Method for preparing nitrogen-free crucible coating

Abstract

The invention discloses a method for preparing a nitrogen-free crucible coating, and belongs to the technical field of semiconductor processing. Comprising the following steps: step 1, preparing raw materials: preparing a crucible, high-purity silicon powder, high-purity quartz powder, silica sol and alcohol; 2, mixing: pouring the high-purity silicon powder, the high-purity quartz powder, the silica sol and the alcohol into a barrel, and stirring to uniformly mix; 3, crucible pretreatment, wherein a crucible is cleaned, subjected to impurity removal and dried; step 4, preparation of brush coating; 5, brush coating is started; step 6, brush coating inspection; and step 7, drying. According to the nitrogen-free crucible coating prepared through the method, a nitrogen-containing compound does not need to be used in the whole preparation process, introduction of nitrogen element impurities is avoided, preparation of the nitrogen-free coating is achieved, and the influence of nitrogen elements on the crystal quality is reduced. The coating is not easy to decompose under the conditions of low furnace pressure and high-temperature ingot casting, can well prevent silicon liquid from being contacted with a crucible, and has a good demolding effect.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor processing, and in particular to a method for preparing a nitrogen-free crucible coating. Background Art

[0002] Crucibles are crucial containers in the semiconductor and photovoltaic industries, and their performance directly impacts product quality and production efficiency. During the casting process of solar polysilicon ingots, a high-purity silicon nitride coating is sprayed onto the inner surface of the crucible. This coating primarily blocks contact between the molten silicon and the crucible, preventing sticking and cracking of the ingot.

[0003] Traditional crucible coating preparation methods often have many problems. For example, nitrogen-containing compounds need to be used as raw materials or auxiliary agents. However, high-purity silicon nitride is expensive. Imported silicon nitride costs 500 yuan per kilogram. Spraying a G5 crucible requires more than 500g, which costs 250 yuan. Silicon nitride is easily decomposed during the ingot casting process under low furnace pressure and high temperature environment, resulting in sticking to the crucible. Improper control of nitrogen content will form gaseous impurities in the crystal. These gaseous impurities will form tiny bubbles or voids in the silicon ingot, affecting the density and uniformity of the silicon ingot, thereby reducing the quality of the silicon ingot. In addition, the presence of nitrogen will aggravate the radial non-uniformity of the resistivity, causing the difference in resistivity between the center and the edge to expand to more than ±12%, seriously affecting the consistency of the device. As a result, not only the production cost is increased, but nitrogen impurities may also be introduced, which will have an adverse effect on the purity and performance of the product. Therefore, the present application provides a method for preparing nitrogen-free crucible coatings to meet the needs. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing nitrogen-free crucible coatings to solve the problems that the existing crucible coatings use nitrogen-containing compounds as raw materials or auxiliary agents, which have high costs and may introduce nitrogen impurities, thereby adversely affecting the purity and performance of the product.

[0005] Technical Solution

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A method for preparing a nitrogen-free crucible coating comprises the following steps:

[0008] Step 1: Raw material preparation: prepare a crucible, high-purity silicon powder, high-purity quartz powder, silica sol and alcohol;

[0009] Step 2: Mixing: Pour high-purity silicon powder, high-purity quartz powder, silica sol and alcohol into a bucket and stir to mix them evenly;

[0010] Step 3, crucible pretreatment: cleaning the crucible, removing impurities, and drying;

[0011] Step 4: Preparation for brushing: Remove the stirred bucket, one operator continues to stir the mixture in the bucket to prevent the silicon powder and high-purity quartz powder from settling and causing uneven brushing, while another operator is responsible for brushing;

[0012] Prepare a brush and a measuring cup. Use the measuring cup to hold the mixture in the bucket and dip the brush into the mixture in the measuring cup.

[0013] Prepare the spray gun;

[0014] Step 5: Start brushing: Dip the brush into the mixture in the measuring cup and brush it evenly back and forth on the inner wall of the crucible;

[0015] Use a spray gun to spray the mixture onto the inner wall of the crucible;

[0016] Brush the four sides and bottom of the crucible back and forth 2 to 3 times to ensure that the coating is evenly covered on the crucible;

[0017] Step 6: Check the coating after finishing the coating. Check whether there is uneven coating or obvious protrusions of particles. If there are any, dip the brush in the mixture again or use a spray gun to evenly coat the area.

[0018] Step seven, drying: the coated crucible is dried to form a nitrogen-free crucible coating on the inner wall of the crucible.

[0019] Optionally, the weight ratio of high-purity silicon powder, high-purity quartz powder and silica sol ranges from 90:9:1 to 1:1:1.

[0020] Optionally, in step 1, raw material preparation:

[0021] The crucible used is G5 crucible, and the size of G5 crucible is: 840mm*840mm*480mm.

[0022] Optionally, in step 2, during mixing:

[0023] The amount of high-purity silicon powder added is 1000g;

[0024] The amount of high-purity quartz powder added is 150g;

[0025] The amount of silica sol added is 50g;

[0026] The amount of alcohol added is 1500g.

[0027] Optionally, in step 1, raw material preparation:

[0028] The crucible used is G6 crucible, and the size of G6 crucible is: 1040mm*1040mm*500mm.

[0029] Optionally, in step 2, during mixing:

[0030] The amount of high-purity silicon powder added is 1500g;

[0031] The amount of high-purity quartz powder added is 200g;

[0032] The amount of silica sol added is 100g;

[0033] The amount of alcohol added is 2000g.

[0034] Optionally, in step 4, in preparation for brushing, the width of the brush is 10 cm.

[0035] Optionally, in step 2, during mixing, manual stirring or stirring with a mixer is adopted, the stirring time is 5 to 10 minutes, and the stirring speed is 50 r / min to 200 r / min.

[0036] Optionally, in step 3, crucible pretreatment:

[0037] First, the crucible to be coated is subjected to surface roughening treatment by sandblasting or chemical etching. When sandblasting, sand particles of appropriate particle size (80-120 mesh) are selected, the sandblasting pressure is controlled at 0.2-0.5 MPa, and the sandblasting time is 1-3 minutes to increase the roughness of the crucible surface and improve the bonding strength between the coating and the crucible substrate. Chemical etching adopts a mixed solution of hydrofluoric acid, nitric acid, etc., and the solution concentration and etching time are adjusted according to the crucible material. The etching time is 30 seconds to 120 seconds.

[0038] Next, the crucible to be coated is cleaned to remove surface oil, impurities, etc. The cleaning can be performed by ultrasonic cleaning with an organic solvent (such as acetone, ethanol), and the ultrasonic cleaning time is controlled within 10 to 30 minutes to fully remove surface contaminants;

[0039] After cleaning, rinse the crucible with deionized water to remove residual organic solvent;

[0040] Next, place the crucible in an oven for drying. The drying temperature is set to 80-120° C. and the drying time is 1-3 hours to ensure that the surface of the crucible is completely dry.

[0041] Optionally, in step seven, during drying:

[0042] Place the coated crucible in an oven for drying at a temperature of 60-100°C for 2-4 hours to allow the solvent in the coating to fully evaporate or allow it to dry naturally for 24 hours.

[0043] After drying, the crucible is placed in a high-temperature furnace for sintering. The sintering process adopts a staged heating method. First, the temperature is raised from room temperature to 800°C at a heating rate of 2-5°C / min and kept at this temperature for 1-2 hours to remove residual organic matter in the coating; then the temperature is raised to 800-1100°C at a heating rate of 3-8°C / min and kept at this temperature for 2-6 hours to densify the coating and form a good bond with the crucible substrate. At the same time, during this process, the silicon powder is exposed to oxygen in the air, and a layer of silicon oxide film is formed on the surface at high temperature. After sintering, it is cooled to room temperature with the furnace.

[0044] The sintered crucible is loaded with materials and placed in the ingot casting furnace. During the ingot melting stage, the silicon powder further reacts with the high-purity quartz powder at a high temperature of 1200-1600°C, forming a dense silicon dioxide film on the surface of the silicon powder, which prevents the melting of the silicon powder coating and achieves the demolding effect.

[0045] Compared with the prior art, the present invention has at least the following beneficial effects:

[0046] The nitrogen-free crucible coating prepared by the present invention eliminates the need for nitrogen-containing compounds during the entire preparation process, avoiding the introduction of nitrogen impurities. This enables the preparation of a nitrogen-free coating, reduces the impact of nitrogen on crystal quality, and improves product purity and performance. It also meets environmental protection requirements and reduces environmental pollution. The coating is resistant to decomposition under low furnace pressure and high-temperature ingot casting conditions, effectively preventing contact between silicon liquid and the crucible, and providing excellent mold release.

[0047] By adopting a specific combination of brushing and spraying, and arranging a dedicated person to continuously stir the mixture during the brushing process, the precipitation of silicon powder and high-purity quartz powder is effectively prevented, ensuring uniform coverage of the coating on the inner wall of the crucible, improving the heating uniformity of the crucible during use, and extending the service life of the crucible.

[0048] During the crucible pretreatment stage, the crucible surface is cleaned, dried, and roughened. This increases the crucible's surface roughness and significantly improves the adhesion between the coating and the crucible substrate, making the coating less likely to fall off during use and ensuring the crucible's stability and reliability. The nitrogen-free crucible coating formed after drying and sintering exhibits excellent density and stability, effectively protecting the crucible substrate and reducing reactions between the crucible and the material in high-temperature environments, thereby improving product quality and production efficiency.

[0049] The preparation method of the present invention has a clear process flow, relatively simple operation steps, and low skill requirements for operators, thereby facilitating large-scale industrial production, reducing production costs, and improving production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0051] Figure 1 A flow chart of the method for preparing a nitrogen-free crucible coating;

[0052] Figure 2 Schematic diagram of the weight ratio of high-purity silicon powder, high-purity quartz powder and silica sol;

[0053] Figure 3 This is a diagram showing the amount of each raw material added in Example 1;

[0054] Figure 4 This is a diagram showing the amount of raw materials added in Example 2;

[0055] Figure 5 It is a diagram of the mixing condition;

[0056] Figure 6 This is a schematic diagram of the crucible pretreatment process;

[0057] Figure 7 Schematic diagram of the drying step. DETAILED DESCRIPTION

[0058] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0059] like Figure 1 and Figure 7 As shown, the embodiment of the present invention provides a method for preparing a nitrogen-free crucible coating: Example 1:

[0060] Raw material preparation: Use a G5 crucible with dimensions of 840mm x 840mm x 480mm. Prepare 1000g of high-purity silicon powder, 150g of high-purity quartz powder, 50g of silica sol, and 1500g of alcohol.

[0061] Mixing: Pour high-purity silicon powder, high-purity quartz powder, silica sol and alcohol into a bucket and stir them with a mixer for 7 minutes at a speed of 120r / min to mix the mixture evenly.

[0062] Crucible pretreatment:

[0063] First, the crucible's surface was roughened by sandblasting with 100-mesh sand at a pressure of 0.3 MPa for 2 minutes to increase the crucible's surface roughness and improve the adhesion of the coating to the crucible substrate. The coated crucible was then ultrasonically cleaned in acetone for 20 minutes to fully remove oil and impurities from the crucible's surface.

[0064] After cleaning, rinse the crucible with deionized water to remove any residual acetone.

[0065] Next, the crucible was placed in an oven for drying at a temperature of 100°C for 2 hours to ensure that the surface of the crucible was completely dry.

[0066] Preparation for brush painting: Remove the mixing bucket. One operator continues stirring the mixture at 50 rpm to prevent sedimentation of the silica powder and high-purity quartz powder, which can lead to uneven application. Another operator will perform brush painting. Prepare a 10cm wide brush and a measuring cup. Place the mixture in the bucket and dip the brush into the cup. Also prepare the spray gun.

[0067] Start painting: Dip a brush into the mixture in the measuring cup and evenly paint it back and forth on the inner wall of the crucible. At the same time, use a spray gun to spray the mixture onto the inner wall of the crucible. Paint the four sides and the bottom of the crucible back and forth twice to ensure that the coating is evenly covered on the crucible.

[0068] Brush coating inspection: After brushing, carefully check the inner wall of the crucible for uneven coating and obvious protrusions of particles. If the above problems exist, dip the brush in the mixture again or use a spray gun to brush the area evenly.

[0069] Drying: Place the coated crucible in an oven for drying. The drying temperature is set to 80°C for 3 hours to allow the solvent in the coating to fully evaporate or dry naturally for 24 hours. After drying, place the crucible in a high-temperature furnace for sintering. The sintering process adopts a staged heating method. First, the temperature is raised from room temperature to 800°C at a heating rate of 3°C / min and kept at this temperature for 1.5 hours to remove residual organic matter in the coating; then the temperature is raised to 900°C at a heating rate of 5°C / min and kept at this temperature for 4 hours to densify the coating and form a good bond with the crucible substrate. At the same time, during this process, the silicon powder is exposed to oxygen in the air, and a layer of silicon oxide film is formed on the surface at high temperature. After sintering, it is cooled to room temperature with the furnace to form a nitrogen-free crucible coating on the inner wall of the crucible.

[0070] The sintered crucible is loaded with materials and placed in the ingot casting furnace. During the ingot melting stage, the silicon powder further reacts with the high-purity quartz powder at a high temperature of 1200-1600°C, forming a dense silicon dioxide film on the surface of the silicon powder, which prevents the melting of the silicon powder coating and achieves the demolding effect.

[0071] Example 2

[0072] Raw material preparation: Use a G6 crucible with dimensions of 1040mm x 1040mm x 500mm. Prepare 1500g of high-purity silicon powder, 200g of high-purity quartz powder, 100g of silica sol, and 2000g of alcohol.

[0073] Mixing: Pour high-purity silicon powder, high-purity quartz powder, silica sol and alcohol into a bucket, and stir manually for 8 minutes at a speed of 150r / min to mix the mixture evenly.

[0074] Crucible pretreatment:

[0075] First, the crucible to be coated is subjected to surface roughening treatment by chemical etching using a mixed solution of hydrofluoric acid, nitric acid, etc. The concentration of the solution is adjusted according to the material of the crucible, and the etching time is 90 seconds to increase the roughness of the crucible surface and improve the bonding strength between the coating and the crucible substrate.

[0076] Then, the crucible to be coated was placed in a container filled with ethanol and ultrasonically cleaned for 25 minutes to fully remove oil stains and impurities on the surface of the crucible.

[0077] After cleaning, rinse the crucible with deionized water to remove any residual ethanol.

[0078] Next, the crucible was placed in an oven for drying at a temperature of 110° C. for 2.5 hours to ensure that the surface of the crucible was completely dry.

[0079] Brush coating preparation: the same brush coating preparation steps as in Example 1, prepare a brush with a width of 10 cm, a measuring cup and a spray gun, and perform corresponding operations.

[0080] Start painting: Dip a brush into the mixture in the measuring cup and evenly paint it back and forth on the inner wall of the crucible. At the same time, use a spray gun to spray the mixture onto the inner wall of the crucible. Paint the four sides and the bottom of the crucible three times to ensure that the coating is evenly covered on the crucible.

[0081] Brush coating inspection: After brushing, carefully check the inner wall of the crucible for uneven coating and obvious protrusions of particles. If the above problems exist, dip the brush in the mixture again or use a spray gun to brush the area evenly.

[0082] Drying: Place the coated crucible in an oven for drying at 90°C for 2.5 hours to allow the solvent in the coating to fully evaporate or dry naturally for 24 hours. After drying, place the crucible in a high-temperature furnace for sintering. The sintering process adopts a staged heating method. First, the temperature is raised from room temperature to 800°C at a heating rate of 4°C / min and kept at this temperature for 1 hour to remove residual organic matter in the coating; then the temperature is raised to 1000°C at a heating rate of 6°C / min and kept at this temperature for 3 hours to densify the coating and form a good bond with the crucible substrate. At the same time, during this process, the silicon powder is exposed to oxygen in the air, and a layer of silicon oxide film is formed on the surface at high temperature. After sintering, it is cooled to room temperature with the furnace to form a nitrogen-free crucible coating on the inner wall of the crucible.

[0083] The sintered crucible is loaded with materials and placed in the ingot casting furnace. During the ingot melting stage, the silicon powder further reacts with the high-purity quartz powder at a high temperature of 1200-1600°C, forming a dense silicon dioxide film on the surface of the silicon powder, which prevents the melting of the silicon powder coating and achieves the demolding effect.

[0084] This method uses relatively inexpensive high-purity silicon powder mixed with high-purity quartz powder and silica sol, and then evenly applies the mixture to the inner wall of the crucible using a brush or a high-pressure spray gun. Under the high temperatures of the polycrystalline ingot casting process, the high-purity silicon powder and high-purity quartz powder react to form a silicon dioxide layer. Oxidized silicon powder resists melting at high temperatures, preventing molten silicon from contacting the crucible, thus effectively releasing the polycrystalline ingot.

[0085] All technical features in this embodiment can be freely combined according to actual needs.

[0086] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen-free crucible coating, characterized in that: The following steps are involved: Step 1: Raw material preparation: prepare a crucible, high-purity silicon powder, high-purity quartz powder, silica sol and alcohol; Step 2: Mixing: Pour high-purity silicon powder, high-purity quartz powder, silica sol and alcohol into a bucket and stir to mix them evenly; Step 3, crucible pretreatment: cleaning the crucible, removing impurities, and drying; Step 4: Preparation for brushing: Remove the stirred bucket, one operator continues to stir the mixture in the bucket to prevent the silicon powder and high-purity quartz powder from settling and causing uneven brushing, while another operator is responsible for brushing; Prepare a brush and a measuring cup. Use the measuring cup to hold the mixture in the bucket and dip the brush into the mixture in the measuring cup. Prepare the spray gun; Step 5: Start painting: Dip a brush into the mixture in the measuring cup and evenly paint it back and forth on the inner wall of the crucible; Use a spray gun to spray the mixture onto the inner wall of the crucible; Brush the four sides and bottom of the crucible back and forth 2 to 3 times to ensure that the coating is evenly covered on the crucible; Step 6: Check the coating after finishing the coating. Check whether there is uneven coating or obvious protrusions of particles. If there are any, dip the brush in the mixture again or use a spray gun to evenly coat the area. Step seven, drying: the coated crucible is dried to form a nitrogen-free crucible coating on the inner wall of the crucible.

2. The method for preparing a nitrogen-free crucible coating according to claim 1, wherein: The weight ratio of high-purity silicon powder, high-purity quartz powder and silica sol ranges from 90:9:1 to 1:1:

1.

3. The method for preparing a nitrogen-free crucible coating according to claim 1, wherein: Step 1: Raw materials preparation: The crucible used is G5 crucible, and the size of G5 crucible is: 840mm*840mm*480mm.

4. The method for preparing a nitrogen-free crucible coating according to claim 3, wherein: Step 2, Mixing: The amount of high-purity silicon powder added is 1000g; The amount of high-purity quartz powder added is 150g; The amount of silica sol added is 50g; The amount of alcohol added is 1500g.

5. The method for preparing a nitrogen-free crucible coating according to claim 1, wherein: Step 1: Raw materials preparation: The crucible used is G6 crucible, and the size of G6 crucible is: 1040mm*1040mm*500mm.

6. The method for preparing a nitrogen-free crucible coating according to claim 5, wherein: Step 2, Mixing: The amount of high-purity silicon powder added is 1500g; The amount of high-purity quartz powder added is 200g; The amount of silica sol added is 100g; The amount of alcohol added is 2000g.

7. The method for preparing a nitrogen-free crucible coating according to claim 1, wherein: Step 4: Prepare for painting with a brush. The width of the brush is 10 cm.

8. The method for preparing a nitrogen-free crucible coating according to claim 1, wherein: In step 2, the mixture is stirred manually or by a mixer for 5 to 10 minutes at a stirring speed of 50 to 200 r / min.

9. The method for preparing a nitrogen-free crucible coating according to claim 1, wherein: Step 3: Crucible pretreatment: First, the crucible to be coated is subjected to surface roughening treatment by sandblasting or chemical etching. When sandblasting, sand particles of appropriate particle size (80-120 mesh) are selected, the sandblasting pressure is controlled at 0.2-0.5 MPa, and the sandblasting time is 1-3 minutes to increase the roughness of the crucible surface and improve the bonding strength between the coating and the crucible substrate. Chemical etching adopts a mixed solution of hydrofluoric acid, nitric acid, etc., and the solution concentration and etching time are adjusted according to the crucible material. The etching time is 30 seconds to 120 seconds. Next, the crucible to be coated is cleaned to remove surface oil, impurities, etc. The cleaning can be performed by ultrasonic cleaning with an organic solvent (such as acetone, ethanol), and the ultrasonic cleaning time is controlled within 10 to 30 minutes to fully remove surface contaminants; After cleaning, rinse the crucible with deionized water to remove residual organic solvent; Next, place the crucible in an oven for drying. The drying temperature is set to 80-120° C. and the drying time is 1-3 hours to ensure that the surface of the crucible is completely dry.

10. The method for preparing a nitrogen-free crucible coating according to claim 1, wherein: Step 7, Drying: Place the coated crucible in an oven for drying at a temperature of 60-100°C for 2-4 hours to allow the solvent in the coating to fully evaporate or allow it to dry naturally for 24 hours. After drying, the crucible is placed in a high-temperature furnace for sintering. The sintering process adopts a staged heating method. First, the temperature is raised from room temperature to 800°C at a heating rate of 2-5°C / min and kept at this temperature for 1-2 hours to remove residual organic matter in the coating; then the temperature is raised to 800-1100°C at a heating rate of 3-8°C / min and kept at this temperature for 2-6 hours to densify the coating and form a good bond with the crucible substrate. At the same time, during this process, the silicon powder is exposed to oxygen in the air, and a layer of silicon oxide film is formed on the surface at high temperature. After sintering, it is cooled to room temperature with the furnace. The sintered crucible is loaded with materials and placed in the ingot casting furnace. During the ingot melting stage, the silicon powder further reacts with the high-purity quartz powder at a high temperature of 1200-1600°C, forming a dense silicon dioxide film on the surface of the silicon powder, which prevents the melting of the silicon powder coating and achieves the demolding effect.

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