.
Smart Images
Figure CN120250135A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of silicon material production, and more particularly, to a method for preparing a single crystal silicon ingot by recycling seed crystals. Background Art
[0002] In the current solar energy material market, crystalline silicon materials dominate, especially single crystal silicon and polycrystalline silicon. Single crystal silicon cells have higher conversion efficiency due to their lower impurity and defect content. However, the preparation process of single crystal silicon is complex and requires extremely high purity of raw materials, resulting in relatively high production costs. In contrast, cast single crystal silicon, as a product that combines the high conversion efficiency of single crystal silicon and the high cost performance of polycrystalline silicon, has been widely used in recent years. Cast single crystal silicon not only has a certain crystal orientation, fewer grain boundaries and low dislocation density, but also adopts an alkaline texturing process, significantly improving the conversion efficiency, approaching that of single crystal silicon cells, and the production cost is much lower than that of traditional single crystal silicon.
[0003] In the production process of cast single crystal silicon, a certain amount of single crystal seed crystals are usually laid at the bottom of the crucible. By heating, the seed crystals are incompletely melted, and then the temperature gradient is controlled to enable the silicon material crystals to grow on the incompletely melted seed crystals. In this process, the quality of the seed crystals has a decisive impact on the performance of the final cast single crystal silicon ingot. In particular, the source and quality of the seed crystals are directly related to the defect density and electrical properties of the silicon ingot. However, the seed crystals required for the current preparation of cast single crystal silicon are usually prepared by the Czochralski method or other high-cost methods, resulting in a relatively high price of single crystal seed crystals and increasing the production cost of cast single crystal silicon. Therefore, recycling used single crystal seed crystals has become a common means to reduce costs.
[0004] The existing seed crystal recycling methods usually cut the silicon ingot into several silicon blocks with a cutting wire after the preparation of the cast single crystal silicon ingot is completed, and then cut out a part of the area perpendicular to the growth direction as the recycled seed crystals, as Figure 1 shown, Figure 1 which is a schematic diagram of the existing seed crystal recycling process. These recycled seed crystals will be re-laid at the bottom of the crucible and continue to be used for the next round of casting. However, there are some technical bottlenecks in the existing recycling methods. As Figure 1As shown in the figure, first of all, there are often high metal impurities at the bottom of the silicon ingot. And during the recycling process, due to operations such as cutting and splicing, it is easy to introduce a high dislocation density. These dislocations often extend along the growth direction, thus affecting the crystal quality of the recycled seed crystal and resulting in a high defect density in the recycled single-crystal silicon ingot. In addition, due to the uneven stress and temperature distribution in the splicing seam area, the performance of the recycled seed crystal is difficult to compare with that of the newly made seed crystal, resulting in many electrical defects in the recycled cast single-crystal silicon ingot, thereby reducing the production yield. More seriously, during the casting process, due to the metal contamination and high defect density problems of the recycled seed crystal, the minority carrier lifetime of the finally cast single-crystal silicon is significantly reduced, affecting the conversion efficiency and product performance of the battery. This problem makes the existing recycling technologies difficult to meet the requirements of large-scale and high-quality cast single-crystal silicon production.
[0005] In summary, the existing seed crystal recycling methods are difficult to effectively avoid metal impurity contamination and excessive defect density while reducing costs, which has a serious impact on the quality and production efficiency of cast single-crystal silicon ingots. In order to improve the quality of recycled single-crystal seeds, reduce metal contamination, and lower the defect density, a new type of seed crystal recycling method is urgently needed, which can effectively solve the defects in the existing recycling technologies. Summary of the Invention
[0006] The technical problem to be solved by the present invention is to provide a method for preparing a single-crystal silicon ingot from recycled seed crystals to solve the problems of high defect density, metal contamination, and poor performance of recycled seed crystals in the existing conventional methods, thereby improving the electrical properties and production yield of cast single-crystal silicon ingots.
[0007] To overcome the defects of the above prior art, the present invention provides a method for preparing a single-crystal silicon ingot from recycled seed crystals, including the following steps: S1: Seed crystal laying: Provide a crucible, and splice and lay multiple single-crystal silicon seed crystals with a growth plane crystal orientation of <110> at the bottom of the crucible to form a seed crystal layer; S2: Growth of cast single-crystal silicon ingot: Fill silicon material above the seed crystal layer processed in the step S1, and by controlling the temperature in the crucible, make the silicon material melt and grow along the crystal orientation structure of the incompletely melted seed crystal to obtain a cast single-crystal silicon ingot with a <110> growth crystal orientation; S3: Ingot cutting: Take out the cast single-crystal silicon ingot obtained in the step S2, and cut it into multiple silicon blocks along the growth direction; S4: Recycled seed crystal cutting: Cut the silicon blocks obtained in the step S3, cut off the areas with lower minority carrier lifetime at the bottom and top of the silicon blocks, and at a position away from the seed crystal splicing seam area, cut along a direction parallel to the growth direction and with a side crystal orientation of <100> or <110> to obtain recycled seed crystals; S5: Recycled seed crystal laying: The recycled seed crystals with the same surface crystal orientation are closely spliced and laid to form a recycled seed crystal layer. Silicon material is laid above the recycled seed crystal layer, and the temperature in the crucible is controlled so that the recycled seed crystals do not completely melt. At the same time, the molten silicon liquid grows along the crystal orientation structure of the recycled seed crystals, and finally a new cast single crystal silicon ingot is obtained.
[0008] A method for preparing a single crystal silicon ingot from recycled seed crystals in this application optimizes the key technical links in the traditional recycling process by precisely controlling the cutting direction, cutting position and laying method of the recycled seed crystals, significantly improves the quality and production efficiency of preparing cast single crystal silicon ingots from recycled seed crystals, solves the problems of metal contamination and too high defect density in the prior art. The method for recycling seed crystals for cast single crystals provided by the present invention has the following advantages compared with the prior art: Effectively reduce the defect density: By cutting the recycled seed crystals from a single crystal silicon ingot with a <110> growth crystal orientation, cutting the recycled seed crystals parallel to the growth direction in the area far from the seed crystal splicing seam and with a <100> or <110> crystal orientation on the side, the defect density in the recycled seed crystals can be effectively reduced. The seed crystals recycled by this method can improve the crystal quality of the new cast single crystal silicon ingot; Reduce metal contamination: In the traditional seed crystal recycling method, due to the usually high metal impurities at the bottom of the silicon ingot, the metal contamination in the seed crystals recycled from the bottom area of the silicon ingot is relatively serious. The above technical solution of the present invention optimizes the cutting position of the recycled seed crystals by removing the metal impurity enrichment areas at the bottom and top of the silicon block, and can effectively reduce the introduction of metal impurities, improving the purity and yield of the newly prepared cast single crystal silicon. Improve electrical properties: The above technical solution of the present invention reduces the metal impurities and defect density in the recycled seed crystals, and finally the minority carrier lifetime and electrical properties of the obtained cast single crystal silicon ingot are relatively high, which can improve the conversion efficiency of solar cells and provide a cost-effective solution for the solar energy industry.
[0009] In a possible implementation manner of seed crystal laying, in step S1, the crystal orientation of the seed crystal growth surface is <110>, the crystal orientations of the sides of the seed crystal layer are <100> and <110> respectively, and the crystal orientations of the sides of adjacent recycled seed crystals are the same.
[0010] Compared with the prior art, in the technical solution of the present invention, a seed crystal with a growth plane crystal orientation of <110> is selected for laying, which can promote the formation of a cast single crystal silicon ingot with a <110> crystal orientation. This crystal orientation structure has obvious advantages during the crystal growth process, especially in terms of the propagation path of dislocations. Compared with the cast single crystal silicon grown with a non-<110> crystal orientation, in the crystal grown with a <110> crystal orientation, crystal defects such as dislocations and small-angle grain boundaries in the splicing seam area tend to expand more vertically along the growth direction, and the lateral expansion range is significantly narrowed, thereby effectively slowing down the propagation trend of defects in the cross-section of the silicon ingot. Further, by reasonably arranging the <100> or <110> crystal orientation on the side surface of the seed crystal, the obtained cast single crystal silicon ingot can obtain recycled seed crystals with consistent crystal orientations during subsequent cutting and recycling, which is convenient for stable reuse, and at the same time improves the structural integrity and crystal quality of the recycled seed crystals.
[0011] In a possible implementation manner, in the step S2, the temperature in the crucible is controlled within a range of 1350 - 1500 °C.
[0012] Compared with the prior art, adopting the above technical solution, controlling the temperature in the range of 1350 - 1500 °C can provide sufficient thermal energy to fully melt and evenly flow the molten silicon material, while avoiding adverse effects on the crystal structure caused by too high temperature. By adjusting the temperature, a certain degree of supercooling can be obtained for the silicon melt. The supercooled melt grows on the incompletely melted seed crystal, which can maintain the directionality and uniformity of crystal growth, reduce the formation of defects, obtain a cast single crystal silicon ingot with higher quality, and improve the utilization efficiency of recycled seed crystals and the overall production yield.
[0013] In a possible implementation manner, in the step S4, the distance from the position far from the growth area of the seed crystal splicing seam is 10 - 50 mm.
[0014] Compared with the prior art, adopting the above technical solution, when cutting and recycling the seed crystal, choosing a position 10 - 50 mm away from the growth area of the seed crystal splicing seam for cutting can effectively avoid the area with dense defects, reduce the probability of defects in the seed crystal splicing seam area laterally expanding into the recycled seed crystal, thereby improving the quality of the recycled seed crystal and ensuring the high quality and stability of the recycled seed crystal.
[0015] In a possible implementation manner, in the step S4, the thickness of the recycled seed crystal is 10 - 40 mm.
[0016] Compared with the prior art, by adopting the above technical solution, by controlling the thickness of the recycled seed crystal between 10 - 40 mm, it is possible to ensure the quality of the recycled seed crystal while avoiding the nucleation instability caused by an overly thin seed crystal or the uneven growth caused by an overly thick seed crystal. This thickness range enables the recycled seed crystal to better withstand the growth of molten silicon material and effectively promotes the nucleation and growth of molten silicon material on the surface of the seed crystal.
[0017] In a possible implementation manner, in the step S4, the surface crystal orientation of the recycled seed crystal is <100> or <110>, and the average defect ratio of the recycled seed crystal is less than 1%.
[0018] Compared with the prior art, by preferentially selecting the surface of the recycled seed crystal with the <100> or <110> crystal orientation, this technical solution can significantly improve the crystal quality and process efficiency. Specifically: 1) The <100> crystal orientation is the mainstream orientation of photovoltaic single-crystalline silicon. After the silicon wafer is treated by alkaline texturing, it can form a uniform pyramid structure, which can reduce the surface light reflectivity to less than 10%, greatly improving the sunlight capture efficiency; 2) The recycled seed crystal with the <110> crystal orientation has excellent crystal integrity. The new single-crystalline silicon ingot prepared from it not only meets the quality standards but can also be recycled for seed crystal reproduction, achieving a resource utilization rate increase of more than 30%. This dual crystal orientation coordination strategy not only ensures the photoelectric conversion efficiency of the photovoltaic cell but also establishes a sustainable seed crystal recycling system.
[0019] In a possible implementation manner, in the step S4, the minority carrier lifetime in the regions with a lower minority carrier lifetime at the bottom and top of the silicon block is less than 3 μs.
[0020] Compared with the prior art, by removing the regions at the bottom and top of the silicon block with a minority carrier lifetime lower than 3 μs, this technical solution can effectively remove the high-defect regions and metal impurity enrichment regions in the crystal, effectively reducing the metal content in the recycled seed crystal, contributing to improving the crystal quality and electrical properties of the single-crystalline silicon ingot prepared from the recycled seed crystal, thereby improving the overall minority carrier lifetime and yield of the newly cast single-crystalline silicon ingot.
[0021] In a possible implementation manner, in the step S5, the condition for the incomplete melting of the recycled seed crystal is that the remaining height of the recycled seed crystal is 10 - 30 mm.
[0022] Compared with the prior art, by adopting the above technical solution, by controlling the degree of incomplete melting of the recycled seed crystal to a remaining height of 10 - 30 mm, by maintaining partial incomplete melting of the seed crystal, random nucleation is effectively inhibited. This process window not only ensures that the silicon melt can effectively continue the crystal orientation transfer of the seed crystal but also provides a buffer space for melt temperature control, significantly improving the crystal quality and process stability.
[0023] The present invention also provides a single-crystal silicon ingot, which is prepared by the above method.
[0024] The single-crystal silicon ingot prepared by the present invention has a low defect density, a higher minority carrier lifetime, and excellent electrical properties, and is applicable to the fields of high-efficiency solar cells and semiconductors. Compared with the cast single-crystal silicon ingot prepared by the traditional method, the technical solution of the present invention optimizes the cutting method, laying method, and melting control of the recycled seed crystal, so that the crystal orientation uniformity of the single-crystal silicon ingot is better, the introduction of metal impurities is reduced, and the dislocation density is lowered. The minority carrier lifetime of the single-crystal silicon ingot prepared by the present invention is significantly improved, the average defect is small, and the overall product yield is high, thereby improving the conversion efficiency of the single-crystal silicon cell and reducing the production cost, and having broad industrial application value. Description of the Drawings
[0025] Figure 1 It is a schematic diagram of the process of recycling the seed crystal by the existing method; Figure 2 It is a schematic diagram of the defect expansion in the seed crystal splicing seam area of the cast single-crystal silicon grown in a non-<110> crystal orientation; Figure 3 It is a schematic diagram of the defect expansion in the seed crystal splicing seam area of the cast single-crystal silicon grown in a <110> crystal orientation; Figure 4 It is a schematic diagram of the seed crystal recycling process of step S4 of the method for recycling the seed crystal to prepare a single-crystal silicon ingot of the present invention; Figure 5 It is a schematic diagram of the laying of the recycled seed crystal in step S5 of the method for recycling the seed crystal to prepare a single-crystal silicon ingot of the present invention. Detailed Embodiments
[0026] First of all, those skilled in the art should understand that these embodiments are only used to explain the technical principles of the embodiments of the present application, and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments according to needs to adapt to specific application scenarios.
[0027] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific situations.
[0028] In the embodiments of the present application, unless otherwise clearly specified and limited, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature being "under", "beneath" and "underneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the horizontal height of the first feature is less than that of the second feature.
[0029] The present invention provides a method for recycling seed crystals to prepare monocrystalline silicon ingots and a monocrystalline silicon ingot, comprising the following steps: S1: Seed crystal laying Provide a crucible, and splice and lay multiple monocrystalline silicon seed crystals with a growth plane crystal orientation of <110> at the bottom of the crucible to form a seed crystal layer. The side crystal orientations of the seed crystals are <100> and <110> respectively, and the side crystal orientations of adjacent spliced seed crystals are the same. By precisely controlling the crystal orientation arrangement of the seed crystals, it is possible to ensure the orientation along the <110> direction during crystal growth, which helps to reduce dislocation propagation and improve the quality of the recycled seed crystals.
[0030] S2: Casting the growth of monocrystalline silicon ingot Set molten silicon material above the seed crystal layer processed in the step S1, and control the temperature in the crucible to make the molten silicon material grow along the crystal orientation structure of the seed crystals, obtaining a cast monocrystalline silicon ingot with a <110> growth crystal orientation. By precisely controlling the growth temperature, the growth direction of the crystal is highly consistent with the structure of the seed crystal, thereby obtaining a high-quality cast monocrystalline silicon ingot.
[0031] S3: Ingot cutting Take out the cast monocrystalline silicon ingot obtained in the step S2, and cut it into multiple silicon blocks along the growth direction. This cutting method can maximize the retention of the crystal structure of the ingot body and reduce defects or non-uniformities caused by cutting.
[0032] S4: Recycling seed crystal cutting Cut the silicon blocks obtained in the step S3, and the specific cutting method is as Figure 4 shown, cut off the regions with lower minority carrier lifetimes at the bottom and top of the silicon blocks, and cut the silicon blocks at a position away from the splicing seam region along the side parallel to <100> or <110> to obtain recycled seed crystals. By removing the low-quality regions, it is ensured that the quality of the recycled seed crystals is higher, reducing the introduction of metal impurities and defects, and thus improving the electrical properties of the recycled cast monocrystalline silicon ingot.
[0033] S5: Recycling seed crystal laying The recycled seeds with the same surface crystal orientation are closely spliced and laid to form a recycled seed layer. The specific laying method is as follows Figure 5 As shown, molten silicon material is set above the recycled seed layer, and the temperature in the crucible is controlled so that the recycled seeds are not completely melted. At the same time, the molten silicon material grows along the crystal orientation structure of the recycled seeds, and finally a new cast single crystal silicon ingot is obtained. The seeds recycled by this method can maintain a low defect density.
[0034] As a preferred solution, in the step S1, the side crystal orientations of the seed layer are <100> and <110> respectively, and the side crystal orientations of adjacent recycled seeds are the same.
[0035] Compared with the prior art, in the technical solution of the present invention, seeds with a growth plane of <110> crystal orientation are selected for laying, and a cast single crystal silicon ingot with <110> crystal orientation can be prepared; as Figure 2 shown, Figure 2 Figure 12 is a schematic diagram of defect expansion in the seed splicing seam area during the growth of non-<110> crystal orientation cast single crystal silicon. The defect expansion area in the non-<110> crystal orientation cast single crystal silicon ingot is relatively large and diverges at a certain angle with the growth direction. As Figure 3 shown, Figure 3 Figure 15 is a schematic diagram of defect expansion in the seed splicing seam area during the growth of <110> crystal orientation cast single crystal silicon. In the <110> crystal orientation cast single crystal silicon, the expansion directions of defects such as dislocations and small-angle grain boundaries in the seed splicing seam area are parallel to the growth direction, and the lateral expansion distance is very narrow. The layout of <100> and <110> crystal orientations on the side of the seeds makes the adjacent side crystal orientations of the prepared cast single crystal silicon ingot be <100> or <110>, so that recycled seeds with a growth plane crystal orientation of <100> or <110> can be obtained during the subsequent seed recycling process.
[0036] As a preferred solution, in the step S2, the temperature in the crucible is 1350 - 1500 °C.
[0037] As a preferred solution, in the step S4, the distance from the growth area far from the splicing seam is 10 - 50 mm.
[0038] As a preferred solution, in the step S4, the thickness of the recycled seeds is 10 - 40 mm.
[0039] As a preferred solution, in the step S4, the surface crystal orientation of the recycled seeds is <100> or <110>, and the average defect ratio of the recycled seeds is less than 1%.
[0040] As a preferred solution, in the step S4, the minority carrier lifetime in the areas with low minority carrier lifetime at the bottom and top of the silicon block is less than 3 μs.
[0041] As a preferred solution, in step S5, the condition for the incomplete melting of the recycled seed crystal is that the remaining height of the recycled seed crystal is 10 - 30 mm.
[0042] The present invention also includes a single crystal ingot prepared by the method of the present invention.
[0043] The following provides specific embodiments in combination with the above technical solutions to further illustrate the present invention: Example 1: Example 1 provides a method for preparing a single crystal ingot from recycled seed crystals and the single crystal ingot prepared thereby, including the following steps: S1: Seed crystal laying Provide a crucible, and splice and lay multiple single crystal silicon seed crystals with a growth plane crystal orientation of <110> at the bottom of the crucible to form a seed crystal layer. The selected seed crystal thickness is 25 mm, ensuring that it can fully support the growth of the molten silicon material during casting and can achieve the required crystal orientation structure.
[0044] S2: Growth of the single crystal ingot casting Set molten silicon material above the seed crystal layer processed in step S1, and control the temperature of the molten silicon material at 1350 - 1500 °C. The temperature inside the crucible is maintained within this temperature range, enabling the molten silicon material to grow along the crystal orientation structure of the seed crystal to obtain a cast single crystal ingot with a <110> growth crystal orientation.
[0045] S3: Ingot cutting Take out the cast single crystal ingot obtained in step S2, cut it into multiple silicon blocks along the growth direction, and then perform subsequent cutting operations on these silicon blocks.
[0046] S4: Recycled seed crystal cutting Cut the silicon blocks obtained in step S3, cut off the regions with lower minority carrier lifetimes at the bottom and top. The minority carrier lifetimes in the regions with lower minority carrier lifetimes at the bottom and top of the silicon blocks are less than 3 μs, and at a position 15 mm away from the growth region of the seed crystal splicing seam, cut along the growth direction and in the direction with a side crystal orientation of <100> to obtain recycled seed crystals. The thickness of the recycled seed crystals is 25 mm to ensure stability and crystal quality in subsequent steps.
[0047] S5: Recycled seed crystal laying Tightly splice and lay the recycled seed crystals with a surface crystal orientation of <100> to form a recycled seed crystal layer. Set molten silicon material above the recycled seed crystal layer and control the temperature inside the crucible to make the recycled seed crystals not completely melt. The condition for the incomplete melting of the recycled seed crystals is that the remaining height of the recycled seed crystals is 15 mm. Subsequently, the molten silicon material grows along the crystal orientation structure of the recycled seed crystals to finally obtain a new cast single crystal ingot.
[0048] In this embodiment, a situation where the thickness of the recycled seed crystal is 25 mm is adopted. The experimental data shows that the defect ratio of the recycled seed crystal under this condition is relatively low, remaining below 0.5%, showing a relatively high recycling quality. Moreover, when using the recycled seed crystal with this thickness, during the process of casting a single crystal silicon ingot, the yield shows a relatively high level, reaching 56%. This also indicates that under this condition, the molten silicon material can grow uniformly along the crystal orientation structure of the recycled seed crystal, producing a high-quality single crystal silicon ingot.
[0049] Example 2: Example 2 provides a method for preparing a single crystal silicon ingot using a recycled seed crystal and the single crystal silicon ingot prepared thereby, including the following steps: S1: Seed crystal laying Provide a crucible, and splice and lay multiple single crystal silicon seed crystals with a growth plane crystal orientation of <110> at the bottom of the crucible to form a seed crystal layer. The selected thickness of the seed crystal is 20 mm to verify the effect of a thinner recycled seed crystal.
[0050] S2: Growth of casting single crystal silicon ingot Set molten silicon material above the seed crystal layer processed in step S1, and control the temperature of the molten silicon material at 1350 - 1500 °C, so that the molten silicon material can grow along the crystal orientation structure of the seed crystal to obtain a casting single crystal silicon ingot with a <110> growth crystal orientation.
[0051] S3: Ingot cutting Take out the casting single crystal silicon ingot obtained in step S2, cut it into multiple silicon blocks along the growth direction, and then perform subsequent cutting operations on these silicon blocks.
[0052] S4: Cutting of recycled seed crystal Cut the silicon blocks obtained in step S3, cut off the regions with lower minority carrier lifetimes at the bottom and top. The minority carrier lifetimes in the regions with lower minority carrier lifetimes at the bottom and top of the silicon blocks are less than 3 μs, and at a position 20 mm away from the growth region of the seed crystal splicing seam, cut along the direction parallel to the growth direction and with a side crystal orientation of <110> to obtain a recycled seed crystal with a thickness of 15 mm, ensuring that the recycled seed crystal can provide the necessary crystal structure in the subsequent steps.
[0053] S5: Laying of recycled seed crystal Tightly splice and lay the recycled seed crystals with a surface crystal orientation of <110> to form a recycled seed crystal layer. Set molten silicon material above the recycled seed crystal layer and control the temperature in the crucible so that the recycled seed crystal does not completely melt. The condition for the recycled seed crystal not to completely melt is: the remaining height of the recycled seed crystal is 20 mm. Subsequently, the molten silicon material grows along the crystal orientation structure of the recycled seed crystal, and finally a new casting single crystal silicon ingot is obtained.
[0054] In Example 2, the condition of using recycled seed crystals with a thickness of 15 mm was adopted. Although this thickness was relatively thin, the average defect ratio of the recycled crystals still remained at 0.7%. This indicates that even under the condition of using relatively thin recycled seed crystals, the defects are still within an acceptable range. Under this condition, the yield of the cast single-crystalline silicon ingot was 52%, slightly lower than the result of Example 1, but still maintaining a relatively high production efficiency. This shows that even when using thin recycled seed crystals, the production process can still maintain relatively stable results.
[0055] Example 3: Example 3 provides a method for preparing a single-crystalline silicon ingot using recycled seed crystals and the prepared single-crystalline silicon ingot, including the following steps: S1: Seed crystal laying Provide a crucible, and splice and lay multiple single-crystalline silicon seed crystals with a growth plane crystal orientation of <110> at the bottom of the crucible to form a seed crystal layer. The selected thickness of the seed crystals is 40 mm to verify the effect of using relatively thick recycled seed crystals.
[0056] S2: Growth of the cast single-crystalline silicon ingot Set molten silicon material above the seed crystal layer processed in step S1, and control the temperature of the molten silicon material at 1350 - 1500 °C, so that the molten silicon material can grow along the crystal orientation structure of the seed crystal to obtain a cast single-crystalline silicon ingot with a <110> growth crystal orientation.
[0057] S3: Ingot cutting Take out the cast single-crystalline silicon ingot obtained in step S2, cut it into multiple silicon blocks along the growth direction, and then perform subsequent cutting operations on these silicon blocks.
[0058] S4: Cutting of recycled seed crystals Cut the silicon blocks obtained in step S3, cut off the regions with lower minority carrier lifetimes at the bottom and top. The minority carrier lifetimes in the regions with lower minority carrier lifetimes at the bottom and top of the silicon blocks are less than 3 μs, and at a position 40 mm away from the growth region of the seed crystal splicing seam, cut along the direction parallel to the growth direction and with a side crystal orientation of <100> to obtain recycled seed crystals with a thickness of 40 mm, ensuring that more crystal structures can be provided in the subsequent steps.
[0059] S5: Laying of recycled seed crystals Tightly splice and lay the recycled seed crystals with a surface crystal orientation of <100> to form a recycled seed crystal layer. Set molten silicon material above the recycled seed crystal layer, and control the temperature in the crucible so that the recycled seed crystals do not completely melt. The condition for the recycled seed crystals not to completely melt is that the remaining height of the recycled seed crystals is 20 mm. Subsequently, the molten silicon material grows along the crystal orientation structure of the recycled seed crystals to finally obtain a new cast single-crystalline silicon ingot.
[0060] In Example 3, the condition of using recycled seed crystals with a thickness of 40 mm was adopted. Since the recycled seed crystals were relatively thick and of good quality, the average defect ratio remained at 0.3%, showing the best recycling quality. When using relatively thick recycled seed crystals (40 mm), the yield of the cast monocrystalline silicon ingot was 58%, showing the optimal production efficiency and the quality of the monocrystalline silicon ingot. This result indicates that with the use of thicker recycled seed crystals, the combination of molten silicon material and recycled seed crystals is more sufficient, thus improving the yield of the cast monocrystalline silicon ingot.
[0061] In summary, the present invention provides a method for preparing a monocrystalline silicon ingot using recycled seed crystals and the monocrystalline silicon ingot prepared thereby. Through the precise cutting of the recycled seed crystals and the optimized casting process, the recycled seed crystals can play an important role in the process of casting the monocrystalline silicon ingot. Compared with the traditional monocrystalline silicon production process, the present invention not only improves the utilization efficiency of the recycled seed crystals, but also significantly increases the yield of the cast monocrystalline silicon ingot.
[0062] The principle of the present invention is to effectively ensure the quality of the recycled seed crystals and promote the crystal orientation growth of the molten silicon material during the casting process by precisely controlling the thickness of the recycled seed crystals, the cutting method, and the temperature and the molten state of the silicon material during the casting process. In this way, the present invention solves the problems of unstable quality, low recovery rate, and low yield of the cast monocrystalline silicon ingot in the prior art, thus realizing the efficient production of high-quality cast monocrystalline silicon ingots, and specifically achieving the following technical advantages:
[0063] Improved the utilization efficiency of recycled seed crystals: By cutting and re-laying the recycled seed crystals, the present invention reduces material waste and makes full use of the originally discarded monocrystalline silicon ingots; Reduced production costs: The recycling process of the present invention greatly reduces the cost of production materials and improves economic benefits; Improved the quality and yield of the cast monocrystalline silicon ingot: By optimizing the quality control of the recycled seed crystals and the casting process, the yield of the cast monocrystalline silicon ingot produced is greatly increased, reaching or exceeding 50%, making the product quality more stable; Met the environmental protection requirements: By recycling waste materials, the present invention not only improves the utilization efficiency of resources, but also reduces the dependence on new raw materials, contributing to the realization of green and environmental protection production; Therefore, the present invention provides an innovative solution for the production of monocrystalline silicon, which can significantly improve production efficiency, reduce costs, and solve multiple technical problems in the prior art, and has broad industrial application prospects.
[0064] In the description of the embodiments of the present application, it should be noted that in the description of the present application, terms indicating directions or positional relationships such as "inside" and "outside" are based on the directions or positional relationships shown in the drawings. This is only for convenience of description and does not indicate or imply that the device or component must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present application.
[0065] In the description of the present application, the description referring to terms such as "one embodiment", "some embodiments", "in this embodiment", "specific examples", or "some examples" means that the specific features, mechanisms, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.
[0066] As described above, the above are only the specific implementation manners of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.
Claims
1. A method for preparing a single crystal silicon ingot by recycling a seed crystal, characterized in that, It includes the following steps: S1: Seed crystal laying: Provide a crucible, and splice and lay multiple single-crystal silicon seed crystals with a growth plane crystal orientation of <110> at the bottom of the crucible to form a seed crystal layer; S2: Growth of cast single-crystal silicon ingot: Fill silicon material above the seed crystal layer processed in the step S1, and by controlling the temperature in the crucible, make the silicon material melt and grow along the crystal orientation structure of the incompletely melted seed crystals to obtain a cast single-crystal silicon ingot with a <110> growth crystal orientation; S3: Ingot cutting: Take out the cast single-crystal silicon ingot obtained in the step S2, and cut it into multiple silicon blocks along the growth direction; S4: Recycling seed crystal cutting: Cut the silicon blocks obtained in the step S3, cut off the regions with lower minority carrier lifetimes at the bottom and top of the silicon blocks, and at a position away from the seed crystal splicing seam region, cut along a direction parallel to the growth direction and with a side crystal orientation of <100> or <110> to obtain recycling seed crystals; S5: Recycling seed crystal laying: Closely splice and lay the recycling seed crystals with the same surface crystal orientation to form a recycling seed crystal layer, lay silicon material above the recycling seed crystal layer, and control the temperature in the crucible to make the recycling seed crystals not completely melt, and at the same time, the molten silicon liquid grows along the crystal orientation structure of the recycling seed crystals to finally obtain a new cast single-crystal silicon ingot.
2. The method for preparing a single crystal silicon ingot by recycling a seed crystal according to claim 1, characterized in that, In the step S1, the side crystal orientations of the seed crystal layer are <100> and <110> respectively, and the side crystal orientations of adjacent recycling seed crystals are the same.
3. The method for preparing a single crystal silicon ingot by recycling a seed crystal according to claim 1, wherein In the step S2, the range of controlling the temperature in the crucible is 1350 - 1500 °C.
4. The method for preparing a single crystal silicon ingot by recycling a seed crystal according to claim 1, characterized in that, In the step S4, the distance of the position away from the seed crystal splicing seam region is 10 - 50 mm.
5. The method for preparing a single crystal silicon ingot by recycling a seed crystal according to claim 1, characterized in that, In the step S4, the thickness of the recycling seed crystals is 10 - 40 mm.
6. The method for preparing a single crystal silicon ingot by recycling a seed crystal according to claim 1, characterized in that, In the step S4, the surface crystal orientation of the recycling seed crystals is <100> or <110>, and the average defective area ratio of the recycling seed crystals is less than 1%.
7. The method for preparing a single crystal silicon ingot by recycling a seed crystal according to claim 1, characterized in that, In the step S4, the minority carrier lifetime of the regions with lower minority carrier lifetimes at the bottom and top of the silicon blocks is less than 3 μs.
8. The method for preparing a single crystal silicon ingot by recycling a seed crystal according to claim 1, characterized in that, In the step S5, the condition for the recycling seed crystals not to completely melt is: the remaining height of the recycling seed crystals is 10 - 30 mm.
9. A single crystal silicon ingot, characterized in that, The single-crystal silicon ingot is prepared by the method according to any one of claims 1 - 7.