Photovoltaic cell preparation process method capable of effectively removing mask material

Abstract

The invention discloses a process method for preparing a photovoltaic cell, which can effectively remove a mask material. The process method comprises the following steps of: carrying out patterned mask on a metal electrode region on the back surface of a Poly rear silicon wafer; carrying out acid etching on the PSG layer in the non-mask area of the silicon wafer by adopting an acid etching mixed solution, removing the PSG layer and the poly layer in the non-mask area, and then cleaning by using overflow water; removing the mask layer of the silicon wafer by using low-concentration alkali liquor, and then rinsing with water; alkali etching is carried out on the poly layer of the non-mask area of the silicon wafer by using alkali etching mixed liquid; and carrying out subsequent treatment on the silicon wafer after alkali etching. According to the method, a step of removing the mask layer is added after the PSG layer is subjected to acid etching. The problems that the service life of an alkali etching solution is short and equipment runs abnormally when poly etching and mask layer etching are carried out in an alkali etching tank at the same time in a traditional process are effectively solved, and the productivity and the product yield are improved.

Description

Technical Field

[0001] This invention relates to the fields of photovoltaic and semiconductor technology, and in particular to a process method for preparing topcon cells that can effectively remove mask materials. Background Technology

[0002] Polyfinger technology is a key process in TOPCon (tunneling oxide passivated contact) cell structures. It primarily optimizes passivation and conductivity by maintaining a thicker doped poly layer (polycrystalline silicon) beneath the electrodes while thinning or removing the poly layer in non-electrode areas. This technology significantly reduces parasitic light absorption and improves photoelectric conversion efficiency.

[0003] Existing poly-finger patterning mask technology combined with chemical thinning can achieve higher patterning accuracy, lower process complexity, better material utilization, better cost-effectiveness, and more significant improvements in electrical performance. Currently, the main steps in the patterning mask process are: poly-finger silicon wafer - PSG removal - patterning mask - acid etching - alkaline etching - subsequent RCA cleaning, etc. However, the alkaline etching tank needs to simultaneously etch both the poly and the mask layer material. This process presents several problems: some mask material detaches and remains suspended in the solution, affecting the solution's activity, reducing its lifespan, and increasing production costs; simultaneously, these suspended particles can clog circulation pipes during solution circulation, causing equipment malfunctions and impacting production capacity and product yield.

[0004] Therefore, how to overcome the shortcomings of existing technologies when performing poly etching and mask layer etching simultaneously in an alkaline etching tank, such as mask detachment causing suspended matter that reduces the service life of the etching solution and increases production costs; and the fact that suspended matter easily clogs circulation pipelines, affecting production capacity and yield, are urgent problems to be solved in this field. Summary of the Invention

[0005] To address the technical problems in existing technologies where, during simultaneous poly etching and mask layer etching in an alkaline etching bath, the mask detaches and becomes suspended, reducing the lifespan of the etching solution and increasing production costs; and where the suspended material easily clogs circulation pipelines, affecting production capacity and yield, this invention provides a process method for preparing topcon batteries that can effectively remove mask material.

[0006] To address the aforementioned technical problem, this invention provides a process for fabricating photovoltaic cells that can effectively remove masking materials, comprising the following steps: Step 1: Pattern the metal electrode area on the back side of the polysilicon wafer using a mask; Step 2: Use an acid etching mixture to etch the PSG layer in the non-mask area of ​​the silicon wafer to remove the PSG layer or PSG layer and part of the poly layer in the non-mask area, and then rinse with overflow water. Step 3: Remove the mask layer of the silicon wafer using a low-concentration alkaline solution, and then rinse with water; Step 4: Use an alkaline etching mixture to perform alkaline etching on the poly layer of the non-mask area of ​​the silicon wafer; Step 5: Perform subsequent processing on the silicon wafer after alkaline etching.

[0007] Preferably, the poly-coated silicon wafer is a PE-poly-coated silicon wafer or an LP-poly-coated silicon wafer.

[0008] Preferably, the acid etching mixture is a mixture of HF, HF and HNO3 or HF and an additive, and deionized water.

[0009] Preferably, in step 2, the volume fraction of HF in the acid etching mixture is 6%, and the reaction time of immersing the silicon wafer in the acid etching mixture at room temperature is 60-100s.

[0010] Preferably, the low-concentration alkaline solution used to remove the mask layer in step 3 is a 0.2%~5% vol alkaline solution.

[0011] Preferably, in step 3, the mask layer is removed at room temperature to 65°C by one of the following methods: circulation of the alkaline solution + bubbling, circulation of the alkaline solution + ultrasound, with an ultrasound frequency of 40kHz to 80kHz, or circulation of the alkaline solution + micron-sized bubbles.

[0012] Preferably, the alkaline etching mixture is a mixture of NaOH and deionized water or NaOH, additives, and deionized water, wherein the volume fraction of NaOH is 5% to 10%, the alkaline etching temperature is 70 to 80°C, and the alkaline etching time is 90 to 300 seconds.

[0013] Preferably, in step 1, the PSG layer deposited on both sides and the front side of the silicon wafer after Poly is removed first, and then the patterned mask is applied.

[0014] Preferably, the PSG layer is first removed using an HF solution with a volume ratio of HF to deionized water of 1:4.8, and the treatment is carried out at 25°C for 100-120 seconds.

[0015] Preferably, in step 2, the volume fraction of HF in the acid etching mixture is 1%, and the reaction time of immersing the silicon wafer in the acid etching mixture at room temperature is 40-60 seconds.

[0016] This invention provides a novel process for effectively removing mask material in the fabrication of topcon solar cells. It primarily utilizes a patterned mask + acid etching + mask removal + alkaline etching approach. Specifically, a mask pattern is applied as a protective layer to the PSG layer in the metal electrode region. First, an acid solution is used to selectively etch the PSG layer or a portion of the poly layer in the non-mask area of ​​the topcon silicon wafer. After this pretreatment, a mask removal step is added, where the mask material on the silicon wafer surface is dissolved and removed. Following water rinsing, alkaline etching is then performed, using an alkaline solution to thin or remove the poly layer in the non-metallic electrode region. This invention, by removing the mask first and then rinsing with water, effectively solves the problem in traditional processes where, during simultaneous poly etching and mask layer etching in the alkaline etching bath, some mask material detaches and remains suspended in the solution, affecting solution activity, reducing solution lifespan, and increasing the cost of the alkaline etching solution. Furthermore, these suspended particles can easily clog circulation pipes during solution circulation, causing equipment malfunctions. This approach is beneficial for improving production capacity and product yield. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the process flow for the first preparation scheme, which involves patterning masking, acid etching, mask removal, alkaline etching, and subsequent processing of the silicon wafer after PE-poly etching. Figure 2 This is a schematic diagram of the process flow for the first preparation scheme, which involves patterning masking, acid etching, mask removal, alkaline etching, and subsequent processing of the silicon wafer after LP-poly. Figure 3 This is a schematic diagram of the process flow for the second preparation method, which involves PSG removal, patterning masking, acid etching, mask removal, alkaline etching, and subsequent processing of the silicon wafer after PE-poly etching. Figure 4 This is a schematic diagram of the process flow for the second preparation scheme, which involves removing PSG, patterning mask, acid etching, mask removal, alkaline etching, and subsequent processing steps on the silicon wafer after LP-poly. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the following specific embodiments are only used to explain the invention and do not constitute a limitation thereof. Two preparation schemes are provided. The process method of the first preparation scheme includes the following steps: The present invention provides a process method for preparing photovoltaic cells that can effectively remove masking materials, which has two preparation schemes. The first preparation scheme includes the following steps: Step 1: Apply a patterned mask to the metal electrode area on the back side of the poly-coated silicon wafer. The poly-coated silicon wafer is either a PE-poly-coated or LP-poly-coated silicon wafer.

[0019] Step 2: The PSG layer and poly layer in the non-mask area of ​​the silicon wafer are etched using an acid etching mixture to thin or remove the poly layer in the non-metallic electrode area. The acid etching mixture is a mixture of hydrofluoric acid and deionized water. The volume fraction of HF in the acid etching mixture is 6%. At room temperature, the silicon wafer is immersed in the acid etching mixture for 60-100 seconds. The acid etching mixture can also be a mixture of HF + HNO3 or HF + additives and deionized water. The etched silicon wafer is then rinsed with overflow water for 120 seconds.

[0020] Step 3: Using a low-concentration alkaline solution (0.2%~5% vol) at room temperature to 65°C, remove the mask layer from the silicon wafer by circulating the alkaline solution and bubbling until the mask layer on the outer surface of the silicon wafer is completely removed, then rinse with water. At this point, no suspended matter precipitates in the solution, and the solution has a normal usage cycle. Alternatively, the mask layer can be removed at room temperature to 65°C by circulating the alkaline solution and using ultrasound at a frequency of 40kHz~80kHz, or by circulating the alkaline solution and using micron-sized bubbles.

[0021] Step 4: Further etch the poly layer of the non-mask area of ​​the silicon wafer using an alkaline etching mixture: the alkaline etching mixture is a mixture of NaOH + deionized water or NaOH + additive + deionized water, with a NaOH volume fraction of 5%~10%, a temperature of 70~80℃, and an alkaline etching time of 90s~300s. Other alkaline solutions, such as KOH solution, can also be used.

[0022] Step 5: Perform subsequent processing on the silicon wafer after acid etching. The process includes: The silicon wafer after acid etching is cleaned once using overflow water; then, it is cleaned again using an alkaline mixture; followed by a second cleaning using overflow water; then a third cleaning using hydrofluoric acid solution; finally, the wafer is slowly pulled up to pre-dehydrate its surface; and finally, the pre-dehydrated wafer is dried. Wherein: The three washing cycles each lasted 120 seconds; the alkaline solution was a mixture of NaOH, H2O2, and deionized water, with a NaOH:H2O2 volume ratio of 1:4; the subsequent alkaline wash was performed at 70°C for 90 seconds; the hydrofluoric acid solution had a HF:water volume ratio of 1:4.8; the HF acid wash was performed at 25°C for 280 seconds; the deionized water was slowly lifted at a speed of 3 mm / s; the pre-dehydration temperature was 48-50°C; and the drying temperature was 95°C for 600 seconds.

[0023] This invention adds a mask removal step after appropriate acid etching, whereby the mask material on the silicon wafer surface is first dissolved and removed, followed by water rinsing. This effectively solves the problems of short alkaline etching solution lifespan and equipment malfunctions in traditional processes where poly etching and mask layer etching are performed simultaneously in an alkaline etching bath, thus improving production capacity and product yield. Alkaline positive etching is then performed to further etch the poly layer. The etching rate is controlled by adjusting the temperature, time, concentration of the alkaline solution, and additives, allowing for control of the alkaline etching depth and width. Furthermore, since the reaction between this alkaline etching mixture and silicon dioxide is extremely slow at both room temperature and high temperature (70-80°C), it is negligible. Therefore, when alkaline etching the poly layer in the non-gateway areas on the back side, the BSG layer on the front side and the underlying texturing surface are not damaged. This is beneficial for mass production on the production line and improves the efficiency and yield of cell fabrication.

[0024] The second preparation method provided by the present invention includes the following steps: Step 1: Remove the PSG (phosphosilicate glass) layer coated on both sides and the front side of the polysilicon wafer. The PSG layer is removed using an HF solution with a volume ratio of HF to deionized water of 1:4.8, and the treatment is carried out at 25°C for 100-120 seconds.

[0025] The poly-polymerized silicon wafer can be either a PE-poly-polymerized silicon wafer or an LP-poly-polymerized silicon wafer.

[0026] Step 2: Pattern the metal electrode area on the back side of the polysilicon wafer using a mask.

[0027] Step 3: Etch the PSG layer in the non-mask area of ​​the silicon wafer using an acid etching solution. This removes the PSG layer or a portion of the PSG layer and poly layer in the non-mask area, including both sides and the front of the wafer. The acid etching solution is a mixture of hydrofluoric acid and deionized water, with an HF volume fraction of 1%. At room temperature, the silicon wafer is immersed in the acid etching solution for 40-60 seconds. Alternatively, the acid etching solution can be a mixture of HF + HNO3 or HF + additives and deionized water. After acid etching, the silicon wafer is rinsed with overflow water for 120 seconds.

[0028] Step 4: Using a low-concentration alkaline solution (0.2%~5% vol) at room temperature to 65°C, remove the mask layer from the silicon wafer by circulating the alkaline solution and bubbling until the mask layer on the outer surface of the silicon wafer is completely removed, then rinse with water. At this point, no suspended matter precipitates in the solution, and the solution has a normal service life. Alternatively, the mask layer can be removed at room temperature to 65°C by circulating the alkaline solution and using ultrasound at a frequency of 40kHz~80kHz, or by circulating the alkaline solution and using micron-sized bubbles.

[0029] Step 5: Further etch the poly layer of the non-mask area of ​​the silicon wafer using an alkaline etching solution, including both sides of the silicon wafer and the front of the winding. The alkaline etching solution is a mixture of NaOH and deionized water or NaOH, additives, and deionized water, with a NaOH volume fraction of 5%~10%, a temperature of 70~80℃, and an alkaline etching time of 90s~300s. Other alkaline solutions, such as KOH solution, can also be used.

[0030] Step 6: Perform subsequent processing on the silicon wafer after alkaline etching. The process includes: The silicon wafer after acid etching is cleaned once using overflow water; then, it is cleaned again using an alkaline mixture; followed by a second cleaning using overflow water; then a third cleaning using hydrofluoric acid solution; finally, the wafer is slowly pulled up to pre-dehydrate its surface; and finally, the pre-dehydrated wafer is dried. Wherein: The three washing cycles each lasted 120 seconds; the alkaline solution was a mixture of NaOH, H2O2, and deionized water, with a NaOH:H2O2 volume ratio of 1:4; the subsequent alkaline wash was performed at 70°C for 90 seconds; the hydrofluoric acid solution had a HF:water volume ratio of 1:4.8; the HF acid wash was performed at 25°C for 280 seconds; the deionized water was slowly lifted at a speed of 3 mm / s; the pre-dehydration temperature was 48-50°C; and the drying temperature was 95°C for 600 seconds.

[0031] In the TopCon battery manufacturing process, the "PE-poly post-processing" refers to a semi-finished product that has undergone the following processing steps: The process involves silicon wafer texturing, front-side boron diffusion, removal of BSG from the front side, back-side polishing, PECVD-poly (deposition of a back-side tunneling oxide layer and a doped amorphous silicon layer), and annealing and crystallization. After completing this step, the "PE-poly post-deposition" silicon wafer is obtained. Then, subsequent processes such as PSG removal, mask removal, poly deposition, and RCA deposition are performed.

[0032] The term "LE-poly post-processing" refers to the semi-finished product after undergoing the following process: After completing the following steps—silicon wafer texturing, front-side boron diffusion, front-side BSG removal + back-side polishing, LPCVD-poly (back-side tunneling oxidation + intrinsic polysilicon deposition), and back-side phosphorus diffusion—the "LP-poly post-" silicon wafer is obtained. Then, subsequent processes including PSG removal, mask removal, poly deposition, and RCA are performed.

[0033] The present invention will be further described below through specific embodiments.

[0034] Example 1 Using the first fabrication method, the silicon wafer after PE-poly is subjected to patterning masking, acid etching, mask removal, alkaline etching, and subsequent processing steps, such as... Figure 1 The process flow shown is as follows.

[0035] 1. Patterned Mask: A patterned mask is applied to the PSG (Power Photocell) on the metal electrode area of ​​the back side of the silicon wafer after PE-polymerization. This involves spraying mask material onto the back of the silicon wafer using a spray printing method to form a mask pattern. The printed grid lines have a height of 15-18µm and a width of 100-120µm. Mask materials mainly include one or more of the following: paraffin wax, ink, resin, or adhesive film.

[0036] 2. Acid Etching: The silicon wafer with the patterned mask is subjected to acid etching. A mixture of HF and deionized water is used, with HF comprising 6% by volume. At room temperature, the silicon wafer is immersed in the acid etching solution for 60-100 seconds. By suppressing the reaction rate at low temperature, the exposed PSG layer or PSG layer and part of the poly layer in the non-patterned mask area is removed, including the PSG layer or PSG layer and part of the poly layer on both sides of the silicon wafer and extending to the front side of the silicon wafer, in order to achieve a controllable poly layer etching depth. The acid etching mixture can also be a mixture of HF + HNO3 or HF + additives and deionized water.

[0037] 3. After acid etching, rinse the silicon wafer with overflow water for 120 seconds to remove impurities and residual acid solution from the surface of the silicon wafer and ensure that the surface of the silicon wafer is clean.

[0038] 4. Using a low-concentration alkaline solution (0.2%~5% vol) at room temperature to 65°C, the mask material on the silicon wafer is removed by circulating and bubbling the alkaline solution until the mask layer on the outer surface of the silicon wafer is completely removed, followed by water rinsing. At this point, no suspended matter precipitates in the solution, and the solution's usage cycle is normal.

[0039] 5. Alkaline etching of the poly layer in the non-mask area of ​​the silicon wafer using an alkaline etching mixture: The alkaline etching solution is a mixture of NaOH and deionized water or NaOH, additives, and deionized water, with a NaOH volume fraction of 5%–10%, a temperature of 70–80°C, and an alkaline etching time of 90–300 seconds. Alkaline etching is performed on the non-mask poly areas on the back and sides of the silicon wafer. By controlling the temperature, time, concentration of the alkaline solution, and additives in the alkaline etching process, the etching rate can be controlled, allowing for precise control of the etching depth and width. This effectively reduces parasitic light absorption in the non-electrode areas on the back side, improving the photoelectric conversion efficiency and yield of the solar cell.

[0040] 6. First rinse: Use overflow water to rinse for 120 seconds to remove impurities and residual acid solution from the silicon wafer surface, ensuring the silicon wafer surface is clean.

[0041] 7. Post-alkaline washing: mainly using a mixed solution of NaOH + H2O2 + deionized water, with a volume ratio of NaOH:H2O2 of 1:4, a temperature of 70℃, and a process time of 90s, to clean the silicon wafer after the previous acid etching, neutralize the solution residue left on the silicon wafer by the acid etching, and remove the porous silicon generated by the acid etching reaction.

[0042] 8. Secondary water rinse: Use overflow water to rinse for 120 seconds to remove impurities and residual alkaline solution from the silicon wafer surface, ensuring the silicon wafer surface is clean.

[0043] 9. HF Wash: A final HF wash is performed to remove the front-side BSG and back-side PSG. Among these steps... HF:water = 1:4.8, cleaning temperature 25℃, cleaning time 280 seconds.

[0044] 10. Three-stage water rinse: Rinse with overflow water for 120 seconds to remove impurities and residual acid solution from the silicon wafer surface, ensuring the silicon wafer surface is clean. 11. Slow lifting: Deionized water (lifting speed 3mm / s, working temperature 48-50℃) is used to pre-dehydrate the surface of the monocrystalline silicon wafer to avoid watermarks during drying.

[0045] 12. Drying: Dry the cleaned silicon wafers. The temperature is 95℃ and the time is 600 seconds.

[0046] Example 2 Using the first fabrication method, the silicon wafer after LP-poly undergoes patterning masking, acid etching, mask removal, alkaline etching, and subsequent processing steps, such as... Figure 2 The process flow shown is as follows: The processing method for patterning, acid etching, mask removal, alkaline etching, and subsequent steps on the silicon wafer after LP-poly etching is basically the same as that in Example 1. The difference is that a poly layer is also deposited on the front side of the silicon wafer in addition to the BSG layer. Therefore, during the acid etching process after patterning, in addition to removing the PSG layer or PSG layer and poly layer exposed in the non-patterned mask area of ​​the silicon wafer, as well as the PSG layer or PSG layer and poly layer on both sides of the silicon wafer and those extending to the front side, the poly layer covering the BSG on the front side of the silicon wafer must also be removed to achieve a controllable poly layer etching depth. Furthermore, Using a low-concentration alkaline solution (0.2%~5% vol) at room temperature to 65°C, the mask material on the silicon wafer is removed by circulating the alkaline solution and using ultrasound at a frequency of 40kHz~80kHz until the mask layer on the outer surface of the silicon wafer is completely removed, followed by water rinsing. At this point, no suspended matter precipitates in the solution, and the solution has a normal service life. The treatment of the silicon wafer after acid etching is the same as in Example 1.

[0047] The second preparation method provided by this invention will be used below to prepare photovoltaic cells.

[0048] Example 3 The second fabrication method involves processing the PE-polysilicon wafer as follows: PSG removal, patterning mask, acid etching, mask removal, alkaline positive etching, and subsequent processes. Figure 3 The process flow shown is as follows.

[0049] 1. PSG Removal: The PE-poly silicon wafer is fed into a chain-type PSG removal device. A mixed solution of HF and deionized water at a volume ratio of 1:4.8 is used, and the wafer is treated at 25°C for 100-120 seconds to remove the PSG layer (phosphosilicate glass) deposited on both sides and the front side of the silicon wafer. The BSG layer (borosilicate glass) on the front side is retained as a mask layer for subsequent protection. The degree of PSG removal is checked by observing the dehydration of the silicon wafer surface; complete dehydration indicates that the PSG has been completely removed.

[0050] 2. Patterned Mask: The PSG (Power Seal) of the metal electrode area on the back side of the silicon wafer after PSG removal is patterned using a mask. This involves spraying mask material onto the back of the silicon wafer using a spray printing method to form a mask pattern. The printed grid lines have a height of 15-18µm and a width of 100-120µm. Mask materials mainly include one or more of the following: paraffin wax, ink, resin, or adhesive film.

[0051] 3. Acid Etching: The silicon wafer with the patterned mask is subjected to acid etching. An acid etching solution of HF + deionized water is used, wherein the HF volume fraction is 1%. At room temperature, the silicon wafer is immersed in the acid etching solution for 40-60 seconds. By suppressing the reaction rate at low temperature, the PSG layer and poly layer exposed in the non-patterned mask area are removed, including the PSG layers on both sides of the silicon wafer and those extending to the front of the silicon wafer, or the PSG layer and part of the poly layer, to achieve a controllable poly layer etching depth. The acid etching solution can also be a mixture of HF + HNO3 or HF + additives and deionized water.

[0052] 4. After acid etching, rinse the silicon wafer with overflow water for 120 seconds to remove impurities and residual acid solution from the surface of the silicon wafer and ensure that the surface of the silicon wafer is clean.

[0053] 5. Using a low-concentration alkaline solution (0.2%~5% vol) at room temperature to 65°C, remove the mask material from the silicon wafer using a combination of circulating the alkaline solution and micron-sized bubbles until the mask layer on the outer surface of the silicon wafer is completely removed, followed by water rinsing. At this point, no suspended matter precipitates in the solution, and the solution's usage cycle is normal.

[0054] 6. Alkaline etching of the poly layer in the non-mask area of ​​the silicon wafer using an alkaline etching mixture: The alkaline etching solution is a mixture of NaOH and deionized water or NaOH, additives, and deionized water, with a NaOH volume fraction of 5%–10%, a temperature of 70–80°C, and an alkaline etching time of 90–300 seconds. Alkaline etching is performed on the non-mask poly areas on the back and sides of the silicon wafer. By controlling the temperature, time, concentration of the alkaline solution, and additives in the alkaline etching process, the etching rate can be controlled, allowing for precise control of the etching depth and width. This effectively reduces parasitic light absorption in the non-electrode areas on the back side, improving the photoelectric conversion efficiency and yield of the solar cell.

[0055] 7. First rinse: Use overflow water to rinse for 120 seconds to remove impurities and residual acid solution from the silicon wafer surface, ensuring the silicon wafer surface is clean.

[0056] 8. Post-alkaline washing: mainly using a mixed solution of NaOH + H2O2 + deionized water, with a volume ratio of NaOH:H2O2 of 1:4, a temperature of 70℃, and a process time of 90s, to clean the silicon wafer after the previous acid etching, neutralize the solution residue left on the silicon wafer by the acid etching, and remove the porous silicon generated by the acid etching reaction.

[0057] 9. Secondary water rinse: Use overflow water to rinse for 120 seconds to remove impurities and residual alkaline solution from the silicon wafer surface, ensuring the silicon wafer surface is clean.

[0058] 10. HF Wash: A final HF wash is performed to remove the front BSG and back PSG. The HF:water ratio is 1:4.8, the washing temperature is 25℃, and the time is 280 seconds.

[0059] 11. Three-stage water rinse: Rinse with overflow water for 120 seconds to remove impurities and residual acid solution from the silicon wafer surface, ensuring the silicon wafer surface is clean. 12. Slow lifting: Deionized water (lifting speed 3mm / s, working temperature 48-50℃) is used to pre-dehydrate the surface of the monocrystalline silicon wafer to avoid watermarks during drying.

[0060] 13. Drying: Dry the cleaned silicon wafers. The temperature is 95℃ and the time is 600 seconds.

[0061] Example 4 The second fabrication method involves processing the LP-poly silicon wafer as follows: PSG removal, patterning mask, acid etching, mask removal, alkaline etching, and subsequent processes, such as... Figure 4 The process flow shown is as follows: The processing method for the silicon wafer after LP-poly etching—PSG removal, patterning mask, acid etching, mask removal, alkaline etching, and subsequent processes—is basically the same as the process in Example 3. The difference is that a poly layer is also deposited on the BSG on the front side of the silicon wafer after LP-poly etching. Therefore, during the acid etching process after patterning masking, in addition to removing the PSG layer or PSG layer and part of the poly layer exposed in the non-patterned mask area on the back side of the silicon wafer, as well as the PSG layer or PSG layer and poly layer on both sides of the silicon wafer that wrap around to the front side, the poly layer covering the BSG on the front side of the silicon wafer must also be removed to achieve a controllable poly layer etching depth. Furthermore, a low-concentration alkaline solution of 0.2%~5% vol is used at room temperature~65°C, employing circulation and bubbling to remove the mask material from the silicon wafer until the mask layer on the outer surface of the silicon wafer is completely removed, followed by water rinsing. At this point, no suspended matter precipitates in the solution, and the solution's usage cycle is normal. The processing of the silicon wafer after acid etching is the same as in Example 3.

[0062] The second preparation method requires first removing the PSG layers deposited around the sides and front of the poly-coated silicon wafer, and then performing the patterning mask-acid etching + mask removal + alkaline etching + subsequent processing. This preparation method is suitable for manufacturers' existing equipment and processes. It allows the continued use of the "chain-type PSG removal" equipment in the current Topcon conventional process flow to remove the PSG layers deposited around the sides and front of the poly-coated silicon wafer. Only the patterning mask equipment and the tanks required for acid etching need to be added to achieve the preparation method of this invention. Production line modification is convenient, saving time and costs.

[0063] The first fabrication scheme, from a process optimization perspective, integrates the second scheme's process of first removing the PSG layers on both sides and the front of the silicon wafer using a chain-type device, and then removing the PSG and poly layers in non-patterned mask areas via subsequent acid etching, by adjusting the acid etching process. In other words, a patterned mask is directly applied to the back of the silicon wafer after POLY (polyethylene terephthalate), followed by a single step of acid etching to remove the PSG and poly layers. This eliminates the need for the existing "chain-type PSG removal equipment," saving process steps and offering better results at lower costs and higher efficiency. However, it requires additional equipment for removing the patterned mask and a tank for acid etching, enabling the etching of the poly layers in the non-gateline areas on the back.

[0064] The above description is merely a specific embodiment of the present invention. It should be noted that any modifications, equivalent substitutions, and variations made within the spirit and framework of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for fabricating photovoltaic cells that can effectively remove masking materials, comprising the following steps: Step 1: Pattern the metal electrode area on the back side of the polysilicon wafer using a mask; Step 2: Use an acid etching mixture to etch the PSG layer in the non-mask area of ​​the silicon wafer to remove the PSG layer or the PSG layer and part of the poly layer in the non-mask area, and then rinse with overflow water. Step 3: Remove the mask layer of the silicon wafer using a low-concentration alkaline solution, and then rinse with water; Step 4: Use an alkaline etching mixture to perform alkaline etching on the poly layer of the non-mask area of ​​the silicon wafer; Step 5: Perform subsequent processing on the silicon wafer after alkaline etching.

2. The process method as described in claim 1, characterized in that, The poly-coated silicon wafer is either a PE-poly-coated silicon wafer or an LP-poly-coated silicon wafer.

3. The process method as described in claim 1, characterized in that, The acid etching mixture is a mixture of HF, HF and HNO3 or HF and an additive, and deionized water.

4. The process method as described in claim 1, characterized in that, In step 2, the volume fraction of HF in the acid etching mixture is 6%, and the silicon wafer is immersed in the acid etching mixture at room temperature for 60-100 seconds.

5. The process method as described in claim 1, characterized in that, The low-concentration alkaline solution used to remove the mask layer in step 3 is a 0.2%~5% vol alkaline solution.

6. The process method as described in claim 1, characterized in that, In step 3, the mask layer is removed at room temperature to 65°C by one of the following methods: circulation of the alkaline solution + bubbling, circulation of the alkaline solution + ultrasound, with an ultrasound frequency of 40KHZ to 80KHZ, or circulation of the alkaline solution + micron-sized bubbles.

7. The process method as described in claim 1, characterized in that, The alkaline etching solution is a mixture of NaOH and deionized water or NaOH, additives, and deionized water, wherein the volume fraction of NaOH is 5% to 10%, the alkaline etching temperature is 70 to 80°C, and the alkaline etching time is 90 to 300 seconds.

8. The process method as described in claim 1, characterized in that, In step 1, the PSG layer that was coated on both sides and the front side of the silicon wafer after Poly was removed is first applied, and then the patterned mask is applied.

9. The process method as described in claim 8, characterized in that, The PSG layer was first removed using an HF solution with a volume ratio of HF to deionized water of 1:4.8, and the treatment was carried out at 25°C for 100-120 seconds.

10. The process method as described in claim 8, characterized in that, In step 2, the volume fraction of HF in the acid etching mixture is 1%, and the silicon wafer is immersed in the acid etching mixture at room temperature for 40-60 seconds.

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