Reworked wafer cleaning method and application thereof

Abstract

The invention belongs to the field of crystalline silicon solar cells, and relates to a cleaning method of a reworked wafer, the reworked wafer comprises a solar cell silicon wafer and a boron-rich layer formed on the surface of the solar cell silicon wafer after a boron diffusion process, and the cleaning method comprises the following steps: providing the solar cell reworked wafer after boron diffusion; hydrofluoric acid and a nitrate additive are uniformly mixed to obtain an acid solution, and the reworked silicon wafer subjected to boron diffusion is subjected to acid pickling through the acid solution to remove the boron-rich layer. According to the method, hydrofluoric acid and a nitrate additive are uniformly mixed to prepare an acid solution, then a boron-rich layer containing boron atoms is cleaned, NO3 <-> ionized from nitrate and H < + > ionized from hydrofluoric acid are mixed to achieve the effect of mixing hydrofluoric acid and nitric acid, the boron atoms are oxidized into B2O3 by nitric acid, and then the B2O3 is dissolved by hydrofluoric acid, so that the boron-rich layer of the boron-expanded reworked wafer is effectively removed by one-step wet cleaning, and the boron-rich layer of the boron-expanded reworked wafer is effectively removed. An overheating oxidation process is not needed, the machine capacity of the thermal oxidation process is saved, manual operation is reduced, and the problem of high hydrofluoric acid consumption in rework wafer cleaning is also greatly solved.

Description

Technical Field

[0001] The present application relates to the technical field of crystalline silicon solar cells, and in particular to a method for cleaning a reworked wafer and an application thereof. Background Art

[0002] The TOPCon battery process is generally as follows: first, the front side is textured and the boron is diffused, then the back side tunneling layer and doped polysilicon layer are performed, then the front side Al2O3 film layer is prepared, the front and back side SiNx films are prepared, and finally metallization is performed. The boron diffusion process is mainly used to prepare PN junctions. This process introduces B atoms into silicon crystals through boron chemical reactions at high temperatures, diffuses P-type elements (boron atoms) on N-type silicon wafers (doped with phosphorus), forms PN junctions, forms a P+ layer on the front side, and an N+ layer on the back side.

[0003] Different types of defective cells are generated due to factors such as process, equipment and human factors. If such defective cells are transmitted according to the normal process flow, it will seriously affect the efficiency and yield of the battery cells and cause serious waste of resources. In order to reduce costs and save raw materials, the defective cells generated in the production process need to be reworked for reuse. Such defective cells are generally called reworked cells in this field.

[0004] The structure of Topcon cells is generally as follows: the back of the N-type silicon substrate has an ultra-thin silicon oxide layer, a doped polysilicon layer is deposited on the silicon oxide, and the ultra-thin silicon oxide and doped polysilicon layers together form a good passivation contact structure, a layer of silicon nitride is plated on the back polysilicon layer, and the front of the N-type silicon substrate has an aluminum oxide layer, and the surface of the aluminum oxide is plated with a layer of silicon amide. It can be seen that Topcon cells have a laminated structure, and the rework and cleaning of the reworked wafers needs to clean the laminated structure to restore it to the state of the N-type silicon substrate so that it can be reused in production.

[0005] However, after boron diffusion, a very thin boron-rich layer will inevitably be formed on the surface of the silicon wafer. This layer is rich in inactive boron atoms and is difficult to be corroded by hydrofluoric acid. Therefore, the reworked wafer after boron diffusion cannot be directly cleaned with hydrofluoric acid wet method and then re-textured. It is necessary to oxidize the boron-rich layer to BSG (borosilicate glass, i.e. silicon oxide containing B2O3) by dry method after thermal oxygen oxidation, and then clean the BSG with hydrofluoric acid with a volume fraction of 80%, that is, a combination of dry and wet methods to achieve the purpose of removing the boron-rich layer.

[0006] However, this greatly occupies the production capacity of thermal oxidation. In addition, the BSG layer is cleaned with a high-concentration hydrofluoric acid solution, which not only increases the consumption cost of hydrofluoric acid, but also increases the risk factor of the strong acid raw material. Summary of the invention

[0007] Based on this, a method for cleaning a reworked wafer after boron expansion and its application are provided, wherein the boron-rich layer containing boron atoms is cleaned by mixing hydrofluoric acid and nitrate additives to make an acid solution, and the nitrate ionizes NO 3- With the H ionized by hydrofluoric acid + The mixture achieves the effect of hydrofluoric acid and nitric acid mixed acid, which is both oxidizing and corrosive. Nitric acid oxidizes boron atoms into B2O3, and then hydrofluoric acid dissolves B2O3, effectively removing the boron-rich layer produced after boron expansion, and realizing one-step wet cleaning to effectively remove the boron-rich layer of the reworked wafer after boron expansion. The reworked wafer after boron expansion does not require an overheating oxidation process, which saves the machine capacity of the thermal oxidation process, reduces manual operations, and also greatly reduces the problem of high hydrofluoric acid consumption in the cleaning of the reworked wafer.

[0008] In one aspect, a method for cleaning a reworked wafer is provided, wherein the reworked wafer comprises a solar cell silicon wafer and a boron-rich layer formed on the surface of the solar cell silicon wafer after a boron diffusion process, and the cleaning method comprises the following steps:

[0009] Provide solar cell rework wafers after boron diffusion;

[0010] An acid solution is obtained by mixing hydrofluoric acid and a nitrate additive, and the reworked silicon wafer after boron expansion is pickled by the acid solution to remove the boron-rich layer, wherein the boron-rich layer contains boron atoms.

[0011] In one embodiment, the volume fraction of the hydrofluoric acid is 3% to 20%;

[0012] Preferably, the concentration of the hydrofluoric acid is 5% to 15%;

[0013] Preferably, the volume ratio of the hydrofluoric acid solution to the nitrate additive is 5-8:1.

[0014] In one embodiment, the nitrate additive comprises nitrate and a surfactant;

[0015] Preferably, the volume fraction of the nitrate is 1% to 5%;

[0016] Preferably, the volume fraction of the nitrate is 1% to 2%;

[0017] Preferably, the nitrate is at least one of sodium nitrate, potassium nitrate, ammonium nitrate and calcium nitrate;

[0018] Preferably, the surfactant is at least one of sodium lauryl sulfate, disodium lauryl sulfosuccinate, disodium coconut oil monoethanolamide sulfosuccinate, and monolauryl phosphate.

[0019] In one embodiment, the nitrate additive includes water, nitrate, surfactant and sodium benzoate;

[0020] Preferably, the proportion of each component in the nitrate additive is: water: nitrate: surfactant: sodium benzoate = 70-85: 10-20: 3-8: 1-5;

[0021] Preferably, the proportions of the components in the nitrate additive are: water: nitrate: surfactant: sodium benzoate = 75-80: 13-18: 4-6: 1-3.

[0022] In one embodiment, the pickling temperature is 35-45°C, and the pickling time is 200-650s;

[0023] Preferably, the pickling temperature is 38-42° C., and the pickling time is 280-620 s.

[0024] In one embodiment, the process further includes washing the silicon wafer after the acid washing;

[0025] Preferably, the water washing method is flowing water washing, and the water washing time is 200-400s.

[0026] In one embodiment, the process further includes performing oxidation cleaning on the silicon wafer after the acid cleaning;

[0027] Preferably, the oxidative cleaning method is cleaning with a mixed solution of sodium hydroxide and hydrogen peroxide.

[0028] In one embodiment, the process further includes performing hydrofluoric acid cleaning, slow pull cleaning and drying on the silicon wafer after the acid cleaning;

[0029] Preferably, the volume fraction of hydrofluoric acid in the hydrofluoric acid cleaning is 2%-15%;

[0030] Preferably, the slow pulling cleaning time is 15-25s;

[0031] Preferably, the temperature of the drying treatment is 70-110° C., and the time of the drying treatment is 500-800 seconds.

[0032] On the other hand, an application of the above cleaning method in a solar cell manufacturing process is provided.

[0033] On the other hand, a process for preparing a crystalline silicon solar cell is provided, wherein any one of the above cleaning methods is used to clean a reworked wafer after a boron diffusion process.

[0034] The present invention has at least one of the following beneficial effects:

[0035] The present invention cleans the boron-rich layer containing boron atoms by mixing hydrofluoric acid and nitrate additives to make acid solution, and nitrate ionizes NO3- With the H ionized by hydrofluoric acid + The mixture achieves the effect of hydrofluoric acid and nitric acid, which is both oxidizing and corrosive. Nitric acid oxidizes boron atoms into B2O3, and then hydrofluoric acid dissolves B2O3, replacing the traditional two-step process of thermal oxidation followed by corrosion cleaning, and effectively removing the boron-rich layer produced after boron expansion. One-step wet cleaning is achieved to effectively remove the boron-rich layer of the reworked wafer after boron expansion. The reworked wafer after boron expansion does not require an overheated oxidation process, which saves the machine capacity of the thermal oxidation process, reduces manual operations, and greatly reduces the problem of high hydrofluoric acid consumption in the cleaning of the reworked wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a diagram showing the cleaning effect of a reworked wafer after boron diffusion in Example 1 of the present invention;

[0037] Figure 2 This is a diagram showing the texturing effect of the reworked wafer after cleaning after boron diffusion in Example 1 of the present invention. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0039] It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner. Therefore, the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0040] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with this technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantive technical significance. Any structural modification, change in proportion or adjustment of size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical contents disclosed by the present invention.

[0041] The directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "middle", "longitudinal", "lateral", "horizontal", "inner", "outer", "radial", "circumferential" and the like in this specification are based on the directions or positional relationships shown in the drawings and are only for the convenience of simplifying the description. They do not indicate or imply that the devices or elements referred to must have a specific direction, be constructed and operate in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0042] After the boron diffusion process, a very thin boron-rich layer will be formed on the surface of the silicon wafer. This layer is difficult to be corroded by hydrofluoric acid because it is rich in inactive boron atoms. The traditional removal method is to oxidize the boron-rich layer into a BSG (borosilicate glass, i.e. silicon oxide containing B2O3) layer through thermal oxygen oxidation, and then clean the BSG with hydrofluoric acid with a volume fraction of 80%, that is, a combination of dry and wet methods to achieve the purpose of removing the boron-rich layer. However, this greatly occupies the production capacity of thermal oxidation. In addition, the BSG layer is cleaned with a high concentration of hydrofluoric acid solution, which not only increases the consumption cost of hydrofluoric acid, but also has a high risk factor for strong acid raw materials.

[0043] In order to release the capacity of thermal oxidation, reduce the cost of raw materials, and facilitate operation, an attempt is made to mix hydrofluoric acid and nitrate additives to make an acid solution during the production process, and the boron-rich layer is directly pickled using the acid solution, omitting the step of thermal oxidation to oxidize the boron-rich layer to BSG. As a result, the boron-rich layer can also be corroded and cleaned, and the use of nitric acid can be avoided, reducing the cost of raw materials and the risk factor, releasing the capacity of thermal oxidation, and improving production efficiency. In addition, the composition of the acid solution is optimized, and it is found that after the water, nitrate, surfactant, and sodium benzoate components of the present invention are compounded in a specific ratio, the cleaning effect achieved is better than the effect of the above components being used separately for cleaning, and it can be carried out in one step, which greatly saves the production line and improves efficiency.

[0044] Example 1

[0045] A method for cleaning a reworked sheet comprises the following steps:

[0046] 1. Provide reworked pieces with unqualified quality after boron expansion in TOPCon battery preparation process

[0047] In the TOPCon battery preparation process, the PN junction of the N-type silicon base needs to be diffused with boron. This process forms a PN junction by diffusing a P-type element (boron) on an N-type silicon wafer (doped with phosphorus), forming a P+ layer on the front and an N+ layer on the back. Defective films are produced due to process, equipment, and human factors. If such defective films are transmitted according to the normal process flow, the efficiency and yield of the battery cells will be seriously affected, resulting in serious waste of resources. In order to reduce costs and save raw materials, it is necessary to rework the defective films produced in the production process to achieve reuse. Such defective films are generally referred to as reworked films in the art. The reworked films of the present invention specifically refer to defective films with unqualified quality after boron diffusion. The rework method for the reworked films with unqualified quality produced after the boron diffusion process is mainly to clean them and then re-texture them.

[0048] 2. Pickling to remove the boron-rich layer

[0049] A low concentration hydrofluoric acid solution and a nitrate additive are mixed to obtain an acid solution, and the acid solution is used to clean the reworked wafer to remove the boron-rich layer.

[0050] In this embodiment, the boron-rich layer refers to a thin layer of boron-rich atoms formed on the surface of the silicon wafer after the boron diffusion process. Since boron atoms are difficult to be directly corroded by hydrofluoric acid, the boron-rich layer is difficult to be corroded by hydrofluoric acid solution. In this embodiment, the hydrofluoric acid solution is mixed with the nitrate additive to obtain an acid solution, and the nitrate is ionized to produce nitrate NO. 3- Ionize H with hydrofluoric acid solution + The mixture achieves the effect of mixed acid of hydrofluoric acid and nitric acid, making the acid liquid both oxidizing and corrosive, oxidizing the boron atoms in the boron-rich layer to B2O3, and then dissolving B2O3 with the hydrofluoric acid solution. Therefore, this corrosive liquid can effectively remove the boron-rich layer produced after boron expansion, and realize one-step wet cleaning to effectively remove the boron-rich layer of the reworked sheet after boron expansion. The reworked sheet after boron expansion does not need an overheating oxidation process. After one-step wet cleaning, the reworked sheet can reach the state of direct re-texturing.

[0051] In some embodiments, the concentration of the hydrofluoric acid solution is 5-15%, such as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc. A lower volume concentration of the hydrofluoric acid solution is not only conducive to reducing the consumption cost of hydrofluoric acid, but also has a lower acidity and a lower risk factor. However, if the concentration of the hydrofluoric acid is too low, the acidity will be insufficient, and the boron-rich layer generated after the boron expansion cannot be removed after corrosion. If the concentration of the hydrofluoric acid solution is too high, not only the consumption cost of hydrofluoric acid is increased, but also the risk factor of the strong acid in the process is higher.

[0052] In some embodiments, the effective components of the nitrate additive are nitrate and surfactant with a volume fraction of 1% to 2%, and the specific effective components of the nitrate additive are 1%, 1.5%, 1.8%, 2%, etc. In this embodiment, if the volume fraction of the effective component of the nitrate additive is too small, the nitrate ions provided are less, and the nitrate ions ionized with the hydrofluoric acid solution are reduced. + The concentration of the mixed nitric acid and hydrofluoric acid solution is low, and it is not possible to corrode and remove the boron-rich layer produced after boron expansion. However, if the volume fraction of the effective component of the nitrate additive is too large, after the boron-rich layer produced after boron expansion is completely corroded, it will cause a waste of the effective component raw materials of the nitrate additive.

[0053] Specifically, in some embodiments, the nitrate can be sodium nitrate, potassium nitrate, ammonium nitrate, calcium nitrate or other nitrates, as long as they can provide nitrate ions; similarly, the surfactant can also be sodium dodecyl sulfate, disodium lauryl sulfosuccinate, disodium coconut oil monoethanolamide sulfosuccinate, monolauryl phosphate or other surfactants, as long as they can remove dirt on the surface of the silicon wafer.

[0054] In some embodiments, the nitrate additive component and ratio are deionized water: sodium nitrate (NaNO3): surfactant (sodium dodecyl sulfate): sodium benzoate = 70-85: 10-20: 3-8: 1-5, for example, deionized water: sodium nitrate (NaNO3): surfactant (sodium dodecyl sulfate): sodium benzoate = 78: 15: 5: 2; deionized water: sodium nitrate (NaNO3): surfactant (sodium dodecyl sulfate): sodium benzoate = 75: 13: 4: 1, deionized water: sodium nitrate (NaNO3): surfactant (sodium dodecyl sulfate): sodium benzoate = 82: 18: 6: 3, etc. In this embodiment, too low a proportion of sodium nitrate will result in too low a nitrate content, which cannot be combined with hydrofluoric acid to produce sufficient nitric acid to corrode the boron-rich layer, but too high a proportion of sodium nitrate will not only lead to a waste of raw materials, but also require more processes to remove excess sodium nitrate. Too high a surfactant content will result in excessive foam, and subsequent removal of the surfactant will require more water resources. Sodium benzoate can effectively prevent silicon wafers from deteriorating or becoming sour during storage or processing, thereby ensuring the quality and stability of the silicon wafers. If its proportion is too low, the anti-corrosion effect will be poor, and if its proportion is too high, it will also lead to waste of raw materials and difficulty in cleaning.

[0055] In some embodiments, the volume ratio of the hydrofluoric acid solution to the nitrate additive is 5-8:1, for example, the hydrofluoric acid solution: nitrate additive is 5:1, the hydrofluoric acid solution: nitrate additive is 6:1, the hydrofluoric acid solution: nitrate additive is 8:1, etc.

[0056] In some embodiments, the pickling temperature is 35-45°C, such as 35°C, 38°C, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, etc. If the pickling temperature is too low, the reaction rate is slow, and the cleaning time is longer and the effect is worse, but if the temperature is too high, the water will evaporate too quickly, requiring more acid solution, increasing the cost of raw materials. The pickling time is 200-650s, such as 200s, 250s, 3000s, 350s, 400s, 450s, 500s, 650s, 550s, 600s, 650s, etc. The pickling time is too short to remove all the boron-rich layers, and the pickling time is too long to improve the cleaning effect of the silicon wafer, but affect the production capacity.

[0057] In some embodiments, the pickling step of removing the boron-rich layer further includes the following steps:

[0058] 3. Wash the silicon wafer after pickling

[0059] Use running pure water to rinse and remove dirt and acid residue from the silicon wafer. There is always water overflowing in the cleaning tank to ensure the cleanliness of the water in the tank until blue bubbles appear, which can more effectively clean the surface of the silicon wafer.

[0060] In some embodiments, the cleaning time is 200-400 seconds, such as 200 seconds, 205 seconds, 210 seconds, 213 seconds, 260 seconds, 280 seconds, 300 seconds, 320 seconds, 350 seconds, 400 seconds, etc. If the cleaning time is too short, the silicon wafer dirt and acid residue cannot be rinsed clean, and if the cleaning time is too long, water capacity and resources are wasted.

[0061] In some embodiments, the washing step further comprises the following steps:

[0062] 4. Oxidation cleaning of the silicon wafer after water washing

[0063] The silicon wafer is cleaned by a mixed solution of sodium hydroxide and hydrogen peroxide to further remove the introduced acid residue and other dirt. In this embodiment, the volume fraction of sodium hydroxide is 48%, the volume fraction of hydrogen peroxide is 31%, and the mixing ratio of sodium hydroxide and hydrogen peroxide is 3.6:16.

[0064] In some embodiments, the oxidation cleaning step further includes the following steps:

[0065] 5. Clean the silicon wafer after oxidation cleaning with hydrofluoric acid

[0066] Use hydrofluoric acid for cleaning to make the surface of the silicon wafer hydrophobic, improve the dehydration ability of the silicon wafer, and remove metal impurities.

[0067] In some embodiments, the volume fraction of hydrofluoric acid is 2%-10%, for example 2%, 2.2%, 2.5%, 2.8%, 3%, 3.5%, 4%, 5%, 6%, 8%, 10%, etc. If the volume fraction of hydrofluoric acid is too small, the reaction with metal impurities is slow and the effect of removing metal impurities is poor. If the volume fraction of hydrofluoric acid is too large, not only the raw material cost is high, but also the risk factor is high.

[0068] In some embodiments, the hydrofluoric acid cleaning step further includes the following steps:

[0069] 6. Slow pull cleaning of silicon wafers after hydrofluoric acid cleaning

[0070] Use cold water to slowly pull and clean for 20 seconds to pre-dehydrate the silicon wafer.

[0071] In some embodiments, the slow pull cleaning step further includes the following steps:

[0072] 7. Dry the silicon wafer after slow pulling and cleaning

[0073] The drying temperature is 90℃±10℃, such as 80℃, 83℃, 85℃, 88℃, 90℃, 95℃, 100℃, etc. If the drying temperature is too low, it is not conducive to the evaporation of water and the drying is slow. If the drying temperature is too high, it may cause thermal stress on the surface of the silicon wafer. The drying time is 600-800s, such as 600s, 650s, 700s, 750s, 780s, 790s, 800s, etc. At this point, the rework wafer cleaning process is completed and the silicon wafer can be re-textured.

[0074] Comparative Example 1

[0075] A method for cleaning a reworked wafer after boron expansion, which differs from Example 1 in that, in the step of pickling to remove the boron-rich layer, nitric acid with the same volume fraction is used instead of the nitrate additive, and then used to clean the reworked wafer, and the corrosion removal of the boron-rich layer can achieve the same effect as in Example 1, indicating that the present invention adopts a hydrofluoric acid solution and a nitrate additive to achieve the effects of hydrofluoric acid and nitric acid, but nitrate has a higher safety factor than nitric acid in terms of raw materials, and is not as good as Example 1 of the present invention in terms of dirt removal and anti-corrosion effects on the silicon wafer surface. Therefore, the present invention finally adopts a nitrate additive instead of nitric acid to be compounded with hydrofluoric acid as a mixed acid to clean the reworked wafer.

[0076] Comparative Example 2

[0077] A method for cleaning a reworked wafer after boron expansion, which differs from Example 1 in that, in step 2, pickling to remove the boron-rich layer, the nitrate additive component and ratio are deionized water: sodium nitrate: surfactant (sodium dodecyl sulfate): sodium benzoate = 50:18:20:12, and the addition ratio of the surfactant is increased.

[0078] However, the cleaning effect is the same as that of the original low-content surfactant in Example 1. Too much foam is generated, and more clean water is needed to remove the remaining surfactant. When the surfactant reaches a certain amount, it shows that increasing the amount of surfactant has no beneficial effect on improving the cleaning effect. Instead, more clean water is needed for cleaning, and the amount of surfactant added does not need to be too much.

[0079] Comparative Example 3

[0080] A method for cleaning a reworked wafer after boron expansion is different from Example 1 in that, in step 2, pickling to remove the boron-rich layer, the amount of surfactant added in the nitrate additive is 0.

[0081] Results After cleaning, the silicon wafer surface was severely mottled. Without the surface additive, the interface between the cleaning solution and the silicon wafer surface would affect the wetting uniformity of the cleaning solution, resulting in poor cleaning effect.

[0082] Comparative Example 4

[0083] A method for cleaning a reworked wafer after boron expansion, which differs from Example 1 in that, in step 2, pickling to remove the boron-rich layer, the ratios of hydrofluoric acid and nitrate additive are 10:1 and 1:1.

[0084] The results showed that increasing the amount of HF used or increasing the proportion of nitrate additives used would increase the weight loss of silicon wafer cleaning, with a weight loss of 0.07g and an increase of 0.19g. The weight loss of silicon wafers increased after rework and cleaning, and the reworked silicon wafers would increase the fragmentation rate of silicon wafers. At the same time, the thinning of silicon wafers would affect the short-circuit current density of the finished battery after rework, which would affect the achievement of efficiency indicators.

[0085] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above 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.

[0086] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for cleaning a reworked wafer, wherein the reworked wafer comprises a solar cell silicon wafer and a boron-rich layer formed on the surface of the solar cell silicon wafer after a boron diffusion process, characterized in that: The cleaning method comprises the following steps: Provide solar cell rework wafers after boron diffusion; An acid solution is obtained by mixing hydrofluoric acid and a nitrate additive, and the reworked sheet is pickled with the acid solution to remove the boron-rich layer, wherein the boron-rich layer contains boron atoms.

2. The cleaning method according to claim 1, characterized in that The volume fraction of the hydrofluoric acid is 3% to 20%; Preferably, the concentration of the hydrofluoric acid is 5% to 15%; Preferably, the volume ratio of the hydrofluoric acid solution to the nitrate additive is 5-8:

1.

3. The cleaning method according to claim 1, characterized in that The nitrate additive comprises nitrate and a surfactant; Preferably, the volume fraction of the nitrate is 1% to 5%; Preferably, the volume fraction of the nitrate is 1% to 2%; Preferably, the nitrate is at least one of sodium nitrate, potassium nitrate, ammonium nitrate and calcium nitrate; Preferably, the surfactant is at least one of sodium lauryl sulfate, disodium lauryl sulfosuccinate, disodium coconut oil monoethanolamide sulfosuccinate, and monolauryl phosphate.

4. The cleaning method according to claim 1, characterized in that: The nitrate additive includes water, nitrate, surfactant and sodium benzoate; Preferably, the proportion of each component in the nitrate additive is: water: nitrate: surfactant: sodium benzoate = 70-85: 10-20: 3-8: 1-5; Preferably, the proportions of the components in the nitrate additive are: water: nitrate: surfactant: sodium benzoate = 75-80: 13-18: 4-6: 1-3.

5. The cleaning method according to claim 1, characterized in that: The pickling temperature is 35-45°C, and the pickling time is 200-650s; Preferably, the pickling temperature is 38-42° C., and the pickling time is 280-620 s.

6. The cleaning method according to claim 1, characterized in that: The process also includes washing the silicon wafer after the acid washing with water; Preferably, the water washing method is flowing water washing, and the water washing time is 200-400s.

7. The cleaning method according to claim 1, characterized in that: The process also includes oxidizing and cleaning the silicon wafer after the acid cleaning; Preferably, the oxidative cleaning method is cleaning with a mixed solution of sodium hydroxide and hydrogen peroxide.

8. The cleaning method according to any one of claims 1 to 7, characterized in that: The process also includes performing hydrofluoric acid cleaning, slow pull cleaning and drying on the silicon wafer after the acid cleaning; Preferably, the volume fraction of hydrofluoric acid in the hydrofluoric acid cleaning is 2%-15%; Preferably, the slow pulling cleaning time is 15-25s; Preferably, the temperature of the drying treatment is 70-110° C., and the time of the drying treatment is 500-800 seconds.

9. Application of the cleaning method according to any one of claims 1 to 8 in a solar cell manufacturing process.

10. A process for preparing a solar cell, characterized in that: The reworked wafer after the boron diffusion process is cleaned using the cleaning method described in any one of claims 1 to 8.

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