Method for reducing pitting defects during gettering annealing of silicon wafers

Abstract

The present invention provides a method for reducing pitting defects during gettering annealing of silicon wafers, comprising the following steps: ultrasonically cleaning a silicon wafer to be processed to remove silicon powder on the silicon wafer to be processed, thereby obtaining a first silicon wafer intermediate; subjecting the first silicon wafer intermediate to a first acid treatment to remove metal impurities and organic contaminants on the first silicon wafer intermediate, thereby obtaining a second silicon wafer intermediate; texturing the second silicon wafer intermediate to form a pyramidal textured surface on the surface of the second silicon wafer intermediate, thereby obtaining a third silicon wafer intermediate; and subjecting the third silicon wafer intermediate to a second acid treatment to remove metal impurities on the third silicon wafer intermediate. The present invention reduces the proportion of pitting defects on silicon wafers after gettering annealing and improves the conversion efficiency of subsequently fabricated solar cells.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, in particular to a method for reducing silicon wafer gettering annealing pitting defects. Background Art

[0002] Heterojunction solar cells, also known as HJT cells (Hereto-junction with Intrinsic Thin-layer), are a type of heterojunction solar cell with an intrinsic thin layer. They were first successfully fabricated in 1992, achieving a conversion efficiency of 18.1%. With improvements in process methods and the introduction of new materials, efficiency has continued to reach new heights, and theoretical values ​​are constantly breaking records.

[0003] During the production of heterojunction solar cells, abnormal pitting frequently occurs on the surface of N-type silicon wafers after gettering annealing. Because existing HJT manufacturing processes fail to effectively address these pitting issues, the wafers exhibit a high number of pitting spots after gettering annealing, which can severely contaminate subsequent processing steps and reduce the conversion efficiency of subsequent heterojunction solar cells. Summary of the Invention

[0004] Based on this, it is necessary to provide a method for reducing pitting defects in silicon wafers during gettering annealing, so as to reduce the defective ratio of pitting on silicon wafers after gettering annealing and improve the conversion efficiency of subsequently prepared solar cells.

[0005] The present invention provides a method for reducing silicon wafer gettering annealing pitting defects, comprising the following steps:

[0006] Performing ultrasonic cleaning on the silicon wafer to be processed to remove silicon powder on the silicon wafer to be processed to obtain a first silicon wafer intermediate;

[0007] performing a first acid treatment on the first silicon wafer intermediate to remove metal impurities and organic contaminants on the first silicon wafer intermediate to obtain a second silicon wafer intermediate;

[0008] performing texturing on the second silicon wafer intermediate to form a pyramid texture surface on the surface of the second silicon wafer intermediate to obtain a third silicon wafer intermediate; and

[0009] The third silicon wafer intermediate is subjected to a second acid treatment to remove metal impurities on the third silicon wafer intermediate.

[0010] In some embodiments, the first acid treatment comprises the following steps:

[0011] The first silicon wafer intermediate is subjected to a first acid treatment using a first treatment liquid containing hydrochloric acid and hydrogen peroxide.

[0012] In some embodiments, the method includes at least one of the following (1) to (3):

[0013] (1) The method for preparing the first treatment liquid comprises the following steps:

[0014] Mixing hydrochloric acid with a mass fraction of 30% to 40%, hydrogen peroxide with a mass fraction of 35% to 40%, and water in a volume ratio of (5 to 7): (10 to 15): (800 to 1000);

[0015] (2) the temperature of the first acid treatment is 23-26°C;

[0016] (3) The time of the first acid treatment is 160s to 220s.

[0017] In some embodiments, the texturing comprises the following steps:

[0018] The second silicon wafer intermediate is textured using a texturing solution containing an alkaline solution and a texturing nucleation additive.

[0019] In some embodiments, the method includes at least one of the following (4) to (5):

[0020] (4) The alkaline solution includes potassium hydroxide solution;

[0021] (5) The texturing nucleating additive includes a nucleating agent, sodium silicate, sodium acetate, a surfactant and a wetting agent, and in the texturing nucleating additive, the mass fraction of the nucleating agent is 10.5% to 12%, the mass fraction of sodium silicate is 2.0% to 4.0%, the mass fraction of sodium acetate is 0.5% to 1.2%, the mass fraction of the surfactant is 2.0% to 6.0%, and the mass fraction of the wetting agent is 3.0% to 8.0%.

[0022] In some embodiments, the method includes at least one of the following (6) to (7):

[0023] (6) The method for preparing the texturing liquid comprises the following steps:

[0024] Mixing 35% to 45% by mass of the alkaline solution, 10% to 15% by mass of the texturing nucleation additive, and water in a volume ratio of (2 to 4):1:(400 to 450);

[0025] (7) The time for making the texturing is 300s to 350s.

[0026] In some embodiments, the base diameter of the pyramid structure of the pyramid velvet surface is 0.7 μm to 1.5 μm.

[0027] In some embodiments, the ultrasonic cleaning comprises the following steps:

[0028] Placing the silicon wafer to be processed in a cleaning solution, and cleaning the silicon wafer to be processed under ultrasonic conditions;

[0029] Wherein, the cleaning solution includes a hydrophilic wetting agent, and the hydrophilic wetting agent includes polyethylene oxide.

[0030] In some embodiments, the second acid treatment comprises the following steps:

[0031] performing a second acid treatment on the third silicon wafer intermediate using a second treatment solution containing an acidic reagent and ozone;

[0032] Wherein, the concentration of the ozone in the second treatment liquid is 40 ppm to 50 ppm.

[0033] In some embodiments, after the second acid treatment, the method further comprises the step of passivating the third silicon wafer intermediate.

[0034] The present invention utilizes a novel gettering annealing pretreatment process, namely, silicon dust removal followed by a first acid treatment followed by texturing and a second acid treatment, rather than the existing simple rough polishing process. This effectively removes metal particles and harmful impurities from the surface of the silicon wafer to be processed. Simultaneously, it thins and etches unfinished silicon wafers, thus avoiding a decrease in wafer quality and weight. Furthermore, the micro-pyramid textured surface on the silicon wafer increases the area for phosphorus deposition, creating optimal conditions for gettering annealing. This invention can reduce the proportion of pitting defects on silicon wafers after gettering annealing and improve the conversion efficiency of solar cells fabricated from these wafers. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A flow chart for reducing silicon wafer gettering annealing pitting defects provided by the present invention;

[0036] Figure 2 Graph showing the defective ratio of pitting on the silicon wafer after gettering annealing in Example 1 of the present invention and the defective ratio of pitting on the silicon wafer after gettering annealing in Comparative Example 1;

[0037] Figure 3 Graphs showing the conversion efficiency of solar cells made from the silicon wafers in Example 1 of the present invention and the conversion efficiency of solar cells made from the silicon wafers in Comparative Example 1. DETAILED DESCRIPTION

[0038] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the accompanying drawings. However, the present invention may 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 comprehensive understanding of the present disclosure.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0040] See also Figure 1 The present invention provides a method for reducing silicon wafer gettering annealing pitting defects, comprising the following steps:

[0041] Step S11: ultrasonically clean the silicon wafer to be processed to remove silicon powder on the silicon wafer to be processed, thereby obtaining a first silicon wafer intermediate.

[0042] Specifically, a cleaning agent with a mass fraction of 15% to 30% and water are mixed in a volume ratio of (10-20):(800-1000) to obtain a cleaning solution, and the cleaning solution is then loaded into a cleaning tank in an ultrasonic cleaning device, and the silicon wafer to be processed is placed in the cleaning tank so that the cleaning solution immerses the silicon wafer to be processed. Then, the ultrasonic cleaning device is started so that the ultrasonic waves emitted by the ultrasonic cleaning device and the cleaning solution jointly clean the silicon wafer to be processed to remove silicon powder on the silicon wafer to be processed, thereby obtaining the first silicon wafer intermediate.

[0043] In one embodiment, the cleaning agent includes a hydrophilic wetting agent. The hydrophilic wetting agent includes polyethylene oxide. The hydrophilic wetting agent allows the silicon wafer to be fully wetted by water, thereby eliminating interfacial energy on the silicon wafer and allowing water to enter pores on the surface of the silicon wafer, thereby removing silicon powder from the pores.

[0044] In one embodiment, the rated power of the ultrasonic cleaning device may be 1500 W to 2000 W. When cleaning the silicon wafer to be processed, the power of the ultrasonic cleaning device may be set to 40% to 50% of the rated power, that is, 40% to 50% of the rated power is used to clean the silicon wafer to be processed, so as to prevent damage to the silicon wafer to be processed by using too high a power and to prevent reduction in the removal effect of silicon powder by using too low a power.

[0045] In one embodiment, the ultrasonic cleaning time may be 300s to 450s.

[0046] The main principle of ultrasonic cleaning is to transfer energy to water by utilizing the ultrasonic cavitation effect, radiation pressure, and acoustic flow. This allows the ultrasonic waves to fully exert their power, thereby vibrating silicon powder out of the pores on the surface of the silicon wafer being processed. Furthermore, due to the relatively light weight of silicon powder, once it is shaken out of the pores on the surface of the silicon wafer being processed, it floats on the surface of the water. The water in the cleaning tank is then circulated and discharged, thereby removing the silicon powder from the silicon wafer being processed and reducing impurities on the surface of the wafer, thereby reducing the occurrence of subsequent pitting.

[0047] The silicon wafer to be processed may be a silicon wafer that has just been shipped.

[0048] In one embodiment, 320 to 400 silicon wafers to be processed may be ultrasonically cleaned as a batch. When ultrasonic cleaning of the next batch of silicon wafers to be processed is performed, 100 mL to 150 ml of the cleaning agent may be added to the cleaning solution.

[0049] It should be noted that when preparing the cleaning solution, it is not limited to mixing the cleaning agent and water of the above concentration. As long as the above cleaning solution can be obtained, the concentration and volume of hydrochloric acid required for preparing the cleaning solution and the volume of the above water can be changed.

[0050] Step S12: performing a first acid treatment on the first silicon wafer intermediate to remove metal impurities and organic dirt on the first silicon wafer intermediate to obtain a second silicon wafer intermediate.

[0051] Specifically, hydrochloric acid (HCl) with a mass fraction of 30% to 40%, hydrogen peroxide (H2O2) with a mass fraction of 35% to 40%, and water are mixed in a volume ratio of (5 to 7): (10 to 15): (800 to 1000) to obtain a first treatment liquid, and then the first silicon wafer intermediate is placed in the first treatment liquid to perform acid treatment on the first silicon wafer intermediate, thereby removing metal impurities and organic dirt on the first silicon wafer intermediate, avoiding the degradation of silicon wafer structure quality caused by rough polishing and thinning in the original process, improving the surface cleanliness of the silicon wafer, and obtaining the second silicon wafer intermediate.

[0052] In one embodiment, the temperature of performing the first acid treatment on the first silicon wafer intermediate using the first treatment liquid may be 23° C. to 26° C. That is, the temperature of the first treatment liquid is 23° C. to 26° C.

[0053] In one embodiment, the time for performing the first acid treatment on the first silicon wafer intermediate using the first treatment liquid is 160s to 220s, so that the first treatment liquid has sufficient time to react with the metal impurities and organic contaminants on the first silicon wafer intermediate, thereby completely removing the metal impurities and organic contaminants on the first silicon wafer intermediate.

[0054] It should be noted that the preparation of the first treatment liquid is not limited to mixing the hydrochloric acid of the above-mentioned concentration, the hydrogen peroxide of the above-mentioned concentration, and water. As long as the above-mentioned first treatment liquid can be obtained, the concentration and volume of the hydrochloric acid, the concentration and volume of the hydrogen peroxide, and the volume of the water required for preparing the first treatment liquid can be changed.

[0055] Step S13: texturing the second silicon wafer intermediate to form a pyramid texture surface on the surface of the second silicon wafer intermediate to obtain a third silicon wafer intermediate.

[0056] Specifically, an alkaline solution with a mass fraction of 35% to 45%, a texturing nucleating additive with a mass fraction of 10% to 15%, and water are mixed in a volume ratio of (2 to 4):1:(400 to 450) to obtain a texturing liquid, and then the texturing liquid is used to texturize the second silicon wafer intermediate by 1 to 2 microns to form the pyramid texturing surface on the surface of the second silicon wafer intermediate to obtain the third silicon wafer intermediate.

[0057] In one embodiment, the alkaline solution includes a potassium hydroxide (KOH) solution. Since crystallization can further cause pitting on the silicon wafer, the alkaline solution in the present invention is a potassium hydroxide solution with less residual foreign matter, rather than a sodium hydroxide (NaOH) solution with more severe non-crystallization. Therefore, the use of potassium hydroxide as the alkaline solution in the present invention can reduce the number of pitting on the silicon wafer after gettering annealing, thereby reducing the defective pitting ratio of the wafer after gettering annealing.

[0058] In one embodiment, the texturing nucleating additive comprises a nucleating agent, sodium silicate, sodium acetate, a surfactant, a wetting agent, and water. In one embodiment, in the texturing nucleating additive, the mass fraction of the nucleating agent is 10.5% to 12%, the mass fraction of the sodium silicate is 2.0% to 4.0%, the mass fraction of the sodium acetate is 0.5% to 1.2%, the mass fraction of the surfactant is 2.0% to 6.0%, and the mass fraction of the wetting agent is 3.0% to 8.0%.

[0059] In one embodiment, the nucleating agent includes hydrolyzed polyacrylonitrile ammonium salt.

[0060] In one embodiment, the surfactant comprises acetylene glycol polyoxyethylene ether.

[0061] In one embodiment, the wetting agent comprises an alkyl sulfate.

[0062] Among them, the texturing nucleating additive used in the present invention is a light texturing nucleating additive, rather than the original macromolecular nucleating additive and high-dose nucleating additive. The light texturing nucleating additive only needs to form a simple velvet surface, forming an uneven micro-pyramid velvet surface, increasing the specific surface area of ​​impurity deposition, and at the same time improving the efficiency of subsequent impurity gettering, so that the subsequently obtained silicon wafer can meet the cleanliness requirements of subsequent impurity gettering annealing.

[0063] In one embodiment, the base diameter of the pyramid structure of the pyramid velvet surface is 0.7 μm to 1.5 μm. If the base diameter of the pyramid structure of the pyramid velvet surface is too large or the second silicon wafer intermediate is etched too deeply, more silicon material will be etched, thereby reducing the quality of the silicon wafer.

[0064] In one embodiment, the time for texturing the second silicon wafer intermediate using the texturing liquid may be 300s to 350s.

[0065] It should be noted that when texturing the second silicon wafer intermediate, the texturing liquid can also remove the surface metal of the second silicon wafer intermediate and impurities on the second silicon wafer intermediate.

[0066] In one embodiment, 320 to 400 pieces of the second silicon wafer intermediates can be texturized as a batch. When texturizing the next batch of second silicon wafer intermediates, 200 mL to 300 ml of the potassium hydroxide solution and 120 mL to 150 ml of the texturizing nucleating additive can be added to the texturizing liquid.

[0067] It should be noted that when preparing the texturing liquid, it is not limited to mixing the alkaline solution of the above-mentioned concentration, the texturing nucleating additive of the above-mentioned concentration and water. As long as the above-mentioned texturing liquid can be obtained, the concentration and volume of the above-mentioned alkaline solution, the concentration and volume of the above-mentioned texturing nucleating additive, and the volume of the above-mentioned water required for preparing the texturing liquid can be changed.

[0068] Step S14: performing a second acid treatment on the third silicon wafer intermediate to remove metal impurities on the third silicon wafer intermediate to obtain a fourth silicon wafer intermediate.

[0069] Specifically, hydrochloric acid (HCl) with a mass fraction of 35% to 40% and water (H2O) are mixed in a volume ratio of (5 to 7): (850 to 950) to obtain a second treatment liquid precursor liquid, and ozone is injected into the second treatment liquid precursor liquid to obtain a second treatment liquid. The third silicon wafer intermediate is placed in the second treatment liquid, and the high concentration of ozone in the second treatment liquid is used to oxidize the surface of the third silicon wafer intermediate to generate an oxide layer, and the metal impurities on the third silicon wafer intermediate are micro-doped. At the same time, HCl neutralizes the potassium hydroxide remaining on the third silicon wafer intermediate and reacts with the metal impurities on the third silicon wafer intermediate to remove the metal impurities on the third silicon wafer intermediate, thereby obtaining the fourth silicon wafer intermediate.

[0070] The chemical reaction formula for ozone oxidation to form an oxide layer on the surface of the third silicon wafer intermediate is:

[0071] Si+2O3=SiO2+3O2(gas)↑.

[0072] In one embodiment, the temperature of the second treatment liquid for performing the second acid treatment on the third silicon wafer intermediate may be 23° C. to 26° C. That is, the temperature of the second treatment liquid is 23° C. to 26° C.

[0073] In one embodiment, the time for the second acid treatment of the third silicon wafer intermediate by the second treatment liquid may be 180s to 240s, so that the hydrochloric acid and the metal impurities on the third silicon wafer intermediate can fully react.

[0074] In one embodiment, the concentration of the ozone in the second treatment liquid may be 40 ppm to 50 ppm.

[0075] In one embodiment, 320 to 400 third silicon wafer intermediates may be treated with acid as a batch.

[0076] It should be noted that when preparing the second treatment liquid, it is not limited to mixing the hydrochloric acid and water of the above concentration. As long as the above second treatment liquid can be obtained, the concentration and volume of hydrochloric acid required for preparing the second treatment liquid, as well as the volume of the above water, can be changed.

[0077] Step S15: passivate the fourth silicon wafer intermediate to obtain a silicon wafer.

[0078] Specifically, hydrochloric acid (HCl) with a mass fraction of 35% to 40%, hydrofluoric acid (HF) with a mass fraction of 45% to 55%, and water (H2O) are mixed in a volume ratio of (7 to 10): (15 to 18): (900 to 1100) to obtain a third processing liquid, and the fourth silicon wafer intermediate is placed in the third processing liquid to passivate the fourth silicon wafer intermediate and simultaneously remove the oxide layer on the fourth silicon wafer intermediate to obtain the silicon wafer.

[0079] In step S15, the oxide film formed on the surface of the third silicon wafer intermediate by ozone oxidation in step S14 is removed by reacting a strong acid with the silicon oxide on the surface of the fourth silicon wafer intermediate. The metal attached to the oxide film dissolves into the third treatment solution, and the third treatment solution also inhibits the formation of a natural oxide film. Therefore, step S15 can remove most of the metal on the surface of the fourth silicon wafer intermediate. However, as the oxide film dissolves into the third treatment solution, some of the metal will adhere to the surface of the fourth silicon wafer intermediate. HF has a weak reactivity with these metals and their compounds, which can easily cause secondary contamination. After a period of time, metal contamination easily occurs due to metal accumulation, resulting in surface contamination of the silicon wafer, which can cause abnormal pitting on the silicon wafer after gettering annealing. Therefore, the hydrochloric acid in the third treatment solution can enhance the secondary metal removal capability of the third treatment solution. Furthermore, the hydrofluoric acid in the third treatment solution not only removes the oxide film but also enhances the hydrophobicity of the fourth silicon wafer intermediate, paving the way for subsequent slow pull-off dehydration and drying.

[0080] The chemical reaction formula in step S15 is:

[0081] SiO2+4HF=SiF4(gas)↑+2H2O(reacts with the oxide layer to remove adsorbed metal impurities);

[0082] Cu+2HCl=CuCl2+H2(gas)↑(demetallization);

[0083] Fe+2HCl=FeCl2+H2(gas)↑(demetallization);

[0084] Mg+2HCl=MgCl2+H2(gas)↑(demetallization).

[0085] Among them, passivating the fourth silicon wafer intermediate can effectively improve the dislocations and defects of the fourth silicon wafer intermediate, so as to improve the conversion efficiency of the subsequently prepared solar cell.

[0086] In one embodiment, 320 to 400 fourth silicon wafer intermediates may be passivated as a batch.

[0087] It should be noted that when preparing the third treatment liquid, it is not limited to mixing the hydrochloric acid of the above-mentioned concentration, the hydrofluoric acid of the above-mentioned concentration and water. As long as the third treatment liquid can be obtained, the concentration and volume of the hydrochloric acid, the concentration and volume of the hydrofluoric acid, and the volume of the water required for preparing the third treatment liquid can be changed.

[0088] Step S16: washing the silicon wafer with water, and taking out the washed silicon wafer through a slow pulling device.

[0089] Specifically, the silicon wafer is placed in water for cleaning, and the slow pulling device is used to slowly lift the washed silicon wafer from the water to reduce the amount of liquid adsorbed on the surface of the silicon wafer, and the washed silicon wafer is slowly dehydrated, so that the surface of the silicon wafer has a higher degree of cleanliness.

[0090] Step S17: drying the removed silicon wafer.

[0091] Specifically, the silicon wafer taken out may be dried by filling it with nitrogen (N2) to remove water on the surface of the silicon wafer.

[0092] Step S18: performing gettering annealing on the dried silicon wafer.

[0093] It is understood that after step S18, the silicon wafer after gettering annealing can be subjected to subsequent processing according to existing methods, such as texturing and cleaning, CVD coating, PVD coating, screen printing and testing, etc., to finally prepare a solar cell.

[0094] Because the surface of the cast single-crystal silicon wafer (i.e., the silicon wafer to be processed) contains both single-crystal and polycrystalline regions, as well as surface particles and metal contamination, the wafer interior is subject to defects such as dislocations, small-angle grain boundaries, and a high defect density. Furthermore, polycrystalline silicon wafers contain a large number of metal impurities such as iron, nickel, copper, and cobalt. These metal impurities form numerous recombination centers, thereby reducing minority carrier lifetime and affecting the electrical performance of the battery. While gettering annealing can only remove trace amounts of metal impurities within the silicon wafer, residual metal impurities on the surface must be effectively removed before gettering. Furthermore, silicon powder, surface particles, and metal contamination on the silicon wafer surface, including dust and oil from packaging and transportation, can diffuse into local areas of the wafer at high temperatures if not cleaned before gettering. Adjacent areas then gradually diffuse and become contaminated, resulting in small black spots and specks. Dense concentrations of these small spots and specks form regional pitting, which in turn seriously contaminates the next process step, leading to excessive defective contamination and low conversion efficiency of subsequently manufactured batteries.

[0095] To address these issues, the present invention utilizes a novel gettering annealing pretreatment process: silicon dust removal followed by a first acid treatment followed by a light texturing process followed by a second acid treatment, rather than the existing simple rough polishing process. This effectively removes metal particles and harmful impurities from the surface of the silicon wafers being processed, while also minimizing etching and thinning of unfinished silicon wafers, thus preventing degradation of the wafer's quality and weight. Furthermore, the micro-pyramid texturing on the silicon wafers increases the area for phosphorus deposition, creating optimal conditions for gettering annealing. This method can reduce the proportion of defective pitting on silicon wafers after gettering annealing and improve the conversion efficiency of solar cells fabricated from these wafers.

[0096] The present invention is further described below with reference to specific examples and comparative examples.

[0097] Example 1

[0098] (1) A hydrophilic wetting agent with a mass fraction of 15% and pure water are mixed in a volume ratio of 10:800 to obtain a cleaning solution, and the cleaning solution is then loaded into a cleaning tank in an ultrasonic cleaning device with a rated power of 1500W, and a silicon wafer to be processed is placed in the cleaning tank so that the cleaning solution immerses the silicon wafer to be processed. Then, the ultrasonic cleaning device is started, and the power of the ultrasonic cleaning device is set to 50% of the rated power, that is, the power of the ultrasonic cleaning device is set to 750W, so that the ultrasonic waves emitted by the ultrasonic cleaning device and the cleaning solution jointly clean the silicon wafer to be processed, and the cleaning is carried out for 300s to remove silicon powder on the silicon wafer to be processed, thereby obtaining a first silicon wafer intermediate.

[0099] (2) 30% by mass of hydrochloric acid, 35% by mass of hydrogen peroxide, and pure water are mixed in a volume ratio of 5:10:800 to obtain a first treatment liquid, and then the first silicon wafer intermediate is placed in the first treatment liquid, and the temperature of the first treatment liquid is set to 23°C to perform a first acid treatment on the first silicon wafer intermediate for 160 seconds, thereby removing metal impurities and organic dirt on the first silicon wafer intermediate to obtain a second silicon wafer intermediate.

[0100] (3) A potassium hydroxide solution with a mass fraction of 35%, a texturing nucleating additive with a mass fraction of 15%, and pure water are mixed in a volume ratio of 2:1:400 to obtain a texturing solution, and then the second silicon wafer intermediate is texturized with the texturing solution and maintained for 300 seconds to form a pyramid velvet surface on the surface of the second silicon wafer intermediate, and the base diameter of the pyramid structure of the pyramid velvet surface is 0.7 μm, thereby obtaining a third silicon wafer intermediate. In the texturing nucleating additive, the mass fraction of hydrolyzed polyacrylonitrile ammonium salt is 10.5%, the mass fraction of sodium silicate is 2.0%, the mass fraction of sodium acetate is 0.5%, the mass fraction of acetylene glycol polyoxyethylene ether is 2.0%, the mass fraction of alkyl sulfate is 3.0%, and the mass fraction of water is 82%.

[0101] (4) Hydrochloric acid with a mass fraction of 35% and pure water are mixed in a volume ratio of 5:850 to obtain a second treatment liquid precursor liquid, and ozone is injected into the second treatment liquid precursor liquid to obtain a second treatment liquid, and the concentration of ozone in the second treatment liquid is controlled to be 40 ppm. At the same time, the temperature of the second treatment liquid is set to 23°C. The third silicon wafer intermediate is then placed in the second treatment liquid, and the high concentration of ozone in the second treatment liquid is used to oxidize the surface of the third silicon wafer intermediate to generate an oxide layer, and the metal impurities on the third silicon wafer intermediate are micro-absorbed. At the same time, HCL neutralizes the potassium hydroxide remaining on the third silicon wafer intermediate and reacts with the metal impurities on the third silicon wafer intermediate for 180 seconds to remove the metal impurities on the third silicon wafer intermediate to obtain a fourth silicon wafer intermediate.

[0102] (5) Mixing hydrochloric acid with a mass fraction of 35%, hydrofluoric acid with a mass fraction of 45%, and pure water in a volume ratio of 7:15:900 to obtain a third treatment liquid, and placing the fourth silicon wafer intermediate in the third treatment liquid to passivate the fourth silicon wafer intermediate and simultaneously remove the oxide layer on the fourth silicon wafer intermediate to obtain a silicon wafer.

[0103] (6) The silicon wafer is placed in pure water for cleaning, and the washed silicon wafer is slowly lifted from the pure water by a slow pulling device to reduce the amount of liquid adsorbed on the surface of the silicon wafer and to slowly dehydrate the washed silicon wafer.

[0104] (7) Dry the removed silicon wafer by filling it with nitrogen.

[0105] (8) Perform gettering annealing on the dried silicon wafer.

[0106] Comparative Example 1

[0107] The silicon wafer to be processed is processed using the existing rough polishing process to obtain a silicon wafer, and then the obtained silicon wafer is subjected to gettering annealing, specifically as follows:

[0108] (1) Placing the silicon wafer to be processed in a sodium hydroxide solution for rough polishing to obtain a first silicon wafer intermediate.

[0109] (2) The first silicon wafer intermediate is placed in a solution containing sodium hydroxide solution and hydrogen peroxide for cleaning to obtain a second silicon wafer intermediate.

[0110] (3) The second silicon wafer intermediate is placed in hydrofluoric acid for passivation to obtain a silicon wafer.

[0111] (4) The silicon wafer is placed in pure water for cleaning, and the washed silicon wafer is slowly lifted from the pure water by a slow pulling device to reduce the amount of liquid adsorbed on the surface of the silicon wafer and to slowly dehydrate the washed silicon wafer.

[0112] (5) Dry the removed silicon wafer by filling it with nitrogen.

[0113] (6) Perform gettering annealing on the dried silicon wafer.

[0114] (1) 1000 silicon wafers to be processed were processed by Example 1 and Comparative Example 1, respectively, and the defective ratio of pitting on the 1000 silicon wafers obtained by Example 1 and Comparative Example 1 after gettering annealing was tested.

[0115] See also Figure 2 , it can be seen that the defective ratio of pitting of the silicon wafer in Example 1 after the impurity annealing treatment (i.e. from August 2022 to October 2022) is 0.21% on average (i.e. Figure 2 After the improvement in the above process, the defective ratio of pitting of the silicon wafers in Comparative Example 1 after the gettering annealing treatment (from February 2022 to July 2022) was 15.22% on average (i.e. Figure 2 Compared to Comparative Example 1, the defective pitting rate of the silicon wafer in Example 1 after gettering annealing was reduced from 15.22% to 0.21%, a decrease of 98.62%. This demonstrates that the present invention can reduce metal impurities and other harmful substances on the silicon wafer, ensure the surface cleanliness of the silicon wafer before gettering annealing, and thus reduce the defective pitting rate of the silicon wafer after gettering annealing.

[0116] (2) The silicon wafers after gettering annealing in Example 1 and Comparative Example 1 were respectively fabricated into solar cells through subsequent steps, and the conversion efficiency of the solar cells prepared from the silicon wafers in Example 1 and the solar cells prepared from the silicon wafers in the comparative example were compared.

[0117] See also Figure 3 , it can be seen that the conversion efficiency of the solar cell prepared from the silicon wafer after gettering annealing in Example 1 is 24.28% (i.e. Figure 3 After the improvement in the above example), the conversion efficiency of the solar cell prepared from the silicon wafer after the gettering annealing treatment in Comparative Example 1 was 24.21% (i.e. Figure 3 This indicates that the conversion efficiency of the solar cell prepared from the silicon wafer after the gettering annealing treatment in Example 1 is higher than the conversion efficiency of the solar cell prepared from the silicon wafer after the gettering annealing treatment in Comparative Example 1, and the conversion efficiency is improved by 0.07%.

[0118] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0119] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for reducing silicon wafer gettering annealing pitting defects, characterized in that: The following steps are involved: Performing ultrasonic cleaning on the silicon wafer to be processed to remove silicon powder on the silicon wafer to be processed to obtain a first silicon wafer intermediate; performing a first acid treatment on the first silicon wafer intermediate to remove metal impurities and organic contaminants on the first silicon wafer intermediate to obtain a second silicon wafer intermediate; The second silicon wafer intermediate is subjected to texturing to form a pyramid textured surface on the surface of the second silicon wafer intermediate, thereby obtaining a third silicon wafer intermediate; the texturing comprises the following steps: texturing the second silicon wafer intermediate using a texturing solution containing an alkaline solution and a texturing nucleating additive; the texturing nucleating additive comprises a nucleating agent, sodium silicate, sodium acetate, a surfactant, and a wetting agent; the nucleating agent comprises hydrolyzed polyacrylonitrile ammonium salt, the surfactant comprises acetylene glycol polyoxyethylene ether, and the wetting agent comprises alkyl sulfate; and The third silicon wafer intermediate is subjected to a second acid treatment to remove metal impurities on the third silicon wafer intermediate.

2. The method for reducing silicon wafer gettering annealing pitting defects according to claim 1, wherein: The first acid treatment comprises the following steps: The first silicon wafer intermediate is subjected to a first acid treatment using a first treatment liquid containing hydrochloric acid and hydrogen peroxide.

3. The method for reducing silicon wafer gettering annealing pitting defects according to claim 2, wherein: The method comprises at least one of the following (1) to (3): (1) The method for preparing the first treatment liquid comprises the following steps: Mixing hydrochloric acid with a mass fraction of 30% to 40%, hydrogen peroxide with a mass fraction of 35% to 40%, and water in a volume ratio of (5 to 7): (10 to 15): (800 to 1000); (2) the temperature of the first acid treatment is 23-26°C; (3) The time of the first acid treatment is 160s to 220s.

4. The method for reducing silicon wafer gettering annealing pitting defects according to claim 1, wherein: The method includes at least one of the following (4) to (5): (4) The alkaline solution includes potassium hydroxide solution; (5) In the texturing nucleating additive, the mass fraction of the nucleating agent is 10.5% to 12%, the mass fraction of sodium silicate is 2.0% to 4.0%, the mass fraction of sodium acetate is 0.5% to 1.2%, the mass fraction of the surfactant is 2.0% to 6.0%, and the mass fraction of the wetting agent is 3.0% to 8.0%.

5. The method for reducing silicon wafer gettering annealing pitting defects according to claim 3, wherein: The method comprises at least one of the following (6) to (7): (6) The method for preparing the texturing liquid comprises the following steps: Mixing 35% to 45% by mass of the alkaline solution, 10% to 15% by mass of the texturing nucleation additive, and water in a volume ratio of (2 to 4):1:(400 to 450); (7) The time for making the texturing is 300s to 350s.

6. The method for reducing silicon wafer gettering annealing pitting defects according to any one of claims 1 to 5, wherein: The bottom surface diameter of the pyramid structure of the pyramid velvet surface is 0.7 μm to 1.5 μm.

7. The method for reducing silicon wafer gettering annealing pitting defects according to any one of claims 1 to 5, wherein: The ultrasonic cleaning comprises the following steps: Placing the silicon wafer to be processed in a cleaning solution, and cleaning the silicon wafer to be processed under ultrasonic conditions; Wherein, the cleaning solution includes a hydrophilic wetting agent, and the hydrophilic wetting agent includes polyethylene oxide.

8. The method for reducing silicon wafer gettering annealing pitting defects according to any one of claims 1 to 5, wherein: The second acid treatment comprises the following steps: performing a second acid treatment on the third silicon wafer intermediate using a second treatment solution containing an acidic reagent and ozone; Wherein, the concentration of the ozone in the second treatment liquid is 40 ppm to 50 ppm.

9. The method for reducing silicon wafer gettering annealing pitting defects according to any one of claims 1 to 5, wherein: After the second acid treatment, the method further includes a step of passivating the third silicon wafer intermediate.

Images