A method for preparing a barium carbonate coated crucible and a polycrystalline silicon ingot.

Abstract

A barium carbonate slurry is sprayed onto the surface of the silicon nitride coating to form the barium carbonate coating. Using the above-mentioned barium carbonate-coated crucible, the probability of micron-level impurities in silicon ingots is significantly reduced during ingot production, decreasing from 8%-20% when using silicon nitride-coated crucibles to 0%. This effectively solves the technical problem of impurities in the ingot silicon production process and reduces the scrap rate of ingot silicon.

Description

Technical Field

[0001] This invention belongs to the field of polycrystalline silicon ingot technology, specifically relating to a barium carbonate coated crucible and a method for preparing polycrystalline silicon ingots. Background Technology

[0002] Crystalline silicon materials (including polycrystalline and monocrystalline silicon) are the most important photovoltaic materials, accounting for over 90% of the market share, and are mainly used in semiconductors and solar cells. The production of cast polycrystalline silicon primarily uses ceramic crucibles. To facilitate the demolding of the silicon material, a layer of silicon nitride is coated onto the inner wall of the crucible, forming a crucible with a silicon nitride coating structure. In the ingot casting process, silicon material is filled into the crucible with the silicon nitride coating structure and undergoes multiple stages such as heating and melting, directional crystal growth, annealing, and cooling to prepare the silicon ingot.

[0003] However, in silicon ingots cast using this silicon nitride coated crucible, due to various factors such as collisions, scratches during loading, and coating instability, after removing the top 25mm impurity layer of the silicon ingot, silicon nitride impurity defects appeared in some batches, resulting in unqualified silicon ingots and an increased scrap rate. The probability of silicon nitride impurity defects is 8%-20%. Summary of the Invention

[0004] Based on this, this application provides a barium polycarbonate coated crucible to solve the technical problem in the prior art that after melting silicon material in a crucible with silicon nitride coating, some batches of finished silicon ingots have impurities and defects, resulting in a high scrap rate.

[0005] This application also provides a method for preparing polycrystalline silicon ingots to solve the technical problem in the prior art that some batches of finished silicon ingots prepared by melting silicon material in a crucible with silicon nitride coating have impurities and defects, resulting in a high scrap rate.

[0006] The technical solution to the above-mentioned technical problems in this application is as follows:

[0007] A barium carbonate coated crucible includes a crucible body and a protective coating sprayed onto the inner wall surface of the crucible body; wherein the protective coating is prepared by the following method:

[0008] S1 is prepared by mixing 20-35 parts barium carbonate, 50-60 parts silica sol, and 100-150 parts deionized water by mass ratio to form a barium carbonate mixed slurry.

[0009] S2. A barium carbonate mixed slurry is sprayed onto the surface of the silicon nitride coating at a rate of 5 g / cm2 to 10 g / cm2.

[0010] After drying and sintering, S3 forms a barium carbonate coating.

[0011] Preferably, the barium carbonate powder has a particle size of 20 μm to 30 μm and a purity of ≥99.999%.

[0012] A method for preparing polycrystalline silicon ingots, using a barium carbonate-coated crucible as described above.

[0013] A method for preparing polycrystalline silicon ingots involves using a silicon nitride coated crucible, laying a seed crystal at the bottom of the crucible, laying several layers of silicon material on the seed crystal, and sprinkling a layer of barium oxide powder on the surface of the seed crystal and / or the surface of the silicon material above the seed crystal.

[0014] Preferably, a silicon nitride coated crucible is used, and the barium oxide powder has a particle size of 20-30 μm and a barium oxide purity of ≥99.999%.

[0015] Preferably, the mass ratio of barium oxide to silicon material is (0.2-1):1000.

[0016] Preferably, the mass ratio of barium oxide to silicon material is (0.5-1):1000.

[0017] Preferably, the method further includes: placing the crucible filled with silicon material into a heating furnace, evacuating the heating furnace, and introducing argon gas into the heating furnace during the evacuation process.

[0018] Preferably, the process further includes: after filling the heating furnace with argon gas, heating the crucible, whereby the silicon material inside the crucible melts and forms a silicon melt.

[0019] Preferably, it further includes: solidification and crystal growth of the silicon melt within the crucible.

[0020] Compared with the prior art, this application has at least the following advantages:

[0021] A barium carbonate slurry is sprayed onto the surface of the silicon nitride coating to form the barium carbonate coating. Using the above-mentioned barium carbonate-coated crucible, the probability of micron-level impurities in silicon ingots is significantly reduced during ingot production, decreasing from 8%-20% when using silicon nitride-coated crucibles to 0%. This effectively solves the technical problem of impurities in silicon ingot production and reduces the scrap rate of silicon ingots. Attached Figure Description

[0022] Figure 1 This is a photograph of a silicon ingot sample with impurity defects produced in one embodiment.

[0023] Figure 2 This is a photograph of a sample of an ingot that "sticks to the pot" produced in one embodiment.

[0024] Figure 3 This is a photograph of a cracked ingot sample produced in one embodiment. Detailed Implementation

[0025] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0026] It should be noted that when an element is referred to as being "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," "top," "bottom," "end," "top," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0028] In one specific embodiment of the present invention, a barium carbonate coated crucible includes a crucible body and a protective coating sprayed onto the inner wall surface of the crucible body.

[0029] The specific preparation method of the protective coating is as follows: 20-35 parts barium carbonate, 50-60 parts silica sol, and 100-150 parts deionized water are mixed according to the following mass ratio to form a barium carbonate mixed slurry; the barium carbonate mixed slurry is then... 2 ~10.0 g / cm 2 It is sprayed onto the surface of the silicon nitride coating; after drying and sintering, a barium carbonate coating is formed.

[0030] After repeated experiments, a barium carbonate mixed slurry was sprayed onto the surface of the silicon nitride coating to form the barium carbonate coating. Using the above-mentioned barium carbonate-coated crucible, the probability of micron-level impurities in silicon ingots was significantly reduced during the production of cast silicon, decreasing from 8%-20% when using silicon nitride-coated crucibles to 0%. This effectively solved the technical problem of impurities in the production of cast silicon and reduced the scrap rate of cast silicon.

[0031] Further description: During the preparation of the protective coating, the drying and sintering processes involve a drying temperature of 60–100°C and a drying time of 1–3 hours. After drying, sintering is performed at a temperature of 500–800°C for 2–4 hours to form a barium carbonate coating. These mild drying conditions effectively remove deionized water from the barium carbonate slurry, ensuring sufficient green strength for the coating while preventing cracking or defects caused by excessively rapid drying.

[0032] Furthermore, the barium carbonate powder has a particle size of 20–30 μm. This particle size range provides the slurry with a suitable viscosity, facilitating spraying operations. The barium carbonate purity is ≥99.999%. High-purity barium carbonate avoids introducing impurities into the molten silicon.

[0033] Although the use of the above-mentioned barium carbonate coating crucible can effectively reduce the probability of silicon nitride impurity defects in silicon ingots, on the one hand, the process of preparing barium carbonate coated crucibles is complicated and requires a waste of manpower and resources; on the other hand, although the silicon carbide coating can effectively prevent silicon nitride impurity defects, it is easy to cause "sticking" phenomenon, and some silicon ingots will crack, resulting in a decrease in product qualification rate.

[0034] To further address the aforementioned technical problems, in another embodiment of the present invention, a method for preparing polycrystalline silicon ingots is provided, comprising: selecting a silicon nitride-coated crucible, laying a seed crystal at the bottom of the crucible, and laying several layers of silicon material on the seed crystal; sprinkling a layer of barium oxide powder on the surface of the seed crystal and / or the surface of the silicon material above the seed crystal. Specifically, a layer of barium oxide powder can be sprinkled on the surface of the seed crystal, on the surface of the first or second layer of silicon material above the seed crystal, or on both the surface of the seed crystal and the surface of the first or second layer of silicon material above the seed crystal. Experiments show that using the above method, the probability of impurities and defects in the ingot silicon is significantly reduced, down to 0. The above method is simple and can significantly suppress impurities and defects in the ingot silicon, reduce the scrap rate, and facilitate quality control for enterprises.

[0035] Furthermore, the barium oxide powder has a particle size of 20 μm to 30 μm and a purity of ≥99.999%. High-purity barium oxide can avoid introducing impurities into the molten silicon.

[0036] Furthermore, the mass ratio of barium oxide to silicon is (0.2-1):1000. Preferably, the mass ratio of barium oxide to silicon is (0.5-1):1000.

[0037] Preferably, the crucible filled with silicon material is placed in a heating furnace, the heating furnace is evacuated, and argon gas is introduced into the heating furnace during the evacuation process until the gas pressure inside the heating furnace is 50 kPa to 70 kPa.

[0038] Furthermore, after argon gas is introduced into the heating furnace, the crucible is heated, and the silicon material inside the crucible melts to form a silicon melt. The gas pressure inside the heating furnace is 40 kPa to 60 kPa, and the temperature of the silicon material inside the crucible is maintained at 1550℃ to 1560℃ until the silicon material is completely melted.

[0039] Furthermore, the silicon melt in the crucible solidifies and grows crystals. The gas pressure in the heating furnace is 50 kPa to 70 kPa, and the temperature in the heating furnace is reduced from 1550 ℃ to 1560 ℃ to 1425 ℃ to 1430 ℃ over 1 h to 2 h to initiate crystal growth.

[0040] Furthermore, annealing is performed, maintaining the gas pressure in the heating furnace at 50 kPa to 70 kPa and the temperature at 1330℃ to 1380℃ for 3 to 4 hours.

[0041] Furthermore, the silicon ingot obtained after annealing is cooled naturally to 300 ℃ to 400 ℃ under a gas pressure of 90 kPa to 100 kPa.

[0042] The following specific experiments further verify the technical solution and technical effects of the present invention.

[0043] I. Preparation of Barium Carbonate Coated Crucible

[0044] (1) Select a ceramic crucible and spray a protective coating on the surface of the ceramic crucible; wherein: the coating is made by mixing 25 parts of 99.999% pure barium carbonate powder, 50 parts of silica sol, and 150 parts of deionized water in a mass ratio to form a barium carbonate mixed slurry; the barium carbonate mixed slurry is sprayed at 5 g / cm 2 The coating is sprayed onto the surface of the silicon nitride coating; dried at 70 °C for 3 h; and after drying, sintered at 600 °C for 3 h to form a barium carbonate coating.

[0045] II. Silicon Ingot Production

[0046] Using the aforementioned crucible and employing a conventional ingot silicon production process, ingot silicon was produced, and the probability of impurities and defects in the ingot silicon was statistically analyzed. The specific ingot silicon production process is as follows: First, a seed crystal is laid at the bottom of the crucible. Then, 10 kg of silicon material is selected and laid on top of the seed crystal, with several layers of silicon material added. The crucible filled with silicon material is placed in a heating furnace. The furnace is evacuated, and argon gas is introduced into the furnace during the evacuation process until the gas pressure inside the furnace reaches 60 kPa. After introducing argon gas into the furnace, the crucible is heated, and the silicon material inside melts, forming a silicon melt. The gas pressure inside the furnace is 50 kPa, and the temperature of the silicon material in the crucible is maintained at 1550 °C until the silicon material is completely melted. The silicon melt in the crucible solidifies and grows crystals. The gas pressure inside the heating furnace is 50 kPa. The temperature inside the furnace is reduced from 1550 °C to 1425 °C over 2 hours to initiate crystal growth. Annealing is then performed, maintaining the gas pressure at 50 kPa and the temperature at 1330 °C for 4 hours. The annealed silicon ingot is then naturally cooled to 300 °C under a gas pressure of 90 kPa. The silicon ingot is then removed from the crucible.

[0047] Table 1. Probability of impurities and defects in silicon nitride production using crucibles with different coatings.

[0048] Crucible type / Process type Ingot batches Batch with silicon nitride impurity defects Probability of millimeter-level impurity defects Remark Silicon nitride coating 200 34 17% It can happen at any time, and the timing is unpredictable. Barium carbonate coating 200 0 0 Although the technical problem of silicon nitride impurity defects was effectively solved, the "sticking" phenomenon occurred more than 50% of the time.

[0049] As shown in Table 1 above, for every 200 batches of silicon ingots using crucibles with silicon nitride coating, if... Figure 1 The probability of impurity defects is approximately 17%, and the timing of their occurrence is uncertain, which is detrimental to quality control. However, using a barium carbonate coating reduces the probability of impurity defects to zero, effectively suppressing the risk of impurity defects in cast silicon ingots. Furthermore, impurity defects mainly occur in the later stages of crucible use, facilitating crucible replacement at any time to control product quality. Although this effectively solves the technical problem of impurity defects in silicon nitride, the frequency of "sticking" exceeds 50% (e.g., ...). Figure 2 At the same time, some silicon ingots will crack (e.g. Figure 3 This cannot meet the actual production needs.

[0050] III. Improvements to the Silicon Ingot Production Process

[0051] Using a silicon nitride-coated crucible, ingot silicon was produced using the ingot silicon production process described below. The probability of ingot silicon containing impurities and defects was statistically analyzed.

[0052] Silicon material is filled into a silicon nitride-coated crucible. Specifically, a seed crystal is first laid at the bottom of the silicon nitride-coated crucible (the same as the seed crystal laying in Comparative Example 1). Then, 10 kg of silicon material is selected, and a first layer of silicon material is laid on the seed crystal. Barium oxide powder is sprinkled on the first layer of silicon material, and then the remaining silicon material is laid, for several layers. The barium oxide powder has a particle size of 20 μm and a purity of 99.999%. In this embodiment of the invention, the impurity defect rate of the cast silicon is statistically analyzed when the mass of the sprinkled silicon material is 0.02%, 0.05%, and 0.1%. The crucible filled with silicon material and sprinkled with barium oxide powder is placed in a heating furnace. The heating furnace is evacuated, and argon gas is introduced into the heating furnace during the evacuation process until the gas pressure inside the heating furnace reaches 60 kPa. Argon gas is introduced into the heating furnace, and a crucible coated with barium oxide powder is heated to melt the silicon material inside the protective coating crucible, forming a silicon melt. The gas pressure inside the heating furnace is 50 kPa, and the temperature of the silicon material inside the protective coating crucible is maintained at 1550°C until the silicon material is completely melted. The silicon melt inside the crucible coated with barium oxide powder solidifies and grows crystals. The gas pressure inside the heating furnace is maintained at 50 kPa, and the temperature inside the heating furnace is reduced from 1550°C to 1425°C over 2 hours to initiate crystal growth. Annealing is performed, maintaining the gas pressure inside the heating furnace at 50 kPa and the temperature at 1330°C for 4 hours. The annealed silicon ingot is then naturally cooled to 300°C under a gas pressure of 90 kPa. The silicon ingot is removed from the crucible coated with barium oxide powder, and the top 25 mm impurity layer and the bottom 15 mm impurity layer are removed to obtain the finished silicon ingot.

[0053] Table 2. Statistical analysis of silicon impurity defects in ingots under different barium oxide application amounts.

[0054] Crucible type / Process type Ingot batches Batch with impurities Probability of impurity defects Remark Silicon nitride coating + 0.02% barium oxide powder 200 19 9.5% It can happen at any time, and the timing is unpredictable. Silicon nitride coating + 0.05% barium oxide powder 200 3 1.5% It can happen at any time, and the timing is unpredictable. Silicon nitride coating + 0.1% barium oxide powder 200 2 1.0% It can happen at any time, and the timing is unpredictable.

[0055] Table 2 shows that sprinkling barium oxide powder into the silicon material can significantly suppress the probability of impurities and defects in silicon ingots. However, when the amount added is too small, impurities and defects will still occur to some extent. When the amount of barium oxide added exceeds 0.05% of the silicon material mass, impurities and defects are basically eliminated.

[0056] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A barium carbonate coated crucible, characterized in that, It includes a crucible body and a protective coating sprayed onto the inner wall surface of the crucible body; wherein the specific preparation method of the protective coating is as follows: S1 is prepared by mixing 20-35 parts barium carbonate, 50-60 parts silica sol, and 100-150 parts deionized water by mass ratio to form a barium carbonate mixed slurry. S2 will mix barium carbonate slurry at 5 g / cm³ 2 ~10 g / cm 2 Sprayed onto the surface of the silicon nitride coating; After drying and sintering, S3 forms a barium carbonate coating.

2. The barium carbonate coated crucible as described in claim 1, characterized in that, The barium carbonate powder has a particle size of 20 μm to 30 μm and a purity of ≥99.999%.

3. A method for preparing polycrystalline silicon ingots, characterized in that, It is prepared using a barium carbonate coated crucible as described in any one of claims 1-2.

4. A method for preparing polycrystalline silicon ingots, comprising using a silicon nitride-coated crucible, laying a seed crystal at the bottom of the silicon nitride-coated crucible, and laying several layers of silicon material on the seed crystal, characterized in that... At least one layer of barium oxide powder is spread on the surface of the seed crystal and / or the silicon material surface above the seed crystal.

5. The method for preparing a polycrystalline silicon ingot as described in claim 4, characterized in that, A silicon nitride coated crucible was selected, and the barium oxide powder had a particle size of 20-30 μm and a purity of ≥99.999%.

6. The method for preparing a polycrystalline silicon ingot as described in claim 5, characterized in that, The mass ratio of barium oxide to silicon is (0.2~1):1000.

7. The method for preparing a polycrystalline silicon ingot as described in claim 6, characterized in that, The mass ratio of barium oxide to silicon is (0.5~1):1000.

8. A method for preparing polycrystalline silicon ingots as described in any one of claims 4-7, characterized in that, Also includes: The crucible filled with silicon material is placed into a heating furnace, and the heating furnace is evacuated. During the evacuation process, argon gas is introduced into the heating furnace.

9. The method for preparing a polycrystalline silicon ingot as described in claim 8, characterized in that, Also includes: After argon gas is introduced into the heating furnace, the crucible is heated, and the silicon material inside the crucible melts to form a silicon melt.

10. The method for preparing a polycrystalline silicon ingot as described in claim 9, characterized in that, Also includes The silicon melt in the crucible solidifies and grows into crystals.

Images