TMAH solution for removing polycrystalline silicon layer, preparation method and application of TMAH solution, and back contact cell

Abstract

The invention provides a TMAH solution for removing a polycrystalline silicon layer, a preparation method and application of the TMAH solution and a back contact cell, and relates to the technical field of photovoltaic cells. The TMAH solution is prepared from the following components in parts by weight: 20 to 250 parts of tetramethylammonium hydroxide, 0.0005 to 6 parts of a main oxidant, 0.001 to 4 parts of an auxiliary oxidant, 3 to 5 parts of a main complexing agent, 2 to 3 parts of an auxiliary complexing agent, 0.001 to 0.5 part of a surfactant and 800 to 1200 parts of water. According to the invention, when the TMAH solution composed of a specific formula is used for corroding the N region, the bottom tunneling oxide layer is reserved, only the surface P-type polycrystalline silicon layer is removed, and side pits are reduced, so that side residues in subsequent procedures are reduced, side corrosion pits are reduced, subsequent residues are reduced, electric leakage is reduced, the yield is improved, and the conversion efficiency of a battery piece is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic cells, in particular to a TMAH solution for removing a polysilicon layer and a preparation method and application thereof, and a back contact cell. BACKGROUND

[0002] The back contact cell refers to a solar cell in which no metal electrode is arranged on the front surface of a cell sheet, and the positive and negative electrodes are arranged on the back surface of the cell sheet. The back contact cell can effectively reduce the shading of the electrodes on the cell sheet, increase the short-circuit current of the cell sheet, and improve the conversion efficiency of the cell sheet.

[0003] In the existing manufacturing process of an N-type back contact cell, laser is used to remove the surface BSG in the N region manufacturing process, and then an acidic solution or a strong alkaline solution is used for etching. In the etching process, pits are formed in the silicon substrate, and the side surface is also etched to form pits. When N-poly is deposited, the side surface is also deposited. When a laser process is used, the PSG in the side pit cannot be removed, so the residual N-poly cannot be removed in the subsequent cleaning process, causing electric leakage and affecting the conversion efficiency of the cell sheet.

[0004] Therefore, the present application is provided. SUMMARY

[0005] The present application aims to provide a TMAH solution for removing a polysilicon layer and a preparation method and application thereof, and a back contact cell. The TMAH solution solves the electric leakage caused by the side surface residue due to the height difference between the N region and the P region, and improves the conversion efficiency of the cell sheet.

[0006] In order to achieve the above-mentioned purpose of the present application, the following technical solutions are adopted:

[0007] In a first aspect, the present application provides a TMAH solution for removing a polysilicon layer, which comprises, by weight fraction:

[0008] 20-250 parts of tetramethylammonium hydroxide, 0.0005-6 parts of a main oxidizing agent, 0.001-4 parts of an auxiliary oxidizing agent, 3-5 parts of a main complexing agent, 2-3 parts of an auxiliary complexing agent, 0.001-0.5 parts of a surfactant, and 800-1200 parts of water.

[0009] Preferably, the main oxidizing agent comprises potassium persulfate and / or ozone.

[0010] Preferably, the auxiliary oxidizing agent comprises hydrogen peroxide and / or sodium periodate.

[0011] Preferably, when the main oxidizing agent is selected from potassium persulfate, the auxiliary oxidizing agent is selected from hydrogen peroxide; and when the main oxidizing agent is selected from ozone, the auxiliary oxidizing agent is selected from sodium periodate.

[0012] Preferably, the content of the potassium persulfate is 4-6 parts.

[0013] Preferably, the content of the hydrogen peroxide is 2-4 parts.

[0014] Preferably, the content of the ozone is 0.0005-0.001 parts.

[0015] Preferably, the content of the sodium periodate is 1-2 parts.

[0016] Preferably, the main complexing agent comprises a 7-hydroxy chelating crosslinking agent.

[0017] Preferably, the 7-hydroxy chelating crosslinking agent is a propylene diamine quaternary ammonium salt containing 7 hydroxyl groups.

[0018] Preferably, the propylene diamine quaternary ammonium salt containing 7 hydroxyl groups has the following formula I:

[0019]

[0020] wherein n is 2-4.

[0021] Preferably, the content of the main complexing agent is 3-5 parts.

[0022] Preferably, the auxiliary complexing agent comprises an N-methyl-D-glucosamine grafted chitosan derivative and / or a glycerol-boric acid chelate, preferably a combination of an N-methyl-D-glucosamine grafted chitosan derivative and a glycerol-boric acid chelate.

[0023] Preferably, the content of the N-methyl-D-glucosamine grafted chitosan derivative is 1-2 parts.

[0024] Preferably, the content of the glycerol-boric acid chelate is 2-3 parts.

[0025] Preferably, the surfactant comprises a main surfactant.

[0026] Preferably, the main surfactant comprises a polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer and / or a fatty alcohol polyoxyethylene ether.

[0027] Preferably, the surfactant further comprises an auxiliary surfactant.

[0028] Preferably, the auxiliary surfactant comprises potassium perfluorooctylsulfonate and / or sodium dodecyl sulfate.

[0029] Preferably, when the main surfactant is selected from a polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer, the auxiliary surfactant is selected from potassium perfluorooctylsulfonate.

[0030] Preferably, when the primary surfactant is selected from fatty alcohol polyoxyethylene ether, the auxiliary surfactant is selected from sodium lauryl sulfate.

[0031] Preferably, the content of the polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer is 0.005 to 0.01 parts, and the content of the potassium perfluorooctane sulfonate is 0.001 to 0.003 parts.

[0032] Preferably, the content of the fatty alcohol polyoxyethylene ether is 0.01 to 0.02 parts, and the content of the sodium lauryl sulfate is 0.005 to 0.01 parts.

[0033] In a second aspect, the present invention provides a method for preparing a TMAH solution for removing a polysilicon layer as described in the first aspect, the preparation method comprising:

[0034] Tetramethylammonium hydroxide, a primary oxidant, an auxiliary oxidant, a primary complexing agent, an auxiliary complexing agent and a surfactant are dissolved in water to obtain the TMAH solution for removing the polysilicon layer.

[0035] In a third aspect, the present invention provides a use of the TMAH solution for removing a polysilicon layer as described in the first aspect in removing a P-type polysilicon layer on a surface of a silicon wafer in which an N region is pre-prepared.

[0036] In a fourth aspect, the present invention provides a method for removing a P-type polysilicon layer on an N-region surface of a silicon substrate, the method comprising:

[0037] Placing the silicon wafer with the N region prepared in advance in a TMAH solution and etching to remove the P-type polysilicon layer on the surface of the silicon wafer with the N region prepared in advance;

[0038] Wherein, the TMAH solution includes the TMAH solution for removing the polysilicon layer as described in the first aspect.

[0039] Preferably, the etching temperature is 20-90°C, preferably 80-85°C.

[0040] Preferably, the etching is performed with the assistance of ultrasound and / or microwaves.

[0041] Preferably, the frequency of the ultrasound is 40-60 kHz.

[0042] Preferably, the power density of the ultrasound is 0.1 to 1 W / cm 2 .

[0043] Preferably, the frequency of the microwave is 2-3 GHz.

[0044] In a fifth aspect, the present invention provides a method for preparing a back-contact battery, the method comprising:

[0045] The back contact cell is prepared by the following steps of double-side polishing, preparing a tunneling oxide layer and an intrinsic amorphous silicon layer, boron diffusion, removing a pre-prepared N region surface BSG layer, removing side and front BSG layers, removing a pre-prepared N region surface P-type polysilicon layer, preparing an N-type polysilicon layer, removing a P region and a pre-prepared GAP region surface PSG layer, texturing, double-side depositing an aluminum oxide layer, double-side depositing a silicon nitride layer, and printing an electrode.

[0046] Preferably, the method for removing the P-type polysilicon layer on the N region surface of the silicon substrate is used to remove the pre-prepared N region surface P-type polysilicon layer.

[0047] Preferably, the thickness of the tunneling oxide layer is 1-2 nm, and the thickness of the intrinsic amorphous silicon layer is 200-400 nm.

[0048] Preferably, the intrinsic amorphous silicon layer is converted into a P-type polysilicon layer and forms a BSG layer after boron diffusion.

[0049] Preferably, the doping concentration of the P-type polysilicon layer is 1E19-1E20.

[0050] Preferably, the thickness of the BSG layer is 40-60 nm.

[0051] Compared with the prior art, the present application has the following beneficial effects:

[0052] In the present application, the TMAH solution with a specific formula is used to replace the acidic or strong alkaline solution, the bottom SiO2 is retained and only the surface P-poly is removed during the corrosion of the N region, the side edge pits are reduced, the side edge residues in the subsequent process are reduced, the side edge corrosion pits are reduced, the subsequent residues are reduced, the electric leakage is reduced, the yield is improved, and the conversion efficiency of the cell sheet is improved. BRIEF DESCRIPTION OF DRAWINGS

[0053] In order to more clearly illustrate the technical solutions in the specific embodiments or the prior art, the drawings needed in the following specific embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0054] Figure 1 The preparation process flow chart of the back contact cell is shown in the present application.

[0055] In the present application, 10 is an N-type silicon substrate, 20 is a tunneling oxide layer, 30 is an intrinsic amorphous silicon layer, 31 is a P-type polysilicon layer, 32 is an N-type polysilicon layer, 40 is a BSG layer, 41 is a PSG layer, 50 is an aluminum oxide layer, 51 is a silicon nitride layer, and 60 is a metal electrode. DETAILED DESCRIPTION

[0056] Unless otherwise defined, scientific and technical terms used in connection with the present application shall have the meanings that are commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear; however, in the event of any latent ambiguity, definitions provided herein take precedent. In this application, the use of "or" means "and / or" unless stated otherwise. Moreover, the use of the term "including" as well as other forms such as "include", is not limiting.

[0057] It should be noted that specific details are set forth in the following description in order to provide a thorough understanding of the application. However, the application can be practiced without many of the details described in this description, many of which are well known in the art. Therefore, the particular implementation described herein is not intended to limit the scope of the application.

[0058] The technical solutions of the present application will be described clearly and completely in connection with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work belong to the scope of protection of the present application.

[0059] In a first aspect, the present application provides a TMAH solution for removing a polysilicon layer, the TMAH solution comprising, by weight fraction:

[0060] 20-250 parts of tetramethylammonium hydroxide, 0.0005-6 parts of a main oxidizing agent, 0.001-4 parts of an auxiliary oxidizing agent, 3-5 parts of a main complexing agent, 2-3 parts of an auxiliary complexing agent, 0.001-0.5 parts of a surfactant, and 800-1200 parts of water.

[0061] In the present application, the TMAH solution contains tetramethylammonium hydroxide (TMAH), primary oxidant, auxiliary oxidant, primary complexing agent, auxiliary complexing agent, and surfactant in specific proportions. The TMAH is an organic base that provides the necessary alkaline environment for the entire etching process. It replaces acidic or strongly basic solutions, retains the bottom SiO2 while etching the N region, and only removes the surface P-poly, reducing the side edge pits. At the same time, since silicon itself etches relatively slowly in alkali, but is oxidized to SiO2, which can be quickly dissolved by the subsequent complexing agent, the present application realizes the dual action of oxidation-etching under the synergistic action of the primary and auxiliary oxidants, maintaining the continuous oxidation ability. At the same time, the primary and auxiliary complexing agents cooperate to facilitate the reaction with the SiO2 generated by the primary oxidant, forming a soluble complex that is removed from the silicon surface. The presence of the surfactant allows the solution to better wet the surface of the silicon wafer, ensuring uniform etching. By adsorbing on the surface of the tunneling oxide layer, it selectively inhibits the etching rate, forming a physical barrier that significantly slows down the speed of the oxidant or complexing agent reaching the surface, reducing the etching or attack rate of the tunneling layer, and ensuring that the bottom SiO2 is retained while etching the N region, only removing the surface polysilicon layer. Therefore, the specific proportions of tetramethylammonium hydroxide (TMAH), primary oxidant, auxiliary oxidant, primary complexing agent, auxiliary complexing agent, and surfactant in the present application, in combination with each component, effectively reduce the side edge pits, thereby reducing the side edge residue in subsequent processes, reducing the side edge etching pits, reducing subsequent residue, reducing leakage, improving yield, and improving the conversion efficiency of the battery sheet.

[0062] As an optional embodiment, the content of tetramethylammonium hydroxide in the TMAH solution is 20-250 parts, for example, it can be 20 parts, 30 parts, 40 parts, 50 parts, 60 parts, 70 parts, 80 parts, 90 parts, 100 parts, 110 parts, 120 parts, 130 parts, 140 parts, 150 parts, 160 parts, 170 parts, 180 parts, 190 parts, 200 parts, 210 parts, 220 parts, 230 parts, 240 parts, 250 parts, etc., preferably 80-120 parts.

[0063] As an optional embodiment, the mass percentage content of tetramethylammonium hydroxide in the TMAH solution is 2-25%, for example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, etc.

[0064] As an optional embodiment, the content of the main oxidizing agent in the TMAH solution is 0.0005-6 parts, for example, it can be 0.0005 parts, 0.001 parts, 0.005 parts, 0.01 parts, 0.05 parts, 0.1 parts, 0.2 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.8 parts, 1 parts, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, etc.

[0065] As an optional embodiment, the mass concentration of the main oxidizing agent in the TMAH solution is 0.0005-6 g / L, for example, it can be 0.0005 g / L, 0.001 g / L, 0.005 g / L, 0.01 g / L, 0.05 g / L, 0.1 g / L, 0.2 g / L, 0.4 g / L, 0.5 g / L, 0.6 g / L, 0.8 g / L, 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L, 5 g / L, etc.

[0066] As an optional embodiment, the content of the auxiliary oxidizing agent in the TMAH solution is 0.001-4 parts, for example, it can be 0.001 parts, 0.005 parts, 0.01 parts, 0.05 parts, 0.1 parts, 0.2 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.8 parts, 1 parts, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, etc.

[0067] As an optional embodiment, the mass concentration of the auxiliary oxidizing agent in the TMAH solution is 0.001-4 g / L, for example, it can be 0.001 g / L, 0.005 g / L, 0.01 g / L, 0.05 g / L, 0.1 g / L, 0.2 g / L, 0.4 g / L, 0.5 g / L, 0.6 g / L, 0.8 g / L, 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, 3.5 g / L, 4 g / L, etc.

[0068] As an optional embodiment, the content of the main complexing agent in the TMAH solution is 3-5 parts, for example, it can be 3 parts, 3.2 parts, 3.4 parts, 3.5 parts, 3.6 parts, 3.8 parts, 4 parts, 4.2 parts, 4.4 parts, 4.5 parts, 4.6 parts, 4.8 parts, 5 parts, etc.

[0069] As an optional embodiment, the mass concentration of the main complexing agent in the TMAH solution is 3-5 g / L, for example, it can be 3 g / L, 3.2 g / L, 3.4 g / L, 3.5 g / L, 3.6 g / L, 3.8 g / L, 4 g / L, 4.2 g / L, 4.4 g / L, 4.5 g / L, 4.6 g / L, 4.8 g / L, 5 g / L, etc.

[0070] As an optional embodiment, the content of the auxiliary complexing agent in the TMAH solution is 2-3 parts, for example, it can be 2 parts, 2.1 parts, 2.2 parts, 2.3 parts, 2.4 parts, 2.5 parts, 2.6 parts, 2.7 parts, 2.8 parts, 2.9 parts, 3 parts, etc.

[0071] As an optional embodiment, the mass concentration of the auxiliary complexing agent in the TMAH solution is 2-3 parts, for example, it can be 2 g / L, 2.1 g / L, 2.2 g / L, 2.3 g / L, 2.4 g / L, 2.5 g / L, 2.6 g / L, 2.7 g / L, 2.8 g / L, 2.9 g / L, 3 g / L, etc.

[0072] As an optional embodiment, the content of the surfactant in the TMAH solution is 0.001-0.5 parts, for example, it can be 0.001 parts, 0.005 parts, 0.01 parts, 0.05 parts, 0.1 parts, 0.15 parts, 0.2 parts, 0.25 parts, 0.3 parts, 0.35 parts, 0.4 parts, 0.45 parts, 0.5 parts, etc.

[0073] As an optional embodiment, the mass percentage content of the surfactant in the TMAH solution is 0.001-0.5%, for example, it can be 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc.

[0074] As an optional embodiment, the content of water in the TMAH solution is 800-1200 parts, for example, it can be 800 parts, 820 parts, 840 parts, 850 parts, 860 parts, 880 parts, 900 parts, 920 parts, 940 parts, 960 parts, 980 parts, 1000 parts, 1020 parts, 1040 parts, 1050 parts, 1060 parts, 1080 parts, 1100 parts, 1120 parts, 1140 parts, 1150 parts, 1160 parts, 1180 parts, 1200 parts, etc.

[0075] As an optional embodiment, the main oxidizing agent includes potassium persulfate and / or ozone.

[0076] In the present application, the potassium persulfate (K2S2O8) has a higher oxidation potential (E=2.01V) than APS, which can accelerate the oxidation and decomposition of boron-doped polysilicon. The ozone (O3) can generate hydroxyl radicals (·OH) in situ, achieve nanoscale surface oxidation, and reduce roughness (Ra<0.3nm); and an online ozone generator is required in the process of preparing the TMAH solution for removing the polysilicon layer.

[0077] As an optional embodiment, the auxiliary oxidant comprises hydrogen peroxide and / or sodium periodate.

[0078] In the present application, the hydrogen peroxide (H2O2) can form superoxide anion (O2 - ) with TMAH, enhancing the penetration of silicon grain boundary, inhibiting side etching. Sodium periodate (NaIO4) can selectively oxidize boron-doped region, improving the p++ / Si selectivity ratio to >5000:1.

[0079] As a preferred embodiment, when the main oxidant is selected from potassium persulfate, the auxiliary oxidant is selected from hydrogen peroxide.

[0080] In the present application, the preferred oxidant is the combination of potassium persulfate and hydrogen peroxide, which can generate sulfate radical (SO4 - ·) and hydroxyl radical (·OH); wherein the sulfate radical (SO4 - ) can penetrate the slight passivation layer of P-Poly surface layer, oxidize the underlying silicon, avoiding residue (deep, fast); the hydroxyl radical (·OH) can supplement the oxidation capacity, preferentially oxidizing the surface P-Poly and micro defects (mild, continuous), potassium persulfate ensures high-speed etching, and hydrogen peroxide maintains surface reactivity, avoiding residue caused by local passivation. In addition, hydrogen peroxide forms hydrophilic hydroxyl terminal (-OH) on the surface of the tunneling layer, which can also promote the adsorption of surfactants, and the surfactants form a dense protective film on the hydrophilic surface, thereby blocking the etching ions from contacting the tunneling layer. Therefore, the depth oxidation capacity of potassium persulfate and the surface regulation capacity of hydrogen peroxide are complementary, and under the synergistic effect of TMAH high pH and surfactants, both the thorough removal of P-Poly residue and the protection of the tunneling oxide layer through physical blocking and chemical passivation are achieved.

[0081] As a preferred embodiment, when the main oxidant is selected from ozone, the auxiliary oxidant is selected from sodium periodate.

[0082] In the present application, the preferred oxidant is the combination of ozone and sodium periodate, O3 decomposes in alkaline solution to generate hydroxyl radical (·OH), which has excellent oxidation capacity (E=2.07V), and ·OH can quickly oxidize the defect sites of P-Poly silicon to generate soluble silicate or SiO2, while dense SiO2 (tunneling layer) has strong resistance to ·OH, and the etching rate is extremely low; sodium periodate has periodate (IO4 - ) which has excellent oxidation capacity (E=1.60V) and can directly oxidize silicon to generate (IO3 - ), and in the presence of O3, O3 re-oxidizes the iodate (IO3 - ) to IO4 - , achieving oxidant regeneration. In addition, IO4 -The iodate adsorption layer (such as ≡Si-O-IO3) is formed on the surface of the dense SiO2 (tunneling layer) to inhibit ion penetration; and the inert silicon hydroxyl group (≡Si-OH) is generated on the surface of the dense SiO2 (tunneling layer) by O3 to enhance hydrophilicity and promote surfactant adsorption. Therefore, the synergistic nature of ozone and sodium periodate is to build a self-sustaining oxidation engine, and the oxidation starts: O3 and IO4 - Synchronous oxidation of P-Poly silicon; regeneration cycle: O3 converts byproduct IO3 - to IO4 - , achieving zero consumption of oxidizing agent; etching cycle: complexing agent dissolves oxidation products to expose fresh silicon surface; selective protection: iodate / surfactant composite passivation film is formed on the surface of the tunneling layer, and O3 is recycled to regenerate IO4 - , reducing direct attack on the tunneling layer, which not only completely removes P-Poly residues, but also protects the tunneling oxidation layer through physical barrier and chemical passivation.

[0083] As an optional implementation, the content of potassium persulfate in the TMAH solution for removing the polysilicon layer is 4-6 parts, for example, it can be 4 parts, 4.2 parts, 4.4 parts, 4.6 parts, 4.8 parts, 5 parts, 5.2 parts, 5.4 parts, 5.6 parts, 5.8 parts, 6 parts, etc.

[0084] As an optional implementation, the mass concentration of potassium persulfate in the TMAH solution for removing the polysilicon layer is 4-6 g / L, for example, it can be 4 g / L, 4.2 g / L, 4.4 g / L, 4.6 g / L, 4.8 g / L, 5 g / L, 5.2 g / L, 5.4 g / L, 5.6 g / L, 5.8 g / L, 6 g / L, etc.

[0085] As an optional implementation, the content of hydrogen peroxide in the TMAH solution for removing the polysilicon layer is 2-4 parts, for example, it can be 2 parts, 2.2 parts, 2.4 parts, 2.6 parts, 2.8 parts, 3 parts, 3.2 parts, 3.4 parts, 3.6 parts, 3.8 parts, 4 parts, etc.

[0086] As an optional implementation, the mass concentration of hydrogen peroxide in the TMAH solution for removing the polysilicon layer is 2-4 g / L, for example, it can be 2 g / L, 2.2 g / L, 2.4 g / L, 2.6 g / L, 2.8 g / L, 3 g / L, 3.2 g / L, 3.4 g / L, 3.6 g / L, 3.8 g / L, 4 g / L, etc.

[0087] As an optional embodiment, the content of the ozone in the TMAH solution for removing the polysilicon layer is 0.0005-0.001 parts, for example, 0.0005 parts, 0.0006 parts, 0.0007 parts, 0.0008 parts, 0.0009 parts, 0.001 parts, etc.

[0088] As an optional embodiment, the concentration of the ozone in the TMAH solution for removing the polysilicon layer is 0.5-1 ppm, for example, 0.5 ppm, 0.6 ppm, 0.7 ppm, 0.8 ppm, 0.9 ppm, 1 ppm, etc.

[0089] As an optional embodiment, the content of the sodium periodate in the TMAH solution for removing the polysilicon layer is 1-2 parts, for example, 1 part, 1.1 part, 1.2 part, 1.3 part, 1.4 part, 1.5 part, 1.6 part, 1.7 part, 1.8 part, 1.9 part, 2 part, etc.

[0090] As an optional embodiment, the mass concentration of the sodium periodate in the TMAH solution for removing the polysilicon layer is 1-2 g / L, for example, 1 g / L, 1.1 g / L, 1.2 g / L, 1.3 g / L, 1.4 g / L, 1.5 g / L, 1.6 g / L, 1.7 g / L, 1.8 g / L, 1.9 g / L, 2 g / L, etc.

[0091] As an optional embodiment, the main complexing agent comprises a 7-hydroxy chelating crosslinking agent.

[0092] As an optional embodiment, the 7-hydroxy chelating crosslinking agent is a propylene diamine quaternary ammonium salt containing 7 hydroxy groups.

[0093] As a preferred embodiment, the propylene diamine quaternary ammonium salt containing 7 hydroxy groups has the following formula I:

[0094]

[0095] In the formula, n is 2-4, for example, 2, 3, 4.

[0096] In the present application, the main complexing agent is a propylene diamine quaternary ammonium salt containing 7 hydroxy groups (C7-OH quaternary ammonium salt), and the 7 hydroxy groups form a dense hydrogen bond network, which is conducive to reducing the activation energy of dissolution. The complexing agent is directly stripped through "polydentate coordination", and the dissolution rate is increased by 3 times. The quaternary ammonium group preferentially adsorbs on the negatively charged P-Poly surface (electrophilic after etching), which promotes the enrichment of the complexing agent in the etching area. In addition, the dense tunneling oxide layer is strongly negatively charged in alkaline TMAH, and is electrostatically repelled by the quaternary ammonium cation, thereby achieving the purpose of inhibiting its adsorption in the tunneling layer. In addition, the presence of multiple hydroxyl groups is conducive to the pH temperature of the solution, and optimizes the silicon oxidation reaction.

[0097] As an optional embodiment, the content of the main complexing agent in the TMAH solution for removing the polysilicon layer is 3-5 parts, for example, it can be 3 parts, 3.2 parts, 3.4 parts, 3.5 parts, 3.6 parts, 3.8 parts, 4 parts, 4.2 parts, 4.4 parts, 4.5 parts, 4.6 parts, 4.8 parts, 5 parts, etc.

[0098] As an optional embodiment, the mass concentration of the main complexing agent in the TMAH solution for removing the polysilicon layer is 3-5 g / L, for example, it can be 3 g / L, 3.2 g / L, 3.4 g / L, 3.5 g / L, 3.6 g / L, 3.8 g / L, 4 g / L, 4.2 g / L, 4.4 g / L, 4.5 g / L, 4.6 g / L, 4.8 g / L, 5 g / L, etc.

[0099] As an optional embodiment, the auxiliary complexing agent comprises N-methyl-D-glucosamine grafted chitosan derivative and / or glycerol-boric acid chelate.

[0100] As a preferred embodiment, the auxiliary complexing agent consists of N-methyl-D-glucosamine grafted chitosan derivative and glycerol-boric acid chelate.

[0101] In the present application, the auxiliary complexing agent is preferably a combination of N-methyl-D-glucosamine (NMG) grafted chitosan derivative and glycerol-boric acid chelate; wherein the hydroxyl group of the NMG group binds with the dangling bond (Si·) generated by P-Poly etching to form a soluble Si-O-C complex, reducing etching residues, and the macromolecular chitosan forms a physical barrier on the surface of the tunneling layer, blocking the penetration of alkaline OH - ; and the boric acid reversibly esterifies with the Si-OH on the surface of the tunneling layer to form a borosilicate protective layer, which is destroyed by etching reaction in the P-Poly region (due to rapid surface renewal) but stably exists in the tunneling layer, and the glycerol group enhances the solution wettability, thereby synergistically improving the etching uniformity.

[0102] As an optional embodiment, the N-methyl-D-glucosamine grafted chitosan derivative has the following structural formula II:

[0103] Chitosan-[GlcN]-O-CH2-CH(OH)-CH2-N(CH3)-CH2(CHOH)4CH2OH;

[0104] Formula II;

[0105] Wherein, GlcN represents a glucosamine unit.

[0106] In the present application, the core structure of the N-methyl-D-glucosamine grafted chitosan derivative is that chitosan (degree of deacetylation ≥ 80%) is taken as a skeleton, and a primary amine group of N-methyl-D-glucosamine (NMDG) is covalently bonded to a hydroxyl group at C6; the modification group is a cis-hydroxyl group (5 hydroxyl groups + 1 secondary amine group) of NMDG, which provides a boron complex site to form a tetrahedral coordination structure.

[0107] As an optional embodiment, the N-methyl-D-glucosamine grafted chitosan derivative can be prepared by a reductive amination method and / or an epoxy activated grafting method.

[0108] As an optional embodiment, the N-methyl-D-glucosamine grafted chitosan derivative is prepared by a reductive amination method:

[0109] Chitosan is dissolved in an acetic acid solution, N-methyl-D-glucosamine and a reducing agent are added, a reductive amination reaction is performed, and dialysis purification is performed to obtain the N-methyl-D-glucosamine grafted chitosan derivative.

[0110] As an optional embodiment, in the reductive amination method, the chitosan is low molecular weight chitosan.

[0111] As an optional embodiment, in the reductive amination method, the molecular weight of the chitosan is 8-12 kDa, for example, it can be 8 kDa, 8.5 kDa, 9 kDa, 9.5 kDa, 10 kDa, 10.5 kDa, 11 kDa, 11.5 kDa, 12 kDa, etc.

[0112] As an optional embodiment, in the reductive amination method, the molar ratio of chitosan to N-methyl-D-glucosamine is 1:(2-4), for example, it can be 1:2, 1:2.5, 1:3, 1:3.5, 1:4, etc.

[0113] As an optional embodiment, the reducing agent is sodium cyanoborohydride.

[0114] As an optional embodiment, the molar ratio of chitosan to reducing agent is 1:(0.05-0.2), for example, it can be 1:0.05, 1:0.06, 1:0.08, 1:0.1, 1:0.15, 1:0.2, etc.

[0115] As an optional embodiment, the temperature of the reductive amination reaction is 55-65°C, for example, it can be 55°C, 56°C, 58°C, 60°C, 62°C, 64°C, 65°C, etc., and the time of the reductive amination reaction is 10-15 h, for example, it can be 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, etc.

[0116] As an optional embodiment, the N-methyl-D-glucosamine grafted chitosan derivative is prepared by an epoxy-activated grafting method.

[0117] The chitosan is activated by epoxy chloropropane to obtain activated chitosan; the activated chitosan and N-methyl-D-glucosamine are mixed in a buffer solution, and then subjected to grafting reaction, precipitation and purification to obtain the N-methyl-D-glucosamine grafted chitosan derivative.

[0118] As an optional embodiment, in the epoxy-activated grafting method, the chitosan is low molecular weight chitosan.

[0119] As an optional embodiment, in the epoxy-activated grafting method, the molecular weight of the chitosan is 8-12 kDa, for example, it can be 8 kDa, 8.5 kDa, 9 kDa, 9.5 kDa, 10 kDa, 10.5 kDa, 11 kDa, 11.5 kDa, 12 kDa, etc.

[0120] As an optional embodiment, in the epoxy-activated grafting method, the molar ratio of the chitosan to N-methyl-D-glucosamine is 1:(1-3), for example, it can be 1:1, 1:1.5, 2:3, 1:2.5, 1:3, etc.

[0121] As an optional embodiment, in the epoxy-activated grafting method, the buffer solution is a pH 9.0 borate buffer solution.

[0122] As an optional embodiment, the temperature of the grafting reaction is 45-55℃, for example, it can be 45℃, 46℃, 48℃, 50℃, 52℃, 54℃, 55℃, etc., and the time of the reductive amination reaction is 6-10 h, for example, it can be 6 h, 7 h, 8 h, 9 h, 10 h, etc.

[0123] As an optional embodiment, the chitosan raw material is Qingdao Haixiu Biological Engineering Co., Ltd. (food grade, degree of deacetylation 85%-95%).

[0124] As an optional embodiment, the N-methyl-D-glucosamine reagent is Sigma-Aldrich, item number M9166 (purity ≥ 99%).

[0125] As an optional embodiment, the chelating structure of the glycerol-boric acid chelate is a five-membered ring ester (boric acid glycerol ester) formed by the primary hydroxyl group of glycerol and boric acid, and the molecular formula is C3H7BO3.

[0126] As an optional embodiment, in the solution, the glycerol-boric acid chelate exists in the form of monoester (1:1), diester (2:1) and free boric acid, and the diester is dominant when the pH is 7-9.

[0127] As an optional embodiment, the glycerol-boric acid chelate is prepared by high-temperature esterification method and / or low-temperature catalysis method.

[0128] As an optional embodiment, the glycerol-boric acid chelate is prepared by high-temperature esterification method.

[0129] The glycerol-boric acid chelate is prepared by mixing glycerol and boric acid, and then performing high-temperature esterification reaction, and vacuum dehydration to obtain water content ≤1.0%.

[0130] As an optional embodiment, in the high-temperature esterification method, the molar ratio of glycerol to boric acid is (2-4):1, for example, it can be 2:1, 2.5:1, 3:1, 3.5:1, 4:1, etc.

[0131] As an optional embodiment, the temperature of the high-temperature esterification reaction is 130-140℃, for example, it can be 130℃, 132℃, 134℃, 135℃, 136℃, 138℃, 140℃, etc., and the time of the high-temperature esterification reaction is 3-4h, for example, it can be 3h, 3.2h, 3.4h, 3.5h, 3.6h, 3.8h, 4h, etc.

[0132] As an optional embodiment, the high-temperature esterification reaction is performed in the presence of a protective gas.

[0133] As an optional embodiment, the protective gas includes nitrogen.

[0134] As an optional embodiment, the glycerol-boric acid chelate is prepared by high-temperature esterification method.

[0135] The glycerol-boric acid chelate is prepared by mixing glycerol and boric acid in a molar ratio of 3:1, protecting by nitrogen, and then performing reaction at 130-140℃ for 3-4h, and vacuum dehydration to obtain water content ≤1.0%.

[0136] As an optional embodiment, the glycerol-boric acid chelate is prepared by low-temperature catalysis method.

[0137] The glycerol-boric acid chelate is prepared by heating glycerol, adding boric acid in batches, and then adding a catalyst, and then performing low-temperature catalysis reaction.

[0138] As an optional embodiment, in the low-temperature catalysis method, the catalyst includes tetrabutylammonium bromide.

[0139] As an optional implementation, the temperature of the low-temperature catalytic reaction is 95-115°C, for example, it can be 95°C, 96°C, 98°C, 100°C, 102°C, 104°C, 105°C, etc., and the time of the high-temperature esterification reaction is 0.5-2h, for example, it can be 0.5h, 0.6h, 0.8h, 1h, 1.2h, 1.4h, 1.5h, 1.6h, 1.8h, 2h, etc.

[0140] As an optional implementation, the glycerol-boric acid chelate is prepared by a low-temperature catalytic method.

[0141] Glycerol is heated in a sand bath at 140-150°C, and boric acid is added in batches; a catalyst is added, and reaction is carried out at 100°C for 1h, and then the temperature is lowered to 50°C to discharge the product.

[0142] As an optional implementation, the boric acid raw material is American horse brand (industrial grade, HBO≥99.9%, CAS 10043-35-3).

[0143] As an optional implementation, the glycerol raw material is Zibo Honggui East Chemical (pharmaceutical grade, purity≥99.5%).

[0144] As an optional implementation, the content of the N-methyl-D-glucosamine grafted chitosan derivative in the TMAH solution for removing the polysilicon layer is 1-2 parts, for example, it can be 1 part, 1.1 part, 1.2 part, 1.3 part, 1.4 part, 1.5 part, 1.6 part, 1.7 part, 1.8 part, 1.9 part, 2 part, etc.

[0145] As an optional implementation, the mass concentration of the N-methyl-D-glucosamine grafted chitosan derivative in the TMAH solution for removing the polysilicon layer is 1-2g / L, for example, it can be 1g / L, 1.1g / L, 1.2g / L, 1.3g / L, 1.4g / L, 1.5g / L, 1.6g / L, 1.7g / L, 1.8g / L, 1.9g / L, 2g / L, etc.

[0146] As an optional implementation, the content of the glycerol-boric acid chelate in the TMAH solution for removing the polysilicon layer is 2-3 parts, for example, it can be 2 parts, 2.1 parts, 2.2 parts, 2.3 parts, 2.4 parts, 2.5 parts, 2.6 parts, 2.7 parts, 2.8 parts, 2.9 parts, 3 parts, etc.

[0147] As an optional embodiment, the mass concentration of the glycerol-boric acid chelate in the TMAH solution for removing the polysilicon layer is 2-3 g / L, for example, it can be 2 g / L, 2.1 g / L, 2.2 g / L, 2.3 g / L, 2.4 g / L, 2.5 g / L, 2.6 g / L, 2.7 g / L, 2.8 g / L, 2.9 g / L, 3 g / L, etc.

[0148] As an optional embodiment, the surfactant comprises a main surfactant.

[0149] As an optional embodiment, the main surfactant comprises a polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer and / or a fatty alcohol polyoxyethylene ether.

[0150] As an optional embodiment, the polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer is Pluronic F-127 (PEO-PPO-PEO block copolymer): reduces the surface tension to 25 mN / m, and improves the permeability of the etching solution to the deep-width ratio structure.

[0151] As an optional embodiment, the fatty alcohol polyoxyethylene ether is AEO-9; non-ionic, high-temperature-resistant (>90°C), and inhibits bubble retention.

[0152] As an optional embodiment, the surfactant further comprises an auxiliary surfactant.

[0153] As an optional embodiment, the auxiliary surfactant comprises potassium perfluorooctyl sulfonate and / or sodium dodecyl sulfate.

[0154] In the present application, the potassium perfluorooctyl sulfonate (PFOS) is a fluorocarbon surfactant, which is directionally adsorbed on the SiO surface to form a hydrophobic barrier, and the damage to the protective layer is less than 0.1 nm. The sodium dodecyl sulfate (SDS) is an anionic surfactant, which enhances the dispersibility of the solution and reduces the etching residue.

[0155] As an optional embodiment, when the main surfactant is selected from a polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer, the auxiliary surfactant is selected from potassium perfluorooctyl sulfonate.

[0156] In the present application, the combination of Pluronic F-127 and PFOS as the surfactant is preferred, and the two cooperate to achieve nanoscale wetting control through hydrophilic-hydrophobic microzone self-assembly.

[0157] As an optional embodiment, when the main surfactant is selected from a fatty alcohol polyoxyethylene ether, the auxiliary surfactant is selected from sodium dodecyl sulfate.

[0158] In the present application, the combination of surfactants, preferably AEO-9 and SDS, cooperatively form mixed micelles, reduce the dynamic surface tension (<40 mN / m), and improve etching uniformity.

[0159] As an optional embodiment, the content of the polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer in the TMAH solution is 0.005-0.01 parts, for example, it can be 0.005 parts, 0.006 parts, 0.007 parts, 0.008 parts, 0.009 parts, 0.01 parts, etc.

[0160] As an optional embodiment, the mass percentage content of the polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer in the TMAH solution is 0.05-0.1%, for example, it can be 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, etc.

[0161] As an optional embodiment, the content of the potassium perfluorooctyl sulfonate in the TMAH solution is 0.001-0.003 parts, for example, it can be 0.001 parts, 0.0015 parts, 0.002 parts, 0.0025 parts, 0.003 parts, etc.

[0162] As an optional embodiment, the mass percentage content of the potassium perfluorooctyl sulfonate in the TMAH solution is 0.01-0.03%, for example, it can be 0.001%, 0.0015%, 0.002%, 0.0025%, 0.003%, etc.

[0163] As an optional embodiment, the content of the fatty alcohol polyoxyethylene ether in the TMAH solution is 0.01-0.02 parts, for example, it can be 0.01 parts, 0.012 parts, 0.014 parts, 0.015 parts, 0.016 parts, 0.018 parts, 0.02 parts, etc.

[0164] As an optional embodiment, the mass percentage content of the fatty alcohol polyoxyethylene ether in the TMAH solution is 0.1-0.2%, for example, it can be 0.01%, 0.012%, 0.014%, 0.015%, 0.016%, 0.018%, 0.02%, etc.

[0165] As an optional embodiment, the content of the sodium dodecyl sulfate in the TMAH solution is 0.005-0.01 parts, for example, it can be 0.005 parts, 0.006 parts, 0.007 parts, 0.008 parts, 0.009 parts, 0.01 parts, etc.

[0166] As an optional embodiment, the mass percentage of sodium dodecyl sulfate in the TMAH solution is 0.05-0.1%, for example, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, etc.

[0167] In a second aspect, the present application provides a preparation method of the TMAH solution for removing a polysilicon layer as described in the first aspect, the preparation method comprising:

[0168] dissolving tetramethylammonium hydroxide, a primary oxidizing agent, an auxiliary oxidizing agent, a primary complexing agent, an auxiliary complexing agent, and a surfactant in water to obtain the TMAH solution for removing a polysilicon layer.

[0169] In a third aspect, the present application provides an application of the TMAH solution for removing a polysilicon layer as described in the first aspect in removing a P-type polysilicon layer on a surface of a silicon wafer with a pre-prepared N region.

[0170] In a fourth aspect, the present application provides a method for removing a P-type polysilicon layer on a surface of an N region of a silicon substrate, the method comprising:

[0171] placing a silicon wafer with a pre-prepared N region in the TMAH solution to etch and remove a P-type polysilicon layer on a surface of the silicon wafer with the pre-prepared N region;

[0172] wherein the TMAH solution comprises the TMAH solution for removing a polysilicon layer as described in the first aspect.

[0173] As an optional embodiment, the etching temperature is 20-90°C, for example, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc.

[0174] As a preferred embodiment, the etching temperature is 80-85°C, for example, 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, etc.

[0175] As a preferred embodiment, the etching is performed with the assistance of ultrasound and / or microwaves.

[0176] As an optional embodiment, the frequency of the ultrasound is 40-60 kHz, for example, 40 kHz, 42 kHz, 44 kHz, 46 kHz, 48 kHz, 50 kHz, 52 kHz, 54 kHz, 56 kHz, 58 kHz, 60 kHz, etc.

[0177] As an optional embodiment, the power density of the ultrasound is 0.1-1 W / cm 2 , for example, 0.1 W / cm 20.2 W / cm2 2 0.3 W / cm2 2 0.4 W / cm2 2 0.5 W / cm2 2 0.6 W / cm2 2 0.7 W / cm2 2 0.8 W / cm2 2 0.9 W / cm2 2 1 W / cm2 2 etc.

[0178] As an optional implementation, the frequency of the microwave is 2-3 GHz, for example, can be 2 GHz, 2.2 GHz, 2.4 GHz, 2.5 GHz, 2.6 GHz, 2.8 GHz, 3 GHz, etc.

[0179] In a fifth aspect, the present application provides a preparation method of a back contact cell, the preparation method comprising:

[0180] polishing the N-type silicon substrate in sequence, preparing a tunneling oxide layer and an intrinsic amorphous silicon layer, boron diffusion, removing a pre-prepared N region surface BSG layer, removing a side edge and a front surface BSG layer, removing a pre-prepared N region surface P-type polysilicon layer, preparing an N-type polysilicon layer, phosphorus diffusion, removing a P region and a pre-prepared GAP region surface PSG layer, texturing, double-sided deposition of an aluminum oxide layer, double-sided deposition of a silicon nitride layer, and printing an electrode to obtain the back contact cell.

[0181] The method for removing the P-type polysilicon layer on the N region surface of the silicon substrate is used to remove the pre-prepared N region surface P-type polysilicon layer.

[0182] As an optional implementation, as shown in the preparation method of the back contact cell specifically comprises the following steps: Figure 1

[0183] S1, double-sided polishing:

[0184] providing an N-type silicon substrate and polishing the surface of the N-type silicon substrate in sequence;

[0185] S2, preparing a tunneling oxide layer and an intrinsic amorphous silicon layer:

[0186] using an LPCVD process to prepare a tunneling oxide layer and an intrinsic amorphous silicon layer on the back surface of the silicon substrate obtained in step S1;

[0187] S3, boron diffusion:

[0188] using a boron diffusion process to convert the intrinsic amorphous silicon layer on the surface of the silicon substrate obtained in S2 into a P-type polysilicon layer, and simultaneously forming a BSG layer on the surface;

[0189] ​S4, removing the BSG layer on the surface of the pre-prepared N region:

[0190] removing the BSG layer on the surface of the pre-prepared N region on the silicon substrate obtained in S3 by a laser process;

[0191] S5, removing the BSG layer on the side and front surface:

[0192] removing the BSG residue on the side and front surface of the silicon substrate obtained in S4 by a chain cleaning process;

[0193] S6, removing the P-type polysilicon layer on the surface of the pre-prepared N region:

[0194] removing the P-type polysilicon layer residue on the surface of the pre-prepared N region on the silicon substrate obtained in S5 by using the TMAH solution for removing the polysilicon layer according to the present application, and retaining the tunneling oxide layer;

[0195] S7, preparing the N-type polysilicon layer:

[0196] preparing the N-type polysilicon layer on the back surface of the silicon substrate obtained in S6, and forming a PSG layer on the surface;

[0197] S8, removing the PSG layer on the surface of the P region and the pre-prepared GAP region:

[0198] removing the PSG layer on the surface of the P region and the pre-prepared GAP region of the silicon substrate obtained in S7 by a laser process;

[0199] S9, texturing:

[0200] removing the plating layer on the front surface of the silicon substrate obtained in S8; preparing the isolation between the N region and the P region on the back surface; and texturing the GAP region;

[0201] S10, depositing the aluminum oxide layer on both surfaces:

[0202] depositing the aluminum oxide on both surfaces of the silicon substrate obtained in S9 by an ALD process;

[0203] S11, depositing the silicon nitride layer on both surfaces:

[0204] depositing the silicon nitride layer on both surfaces of the silicon substrate obtained in S10 by a PECVD process;

[0205] S12, printing the electrode:

[0206] preparing the metal electrode on the back surface of the silicon substrate obtained in S11 by a screen printing process, to obtain the back contact cell.

[0207] As an optional embodiment, the thickness of the tunneling oxide layer is 1-2 nm, for example, 1 nm, 1.2 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.8 nm, 2 nm, etc.

[0208] As an optional embodiment, the thickness of the intrinsic amorphous silicon layer is 200-400 nm, for example, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, etc.

[0209] As an optional embodiment, the intrinsic amorphous silicon layer after boron diffusion is converted into a P-type polysilicon layer and forms a BSG layer.

[0210] As an optional embodiment, the doping concentration of the P-type polysilicon layer is 1E19-1E20, for example, 1E19, 2E19, 3E19, 4E19, 5E19, 6E19, 7E19, 8E19, 9E19, 10E19, etc.

[0211] As an optional embodiment, the thickness of the BSG layer is 40-60 nm, for example, 40 nm, 42 nm, 44 nm, 46 nm, 48 nm, 50 nm, 52 nm, 54 nm, 56 nm, 58 nm, 60 nm, etc.

[0212] The application will be further described by examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or directly purchased from the market.

[0213] The structure of the 7-hydroxy chelating crosslinking agent in the following examples is as follows:

[0214]

[0215] The N-methyl-D-glucosamine grafted chitosan derivative in the following examples is prepared by the following steps: chitosan (1 mol) is dissolved in 1% acetic acid solution, and NMDG (3 mol) is added; the pH is adjusted to 6.0, and NaBH3CN (0.1 mol) is added, and the reaction is carried out at 60°C for 12 h; dialysis purification (molecular weight cut-off 3.5 kDa), and freeze-drying to obtain a white solid. Among them, the raw materials are: low molecular weight chitosan (10 kDa, deacetylation degree 90%); N-methyl-D-glucosamine (NMDG, purity ≥99%); sodium cyanoborohydride (NaBH3CN, reducing agent).

[0216] The glycerol-boric acid chelate in the following examples is prepared by the following steps: glycerol and boric acid are mixed in a molar ratio of 3:1, and protected by nitrogen; the reaction is carried out at 135°C for 3.5 h, and vacuum dehydration is carried out until the water content is ≤1.0%, to obtain the glycerol-boric acid chelate. Among them, the raw materials are: glycerol (medical grade, purity ≥99.5%) boric acid (industrial grade, H3BO3≥99.9%).

[0217] Example 1

[0218] The embodiment provides a TMAH solution for removing a polysilicon layer, and the TMAH solution for removing the polysilicon layer comprises the following components:

[0219]

[0220]

[0221] The preparation method of the TMAH solution comprises the following steps: dissolving tetramethylammonium hydroxide, a main oxidizing agent, an auxiliary oxidizing agent, a main complexing agent, an auxiliary complexing agent, a main surfactant and an auxiliary surfactant in water according to the above-mentioned proportion, so as to obtain the TMAH solution for removing the polysilicon layer.

[0222] Embodiment 2

[0223] The embodiment provides a TMAH solution for removing a polysilicon layer, and the TMAH solution for removing the polysilicon layer comprises the following components:

[0224]

[0225] The preparation method of the TMAH solution comprises the following steps: dissolving tetramethylammonium hydroxide, a main oxidizing agent, an auxiliary oxidizing agent, a main complexing agent, an auxiliary complexing agent, a main surfactant and an auxiliary surfactant in water according to the above-mentioned proportion, so as to obtain the TMAH solution for removing the polysilicon layer.

[0226] Embodiment 3

[0227] The embodiment provides a TMAH solution for removing a polysilicon layer, and the TMAH solution for removing the polysilicon layer comprises the following components:

[0228]

[0229]

[0230] The preparation method of the TMAH solution comprises the following steps: dissolving tetramethylammonium hydroxide, a main oxidizing agent, an auxiliary oxidizing agent, a main complexing agent, an auxiliary complexing agent, a main surfactant and an auxiliary surfactant in water according to the above-mentioned proportion, so as to obtain the TMAH solution for removing the polysilicon layer.

[0231] Embodiment 4

[0232] The embodiment provides a TMAH solution for removing a polysilicon layer, and the TMAH solution for removing the polysilicon layer comprises the following components:

[0233] Embodiment 5

[0234] The embodiment provides a TMAH solution for removing a polysilicon layer, which is identical to the solution in the embodiment 1 except that the N-methyl-D-glucamine grafted chitosan derivative is no longer added in the auxiliary complexing agent, the content of the glycerol-boric acid chelate is increased, and the total concentration of the auxiliary complexing agent is unchanged.

[0235] Embodiment 6

[0236] The embodiment provides a TMAH solution for removing a polysilicon layer, which is identical to the solution in the embodiment 1 except that the glycerol-boric acid chelate is no longer added in the auxiliary complexing agent, the content of the N-methyl-D-glucamine grafted chitosan derivative is increased, and the total concentration of the auxiliary complexing agent is unchanged.

[0237] Embodiment 7

[0238] The embodiment provides a TMAH solution for removing a polysilicon layer, which is identical to the solution in the embodiment 1 except that the Pluronic F-127 is no longer added in the surfactant, the content of the PFOS is increased to 0.09 wt%, and other settings are identical to those in the embodiment 1.

[0239] Embodiment 8

[0240] The embodiment provides a TMAH solution for removing a polysilicon layer, which is identical to the solution in the embodiment 1 except that the PFOS is no longer added in the surfactant, the content of the Pluronic F-127 is increased to 0.09 wt%, and other settings are identical to those in the embodiment 1.

[0241] Embodiment 9

[0242] The embodiment provides a TMAH solution for removing a polysilicon layer, which is identical to the solution in the embodiment 3 except that the AEO-9 is no longer added in the surfactant, the content of the SDS is increased to 0.9 wt%, and other settings are identical to those in the embodiment 3.

[0243] Embodiment 10

[0244] The embodiment provides a TMAH solution for removing a polysilicon layer, which is identical to the solution in the embodiment 3 except that the SDS is no longer added in the surfactant, the content of the AEO-9 is increased to 0.9 wt%, and other settings are identical to those in the embodiment 3.

[0245] Comparative Example 1

[0246] The comparative example provides a base solution, which is an aqueous solution of KOH; wherein the content of KOH is 12.5 wt%.

[0247] Comparative Example 2

[0248] The comparative example provides a base solution, which is different from example 1 in that no main oxidant potassium persulfate is added, and other settings are completely consistent with example 1.

[0249] Comparative example 3

[0250] The comparative example provides a base solution, which is different from example 1 in that no auxiliary oxidant hydrogen peroxide is added, and other settings are completely consistent with example 1.

[0251] Comparative example 4

[0252] The comparative example provides a base solution, which is different from example 1 in that no main complexing agent 7-hydroxy chelate crosslinking agent is added, and other settings are completely consistent with example 1.

[0253] Comparative example 5

[0254] The comparative example provides a base solution, which is different from example 1 in that no auxiliary complexing agent is added, and other settings are completely consistent with example 1.

[0255] Comparative example 6

[0256] The comparative example provides a base solution, which is different from example 1 in that no main surface active agent and auxiliary surface active agent are added, and other settings are completely consistent with example 1.

[0257] Application example 1

[0258] The application example provides a back contact battery, and a preparation method of the back contact battery specifically includes the following steps:

[0259] S1, double-sided polishing processing is performed on the surface of an N-type silicon substrate;

[0260] S2, a tunneling oxide layer (the thickness of the tunneling oxide layer is 1.8 nm) and an intrinsic amorphous silicon layer (the thickness of the i-poly layer is 300 nm) are made on the back surface of the silicon substrate treated in step S1 by using an LPCVD process;

[0261] S3, the intrinsic amorphous silicon layer on the surface of the silicon substrate treated in S2 is converted into a P-type polysilicon layer (the doping concentration is 5E19) by using a boron diffusion process, and a BSG layer (the thickness of the BSG layer is 50 nm) is formed on the surface at the same time;

[0262] S4, the pre-prepared N region surface BSG layer on the silicon substrate treated in S3 is removed by a laser process;

[0263] S5, the side edge and the front surface BSG residue of the silicon substrate treated in S4 are removed by a chain cleaning process;

[0264] S6, using the TMAH solution for removing the polysilicon layer provided in Embodiment 1 to remove the residual P-type polysilicon layer on the pre-prepared N region surface of the silicon substrate obtained in S5, and to retain the tunneling oxide layer;

[0265] wherein the temperature is 82℃, and the process is performed under ultrasonic assistance (frequency of 50 kHz, power density of 0.5 W / cm 2 ), to reduce bubble retention and improve etching uniformity.

[0266] S7, preparing an N-type polysilicon layer on the back surface of the silicon substrate obtained in S6, and forming a PSG layer on the surface;

[0267] S8, removing the PSG layer on the surface of the P region and the pre-prepared GAP region of the silicon substrate obtained in S7 by a laser process;

[0268] S9, removing the front side wrap layer of the silicon substrate obtained in S8; preparing isolation between the N region and the P region on the back surface; and texturing the GAP region;

[0269] S10, depositing aluminum oxide on both surfaces of the silicon substrate obtained in S9 by an ALD process;

[0270] S11, depositing a silicon nitride layer on both surfaces of the silicon substrate obtained in S10 by a PECVD process;

[0271] S12, preparing a metal electrode on the back surface of the silicon substrate obtained in S11 by a screen printing process, to obtain the back contact cell.

[0272] Application Example 2

[0273] The application example provides a back contact cell, and a preparation method of the back contact cell specifically comprises the following steps.

[0274] S1, performing double-side polishing processing on the surface of an N-type silicon substrate;

[0275] S2, using an LPCVD process to prepare a tunneling oxide layer (thickness of the tunneling oxide layer is 1.8 nm) and an intrinsic amorphous silicon layer (thickness of the i-poly layer is 300 nm) on the back surface of the silicon substrate obtained in step S1;

[0276] S3, using a boron diffusion process to convert the intrinsic amorphous silicon layer on the surface of the silicon substrate obtained in S2 into a P-type polysilicon layer (doping concentration is 5E19), and to form a BSG layer (thickness of the BSG layer is 50 nm) on the surface;

[0277] S4, removing the pre-prepared BSG layer on the surface of the silicon substrate obtained in S3 by a laser process;

[0278] S5, removing the side edge and the front side BSG residue of the silicon substrate obtained in S4 by a chain cleaning process;

[0279] S6, removing the pre-prepared N region surface P type polysilicon layer residue on the silicon substrate obtained in S5 using the TMAH solution for removing polysilicon layer provided in embodiment 2, and retaining the tunneling oxide layer;

[0280] wherein, wherein ozone is introduced through an online ozone generator, the temperature is 80℃, and the process is carried out under microwave assistance (the frequency is 2.4GHz), reducing bubble retention and improving etching uniformity.

[0281] S7, preparing an N type polysilicon layer on the back surface of the silicon substrate obtained in S6, and forming a PSG layer on the surface;

[0282] S8, removing the P region and the pre-prepared GAP region surface PSG layer of the silicon substrate obtained in S7 by a laser process;

[0283] S9, removing the front side wrap plating layer of the silicon substrate obtained in S8; preparing isolation of the back surface N region and the P region; and texturing the GAP region;

[0284] S10, depositing aluminum oxide on both surfaces of the silicon substrate obtained in S9 by an ALD process;

[0285] S11, depositing a silicon nitride layer on both surfaces of the silicon substrate obtained in S10 by a PECVD process;

[0286] S12, preparing a metal electrode on the back surface of the silicon substrate obtained in S11 by a screen printing process, to obtain the back contact battery.

[0287] Application Example 3

[0288] The application example provides a back contact battery, which is different from the application example 2 only in that the TMAH solution for removing polysilicon layer provided in embodiment 2 is replaced by the TMAH solution for removing polysilicon layer provided in embodiment 3, and other settings are consistent with the application example 2.

[0289] Application Example 4

[0290] The application example provides a back contact battery, which is different from the application example 1 only in that the TMAH solution for removing polysilicon layer provided in embodiment 1 is replaced by the TMAH solution for removing polysilicon layer provided in embodiment 4, and other settings are consistent with the application example 1.

[0291] Application Example 5

[0292] The application example provides a back contact battery, which is different from the application example 1 only in that the TMAH solution for removing the polysilicon layer provided in the embodiment 1 is replaced by the TMAH solution for removing the polysilicon layer provided in the embodiment 5, and other settings are consistent with the application example 1.

[0293] Application example 6

[0294] The application example provides a back contact battery, which is different from the application example 1 only in that the TMAH solution for removing the polysilicon layer provided in the embodiment 1 is replaced by the TMAH solution for removing the polysilicon layer provided in the embodiment 6, and other settings are consistent with the application example 1.

[0295] Application example 7

[0296] The application example provides a back contact battery, which is different from the application example 1 only in that the TMAH solution for removing the polysilicon layer provided in the embodiment 1 is replaced by the TMAH solution for removing the polysilicon layer provided in the embodiment 7, and other settings are consistent with the application example 1.

[0297] Application example 8

[0298] The application example provides a back contact battery, which is different from the application example 1 only in that the TMAH solution for removing the polysilicon layer provided in the embodiment 1 is replaced by the TMAH solution for removing the polysilicon layer provided in the embodiment 8, and other settings are consistent with the application example 1.

[0299] Application example 9

[0300] The application example provides a back contact battery, which is different from the application example 2 only in that the TMAH solution for removing the polysilicon layer provided in the embodiment 2 is replaced by the TMAH solution for removing the polysilicon layer provided in the embodiment 9, and other settings are consistent with the application example 2.

[0301] Application example 10

[0302] The application example provides a back contact battery, which is different from the application example 2 only in that the TMAH solution for removing the polysilicon layer provided in the embodiment 2 is replaced by the TMAH solution for removing the polysilicon layer provided in the embodiment 10, and other settings are consistent with the application example 2.

[0303] Comparative application example 1

[0304] The comparative application example provides a back contact battery, which is different from the application example 1 only in that the TMAH solution for removing the polysilicon layer provided in the embodiment 1 is replaced by the alkali solution provided in the comparative example 1, and other settings are consistent with the application example 1.

[0305] Comparative application example 2

[0306] The comparative application example provides a back contact battery, which is different from the application example 1 only in that the TMAH solution for removing the polysilicon layer provided in the example 1 is replaced by the alkali solution provided in the comparative example 2, and other settings are consistent with the application example 1.

[0307] Comparative application example 3

[0308] The comparative application example provides a back contact battery, which is different from the application example 1 only in that the TMAH solution for removing the polysilicon layer provided in the example 1 is replaced by the alkali solution provided in the comparative example 3, and other settings are consistent with the application example 1.

[0309] Comparative application example 4

[0310] The comparative application example provides a back contact battery, which is different from the application example 1 only in that the TMAH solution for removing the polysilicon layer provided in the example 1 is replaced by the alkali solution provided in the comparative example 4, and other settings are consistent with the application example 1.

[0311] Comparative application example 5

[0312] The comparative application example provides a back contact battery, which is different from the application example 1 only in that the TMAH solution for removing the polysilicon layer provided in the example 1 is replaced by the alkali solution provided in the comparative example 5, and other settings are consistent with the application example 1.

[0313] Comparative application example 6

[0314] The comparative application example provides a back contact battery, which is different from the application example 1 only in that the TMAH solution for removing the polysilicon layer provided in the example 1 is replaced by the alkali solution provided in the comparative example 6, and other settings are consistent with the application example 1.

[0315] Test example 1

[0316] Test sample: The back contact batteries provided in the application examples 1-10 and the back contact batteries provided in the comparative application examples 1-6.

[0317] Test method: According to the IEC / EN 61215 standard, a special I-V tester is used to test the irradiance of 1000 W / m 2 , and the test temperature is 25℃.

[0318] The specific test results are shown in Table 1 below:

[0319] Table 1

[0320]

[0321]

[0322] From the test data in Table 1, it can be seen that the application uses a TMAH solution with a specific formula composition to retain the bottom tunnel oxide layer when etching the N region, remove only the surface P-type polysilicon layer, reduce the side edge pits, thereby reducing the side edge residue of the subsequent process, reducing the side edge etching pits, reducing the subsequent residue, reducing the leakage, improving the yield, and improving the conversion efficiency of the battery sheet.

[0323] From the comparison of application example 1 and application examples 4-6, it can be seen that the auxiliary complexing agent is preferably composed of N-methyl-D-glucosamine grafted chitosan derivative and glycerol-boric acid chelate, which cooperate with each other and synergistically remove the surface P-type polysilicon layer, protect the silicon wafer, reduce the leakage, improve the yield, and improve the conversion efficiency of the battery sheet.

[0324] From the comparison of application example 1 and application examples 7-10, it can be seen that the surfactant is preferably a combination of Pluronic F-127 and PFOS, which cooperate to realize nanoscale wetting control through hydrophilic-hydrophobic microzone self-assembly; the surfactant is preferably a combination of AEO-9 and SDS, which cooperate to form mixed micelles, reduce the dynamic surface tension (<40 mN / m), and improve etching uniformity. The application uses a specific combination of surfactants, which can better remove the surface P-type polysilicon layer, protect the silicon wafer, reduce the leakage, improve the yield, and improve the conversion efficiency of the battery sheet.

[0325] From the comparison of application example 1 and comparative application examples 1-6, it can be seen that the TMAH solution contains a specific proportion of tetramethylammonium hydroxide (TMAH), a main oxidizing agent, an auxiliary oxidizing agent, a main complexing agent, an auxiliary complexing agent, and a surfactant, which cooperate to effectively reduce the side edge pits, thereby reducing the side edge residue of the subsequent process, reducing the side edge etching pits, reducing the subsequent residue, reducing the leakage, improving the yield, and improving the conversion efficiency of the battery sheet.

[0326] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application.

Claims

1. A TMAH solution for removing a polysilicon layer, characterized by, The TMAH solution comprises, by weight fraction: 20-250 parts of tetramethylammonium hydroxide, 0.0005-6 parts of a main oxidizing agent, 0.001-4 parts of an auxiliary oxidizing agent, 3-5 parts of a main complexing agent, 2-3 parts of an auxiliary complexing agent, 0.001-0.5 parts of a surfactant, and 800-1200 parts of water.

2. The TMAH solution of claim 1, wherein, The main oxidizing agent comprises potassium persulfate and / or ozone; Preferably, the auxiliary oxidizing agent comprises hydrogen peroxide and / or sodium periodate; Preferably, when the main oxidizing agent is selected from potassium persulfate, the auxiliary oxidizing agent is selected from hydrogen peroxide; when the main oxidizing agent is selected from ozone, the auxiliary oxidizing agent is selected from sodium periodate; Preferably, the content of potassium persulfate is 4-6 parts; the content of hydrogen peroxide is 2-4 parts; Preferably, the content of ozone is 0.0005-0.001 parts; the content of sodium periodate is 1-2 parts.

3. The TMAH solution of claim 1, wherein, The main complexing agent comprises a 7-hydroxy chelating crosslinking agent; Preferably, the 7-hydroxy chelating crosslinking agent is a propylene diamine quaternary ammonium salt containing 7 hydroxyl groups; Preferably, the propylene diamine quaternary ammonium salt containing 7 hydroxyl groups has the following formula I: wherein n is 2-4; Preferably, the content of the main complexing agent is 3-5 parts; Preferably, the auxiliary complexing agent comprises an N-methyl-D-glucosamine grafted chitosan derivative and / or a glycerol-boric acid chelate, preferably a combination of an N-methyl-D-glucosamine grafted chitosan derivative and a glycerol-boric acid chelate; Preferably, the content of the N-methyl-D-glucosamine grafted chitosan derivative is 1-2 parts; Preferably, the content of the glycerol-boric acid chelate is 2-3 parts.

4. The TMAH solution of claim 1, wherein, The surfactant comprises a main surfactant; Preferably, the main surfactant comprises a polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer and / or a fatty alcohol polyoxyethylene ether; Preferably, the surfactant further comprises an auxiliary surfactant; Preferably, the auxiliary surfactant comprises potassium perfluorooctyl sulfonate and / or sodium dodecyl sulfate; Preferably, when the main surfactant is selected from a polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer, the auxiliary surfactant is selected from potassium perfluorooctyl sulfonate; Preferably, when the main surfactant is selected from a fatty alcohol polyoxyethylene ether, the auxiliary surfactant is selected from sodium dodecyl sulfate; Preferably, the content of the polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymer is 0.005-0.01 parts; the content of the potassium perfluorooctyl sulfonate is 0.001-0.003 parts; Preferably, the content of the fatty alcohol polyoxyethylene ether is 0.01-0.02 parts; the content of the sodium dodecyl sulfate is 0.005-0.01 parts.

5. A method for producing the TMAH solution according to any one of claims 1 to 4, characterized by, Comprising: Dissolving tetramethylammonium hydroxide, a main oxidizing agent, an auxiliary oxidizing agent, a main complexing agent, an auxiliary complexing agent, and a surfactant in water to obtain the TMAH solution for removing a polysilicon layer.

6. Use of the TMAH solution according to any one of claims 1-4 in removing a surface P-type polysilicon layer of a silicon wafer with a pre-prepared N region.

7. A method of removing a P-type polysilicon layer from an N-region surface of a silicon substrate, characterized by, Comprising: placing the silicon wafer of the pre-prepared N region into a TMAH solution to etch and remove the surface P-type polysilicon layer of the silicon wafer of the pre-prepared N region; The TMAH solution comprises the TMAH solution according to any one of claims 1-4.

8. The method of claim 7, wherein, The etching temperature is 20-90°C, preferably 80-85°C; Preferably, the etching is assisted by ultrasound and / or microwave. Preferably, the frequency of the ultrasound is 40-60 kHz. Preferably, the power density of the ultrasound is 0.1 to 1 W / cm 2 ; Preferably, the frequency of the microwave is 2-3 GHz.

9. A method of producing a back contact cell, characterized by, comprising: sequentially performing double-side polishing, preparing a tunneling oxide layer and an intrinsic amorphous silicon layer, boron diffusion, removing a surface BSG layer of the pre-prepared N region, removing side and front BSG layers, removing a surface P-type polysilicon layer of the pre-prepared N region, preparing an N-type polysilicon layer, removing surface PSG layers of P regions and a pre-prepared GAP region, texturing, double-side depositing an aluminum oxide layer, double-side depositing a silicon nitride layer, and printing electrodes on the back contact cell; The method for removing the surface P-type polysilicon layer of the N region of the silicon substrate is the method according to claim 7 or 8.

10. The method of claim 9, wherein, The thickness of the tunneling oxide layer is 1-2 nm; and the thickness of the intrinsic amorphous silicon layer is 200-400 nm. Preferably, the intrinsic amorphous silicon layer is converted into a P-type polysilicon layer and forms a BSG layer after the boron diffusion. Preferably, the doping concentration of the P-type polysilicon layer is 1E19-1E20. Preferably, the thickness of the BSG layer is 40-60 nm.

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