Alkaline etching additive, alkaline etching solution, and method for cleaning wrap-around polycrystalline silicon

Abstract

The present invention provides an alkaline etching additive, an alkaline etching solution, and a method for cleaning wrap-around polycrystalline silicon. The alkaline etching additive comprises a protective component and a component for accelerating the etching of silicon, and can increase the etching rate of polycrystalline silicon, protect an oxide layer of a PN junction and increase the difference between the etching rates of B / PSG and polycrystalline silicon etched by an alkali. The additive enables the etching rate of polycrystalline silicon to reach 960 nm / min, whereas the reaction rates for PSG and BSG are 5.4 nm / min and 7.2 nm / min, respectively, thereby achieving the complete isolation of P and N regions and improving the battery yield. An anionic surfactant and a dispersant improve the cleaning efficiency and a polishing effect. Compared with traditional acid washing and soda ash washing methods, the additive can not only increase the removal rate of polycrystalline silicon, but can also protect the structure of a battery, expand a process window and improve the production stability. The technique is particularly suitable for the preparation of batteries having a TOPCon structure, and improves the performance and stability of a battery by optimizing the deposition and cleaning processes of polycrystalline silicon.

Description

Alkali etching auxiliary agent, alkali etching solution and method for cleaning wrap-around poly-silicon TECHNICAL FIELD

[0001] The present application relates to the field of photovoltaics, and in particular to an alkali etching auxiliary agent, an alkali etching solution and a method for cleaning wrap-around poly-silicon. BACKGROUND

[0002] TOPCon (Tunnel Oxide Passivated Contact) structure cells, i.e. passivated contact cells, are a kind of high-efficiency crystalline silicon solar cell technology. The key is to form an ultra-thin tunnel oxide layer and a highly doped polysilicon thin layer on the back of the cell, which together form a passivated contact structure. This structure can significantly reduce the recombination effect caused by metal contact on the back of the cell, while improving the transport capacity of the carriers, thus having significant advantages in improving open-circuit voltage and short-circuit current, and becoming a new mainstream technology in the field of solar cells.

[0003] In the preparation of TOPCon structure cells, polysilicon deposition must be performed on the back of the silicon wafer. Doped polysilicon is usually prepared by two main methods: 1) LPCVD method: first depositing microcrystalline or polysilicon, then performing offline thermal diffusion or ion implantation annealing treatment; 2) PECVD method: depositing doped amorphous silicon online and performing high-temperature annealing treatment. Although the two methods differ in process, the film deposition is not directional, resulting in the attachment of the oxide layer and the intrinsic polysilicon layer to the side and front of the cell, forming a wrapping phenomenon, i.e. "wrap-around".

[0004] In order to improve productivity, double-insertion technology is commonly used in the market, which results in a thin middle and thick edges of the wrap-around layer. Therefore, when removing the wrap-around layer, the removal degree of the uneven thickness of the front polysilicon layer needs to be considered. Wrap-around can cause the diffusion of doped atoms to the silicon substrate, resulting in the conduction of the front emitter and the back of the cell, causing the cell to leak current and affecting its electrical performance. Therefore, in the process of manufacturing solar cells, it is crucial to ensure the high-quality isolation of the p and n regions to improve the performance and stability of the cell.

[0005] For the problem of removing polysilicon wrap-around, the industry usually adopts the following two solutions:

[0006] 1) Acid cleaning: HF-HNO3 mixed acid etching is used to remove the poly-silicon layer. The etching rate of different materials is as follows: BSG (boron-silicon glass) is 288 nm / min, PSG (phosphor-silicon glass) is 483 nm / min, and poly-silicon is 820 nm / min. When the edge of the poly-silicon layer is completely removed, the middle thin poly-silicon layer is over-etched, which destroys the normal texture structure. This results in a significant increase in the square resistance of the cell emitter, with an increase of 13-34Ω, and a significant decrease in the PN junction depth and the surface concentration of the boron-doped layer. Therefore, the process window is narrow.

[0007] 2) Alkaline cleaning: only inorganic alkali (such as KOH or NaOH) is used to remove the poly-silicon on the front surface of the silicon wafer. After alkaline etching, the square resistance of the cell is increased by 6-10Ω compared with the acid cleaning process. The etching rate of potassium hydroxide on BSG is 11.4 nm / min, so although the surface concentration of the boron-doped layer changes relatively unobviously during the cleaning process, the etching rate of PSG is 210 nm / min, and the difference between the two rates is large, which will result in a decrease in the PN junction depth and affect the cell performance. In addition, the removal rate of poly-silicon treated by pure alkali is slow, only 604 nm / min, which is 216 nm / min slower than the acid etching rate. Therefore, only when the BSG is thick enough, can it be ensured that part of the BSG remains after the poly-silicon is removed to protect the texture from being damaged. However, the thick BSG may also lead to insufficient boron expansion capacity and a decrease in cell efficiency, which reduces the process window.

[0008] In order to solve the limitations of the prior art and expand the process window, the present application provides an alkaline etching auxiliary agent, an alkaline etching solution and a method for cleaning the poly-silicon.

[0009] SUMMARY

[0010] The purpose of the present application is to provide an alkaline etching auxiliary agent, an alkaline etching solution and a method for cleaning the poly-silicon. The function of the additive is to slow down the etching rate of alkali on BSG / PSG, while increasing the etching rate of poly-silicon, thereby increasing the reaction difference. This improvement makes it possible to completely remove the poly-silicon while ensuring that the changes in the PN junction depth and the surface concentration of the boron-doped layer are basically unchanged. Thus, the process window for the preparation of the cell electrode in the later stage is expanded, thereby achieving better control of production stability.

[0011] To solve the above technical problems, the purpose of the present application is achieved as follows:

[0012] The alkaline etching auxiliary agent for cleaning the poly-silicon according to the present application comprises the following components in the following mass percentage:

[0013] 2% to 5% of a promoter,

[0014] 1-2.5% anionic surfactant,

[0015] 0.5-2% protective component,

[0016] 1-2.5% dispersant;

[0017] the balance being deionized water.

[0018] On the basis of the above scheme and as a preferred scheme of the above scheme: the accelerator is selected from one or more of ammonium chloride, ammonium persulfate, sodium p-hydroxybenzenesulfonate, sodium p-aminosalicylate and ammonium thiocyanate.

[0019] On the basis of the above scheme and as a preferred scheme of the above scheme: the protective component is selected from one or more of acrylamide, methyl triethoxysilane, isopropyl trimethoxysilane.

[0020] On the basis of the above scheme and as a preferred scheme of the above scheme: the anionic surfactant is selected from one or more of sodium dodecylbenzenesulfonate, sodium alkylsulfonate, sodium alkyl polyether sulfonate, sodium dodecyl polyoxyethylene ether phosphate.

[0021] On the basis of the above scheme and as a preferred scheme of the above scheme: the dispersant is selected from one or more of sodium polyacrylate, sodium acrylate-maleic acid copolymer, sodium acrylate.

[0022] The present application also relates to a kind of for cleaning the alkali etching solution of polycrystalline silicon, including lye and the alkali etching auxiliary agent for cleaning the polycrystalline silicon of any one of claims 1 to 5.

[0023] On the basis of the above scheme and as a preferred scheme of the above scheme: the mass ratio of the alkali etching auxiliary agent and alkali solution is 2-6:100, and the alkali solution is KOH solution or NaOH solution.

[0024] On the basis of the above scheme and as a preferred scheme of the above scheme: the mass percentage content of KOH in the KOH solution is 0.3%-2%; the mass percentage content of NaOH in the NaOH solution is 0.3%-2%.

[0025] The present application also relates to a kind of for cleaning the alkali etching solution of polycrystalline silicon, including lye and the alkali etching auxiliary agent for cleaning the polycrystalline silicon of any one of claims 1 to 5.

[0026] The beneficial effects of the present application are: the present application provides a kind of polycrystalline silicon auxiliary alkali cleaning additive for around plating layer, its formula contains the component (mainly for ammonium persulfate and ammonium thiocyanate) for accelerating silicon corrosion, can improve the corrosion speed of silicon.In addition, the additive also contains protective ingredients (mainly for acrylamide, methyl triethoxysilane), which can be combined with the oxide layer, enhance the protective property of the oxide layer, extend its destruction time, so as to protect the oxide layer of PN junction.Through the cooperation of the two, the difference between the corrosion rate of B / PSG and polycrystalline silicon can be expanded.The reaction rate of PSG after auxiliary alkali cleaning using the additive is 7.2nm / min, the reaction rate of BSG is 5.4nm / min, and the reaction rate of polycrystalline silicon can reach 960nm / min.In this way, the excess polycrystalline silicon on the front and edge can be removed within the set process time, the complete separation of P and N area is realized, and the yield of the cell is greatly improved.In addition, the additive also contains a certain amount of anionic surfactant and dispersant, wherein the main components are sodium dodecyl benzene sulfonate and sodium alkyl sulfonate, etc.These components can form an effective wetting layer between the liquid and the surface of the silicon wafer, improve the wettability of the liquid on the surface of the silicon wafer, and facilitate the cleaning process.At the same time, the dispersant can adjust the dispersion state of the particles in the liquid, reduce the mutual adsorption force between the particles, improve the distribution of the liquid on the surface of the silicon wafer, and promote the cleaning process. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is an SEM image of the front surface of the cleaning after pure alkali cleaning of the around plating wafer;

[0028] Figure 2 is an SEM image of the front surface of the cleaning after removing the around plating of example one;

[0029] Figure 3 is an apparent image of the cleaning before removing the around plating of example one;

[0030] Figure 4 is an apparent image of the cleaning before removing the around plating of example one. DETAILED DESCRIPTION

[0031] The present application will be further described below in conjunction with the drawings and specific examples.

[0032] Example 1

[0033] The present application relates to a kind of for cleaning around plating polycrystalline silicon alkali corrosion auxiliary agent, for removing TOPCon cell wafer polycrystalline silicon around plating layer, using 5L of PP reagent bottle, 4.5L of deionized water is added to it, 150g of ammonium persulfate is added, 60g of sodium alkyl sulfonate, 50g of sodium dodecyl polyoxyethylene ether phosphate, 75g of acrylamide, 25g of isopropyl trimethoxysilane, 70g of sodium polyacrylate are taken, deionized water is added to 5L, stirring is uniform, and it is prepared into around plating polycrystalline silicon removing additive.

[0034] The process of removing polysilicon only with alkali will not only damage the back PSG and front BSG, but also damage the back PN junction and the front roughened base. In order to solve this problem, protective agents acrylamide and isopropyl trimethoxysilane are added, which can selectively adsorb on the surface of P / BSG, and the adsorption capacity on polysilicon is weak, thereby effectively protecting the front BSG and the back PSG, providing a good barrier effect, and widening the rate difference of the reaction of alkali on PSG, BSG and polysilicon.

[0035] At the same time, the addition of ammonium persulfate further accelerates the corrosion rate of alkali on polysilicon, so that the plating layer can be removed in the shortest time. In addition, the addition of surfactants such as sodium alkyl sulfonate and sodium dodecyl polyoxyethylene ether phosphate can significantly reduce the solid-liquid surface tension and accelerate the mass transfer rate of the reaction. More importantly, this kind of surfactant can form a wedge-shaped structure between the polysilicon and the adsorbed particles, desorb the particles from the surface of the silicon wafer and wrap them, while forming a dense adsorption layer on the surface of the silicon wafer.

[0036] Finally, the addition of sodium polyacrylate dispersant plays a key role in maintaining the dispersion of particulate matter, improving the performance of the cleaning solution, and reducing redeposition during the plating cleaning, thereby ensuring the cleanliness of the surface of the silicon wafer and meeting the needs of subsequent processes.

[0037] The present embodiment also relates to a method for cleaning the polysilicon plating of a TOPCon cell wafer:

[0038] (1) After the silicon wafer is completed with double-sided texturing, boron doping is performed on the front side, and after the back side is polished, a tunnel oxide layer is deposited, and then a layer of polysilicon is grown on the back side by LPCVD / PECVD, and phosphorus doping is performed by phosphorus diffusion; the sheet resistance of the silicon wafer after boron doping is 120-200 Ω / Sq, and the thickness of the tunnel oxide layer and the polysilicon layer is 110-200 nm; the sheet resistance of the silicon wafer after phosphorus doping is 10-50 Ω / Sq;

[0039] (2) Before RCA cleaning, the silicon wafer obtained in step (2) is placed in a chain-type acid polishing device, the concentration of hydrofluoric acid in the chain-type acid polishing device is 15-30%, and the back side is protected by a water film, so that the front side and the side can be in contact with the acid solution, the cleaning time is 40-80 s, and the temperature is 20-25°C. This process can remove the phosphorus-doped layer on the front side and the side, and then dry.

[0040] (3) The silicon wafer obtained in step (2) is placed in an alkali tank containing the additive of the present embodiment for cleaning, the temperature is controlled at 75°C, and the cleaning is repeated for 3 min to remove the polysilicon plating on the front side; wherein the additive is the additive prepared above, the concentration of sodium hydroxide solution is 45wt%, and the volume ratio of additive to sodium hydroxide solution is 1:25;

[0041] (4) the silicon wafer after the alkali cleaning in step (3) is transferred to a water tank for wet cleaning for 1 min, and then is transferred to an H2O2 tank for cleaning for 1 min, with the temperature controlled at 65 DEG C, and the content of H2O2 being 2-7%, and the concentration of H2O2 being 35 wt%;

[0042] (5) the silicon wafer obtained in step (4) is transferred to a water tank for wet cleaning for 3 min, and then is transferred to an acid tank provided with HF to remove PSG and BSG,

[0043] with the temperature controlled at 20 DEG C, and the cleaning being circular for 3 min, and the concentration of HF being 20 wt%;

[0044] (6) the silicon wafer after the acid cleaning in step (5) is transferred to a water tank for wet cleaning for 2 min, and then is transferred to an H2O2 tank for cleaning for 2 min, with the temperature controlled at 65 DEG C, to further remove the dirt on the surface of the silicon wafer after the reaction;

[0045] (7) the silicon wafer in step (6) is transferred to an acid tank for further cleaning for 1 min, and then is transferred to a water tank and a slow lifting tank for dehydration treatment, and then is transferred to a drying tank for drying, with the temperature of the drying tank controlled at 85 DEG C, and the time being 600 s.

[0046] The embodiment also provides a preparation method of the TOPCon cell, including the following steps: (1) texturing; (2) boron diffusion; (3) acid etching to remove BSG; (4) backside alkali polishing; (5) LPCVD: using a heating method to make a gaseous compound react on the surface of the silicon wafer and deposit a solid thin film under a low pressure condition; (6) phosphorus diffusion; (7) removing PSG on the front side and the side; (8) RCA cleaning to remove the deposited polycrystalline silicon; (9) ALD, i.e. depositing a layer of aluminum oxide on the boron diffusion surface; (10) front film deposition, i.e. depositing a silicon nitride film on the boron diffusion surface; (11) back film deposition, i.e. depositing a silicon nitride film on the phosphorus diffusion surface; (12) screen printing, i.e. double-sided metallization + sintering + photo injection.

[0047] The components (ammonium persulfate and ammonium thiocyanate) that accelerate silicon corrosion and protective components (acrylamide, methyl triethoxysilane) can improve the polysilicon corrosion rate while protecting the PN junction oxide layer. Through the cooperation of additives, the difference in corrosion rate between B / PSG and polysilicon is significantly expanded, and the corrosion rate of polysilicon reaches 937 nm / min, while the reaction rates of PSG and BSG are 6.4 nm / min and 5.2 nm / min, respectively. The anionic surfactant and dispersant in the additive improve the wettability and distribution of the cleaning solution on the silicon wafer surface, promoting cleaning and polishing. The additive can remove polysilicon while ensuring that the PN junction depth and the surface concentration of the boron-doped layer remain essentially unchanged, expanding the process window for later cell electrode preparation and improving production stability. This technology is particularly suitable for preparing TOPCon structure cells, and by optimizing the polysilicon deposition and cleaning process, the performance and stability of the cell are improved.

[0048] Comparative Example 1

[0049] (1) After the silicon wafer completes double-sided texturing, boron doping is performed on the front side, and a tunnel oxide layer is deposited on the back side after polishing. Then, a layer of polysilicon is grown on the back side by LPCVD / PECVD, and phosphorus doping is performed by phosphorus diffusion; the sheet resistance after boron doping is 120-200 Ω / Sq, and the thickness of the tunnel oxide layer and the polysilicon layer is 110-200 nm; the sheet resistance of the silicon wafer after phosphorus doping is 10-50 Ω / Sq;

[0050] (2) Before RCA cleaning, the silicon wafer obtained in step (1) is placed in a chain-type acid polishing device, and the concentration of hydrofluoric acid in the chain-type acid polishing device is 15-30%. The back side is protected by a water film, and the front side and the side edges are allowed to contact the acid solution. The cleaning time is 40-80 s, and the temperature is 20-25°C. This process can remove the phosphorus-doped layer on the front side and the side edges, and the silicon wafer is dried;

[0051] (3) The silicon wafer obtained in step (2) is placed in a NaOH only alkali tank for cleaning. The temperature is controlled at 75°C, and the silicon wafer is cleaned for 3 min to remove the polysilicon on the front side. The concentration of the sodium hydroxide solution is 45 wt%;

[0052] (4) The silicon wafer after alkali cleaning in step (3) is transferred to a water tank for 1 min, and then placed in an H2O2 tank for 1 min. The temperature is controlled at 65°C, and the content of H2O2 is 2-7%. The concentration of H2O2 is 35 wt%;

[0053] (5) The silicon wafer obtained in step (4) is transferred to a water tank for 3 min, and then placed in an acid tank with HF to remove PSG and BSG. The temperature is controlled at 20°C, and the silicon wafer is cleaned for 3 min. The concentration of HF is 20 wt%;

[0054] (6) The silicon wafer after acid washing in step (5) is transferred to a water tank for rinsing for 2 min, and then is transferred to a H2O2 tank for cleaning for 2 min, with the temperature controlled at 65°C, to further remove dirt on the surface of the silicon wafer after reaction;

[0055] (7) The silicon wafer in step (6) is transferred to an acid tank for further cleaning for 1 min, and then is transferred to a water tank and a slow pull-up tank for dehydration treatment, and then is transferred to a drying tank for drying, with the temperature of the drying tank controlled at 85°C and the time controlled at 600 s.

[0056] Then, the cell sheet is prepared according to the preparation method of the TOPCon cell.

[0057] It can be seen from FIG. 1 that the tower top of the pyramid has been corroded, showing a downwardly concave tower base morphology, indicating that the texturing is damaged, and the soda cleaning does not have protective effect. It can be seen from FIG. 2 that the tower top of the pyramid is not damaged, indicating that the additive has a certain protective effect and can ensure that the texturing is not damaged during the cleaning process.

[0058] Example 2

[0059] The alkali corrosion auxiliary agent for cleaning the poly-si around plating in this embodiment is used for removing the poly-si around plating layer of the TOPCon cell sheet. A 5L PP reagent bottle is used, 4.5L deionized water is added to the bottle, and then 200g ammonium persulfate, 80g sodium dodecyl benzene sulfonate, 60g sodium dodecyl polyoxyethylene ether phosphate, 100g acrylamide, 30g isopropyl trimethoxysilane and 90g sodium polyacrylate are sequentially added. Then, deionized water is added to 5L, and the mixture is stirred uniformly to prepare the poly-si around plating additive. The corrosion of alkali to poly-si not only damages the PSG on the back surface and the BSG on the front surface, but also damages the PN junction on the back surface and the texturing tower base on the front surface. In order to solve this problem, protective agents acrylamide and isopropyl trimethoxysilane are added. These substances can selectively adsorb on the SG surface, and have weak adsorption capacity on poly-si, thereby effectively protecting the BSG on the front surface and the PSG on the back surface, providing a good barrier effect and widening the rate difference of the reaction of alkali to PSG, BSG and poly-si. At the same time, the addition of ammonium persulfate further accelerates the corrosion rate of alkali to poly-si, so that the around plating layer can be removed in the shortest time. In addition, surfactants such as sodium dodecyl benzene sulfonate and sodium dodecyl polyoxyethylene ether phosphate are added. These substances have strong penetration and wetting effect, significantly reduce the solid-liquid surface tension, and accelerate the mass transfer rate of the reaction. More importantly, this kind of surfactant can form a wedge-shaped structure between the poly-si and the adsorbed particles, desorb the particles from the surface of the silicon wafer and wrap them, and at the same time form a dense adsorption layer on the surface of the silicon wafer which is easy to clean.

[0060] Finally, the sodium polyacrylate dispersant is added, which plays a key role in keeping particles dispersed, improving cleaning ability, and reducing redeposition in the plating around cleaning, thereby ensuring the cleanliness of the silicon wafer surface and meeting the needs of subsequent processes.

[0061] And according to the steps in Example 1, the finished battery piece is made.

[0062] Example 3

[0063] The present embodiment relates to an alkali corrosion auxiliary agent for cleaning the plating around the polysilicon, which is used to remove the plating around the polysilicon layer of TOPCon battery piece. A 5L PP reagent bottle is used, 4.5L of deionized water is added, and then 220g of ammonium persulfate, 80g of sodium alkyl polyether sulfonate sodium dodecyl polyoxyethylene ether phosphate, 100g of acrylamide, 30g of methyl triethoxysilane and 95g of acrylic acid-maleic acid copolymer sodium salt are added in turn. Then, deionized water is added to 5L, stirred uniformly, and prepared into a plating around polysilicon additive. The corrosion of alkali to polysilicon not only destroys the PSG on the back and BSG on the front, but also damages the PN junction on the back and the textured tower on the front. In order to solve this problem, protective agents acrylamide and methyl triethoxysilane are added, which can selectively adsorb on the SG surface, and have weak adsorption capacity on polysilicon, thereby effectively protecting the BSG on the front and the PSG on the back, providing a good barrier effect and widening the rate difference of the reaction of alkali to PSG, BSG and polysilicon. At the same time, the addition of ammonium persulfate further accelerates the corrosion rate of alkali to polysilicon, so that the plating around layer can be removed in the shortest time. In addition, sodium dodecyl polyoxyethylene ether phosphate surfactant is added, which has strong penetration and wetting effect, significantly reduces the solid-liquid surface tension, and accelerates the mass transfer rate of the reaction. More importantly, this kind of surfactant can form a wedge-shaped structure between polysilicon and adsorbed particles, desorb and wrap the particles from the surface of the silicon wafer, and at the same time form a dense adsorption layer on the surface of the silicon wafer, which is easy to clean.

[0064] Finally, the sodium polyacrylate dispersant is added, which plays a key role in keeping particles dispersed, improving cleaning ability, and reducing redeposition in the plating around cleaning, thereby ensuring the cleanliness of the silicon wafer surface and meeting the needs of subsequent processes.

[0065] And according to the steps in Example 1, the finished battery piece is made.

[0066] Example 4

[0067] The embodiment relates to an alkali corrosion auxiliary agent for cleaning around-plated polysilicon, which is used for removing the around-plated layer of the polysilicon of a TOPCon cell piece. A 5L PP reagent bottle is used, 4.5L deionized water is added into the reagent bottle, 225g of ammonium chloride, 75g of sodium dodecyl benzene sulfonate, 50g of isopropyl trimethoxysilane, 100g of acrylamide and 90g of sodium polyacrylate are sequentially added into the reagent bottle, then deionized water is supplemented to 5L, and the around-plated polysilicon additive is prepared by uniformly stirring. The addition of the ammonium chloride can enhance the corrosion rate of the alkali on the polysilicon and improve the process efficiency. The isopropyl trimethoxysilane and the acrylamide serve as protection components, can effectively protect the BSG on the front surface and the PSG on the back surface, and reduce the damage to the PN junction and the tower base. The sodium dodecyl benzene sulfonate serves as a surfactant, has good penetration and wetting effects, significantly reduces the solid-liquid surface tension, and promotes the reaction. The sodium polyacrylate dispersant can effectively prevent the redeposition of particles in the cleaning process, and ensures the cleanliness of the surface of the silicon piece. And the finished cell piece is prepared according to the steps in Example 1.

[0068] Example 5

[0069] The embodiment relates to an alkali corrosion auxiliary agent for cleaning around-plated polysilicon, which is used for removing the around-plated layer of the polysilicon of a TOPCon cell piece. A 5L PP reagent bottle is used, 4.5L deionized water is added into the reagent bottle, 225g of ammonium chloride, 75g of sodium dodecyl benzene sulfonate, 50g of isopropyl trimethoxysilane, 100g of acrylamide and 90g of sodium polyacrylate are sequentially added into the reagent bottle, then deionized water is supplemented to 5L, and the around-plated polysilicon additive is prepared by uniformly stirring. The addition of the ammonium chloride can enhance the corrosion rate of the alkali on the polysilicon and improve the process efficiency. The isopropyl trimethoxysilane and the acrylamide serve as protection components, can effectively protect the BSG on the front surface and the PSG on the back surface, and reduce the damage to the PN junction and the tower base. The sodium dodecyl benzene sulfonate serves as a surfactant, has good penetration and wetting effects, significantly reduces the solid-liquid surface tension, and promotes the reaction. The sodium polyacrylate dispersant can effectively prevent the redeposition of particles in the cleaning process, and ensures the cleanliness of the surface of the silicon piece. And the finished cell piece is prepared according to the steps in Example 1.

[0070] Example 6

[0071] The embodiment relates to an alkali corrosion auxiliary agent for cleaning around-plated polycrystalline silicon, which is used for removing the around-plated layer of polycrystalline silicon of a TOPCon cell piece. A 5L PP reagent bottle is used, 4.5L deionized water is added into the reagent bottle, 230g sodium p-aminosalicylate, 85g alkyl polyether sodium sulfonate, 70g acrylamide, 35g isopropyl trimethoxysilane and 110g acrylic acid-maleic acid copolymer sodium salt are sequentially added into the reagent bottle, then deionized water is added into the reagent bottle to 5L, and the mixture is uniformly stirred to prepare the around-plated polycrystalline silicon additive. The sodium p-aminosalicylate improves the corrosion speed of alkali on polycrystalline silicon, and shortens the process time. The acrylamide and the isopropyl trimethoxysilane protect the front BSG and the back PSG, and reduce the damage to the PN junction and the tower base. The alkyl polyether sodium sulfonate serves as a surfactant, reduces the solid-liquid surface tension, and promotes the reaction. The acrylic acid-maleic acid copolymer sodium salt dispersant keeps the dispersed state of particulate matters in the cleaning process, improves the cleaning liquid performance, reduces redeposition, and ensures the cleanliness of the silicon wafer surface. And the finished cell piece is prepared according to the steps in Example 1.

[0072] It is detected that the value of the rear side resistance after the cleaning of the around-plated layer of the single crystal silicon in the above-mentioned Comparative Example 1, Example 1, Example 2, Example 3, Example 4, Example 5 and Example 6 is shown in the following table 1.

[0073] Table 1: Change of rear side resistance of single crystal silicon after removing the around-plated layer in Comparative Example 1 and Examples 1-6

[0074] It is detected that the photoelectric conversion efficiency value of the single crystal silicon after the treatment in the above-mentioned Comparative Example 1, Example 1 and Example 2 is shown in the following table 2.

[0075] Table 2: Comparison of photoelectric conversion efficiency values of single crystal silicon after removing the around-plated layer in Examples 1-3

[0076] The above describes the preferred embodiments of the application in detail. It should be understood that those skilled in the art can make many modifications and changes without creative work according to the concept of the application. Therefore, any technical solution obtained by logical analysis, reasoning or limited experiment on the basis of the prior art according to the concept of the application should be within the protection scope determined by the claims.

Claims

1. An alkali corrosion auxiliary agent for cleaning around a polysilicon plating, characterized by, The mass percentage of each component is: 2% to 5% of an accelerator, 1% to 2.5% of an anionic surfactant, 0.5% to 2% of a protective component, 1% to 2.5% of a dispersant; the balance being deionized water.

2. The etching aid for cleaning the poly-silicon around the plating according to claim 1, wherein, The accelerator is selected from one or more of ammonium chloride, ammonium persulfate, sodium p-hydroxybenzenesulfonate, sodium p-aminosalicylate, and ammonium thiocyanate.

3. The etching aid for cleaning the poly-silicon around the plating according to claim 1, wherein, The protective component is selected from one or more of acrylamide, methyl triethoxysilane, and isopropyl trimethoxysilane.

4. The etching aid for cleaning the poly-silicon around the plating according to claim 1, wherein, The anionic surfactant is selected from one or more of sodium dodecylbenzenesulfonate, sodium alkylsulfonate, sodium alkyl polyether sulfonate, and sodium dodecyl polyoxyethylene ether phosphate.

5. The etching aid for cleaning the poly-silicon around the plating according to claim 1, wherein, The dispersant is selected from one or more of sodium polyacrylate, sodium acrylate-maleic acid copolymer, and sodium acrylate.

6. An alkaline etching solution for cleaning around a polysilicon deposition, characterized by, The alkaline etching auxiliary agent for cleaning the polysilicon around the plating is included in the alkaline solution and the alkaline etching auxiliary agent according to any one of claims 1 to 5.

7. The alkaline etching solution for cleaning around the plated polysilicon according to claim 6, wherein The mass ratio of the alkaline etching auxiliary agent to the alkaline solution is 2 to 6:100, and the alkaline solution is a KOH solution or a NaOH solution.

8. The alkaline etching solution for cleaning around the plated polysilicon according to claim 6, wherein The mass percentage of KOH in the KOH solution is 0.3% to 2%, and the mass percentage of NaOH in the NaOH solution is 0.3% to 2%.

9. A method of cleaning around a deposited polysilicon, characterized by, The silicon wafer with PSG removed on the front surface after phosphorus diffusion is immersed in the alkaline etching solution for cleaning the polysilicon around the plating according to any one of claims 6 to 8 for 180 to 300 seconds, and the temperature of the alkaline etching solution is controlled at 65 to 85°C. After cleaning, the silicon wafer is cleaned with deionized water, and then cleaned with H2O2 and NaOH solution. Next, BSG and PSG are removed with HF, and then the silicon wafer is cleaned with water, alkaline solution, and acid solution.

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