Silicon wafer texturing and cleaning method and crystalline silicon solar cell preparation method

Abstract

The present invention relates to a method for texturing and cleaning silicon wafers and a method for preparing crystalline silicon solar cells, comprising the following steps: sequentially subjecting silicon wafers to rough polishing, pickling, a first alkali washing, texturing, a second alkali washing, rounding, passivation and drying treatments; the pickling solution used in the pickling contains ozone, HCl and HF; the first alkali washing solution used in the first alkali washing contains soluble alkali metal hydroxides and H2O2. The present invention adds a pickling and a first alkali washing between the rough polishing and texturing treatments; the combination of the two can greatly improve the cleaning effect, and furthermore, the post-cleaning step between the subsequent rounding and passivation treatments can be omitted, so that the consumption of hydrogen peroxide and hydrochloric acid is greatly reduced, and production costs are saved, while there is no significant difference in the efficiency of the process.

Description

Technical Field

[0001] The invention relates to the technical field of crystalline silicon solar cells, and in particular to a method for texturing and cleaning a silicon wafer and a method for preparing a crystalline silicon solar cell. Background Art

[0002] Crystalline silicon solar cells are solar cells that use silicon wafers as the base material. Texturing silicon wafers is the first process in manufacturing crystalline silicon cells, also known as "surface texturing". An effective velvet structure can cause incident light to be reflected and refracted multiple times on the surface of the silicon wafer, increasing the light absorption rate and reducing the reflectivity, which helps to improve the performance of the cell.

[0003] Heterojunction cells, also known as HJT cells (Hereto-junction with Intrinsic Thin-layer), are known as the most promising solar cell technology after PERC (Passivated Emitter and Rear Cell). Compared with traditional crystalline silicon technology, due to the introduction of amorphous silicon thin film, the front and rear surfaces of the crystalline silicon substrate of silicon heterojunction solar cells have achieved good passivation, so its surface passivation is more perfect. In addition, the amorphous silicon thin film isolates the direct contact between the metal electrode and the silicon material, and its carrier recombination loss is further reduced, which can improve the conversion efficiency.

[0004] HJT batteries have the natural advantages of high efficiency and high power generation. Compared with the current mainstream PERC technology, the biggest problem is cost. HJT requires high investment in raw and auxiliary materials and equipment, which has become the main factor restricting its rapid development. It does not yet have the cost-effectiveness for large-scale production and is currently in the small-scale pilot research and development stage. Therefore, the current industry is committed to continuous efforts to continuously improve the conversion efficiency of HJT. On the other hand, reducing manufacturing costs and improving the cost-effectiveness of production are also top priorities.

[0005] The current textile cleaning process, hydrogen peroxide (H 2 O 2 ) and hydrochloric acid (HCl) and other chemicals are consumed in high quantities, resulting in excessively high process costs, so traditional technologies still need to be improved. Summary of the invention

[0006] Based on this, it is necessary to provide a method for texturing and cleaning silicon wafers and a method for preparing crystalline silicon solar cells in order to address the problem of high unit consumption of chemicals such as hydrogen peroxide and hydrochloric acid in traditional technologies.

[0007] The present invention is achieved through the following technical solutions.

[0008] One aspect of the present invention provides a method for cleaning a silicon wafer, comprising the following steps:

[0009] The silicon wafer is sequentially subjected to rough polishing, pickling, first alkali cleaning, texturing, second alkali cleaning, rounding, passivation and drying;

[0010] The pickling solution used in the pickling treatment contains ozone, HCl and HF;

[0011] The first alkaline washing solution used in the first alkaline washing treatment contains a soluble alkali metal hydroxide and H 2 O 2 .

[0012] In some embodiments, the concentration of ozone in the pickling solution is 30-50 ppm; and / or

[0013] In the pickling solution, the mass concentration of HCl is 0.02% to 0.05%, and the mass concentration of HF is 0.9% to 1.2%.

[0014] In some of the embodiments, the pickling treatment is carried out at a temperature of 20 to 30° C., for a time of 180 to 280 seconds, and at a circulation flow rate of 30 to 40 L / min.

[0015] In some embodiments, in the first alkaline washing solution, the mass concentration of the soluble alkali metal hydroxide is 0.9% to 1.2%, H 2 O 2 The mass concentration is 4% to 5%.

[0016] In some embodiments, the temperature of the first alkali washing treatment is 60-70° C., the time is 210-280 s, and the circulation flow rate is 35-45 L / min.

[0017] In some embodiments, the reagent used for the rough polishing treatment is an alkaline solution; and / or

[0018] The rough polishing treatment is carried out at a temperature of 75° C. to 90° C., for a time of 120 s to 200 s, and at a circulation flow rate of 30 to 40 L / min.

[0019] In some embodiments, the reagent used in the texturing treatment is an alkaline solution; and / or

[0020] The temperature of the texturing treatment is 75-90° C., the time is 500-700 seconds, and the circulation flow rate is 20-30 L / min.

[0021] In some embodiments, the second alkaline washing solution used in the second alkaline washing treatment contains a soluble alkali metal hydroxide and H 2 O 2 .

[0022] In some embodiments, in the second alkaline washing solution, the mass concentration of the soluble alkali metal hydroxide is 0.9% to 1.2%. 2 O 2 The mass concentration is 4% to 5%.

[0023] In some embodiments, the temperature of the second alkali washing treatment is 60-70° C., the time is 210-280 s, and the circulation flow rate is 35-45 L / min.

[0024] In some embodiments, the reagent used in the rounding treatment contains HCl and HF; and / or

[0025] The temperature of the rounding treatment is 20-30° C., the time is 180-240 seconds, and the circulation flow rate is 35-45 L / min.

[0026] In some embodiments, the reagent used in the passivation treatment is a hydrofluoric acid solution; and / or

[0027] The temperature of the passivation treatment is 20-30° C., the time is 180-240 seconds, and the circulation flow rate is 50-70 L / min.

[0028] Another aspect of the present invention provides a method for preparing a crystalline silicon solar cell, comprising the following steps:

[0029] Using any of the above-mentioned texturing and cleaning methods to texturize the silicon wafer;

[0030] The textured silicon wafer is sequentially subjected to the steps of depositing an amorphous silicon film, depositing a transparent conductive oxide film and manufacturing a metal electrode.

[0031] The above-mentioned texturing and cleaning method of silicon wafers sequentially performs rough polishing, pickling, first alkali cleaning, texturing, second alkali cleaning, rounding, passivation and drying on the silicon wafers. In particular, between the rough polishing and texturing, pickling and first alkali cleaning are sequentially performed. The pickling uses ozone to oxidize the surface of the silicon wafer after the rough polishing, so as to form a dense SiO 2 While removing the oxide film, it can also remove a considerable amount of metal impurities. At the same time, HCl has the dual functions of adjusting the pH value of the pickling solution and removing heavy metal ions. HF can effectively corrode the silicon oxide layer, thereby removing the silicon oxide layer, organic matter and metal contamination. Then the first alkaline washing treatment uses a soluble alkali metal hydroxide and H 2 O 2The combination of the two can greatly improve the cleaning effect, thereby omitting the post-cleaning step between the subsequent rounding treatment and passivation treatment, greatly reducing the consumption of hydrogen peroxide and hydrochloric acid, saving production costs, and at the same time having no significant difference in process efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The actual photo and PL image of the silicon wafer obtained in Example 1;

[0033] Figure 2 This is a SEM image of the silicon wafer obtained in Example 1;

[0034] Figure 3 The actual photo and PL image of the silicon wafer obtained in Comparative Example 5;

[0035] Figure 4 This is a SEM image of the silicon wafer obtained in Comparative Example 5;

[0036] Figure 5 The actual photo and PL image of the silicon wafer obtained in Comparative Example 6;

[0037] Figure 6 This is the SEM image of the silicon wafer obtained in Comparative Example 6. DETAILED DESCRIPTION

[0038] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively below, and preferred embodiments of the present invention are given. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. It should be understood that the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

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

[0040] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0041] An embodiment of the present invention provides a method for cleaning a silicon wafer, comprising the following steps S1 to S8.

[0042] S1: Roughly polish the silicon wafer.

[0043] The rough polishing process is used to remove the damaged layer on the surface of the silicon wafer. In a specific example, the single-side etching depth of the silicon wafer is about 4 μm.

[0044] In some of the embodiments, the reagent used for the rough polishing treatment is an alkaline solution, such as an aqueous solution of a soluble alkali metal hydroxide such as sodium hydroxide or potassium hydroxide.

[0045] Furthermore, in the aqueous solution of the soluble alkali metal hydroxide, the mass concentration of the soluble alkali metal hydroxide is 5% to 10%.

[0046] Furthermore, the reagent used for the rough polishing treatment is an aqueous solution of at least one of sodium hydroxide and potassium hydroxide.

[0047] In some embodiments, the temperature of the rough polishing treatment is 75°C to 90°C, the time is 120s to 200s, and the circulation flow rate is 30 to 40L / min. Further, the temperature can be 75°C, 80°C, 85°C, 90°C, the time can be 120s, 130s, 140s, 150s, 160s, 170s, 180s, 190s, 200s, and the circulation flow rate is 30L / min, 35L / min, 40L / min. In a specific example, the temperature of the rough polishing treatment is 80°C, the time is 180s, and the circulation flow rate is 35L / min.

[0048] S2: The silicon wafer obtained in step S1 is subjected to pickling treatment, wherein the pickling solution used for the pickling treatment contains ozone, HCl and HF.

[0049] Step S2: acid-wash and ozone-clean the silicon wafer obtained in step S1, using ozone (O 3 ) Oxidize the surface of the rough-polished silicon wafer to form a dense SiO 2 The HCl contained in the pickling solution has the dual functions of adjusting the pH value of the pickling solution and removing heavy metal ions. The HF contained in the pickling solution can effectively corrode the silicon oxide layer, thereby removing the silicon oxide layer, organic matter and metal contamination. The chemical reaction equation of the whole process is:

[0050] 2O 3 +3Si=3SiO 2 ;

[0051] SiO 2 +4HF=SiF 4 +2H 2 O;

[0052] SiO2 +6HF=H 2 SiF 6 +2H 2 O(when HF is in excess).

[0053] In some embodiments, the concentration of ozone in the pickling solution is 30-50 ppm, such as 30 ppm, 32 ppm, 35 ppm, 38 ppm, 40 ppm, 45 ppm, 50 ppm. Ozone at this preferred concentration has a very strong oxidation potential, which enables it to have a very strong ability to remove organic matter and metal pollution, and at the same time has a better oxidation effect on the surface of the silicon wafer after rough polishing.

[0054] Furthermore, in the pickling solution, the mass concentration of HCl is 0.02% to 0.05%, for example, 0.02%, 0.03%, 0.04%, 0.05%; the mass concentration of HF is 0.9% to 1.2%, for example, 0.9%, 1.0%, 1.1%, 1.2%.

[0055] In some embodiments, the temperature of the pickling treatment is 20-30°C, the time is 180-280s, and the circulation flow rate is 30-40L / min. Further, the temperature can be 20°C, 25°C, 30°C, the time can be 180s, 190s, 200s, 210s, 220s, 230s, 240s, 250s, 260s, 270s, 280s, and the circulation flow rate is 30L / min, 35L / min, 40L / min. In a specific example, the temperature of the pickling treatment is 25°C, the time is 240s, and the circulation flow rate is 35L / min.

[0056] S3: subjecting the silicon wafer obtained in step S2 to a first alkaline washing treatment.

[0057] The function of step S3 is to remove organic dirt, particles and metals on the surface of the silicon wafer.

[0058] Furthermore, the first alkaline washing solution used in the first alkaline washing treatment contains soluble alkali metal hydroxide and H 2 O 2 , specifically soluble alkali metal hydroxide and H 2 O 2 After step S2 uses ozone and acid washing, step S3 uses a soluble alkali metal hydroxide and H 2 O 2 The aqueous solution is used for alkaline washing, because H 2 O 2 The organic matter on the surface of the silicon wafer is decomposed into CO 2 , H 2 O is removed, and the surface of the silicon wafer is 2 O2 Oxidation generates an oxide film, which is corroded by soluble alkali metal hydroxides such as KOH. After corrosion, oxidation occurs again immediately. Oxidation and corrosion are repeated, so particles attached to the surface of the silicon wafer also fall into the cleaning solution with the corrosion layer and are removed; the combination of step S2 and step S3 can greatly enhance the cleaning ability of the silicon wafer surface, thereby omitting the post-cleaning step between the subsequent smoothing treatment of step S6 and the surface passivation treatment of step S7, so that hydrogen peroxide (H 2 O 2 ) and hydrochloric acid (HCl) consumption is greatly reduced, saving production costs.

[0059] In some embodiments, the mass concentration of the soluble alkali metal hydroxide in the first alkaline washing solution is 0.9% to 1.2%. 2 O 2 The mass concentration of is 4% to 5%. Further, the soluble alkali metal hydroxide may be at least one of sodium hydroxide and potassium hydroxide, preferably sodium hydroxide.

[0060] In some embodiments, the temperature of the first alkali washing treatment is 60-70°C, the time is 210-280s, and the circulation flow rate is 35-45L / min. Further, the temperature can be 60°C, 65°C, 70°C, the time can be 210s, 220s, 230s, 240s, 250s, 260s, 270s, 280s, and the circulation flow rate is 35L / min, 40L / min, 45L / min. In a specific example, the temperature of the first alkali washing treatment is 65°C, the time is 240s, and the circulation flow rate is 40L / min.

[0061] S4: performing texturing treatment on the silicon wafer obtained in step S3.

[0062] Texturing refers to making the surface of the silicon wafer concave and convex (pyramid velvet) to increase the number of refractions of light on the surface of the solar cell, which is beneficial to the solar cell's absorption of light, so as to achieve the maximum utilization of the solar energy value of the cell.

[0063] For HJT cells, the texturing process is carried out using an alkaline solution. The working principle of texturing is that when a single crystal silicon wafer is corroded in an alkaline solution of a certain concentration, it is anisotropic, and the corrosion rate on different crystal directions is different. When a single crystal silicon wafer is corroded in an alkaline solution, many fine "pyramid"-shaped textures can be produced on the surface of the silicon wafer. The chemical reaction equation of this process is:

[0064] Si+2KOH+H 2 O=K 2 SiO 3 +2H 2 ↑.

[0065] Texturing can improve the light trapping effect of silicon wafers, reduce reflection, increase light absorption, and reduce the reflectivity of the silicon wafer surface. In a specific example, KOH etching solution is used to perform anisotropic etching on N-type silicon wafers, and the Si (100) crystal plane is etched into a tetragonal pyramid structure ("pyramid structure") of the Si (111) crystal plane, that is, a velvet surface is formed on the silicon wafer surface, which can reduce the reflectivity of the silicon wafer surface to below 12.5%, thereby generating more photogenerated carriers and forming a clean silicon wafer surface. Since the surface of the silicon wafer substrate in the HJT cell is directly part of the heterojunction interface, a clean silicon wafer surface needs to be formed to avoid the recombination of carriers at the junction interface caused by defects and impurities introduced by uncleanness.

[0066] In a specific example, the single-side etching depth of the silicon wafer obtained in step S4 is deepened by about 4 μm, and the reflectivity is about 9%.

[0067] Furthermore, the alkaline solution can be an aqueous solution of a soluble alkali metal hydroxide such as sodium hydroxide or potassium hydroxide. Furthermore, the mass concentration of the soluble alkali metal hydroxide in the alkaline solution is 1.1% to 1.5%, such as 1.1%, 1.2%, 1.3%, 1.4%, 1.5%. Furthermore, the alkaline solution also contains an additive, and the mass concentration of the additive is 0.5% to 0.6%.

[0068] In some embodiments, the temperature of the texturing treatment is 75-90°C, the time is 500-700s, and the circulation flow rate is 20-30L / min. Further, the temperature can be 75°C, 80°C, 85°C, 90°C, the time can be 500s, 530s, 550s, 580s, 600s, 630s, 650s, 680s, 700s, and the circulation flow rate is 30L / min, 35L / min, 40L / min. In a specific example, the temperature of the texturing treatment is 80°C, the time is 600s, and the circulation flow rate is 25L / min.

[0069] S5: subjecting the silicon wafer obtained in step S4 to a second alkaline washing treatment.

[0070] The function of step S5 is to remove organic dirt, particles and metals on the surface of the silicon wafer.

[0071] In some embodiments, the second alkaline washing solution used in the second alkaline washing treatment contains a soluble alkali metal hydroxide and H 2 O 2 , specifically soluble alkali metal hydroxide and H 2 O 2 of aqueous solution.

[0072] Furthermore, in the second alkaline washing solution, the mass concentration of the soluble alkali metal hydroxide is 0.9% to 1.2%, H2 O 2 The mass concentration is 4% to 5%.

[0073] In some embodiments, the temperature of the second alkali washing treatment is 60-70°C, the time is 210-280s, and the circulation flow rate is 35-45L / min. Further, the temperature can be 60°C, 65°C, 70°C, the time can be 210s, 220s, 230s, 240s, 250s, 260s, 270s, 280s, and the circulation flow rate is 35L / min, 40L / min, 45L / min. In a specific example, the temperature of the second alkali washing treatment is 65°C, the time is 240s, and the circulation flow rate is 40L / min.

[0074] S6: Smoothing the silicon wafer obtained in step S5.

[0075] The purpose of the rounding treatment step in step S6 is to polish the bottom and top of the "pyramid" to make the top and bottom of the pyramid smooth, which is convenient for subsequent CVD coating deposition.

[0076] In some embodiments, the reagent used in the rounding treatment contains HCl and HF. Further, in the reagent used in the rounding treatment, the mass concentration of HCl is 0.02% to 0.05%, and the mass concentration of HF is 0.2% to 0.5%.

[0077] Furthermore, the reagent used for the rounding treatment also contains ozone. Furthermore, the concentration of ozone in the reagent is 40 to 50 ppm, such as 40 ppm, 45 ppm, or 50 ppm.

[0078] Further, the temperature of the rounding treatment is 20-30°C, the time is 180-240s, and the circulation flow rate is 35-45L / min. Further, the temperature can be 20°C, 25°C, 30°C, the time can be 180s, 190s, 200s, 210s, 220s, 230s, 240s, and the circulation flow rate is 35L / min, 40L / min, 45L / min. In a specific example, the temperature of the rounding treatment is 25°C, the time is 200s, and the circulation flow rate is 40L / min.

[0079] S7: performing surface passivation treatment on the silicon wafer obtained in step S6.

[0080] In some embodiments, the reagent used for the passivation treatment is a hydrofluoric acid solution. The main function of step S7 is to remove the silicon oxide layer by HF treatment, and the dangling bonds on the surface of the silicon wafer are saturated with hydrogen, so that the silicon wafer has good passivation performance.

[0081] Furthermore, the mass concentration of HF in the hydrofluoric acid solution is 4.5% to 5.5%.

[0082] In some embodiments, the temperature of the passivation treatment is 20-30°C, the time is 180-240s, and the circulation flow rate is 50-70L / min. Further, the temperature can be 20°C, 25°C, 30°C, the time can be 180s, 190s, 200s, 210s, 220s, 230s, 240s, and the circulation flow rate is 50L / min, 55L / min, 60L / min, 65L / min, 70L / min. In a specific example, the temperature of the passivation treatment is 25°C, the time is 210s, and the circulation flow rate is 60L / min.

[0083] Furthermore, there is no acid cleaning or alkali cleaning step between the rounding treatment in step S6 and the passivation treatment in step S7.

[0084] S8: Drying the silicon wafer obtained in step S7.

[0085] Furthermore, the drying treatment may be performed by drying at a temperature of 55 to 75° C. for a time of 800 s to 1000 s.

[0086] It is understood that, except for step S8, any of the above individual steps also includes a step of washing with water to remove the residue of reagents used in a process on the surface of the silicon wafer. Preferably, pure water or a deionized water machine is used for washing.

[0087] The above-mentioned texturing and cleaning method of silicon wafers sequentially performs rough polishing, pickling, first alkali cleaning, texturing, second alkali cleaning, rounding, passivation and drying on the silicon wafers. In particular, between the rough polishing and texturing, pickling and first alkali cleaning are sequentially performed. The pickling uses ozone to oxidize the surface of the silicon wafer after the rough polishing, so as to form a dense SiO 2 While removing the oxide film, it can also remove a considerable amount of metal impurities. At the same time, HCl has the dual functions of adjusting the pH value of the pickling solution and removing heavy metal ions. HF can effectively corrode the silicon oxide layer, thereby removing the silicon oxide layer, organic matter and metal contamination. Then the first alkaline washing treatment uses a soluble alkali metal hydroxide and H 2 O 2 The combination of the two can greatly improve the cleaning effect, thereby omitting the post-cleaning step between the subsequent rounding treatment and the passivation treatment, making the hydrogen peroxide (H 2 O 2 ) and hydrochloric acid (HCl) consumption is greatly reduced, saving production costs, while there is no significant difference in process efficiency.

[0088] The present invention also provides a method for preparing crystalline silicon solar cells, which includes the steps of the above-mentioned silicon wafer texturing and cleaning method, and after the texturing and cleaning, also includes the steps of sequentially depositing an amorphous silicon film, depositing a transparent conductive oxide film and making a metal electrode.

[0089] In some embodiments, the crystalline silicon solar cell is a HJT cell. Specifically, the crystalline silicon solar cell comprises the following steps:

[0090] A very thin intrinsic amorphous silicon film (ia-Si:H) and a p-type amorphous silicon film (pa-Si:H) are deposited on the front of an N-type single crystal silicon wafer (c-Si), and then a very thin intrinsic amorphous silicon film (ia-Si:H) and an n-type amorphous silicon film (na-Si:H) are deposited on the back of the silicon wafer to form a back surface field; a transparent oxide conductive film (TCO) is then deposited on both sides of the silicon wafer. The TCO can not only reduce the series resistance when collecting current, but also play an anti-reflection role like the silicon nitride layer on a crystalline silicon cell; finally, a metal electrode is made on the TCO.

[0091] In order to make the purpose, technical solutions and advantages of the present invention more concise and clear, the present invention is described with the following specific embodiments, but the present invention is by no means limited to these embodiments. The embodiments described below are only preferred embodiments of the present invention, which can be used to describe the present invention and cannot be understood as limiting the scope of the present invention. It should be pointed out that any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0092] In order to better illustrate the present invention, the present invention is further described below in conjunction with the embodiments. The following are specific embodiments.

[0093] In each embodiment and comparative example, a YAC machine is used to texturize the silicon wafer of the HJT heterojunction solar cell.

[0094] Example 1

[0095] S1: Rough polishing. The reagent used for rough polishing is a 5% KOH aqueous solution, the temperature is set to 80°C, the time is 180s, and the circulation flow rate is maintained at about 35L / min. The function is to remove the damaged layer on the surface of the silicon wafer. At this time, the single-side corrosion depth of the silicon wafer is about 4μm.

[0096] S2: Pickling (ozone cleaning). The mass concentration of HCl in the pickling solution is 0.02%, the mass concentration of HF is 1%, and the mass concentration of ozone (O 3 ) concentration was set to 30ppm, temperature to 25°C, time to 240s, 35L / min.

[0097] S3: Pre-cleaning (first alkaline washing). The first alkaline washing solution is KOH, H 2 O 2 The aqueous solution contains KOH with a mass concentration of 1.1%, H 2 O 2 The mass concentration is 4.5%, the temperature is set at 65℃, the time is set at 240s, and the circulation flow rate is maintained at about 40L / min. The function is to remove organic dirt, particles and metals on the surface of the silicon wafer.

[0098] S4: Texturing. The reagents used are aqueous solutions of KOH and additives, where the mass concentration of KOH is 1.5%, the mass concentration of ADD (additive) is 0.6%, the temperature is set to 80°C, the time is set to 600s, and the circulation flow rate is maintained at about 25L / min. In this step, the single-sided etching depth of the silicon wafer is deepened by about 4μm, and the reflectivity is about 9%.

[0099] S5: Pre-cleaning (second alkaline washing). The second alkaline washing solution is KOH, H 2 O 2 The aqueous solution contains KOH with a mass concentration of 1.1%, H 2 O 2 The mass concentration is 4.5%, the temperature is set to 65℃, the time is set to 240s, and the circulation flow rate is maintained at around 40L / min. Its function is to remove organic dirt, particulate matter and metal on the surface of the silicon wafer.

[0100] S6: Smoothing treatment. The mass concentration of HCl in the reagents used is 0.02%, the mass concentration of HF is 0.3%, and the mass concentration of ozone (O 3 ) concentration is set to 45ppm, temperature is set to 25℃, time is set to 200s, and circulation flow rate is set to about 40L / min; its function is to polish the bottom and top of the "pyramid" to facilitate subsequent CVD coating deposition.

[0101] S7: Surface passivation. The reagent used is HF aqueous solution, the mass concentration of HF is 5%, the temperature is set at 25°C, the time is 210s, and the circulation flow rate is maintained at about 60L / min. Its main function is to remove the silicon oxide layer, and the saturated dangling bonds play a role in surface passivation.

[0102] S8: dehydration and drying. The drying temperature is 65°C and the time is 800s.

[0103] It is understood that, except for step S8, any of the above individual steps also includes a step of washing with water to remove the residue of reagents used in a process on the surface of the silicon wafer. Preferably, pure water or a deionized water machine is used for washing.

[0104] Through the above steps, a silicon wafer with a uniform velvet surface and a weight loss of about 0.85 g and a reflectivity of about 9.5% is obtained.

[0105] Embodiments 2 to 4

[0106] The steps of Examples 2 to 4 are the same as those of Example 1, except that the concentration of the reagents used in each step and the temperature, time and flow rate of the treatment are adjusted, as shown in Table 1.

[0107] Comparative Example 1

[0108] Comparative Example 1 is substantially the same as Example 1, except that the pickling step S2 in Example 1 is omitted, and a post-cleaning step is added between the rounding treatment and the surface passivation treatment.

[0109] The specific steps of Comparative Example 1 are as follows:

[0110] S1: Rough polishing. The reagent used for rough polishing is a 5% KOH aqueous solution, the temperature is set to 80°C, the time is 180s, and the circulation flow rate is maintained at about 35L / min. The function is to remove the damaged layer on the surface of the silicon wafer. At this time, the single-side corrosion depth of the silicon wafer is about 4μm.

[0111] S2: Pre-cleaning. The first alkaline cleaning solution is KOH, H 2 O 2 The aqueous solution contains KOH with a mass concentration of 1.1%, H 2 O 2 The mass concentration is 4.5%, the temperature is set at 65℃, the time is set at 240s, and the circulation flow rate is maintained at about 40L / min. The function is to remove organic dirt, particles and metals on the surface of the silicon wafer.

[0112] S3: Texturing. The reagents used are aqueous solutions of KOH and additives, where the mass concentration of KOH is 1.5%, the mass concentration of ADD (additive) is 0.6%, the temperature is set to 80°C, the time is set to 600s, and the circulation flow rate is maintained at about 25L / min. In this step, the single-sided etching depth of the silicon wafer is deepened by about 4μm, and the reflectivity is about 9%.

[0113] S4: Pre-cleaning. The second alkaline cleaning solution is KOH, H 2 O 2 The aqueous solution contains KOH with a mass concentration of 1.1%, H 2 O 2 The mass concentration is 4.5%, the temperature is set to 65℃, the time is set to 240s, and the circulation flow rate is maintained at around 40L / min. Its function is to remove organic dirt, particulate matter and metal on the surface of the silicon wafer.

[0114] S5: Smoothing treatment. The mass concentration of HCl in the reagents used is 0.02%, the mass concentration of HF is 0.3%, and the mass concentration of ozone (O 3 ) concentration is set to 45ppm, temperature is set to 25℃, time is set to 200s, and circulation flow rate is set to about 40L / min; its function is to polish the bottom and top of the "pyramid" to facilitate subsequent CVD coating deposition.

[0115] S6: Post-cleaning. The reagents used are HCl, H 2 O 2 The aqueous solution contains 6% HCl and 6% H 2 O 2 The mass concentration is 5%, the temperature is set to 65℃, the time is set to 240s, and the circulation flow rate is about 40L / min. The purpose is to remove some metal ions.

[0116] S7: Surface passivation. The reagent used is HF aqueous solution, the mass concentration of HF is 5%, the temperature is set at 25°C, the time is 210s, and the circulation flow rate is maintained at about 60L / min. Its main function is to remove the silicon oxide layer, and the saturated dangling bonds play a role in surface passivation.

[0117] S8: dehydration and drying. The drying temperature is 65°C and the time is 800s. It is understood that, except for step S8, any of the above individual steps also includes a step of washing with water to remove the residue of the reagent used in the previous process on the surface of the silicon wafer. Preferably, pure water or a deionized water machine is used for washing.

[0118] Through the above steps, a silicon wafer with a uniform velvet surface and a weight loss of about 0.85 g and a reflectivity of about 9.5% is obtained.

[0119] Comparative Examples 2 to 4

[0120] They are basically the same as Examples 2 to 4, except that the pickling step S2 in Example 1 is omitted, and a post-cleaning step is added between the rounding treatment and the surface passivation treatment steps. The conditions of the post-cleaning step are the same as those in Comparative Example 1.

[0121] Comparative Example 5

[0122] Comparative Example 5 is basically the same as Example 1, with the only difference being that the ozone cleaning of step S2 and the pre-cleaning of step S3 in Example 1 are swapped in order; that is, after the rough polishing treatment, Comparative Example 5 first performs the pre-cleaning step under the same conditions as Example 1, and then performs the ozone cleaning step under the same conditions as Example 1.

[0123] Comparative Example 6

[0124] Comparative Example 6 is substantially the same as Example 1, except that the reagent used for ozone cleaning in step S2 does not contain HF.

[0125] Some process parameters of the above embodiments and comparative examples are shown in Table 1 below:

[0126] Table 1

[0127]

[0128]

[0129] The production efficiency of the silk-making and cleaning processes of the above-mentioned embodiments and comparative examples was statistically analyzed, and no significant difference was found. Furthermore, the total consumption of chemical reagents used in the embodiments and comparative examples was statistically analyzed, and based on the corresponding number of silicon wafers produced, the unit consumption of each chemical corresponding to a single silicon wafer was obtained, as shown in Table 2 below.

[0130] Among them, hydrogen peroxide and hydrochloric acid refer to the H 2 O 2 The total amount of initial raw materials corresponding to HCl, where H 2 O 2 The mass concentration of the initial raw material hydrogen peroxide used is 30%, and the mass concentration of the initial raw material hydrochloric acid corresponding to HCl is 37%. The unit consumption in Table 2 is the unit consumption corresponding to the maximum production capacity of a single shift (5000 pcs per hour).

[0131] Table 2

[0132]

[0133]

[0134] As can be seen from the above table, compared with the process flow of Comparative Example 1, the unit consumption of hydrogen peroxide in Example 1 is reduced from 7.3832 mL / pcs to 4.1390 ​​mL / pcs, with a reduction of up to 43.9%; the unit consumption of hydrochloric acid is reduced from 1.2857 mL / pcs to 0.0658 mL / pcs, with a reduction of up to 94.9%.

[0135] Compared with the process flow of Comparative Example 2, the unit consumption of hydrogen peroxide in Example 2 is reduced from 7.8168 mL / pcs to 4.5600 mL / pcs, with a reduction of up to 41.6%; the unit consumption of hydrochloric acid is reduced from 1.2898 mL / pcs to 0.3798 mL / pcs, with a reduction of up to 70.5%.

[0136] Compared with the process flow of Comparative Example 3, the unit consumption of hydrogen peroxide in Example 3 is reduced from 7.5702 mL / pcs to 4.3133 mL / pcs, with a reduction of up to 43%; the unit consumption of hydrochloric acid is reduced from 1.0408 mL / pcs to 0.1308 mL / pcs, with a reduction of up to 87.4%.

[0137] Compared with the process flow of Comparative Example 4, the unit consumption of hydrogen peroxide in Example 4 is reduced from 7.7518 mL / pcs to 4.4950 mL / pcs, with a reduction of up to 42%; the unit consumption of hydrochloric acid is reduced from 1.2275 mL / pcs to 0.3175 mL / pcs, with a reduction of up to 74.1%.

[0138] It can be seen that the texturing cleaning method of the present invention can make hydrogen peroxide (H 2 O 2 ) and hydrochloric acid (HCl) consumption is greatly reduced, saving production costs.

[0139] The actual photographs, PL images and SEM images of the silicon wafers obtained in Example 1 and Comparative Examples 5 to 6 are as follows: Figures 1 to 6 As shown. Figure 1 , Figure 3 and Figure 5 In the figure, a is a real photo and b is a PL diagram.

[0140] Among them, photoluminescence (PL) is a luminescence phenomenon of semiconductor materials. It refers to the process in which electrons in semiconductors are excited after absorbing external photons. The electrons in the excited state are unstable and can transition to lower energy levels to release energy in the form of light radiation. The frequency, phase, amplitude, direction, polarization state, etc. of the luminescence carry a lot of basic information about the material. It is a very important method for detecting the electronic structure of the material. In the photovoltaic industry, PL is used to detect defects in the production process of solar cells, such as scratches, hidden cracks in solar cells, surface contamination, black spots and other defects. It is these defects that limit the photoelectric conversion efficiency and service life of the battery.

[0141] from Figure 1 and Figure 2 It can be seen that the appearance and PL of Example 1 are normal, and the suede surface is uniform.

[0142] from Figure 3 and Figure 4 It can be seen that the comparative example 5 has a dirty appearance and an abnormal velvet surface at the edge.

[0143] from Figure 5 and Figure 6It can be seen that in the appearance of Comparative Example 6, there are tooth marks at the contact between the silicon wafer and the flower basket carrier, the PL tooth marks are obvious, and the velvet surface at the tooth position is abnormal. In Comparative Example 6, since the reagent used for ozone cleaning in step S2 does not contain HF, a thick oxide layer is formed on the surface of the silicon wafer after ozone oxidation in step S2, which is not removed in time. In addition, because the reaction space at the contact position between the silicon wafer and the flower basket is small, a small amount of oxide at the contact position between the silicon wafer and the flower basket is not completely removed and attached to the surface during a series of subsequent steps, resulting in tooth marks, which are not easy to see from the appearance, but the PL is more obvious, affecting the conversion efficiency of the battery cell.

[0144] In summary, Example 1 has the best cleaning effect.

[0145] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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.

[0146] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims, and the description can be used to interpret the content of the claims.

Claims

1. A method for cleaning a silicon wafer, characterized in that: The steps include: The silicon wafer is sequentially subjected to rough polishing, pickling, first alkali cleaning, texturing, second alkali cleaning, rounding, passivation and drying; The pickling solution used in the pickling treatment contains ozone, HCl and HF, and the mass concentration of HF in the pickling solution is 0.9% to 1.2%; The first alkaline washing solution used in the first alkaline washing treatment contains soluble alkali metal hydroxide and H2O2.

2. The method for cleaning the velvet according to claim 1, characterized in that: The concentration of ozone in the pickling solution is 30 to 50 ppm; and / or In the pickling solution, the mass concentration of HCl is 0.02% to 0.05%.

3. The method for cleaning the velvet according to claim 1, characterized in that: The temperature of the pickling treatment is 20-30° C., the time is 180-280 seconds, and the circulation flow rate is 30-40 L / min.

4. The method for cleaning the velvet according to claim 1, characterized in that: In the first alkaline washing solution, the mass concentration of the soluble alkali metal hydroxide is 0.9% to 1.2%, and the mass concentration of H2O2 is 4% to 5%.

5. The texturing cleaning method according to claim 1, characterized in that: The temperature of the first alkali washing treatment is 60-70° C., the time is 210-280 s, and the circulation flow rate is 35-45 L / min.

6. The texturing cleaning method according to any one of claims 1 to 5, characterized in that: The reagent used in the rough polishing treatment is an alkaline solution; and / or The rough polishing treatment is carried out at a temperature of 75° C. to 90° C., for a time of 120 s to 200 s, and at a circulation flow rate of 30 to 40 L / min.

7. The texturing cleaning method according to any one of claims 1 to 5, characterized in that: The reagent used in the texturing treatment is an alkaline solution; and / or The temperature of the texturing treatment is 75-90° C., the time is 500-700 seconds, and the circulation flow rate is 20-30 L / min.

8. The texturing cleaning method according to any one of claims 1 to 5, characterized in that: The second alkaline washing solution used in the second alkaline washing treatment contains soluble alkali metal hydroxide and H2O2.

9. The texturing cleaning method according to claim 8, characterized in that: In the second alkaline washing solution, the mass concentration of the soluble alkali metal hydroxide is 0.9% to 1.2%, and the mass concentration of H2O2 is 4% to 5%.

10. The texturing cleaning method according to any one of claims 1 to 5, characterized in that: The temperature of the second alkali washing treatment is 60-70° C., the time is 210-280 s, and the circulation flow rate is 35-45 L / min.

11. The texturing cleaning method according to any one of claims 1 to 5, characterized in that: The reagent used in the rounding treatment contains HCl and HF; and / or The temperature of the rounding treatment is 20-30° C., the time is 180-240 seconds, and the circulation flow rate is 35-45 L / min.

12. The texturing cleaning method according to any one of claims 1 to 5, characterized in that: The reagent used in the passivation treatment is a hydrofluoric acid solution; and / or The temperature of the passivation treatment is 20-30° C., the time is 180-240 seconds, and the circulation flow rate is 50-70 L / min.

13. A method for preparing a crystalline silicon solar cell, characterized in that: The steps include: The silicon wafer is textured using the texturing and cleaning method as described in any one of claims 1 to 12; The textured silicon wafer is sequentially subjected to the steps of depositing an amorphous silicon film, depositing a transparent conductive oxide film and manufacturing a metal electrode.

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