CN116314463A - Method for reducing silicon wafer gettering annealing pit defects - Google Patents

Abstract

The invention provides a method for reducing defect of silicon wafer gettering annealing pits, which comprises the following steps: carrying out ultrasonic cleaning on the silicon wafer to be treated to remove silicon powder on the silicon wafer to be treated, so as to obtain a first silicon wafer intermediate; performing first acid treatment on the first silicon wafer intermediate to remove metal impurities and organic dirt on the first silicon wafer intermediate and obtain a second silicon wafer intermediate; texturing the second silicon wafer intermediate to form pyramid textured surfaces on the surface of the second silicon wafer intermediate to obtain a third silicon wafer intermediate; and carrying out second acid treatment on the third silicon wafer intermediate to remove metal impurities on the third silicon wafer intermediate. The invention reduces the bad proportion of pocks of the silicon wafer after gettering annealing and improves the conversion efficiency of the subsequently prepared solar cell.

Description

Method for reducing silicon wafer gettering annealing pit defects

technical field

The invention relates to the technical field of solar cells, in particular to a method for reducing silicon chip gettering and annealing pit defects.

Background technique

Heterojunction solar cell, also known as HJT cell (Hereto-junction with Intrinsic Thin-layer), is a heterojunction solar cell with intrinsic thin layer, which was successfully prepared for the first time in 1992, with a conversion efficiency of 18.1%. With the improvement of process methods and the introduction of new materials, the efficiency continues to break through new highs, and the theoretical value is also constantly refreshing records.

In the production process of heterojunction solar cells, after gettering annealing is performed on N-type silicon wafers, abnormally many pits frequently appear on the surface of silicon wafers. Since the existing HJT preparation process does not effectively deal with pitting abnormalities, resulting in more pitting on silicon wafers after gettering annealing, which seriously pollutes the next process, thereby reducing the conversion efficiency of subsequent heterojunction solar cells.

Contents of the invention

Based on this, it is necessary to provide a method for reducing pitting defects of silicon wafers after gettering annealing, so as to reduce the ratio of pitting defects of silicon wafers after gettering annealing and improve the conversion efficiency of subsequent solar cells.

The invention provides a method for reducing silicon chip gettering and annealing pit defects, comprising the following steps:

Ultrasonic cleaning is performed on the silicon wafer to be treated to remove the silicon powder on the silicon wafer to be treated to obtain a first silicon wafer intermediate;

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;

Texturing the second silicon wafer intermediate to form a pyramid texture on the surface of the second silicon wafer intermediate to obtain a third silicon wafer intermediate; and

performing a second acid treatment on the third intermediate silicon wafer to remove metal impurities on the third intermediate silicon wafer.

In some of these embodiments, the first acid treatment comprises the following steps:

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

In some of these embodiments, the method includes at least one of the following (1)-(3):

(1) The preparation method of the first treatment liquid comprises the following steps:

Mixing hydrochloric acid with a mass fraction of 30% to 40%, hydrogen peroxide and water with a mass fraction of 35% to 40% 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 for the first acid treatment is 160s-220s.

In some of these embodiments, the texturing comprises the following steps:

Texturing the second silicon wafer intermediate is carried out by using a texturing solution containing an alkaline solution and a texturing nucleating additive.

In some of these embodiments, the method includes at least one of the following (4)-(5):

(4) described alkaline solution comprises potassium hydroxide solution;

(5) described nucleating additive for making texture comprises nucleating agent, sodium silicate, sodium acetate, surfactant and wetting agent, and in described nucleating additive for making texture, the mass fraction of described 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%, the wetting The mass fraction of the agent is 3.0%-8.0%.

In some of these embodiments, the method includes at least one of the following (6)-(7):

(6) the preparation method of described texturizing liquid comprises the following steps:

The alkaline solution with a mass fraction of 35% to 45%, the texturing nucleating additive with a mass fraction of 10% to 15%, and water in a volume of (2 to 4):1:(400 to 450) than to mix;

(7) The time for making texture is 300s-350s.

In some of the embodiments, the diameter of the bottom surface of the pyramid structure of the pyramid texture is 0.7 μm˜1.5 μm.

In some of these embodiments, the ultrasonic cleaning includes 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 treatment liquid includes a hydrophilic wetting agent, and the hydrophilic wetting agent includes polyoxyethylene.

In some of these embodiments, the second acid treatment includes the following steps:

performing a second acid treatment on the third silicon wafer intermediate by 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˜50 ppm.

In some embodiments, after the second acid treatment, the method further includes the step of passivating the third silicon wafer intermediate.

The present invention adopts a brand-new gettering annealing pretreatment process method, that is, silicon powder removal + first acid treatment + texturing + second acid treatment, instead of the existing simple rough polishing process, to effectively remove the surface of the silicon wafer to be treated The metal particles and harmful impurities on the silicon wafers are etched and thinned at the same time, which avoids the decrease in the quality and weight of the silicon wafers, and the micro-pyramid texture on the silicon wafers increases the area of phosphorus deposition, which is an important step for annealing. Sufficient conditions are made for gettering. The invention can reduce the bad ratio of pitting of the silicon chip after gettering annealing and improve the conversion efficiency of the solar cell prepared by the silicon chip.

Description of drawings

Fig. 1 is the flow chart of reducing silicon chip gettering annealing pit defect provided by the present invention;

Fig. 2 is a bad ratio of pitting of the silicon wafer in Example 1 of the present invention after gettering annealing treatment and a bad ratio of pitting of the silicon wafer in Comparative Example 1 after gettering annealing treatment;

3 is a graph showing the conversion efficiency of the solar cell made of the silicon wafer in Example 1 of the present invention and the conversion efficiency of the solar cell made of the silicon wafer in Comparative Example 1. FIG.

Detailed ways

In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the associated drawings. Preferred embodiments of the invention are shown in the accompanying drawings. However, the present invention can be embodied in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field of the invention. The terms used herein in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Please refer to Fig. 1, the present invention provides a kind of method for reducing silicon chip gettering annealing pit defect, comprises the following steps:

Step S11 , performing ultrasonic cleaning on the silicon wafer to be processed, so as to remove silicon powder on the silicon wafer to be processed, and obtain a first intermediate silicon wafer.

Specifically, the cleaning agent with a mass fraction of 15% to 30% and water are mixed at a volume ratio of (10 to 20): (800 to 1000) to obtain a cleaning treatment solution, and then the cleaning treatment solution is loaded into the In the cleaning tank in the ultrasonic cleaning device, and place the silicon chip to be processed in the cleaning tank, so that the cleaning treatment liquid is immersed in the silicon chip to be processed, and then start the ultrasonic cleaning device, so that The ultrasonic wave emitted by the ultrasonic cleaning device and the cleaning solution jointly clean the silicon wafer to be processed, so as to remove the silicon powder on the silicon wafer to be processed, and obtain the first intermediate silicon wafer.

In one embodiment, the cleaning agent includes a hydrophilic wetting agent. Wherein, the hydrophilic wetting agent includes polyoxyethylene. Wherein, the hydrophilic wetting agent makes the silicon wafer to be treated fully contact and wet with water, so as to eliminate the interfacial energy of the silicon wafer to be treated, and make water enter the pores on the surface of the silicon wafer to be treated, thereby The silicon powder in the pores of the silicon wafer to be processed is removed.

In one embodiment, the rated power of the ultrasonic cleaning device may be 1500W-2000W. When cleaning the silicon wafer to be processed, the power of the ultrasonic cleaning device can be set to 40% to 50% of the rated power, that is, to use 40% to 50% of the rated power to clean the silicon wafer to be processed, so as to Preventing the use of too high power from damaging the silicon wafer to be processed, and preventing the use of too low power from reducing the removal effect of silicon powder.

In one embodiment, the ultrasonic cleaning time may be 300s˜450s.

Among them, the main principle of ultrasonic cleaning is to use ultrasonic cavitation effect, radiation pressure and acoustic flow to transfer energy to water, so that ultrasonic waves can be fully exerted, thereby shaking silicon powder out of the surface pores of the silicon wafer to be treated. In addition, due to the relatively light quality of the silicon powder, when the silicon powder is shaken out from the surface pores of the silicon wafer to be treated, it will float on the surface of the water, and then the water in the cleaning tank will be discharged by circulation, thereby removing all The silicon powder on the silicon wafer to be processed and the impurities on the surface of the silicon wafer to be processed are reduced to reduce the generation of subsequent pits.

Wherein, the silicon wafers to be processed may be silicon wafers just shipped from the factory.

In one embodiment, 320 to 400 silicon wafers to be processed can be used as a batch for ultrasonic cleaning, and when the next batch of silicon wafers to be processed is ultrasonically cleaned, the cleaning solution can be added Add 100mL-150ml of the cleaning agent.

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

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

Specifically, hydrochloric acid (HCl) with a mass fraction of 30% to 40%, hydrogen peroxide (H ₂ O ₂ ) with a mass fraction of 35% to 40%, and water are mixed in a ratio of (5 to 7): (10 to 15): ( 800-1000) to obtain a first treatment solution, and then place the first silicon wafer intermediate in the first treatment solution to acid-treat the first silicon wafer intermediate, Thereby removing metal impurities and organic dirt on the intermediate of the first silicon wafer, avoiding the degradation of the structural quality of the silicon wafer caused by rough polishing and thinning of the original process, improving the cleanliness of the surface of the silicon wafer, and obtaining the first silicon wafer. Two silicon wafer intermediates.

In one embodiment, the temperature for performing the first acid treatment on the first silicon wafer intermediate by using the first treatment solution may be 23°C-26°C. That is, the temperature of the first treatment liquid is 23°C to 26°C.

In one embodiment, the time for using the first treatment liquid to perform the first acid treatment on the first silicon wafer intermediate is 160s-220s, so that the first treatment liquid can have sufficient time to interact with the The metal impurities and organic dirt on the first silicon wafer intermediate react to remove the metal impurities and organic dirt on the first silicon wafer intermediate.

It should be noted that when preparing the first treatment liquid, it is not limited to mixing the hydrochloric acid of the above-mentioned concentration, the hydrogen peroxide and water of the above-mentioned concentration, as long as the above-mentioned first treatment liquid can be obtained, the preparation of the first treatment liquid can be changed. The concentration and volume of the above-mentioned hydrochloric acid, the concentration and volume of the above-mentioned hydrogen peroxide, and the volume of the above-mentioned water.

Step S13, performing texturing on the second silicon wafer intermediate to form a pyramid texture on the surface of the second silicon wafer intermediate to obtain a third silicon wafer intermediate.

Specifically, an alkaline solution with a mass fraction of 35% to 45%, a texturizing nucleating additive with a mass fraction of 10% to 15%, and water in a volume ratio of (2 to 4):1:(400 to 450) mixing to obtain a texturing solution, and then using the texturing solution to perform 1-2 micron texturing on the second silicon wafer intermediate to form the pyramid texture on the surface of the second silicon wafer intermediate On the other hand, the third intermediate silicon wafer is obtained.

In one embodiment, the alkaline solution includes potassium hydroxide (KOH) solution. Since the crystallization will further cause pitting to occur in the follow-up of the silicon wafer, the alkaline solution in the present invention selects a potassium hydroxide solution with less foreign matter, rather than a sodium hydroxide (NaOH) solution with severe crystallization, so the present invention selects Potassium hydroxide as the alkaline solution can reduce the number of pits on the silicon wafer after gettering annealing, thereby reducing the bad ratio of pitting on the wafer after gettering annealing.

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

In one embodiment, the nucleating agent includes ammonium hydrolyzed polyacrylonitrile.

In one embodiment, the surfactant includes acetylene glycol polyoxyethylene ether.

In one embodiment, the wetting agent includes alkyl sulfates.

Wherein, the described 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, and the light texturing nucleating additive only needs to form a simple The suede surface forms an uneven micro-pyramid suede surface, increases the specific surface area of gettering deposition, and at the same time improves the efficiency of subsequent gettering, so that the subsequent obtained silicon wafers can meet the cleanliness requirements of subsequent gettering annealing.

In one embodiment, the diameter of the bottom surface of the pyramid structure of the pyramid texture is 0.7 μm˜1.5 μm. Wherein, if the bottom diameter of the pyramid structure of the pyramid texture 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.

In one embodiment, the time for texturing the second silicon wafer intermediate by using the texturing solution may be 300s˜350s.

It should be noted that when the second silicon wafer intermediate is textured, the texturing solution can also remove the surface metal of the second silicon wafer intermediate and impurities on the second silicon wafer intermediate .

In one embodiment, 320 to 400 pieces of the second silicon wafer intermediates can be used as a batch for texturing, and when the next batch of second silicon wafer intermediates is textured, the 200mL-300ml of the potassium hydroxide solution and 120mL-150ml of the velvet nucleating additive are added to the texturing solution.

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 preparation of the texturing liquid can be changed. The concentration and volume of the above-mentioned alkaline solution required by the liquid, the concentration and volume of the above-mentioned texture nucleating additive, and the volume of the above-mentioned water.

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

Specifically, mixing hydrochloric acid (HCl) with a mass fraction of 35% to 40% and water (H ₂ O) at a volume ratio of (5 to 7): (850 to 950) to obtain the second treatment liquid precursor liquid, Then inject ozone into the precursor liquid of the second processing liquid to obtain a second processing liquid, place the third silicon wafer intermediate in the second processing liquid, and utilize the high concentration of ozone in the second processing liquid Oxidize the surface of the third silicon wafer intermediate to form an oxide layer, and perform micro-gettering on the metal impurities on the third silicon wafer intermediate, and at the same time HCL and the residual hydrogen on the third silicon wafer intermediate Potassium oxide neutralizes and reacts with the metal impurities on the third intermediate silicon wafer to remove the metal impurities on the third intermediate silicon wafer to obtain the fourth intermediate silicon wafer.

Wherein, ozone oxidizes the surface of the third silicon wafer intermediate, and the chemical reaction formula for generating an oxide layer is:

Si+2O ₃ =SiO ₂ +3O ₂ (gas)↑.

In one embodiment, the temperature at which the second treatment solution performs the second acid treatment on the third silicon wafer intermediate may be 23°C-26°C. That is, the temperature of the second treatment liquid is 23°C to 26°C.

In one embodiment, the time for the second treatment liquid to perform the second acid treatment on the third intermediate silicon wafer may be 180s to 240s, so that the hydrochloric acid and the metal impurities on the third intermediate silicon wafer able to respond adequately.

In one embodiment, the concentration of the ozone in the second treatment liquid may be 40 ppm˜50 ppm.

In one embodiment, 320-400 pieces of the third silicon wafer intermediates may be treated with acid as a batch.

It should be noted that when preparing the second treatment liquid, it is not limited to mixing the hydrochloric acid of the above-mentioned concentration with water, as long as the above-mentioned second treatment liquid can be obtained, the concentration and concentration of hydrochloric acid required for the preparation of the second treatment liquid can be changed. volume, and the volume of the aforementioned water.

Step S15 , passivating the fourth silicon wafer intermediate to obtain a silicon wafer.

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 (H ₂ O) are mixed in a ratio of (7 to 10): (15 to 18): Mixing at a volume ratio of (900-1100) to obtain a third treatment solution, and placing the fourth silicon wafer intermediate in the third treatment solution to process the fourth silicon wafer intermediate passivation, and at the same time remove the oxide layer on the fourth intermediate silicon wafer to obtain the silicon wafer.

Wherein, in step S15, the reaction of strong acid and silicon oxide on the surface of the fourth silicon wafer intermediate body is used to remove the oxide film generated by ozone oxidation on the surface of the third silicon wafer intermediate body in step S14. The metal on the oxide film dissolves into the third treatment solution, and the third treatment solution can also inhibit the formation of the natural oxide film, so step S15 can remove the surface layer of the fourth silicon wafer intermediate Most metals. However, as the oxide film dissolves into the third treatment solution, a part of metals will adhere to the surface of the fourth silicon wafer intermediate, and HF has a weak reaction ability with these metals and their compounds, which may easily cause secondary Secondary pollution, it is very easy to have metal pollution due to metal accumulation after a period of time, resulting in dirty silicon wafer surface, resulting in abnormal pitting of silicon wafer after gettering annealing. Therefore, the hydrochloric acid in the third treatment liquid can improve the second metal removal ability of the third treatment liquid. In addition, the hydrofluoric acid in the third treatment solution also enhances the hydrophobicity of the fourth silicon wafer intermediate while removing the oxide layer, which fully paves the way for the subsequent slow pulling, dehydration and drying. .

Wherein, the chemical reaction formula in step S15 is:

SiO ₂ +4HF=SiF ₄ (gas) ↑+2H ₂ O (reactive oxide layer, removing adsorbed metal impurities);

Cu+2HCl=CuCl ₂ +H ₂ (gas) ↑ (demetallization);

Fe+2HCl=FeCl ₂ +H ₂ (gas) ↑ (demetallization);

Mg+2HCl=MgCl ₂ +H ₂ (gas) ↑ (demetallization).

Wherein, 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.

In an embodiment, 320-400 pieces of the fourth intermediate silicon wafer may be passivated as a batch.

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 above-mentioned third treatment liquid can be obtained, the preparation of the third treatment liquid can be changed. The required concentration and volume of the above-mentioned hydrochloric acid, the concentration and volume of the above-mentioned hydrofluoric acid, and the volume of the above-mentioned water.

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

Specifically, place the silicon wafer in water for cleaning, and slowly lift the washed silicon wafer from the water by the slow lifting device to reduce the amount of liquid adsorbed on the surface of the silicon wafer, and make the water wash After the silicon wafer is slowly dehydrated, the surface of the silicon wafer has a higher degree of cleanliness.

Step S17, drying the removed silicon wafer.

Specifically, the silicon wafer taken out may be dried by filling nitrogen (N ₂ ) to remove water on the surface of the silicon wafer.

Step S18 , performing gettering annealing on the dried silicon wafer.

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

Due to the presence of both monocrystalline and polycrystalline regions on the surface of the cast monocrystalline wafer (i.e. the wafer to be processed), along with the presence of surface particles and surface metal contamination levels, there are dislocations inside the wafer , Small-angle grain boundaries, high defect density and other shortcomings, and polycrystalline silicon wafers contain a large amount of metal impurities such as iron, nickel, copper and cobalt, these metal impurities will form a large number of recombination centers, thereby reducing the minority carrier lifetime and affecting the electrical performance of the battery. Gettering annealing can only getter and remove a small amount of metal impurities inside the silicon wafer, and the residual metal impurities on the surface must be effectively removed before gettering. At the same time, silicon powder, surface particles, and surface metal contamination on the surface of the silicon wafer will Including dust and oil stains during packaging and transportation. If cleaning is not carried out before gettering, the pollutants will diffuse to the local silicon wafer with high temperature, and the adjacent areas will gradually diffuse and be polluted, resulting in small black spots, small black spots, dense Small black spots and small black spots form regional pits, which seriously pollute the next process, resulting in more bad dirt and low conversion efficiency of the subsequently prepared cells.

In view of the above problems, the present invention adopts a brand-new gettering annealing pretreatment process method, that is, silicon powder removal + first acid treatment + light texturing + second acid treatment, instead of the existing simple rough throwing process, which can effectively remove Metal particles and harmful impurities on the surface of the silicon wafer to be treated, and at the same time less etching and thinning of the unproduced silicon wafer, avoiding the decline in the quality and weight of the silicon wafer, and increasing the micro-pyramid texture on the silicon wafer The area of phosphorus deposition is reduced, and sufficient conditions are prepared for annealing and gettering. The invention can reduce the bad ratio of pitting of the silicon chip after gettering annealing and improve the conversion efficiency of the solar cell prepared by the silicon chip.

The present invention will be further described below by specific examples and comparative examples.

Example 1

(1) Mix the hydrophilic wetting agent with a mass fraction of 15% and pure water at a volume ratio of 10:800 to obtain a cleaning treatment solution, and then put the cleaning treatment solution into an ultrasonic cleaning device with a rated power of 1500W In the cleaning tank, place the silicon wafers to be processed in the cleaning tank so that the cleaning treatment solution is immersed in the silicon wafers to be processed, and then start the ultrasonic cleaning device so that the power of the ultrasonic cleaning device is 50% of the rated power, that is, set The power of the ultrasonic cleaning device is 750W, so that the ultrasonic wave emitted by the ultrasonic cleaning device and the cleaning treatment liquid jointly clean the silicon wafer to be processed, and clean for 300s to remove the silicon powder on the silicon wafer to be processed, and obtain the first intermediate silicon wafer.

(2) Mix hydrochloric acid with a mass fraction of 30%, hydrogen peroxide with a mass fraction of 35%, and pure water at a volume ratio of 5:10:800 to obtain the first treatment solution, and then place the first silicon wafer intermediate on In the first treatment liquid, and set the temperature of the first treatment liquid to be 23°C, to carry out the first acid treatment on the first silicon wafer intermediate body, and treat it for 160s, so as to remove the metal impurities and organic matter on the first silicon wafer intermediate body. Dirty, yielding a second silicon wafer intermediate.

(3) Mix the potassium hydroxide solution with a mass fraction of 35%, the texture nucleating additive with a mass fraction of 15%, and pure water at a volume ratio of 2:1:400 to obtain a texture liquid, and then use the texture liquid to texture the second silicon wafer intermediate, and keep it for 300s to form a pyramid texture on the surface of the second silicon wafer intermediate, and make the diameter of the bottom surface of the pyramid structure of the pyramid texture be 0.7 μm to obtain the third silicon wafer. film intermediates. Among them, in the nucleating additive for wool making, 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%, and the mass fraction of acetylene glycol polyoxyethylene ether The mass fraction is 2.0%, the mass fraction of alkyl sulfate is 3.0%, and the mass fraction of water is 82%.

(4) Mix hydrochloric acid and pure water with a mass fraction of 35% at a volume ratio of 5:850 to obtain a second treatment liquid precursor liquid, and then inject ozone into the second treatment liquid precursor liquid to obtain a second treatment liquid, And control the concentration of ozone in the second treatment liquid to be 40ppm, set the temperature of the second treatment liquid to be 23°C at the same time, then place the third silicon wafer intermediate in the second treatment liquid, utilize the high concentration of ozone in the second treatment liquid Oxidize the surface of the third silicon wafer intermediate to form an oxide layer, and micro-getter the metal impurities on the third silicon wafer intermediate, while HCL neutralizes the residual potassium hydroxide on the third silicon wafer intermediate, and react with the metal impurities on the third intermediate silicon wafer, and keep for 180s to remove the metal impurities on the third intermediate silicon wafer to obtain a fourth intermediate silicon wafer.

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

(6) Place the silicon wafer in pure water for cleaning, and slowly lift the above-mentioned washed silicon wafer from the pure water by a slow pulling device to reduce the amount of liquid adsorbed on the surface of the silicon wafer, and make the washed silicon wafer Dehydrate slowly.

(7) Dry the silicon wafer taken out by filling nitrogen gas.

(8) Gettering annealing is performed on the dried silicon wafer.

Comparative example 1

Use the existing rough polishing process to process the silicon wafer to be treated to obtain the silicon wafer, and then perform gettering annealing on the obtained silicon wafer, as follows:

(1) Place the silicon wafer to be treated in a sodium hydroxide solution for rough polishing to obtain a first intermediate silicon wafer.

(2) Cleaning the first silicon wafer intermediate in a solution containing sodium hydroxide solution and hydrogen peroxide to obtain a second silicon wafer intermediate.

(3) Place the second silicon wafer intermediate in hydrofluoric acid for passivation to obtain a silicon wafer.

(4) Place the silicon wafer in pure water for cleaning, and slowly lift the above-mentioned washed silicon wafer from the pure water by a slow pulling device to reduce the amount of liquid adsorbed on the surface of the silicon wafer, and make the washed silicon wafer Dehydrate slowly.

(5) Dry the silicon wafer taken out by filling nitrogen gas.

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

(1) 1000 silicon wafers to be processed were respectively processed by Example 1 and Comparative Example 1, and the defective ratios of pitting after gettering annealing treatment of the 1000 silicon wafers obtained in Example 1 and Comparative Example 1 were tested respectively.

Please refer to Fig. 2, it can be seen that the bad ratio of pitting of the silicon wafer in Example 1 after the gettering annealing treatment (that is, 2022-August to 2022-October) is 0.21% on average (that is, the improvement in Fig. 2 After gettering annealing), the bad ratio of pits (from February 2022 to July 2022) of the silicon wafer in Comparative Example 1 after gettering annealing was 15.22% on average (that is, before improvement in Figure 2). Compared with Comparative Example 1, the defect ratio of pitting of the silicon wafer in Example 1 after the gettering annealing treatment was reduced from 15.22% to 0.21%, a decrease of 98.62%. This shows that the invention can reduce the metal impurities and other harmful substances on the silicon chip, ensure the surface cleanliness of the silicon chip before gettering annealing, thereby reducing the bad ratio of pitting of the silicon chip after gettering annealing.

(2) The silicon wafers after the gettering annealing treatment in Example 1 and Comparative Example 1 are made into solar cells respectively through subsequent steps, and the solar cells prepared by the silicon wafers in Example 1 are compared with those obtained by the silicon wafers in Comparative Example The conversion efficiency of solar cells prepared from silicon wafers.

Please refer to Fig. 3, it can be seen that the conversion efficiency of the solar cell prepared from the silicon wafer after the gettering annealing treatment in Example 1 is 24.28% (that is, after the improvement in Fig. The conversion efficiency of the solar cell prepared by the silicon wafer after the gettering annealing treatment is 24.21% (before improvement in Fig. 3), which shows that the solar cell prepared by the silicon wafer after the gettering annealing treatment in Example 1 The conversion efficiency is higher than that of the solar cell prepared from the silicon wafer after gettering annealing in Comparative Example 1, and the conversion efficiency is increased by 0.07%.

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

The above-mentioned embodiments only express several implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but should not be construed as limiting the patent scope of the invention. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (10)

1. The method for reducing the defect of the impurity absorption annealing pits of the silicon wafer is characterized by comprising the following steps of:

carrying out ultrasonic cleaning on a silicon wafer to be treated to remove silicon powder on the silicon wafer to be treated, so as to obtain a first silicon wafer intermediate;

performing first acid treatment on the first silicon wafer intermediate to remove metal impurities and organic dirt on the first silicon wafer intermediate and obtain a second silicon wafer intermediate;

texturing the second silicon wafer intermediate to form pyramid textured surfaces on the surface of the second silicon wafer intermediate so as to obtain a third silicon wafer intermediate; and

and carrying out second acid treatment on the third silicon wafer intermediate to remove metal impurities on the third silicon wafer intermediate.

2. The method of reducing wafer gettering annealing pock defects as defined in claim 1, wherein the first acid treatment comprises the steps of:

and carrying out first acid treatment on the first silicon wafer intermediate by adopting a first treatment liquid containing hydrochloric acid and hydrogen peroxide.

3. The method for reducing defects in gettering and annealing of silicon wafers according to claim 2, wherein the method comprises at least one of the following (1) to (3):

(1) The preparation method of the first treatment fluid comprises the following steps:

hydrochloric acid with the mass fraction of 30-40% and hydrogen peroxide with the mass fraction of 35-40% are mixed with water (5-7): (10-15): (800-1000) mixing;

(2) The temperature of the first acid treatment is 23-26 ℃;

(3) The time of the first acid treatment is 160 s-220 s.

4. The method for reducing defect of gettering and annealing pits of a silicon wafer according to claim 1, wherein the texturing comprises the steps of:

and texturing the second silicon wafer intermediate by adopting a texturing solution containing an alkaline solution and a texturing nucleation additive.

5. The method of reducing wafer gettering annealing pock defects according to claim 4, wherein the method comprises at least one of the following (4) to (5):

(4) The alkaline solution comprises potassium hydroxide solution;

(5) The texturing nucleation additive comprises a nucleating agent, sodium silicate, sodium acetate, a surfactant and a wetting agent, wherein in the texturing nucleation additive, the mass fraction of the nucleating agent is 10.5% -12%, the mass fraction of the sodium silicate is 2.0% -4.0%, the mass fraction of the sodium acetate is 0.5% -1.2%, the mass fraction of the surfactant is 2.0% -6.0%, and the mass fraction of the wetting agent is 3.0% -8.0%.

6. The method of reducing wafer gettering annealing pock defects according to claim 4, wherein the method comprises at least one of the following (6) to (7):

(6) The preparation method of the wool making liquid comprises the following steps:

the alkaline solution with the mass fraction of 35-45%, the texturing nucleation additive with the mass fraction of 10-15% and water are mixed according to the following proportion (2-4): 1: mixing the components according to the volume ratio of (400-450);

(7) The texturing time is 300-350 s.

7. The method of reducing dishing in a silicon wafer gettering anneal of any of claims 1 to 6, wherein the diameter of the base of the pyramidal structures of the pyramidal textured surface is 0.7 μm to 1.5 μm.

8. The method for reducing defects in gettering annealing of silicon wafers according to any one of claims 1 to 6, wherein the ultrasonic cleaning comprises the steps of:

placing the silicon wafer to be treated in a cleaning treatment liquid, and cleaning the silicon wafer to be treated under an ultrasonic condition;

wherein the cleaning treatment liquid comprises a hydrophilic wetting agent, and the hydrophilic wetting agent comprises polyoxyethylene.

9. The method of reducing dishing in a gettering anneal of a silicon wafer according to any one of claims 1 to 6, wherein the second acid treatment comprises the steps of:

performing second acid treatment on the third silicon wafer intermediate by adopting a second treatment solution containing an acidic reagent and ozone;

wherein the concentration of ozone in the second treatment liquid is 40ppm to 50ppm.

10. The method of reducing dishing in a gettering anneal of a silicon wafer according to any one of claims 1 to 6, wherein the method further comprises the step of passivating the third silicon wafer intermediate after the second acid treatment.

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