Laser-assisted etching slotting method for preparing high-doping-concentration P + polycrystalline silicon and application

Abstract

The invention relates to the technical field of solar cells, and discloses a laser-assisted etching slotting method for preparing high-doping-concentration P + polycrystalline silicon and application. The grooving method comprises the following steps: preparing a tunneling SiOx layer and an i-polysi layer on the back surface of a silicon wafer; performing patterning etching by using green picosecond laser so as to remove the i-polysi layer and the tunneling SiOx layer in a laser region; removing impurities in a laser area through single-side acid pickling; boron diffusion is carried out, P + polycrystalline silicon is formed on the i-polysi layer in the non-laser area, a P + emission layer is generated in the laser area, and a BSG layer is generated on the back faces of the P + polycrystalline silicon and the P + emission layer; performing patterning etching by using green picosecond laser to remove the BSG layer in the laser area; and carrying out alkali wet etching to remove the P + emission layer in the laser area so as to form a notch. According to the grooving method, the notch with the ideal grooving depth is formed, P + polycrystalline silicon with high doping concentration can be formed in the non-laser area to reduce the contact resistivity, and the cost is low.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and particularly relates to a laser-assisted etching and grooving method for preparing P+-type polysilicon with a high doping concentration and its application. Background Art

[0002] TOPCon cells (tunnel oxide passivated contact cells) can achieve carrier selective transport due to their unique structure, thereby increasing the open-circuit voltage (Voc) and fill factor (FF) of the cells, and further improving the cell efficiency. BC cells (back contact cells) mean that the PN junction (and metal electrodes) is integrated in a finger-like pattern on the back of the cell. There are no metal electrodes on the front of this type of cell, so there is no shading loss of the electrodes on the front of the cell. Therefore, it has a higher short-circuit current and can effectively improve the cell efficiency. TBC cells are solar cells that combine TOPCon and BC technologies, and P+-type and N+-type polysilicon structures are simultaneously prepared on the back of the cell, greatly improving the cell efficiency.

[0003] Currently, for TBC cells, high-temperature P+-type polysilicon is usually prepared first, and then lower-temperature N+-type polysilicon is prepared. Before preparing N+-type polysilicon, grooves need to be formed on the P+-type polysilicon; as Figure 4 shown, the middle is the notch 7; N+-type polysilicon needs to be prepared in the notch 7 later. Therefore, grooving to locally remove P+-type polysilicon is one of the key technologies in the production of TBC cells. Currently, the commonly used methods for grooving and removing P+-type polysilicon mainly include: mask combined with wet etching, or laser grooving combined with wet etching. The more common method is laser grooving combined with wet etching.

[0004] The grooving and etching removal of P+-type polysilicon in TBC cells is related to its doping concentration. P+-type polysilicon with a high doping concentration can resist the etching rate, so it is very difficult to form grooves. In this regard, in the prior art, such as the publication number CN118610280A, by reducing the thickness of P+-type polysilicon, the doping concentration of P+-type polysilicon is reduced to reduce the difficulty of grooving and etching removal of P+-type polysilicon; however, reducing the doping concentration of P+-type polysilicon will bring other problems: the contact resistivity between the metal electrode and the P+-type polysilicon with a low doping concentration will increase, and the thickness of the P+-type polysilicon is thin. During the process of preparing the metal electrode (i.e., metallization), the P+-type polysilicon is more likely to be burned through, thus damaging the structure of the back of the cell and reducing the cell efficiency. At the same time, using expensive laser equipment such as femtosecond lasers to etch P+-type polysilicon with a high doping concentration will greatly increase the equipment investment cost and is not conducive to production and manufacturing.

[0005] For another example, the publication number CN119342910A designs P+ polysilicon with high and low doping concentrations; however, the thickness of the P+ polysilicon with a high doping concentration is greater than that of the P+ polysilicon with a low doping concentration. Moreover, if the doping concentration of the P+ polysilicon is further increased in the later stage, it is still difficult to remove it by laser and wet local etching, which is not conducive to large-scale production. Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a laser-assisted etching and grooving method for preparing P+ polysilicon with a high doping concentration and its application.

[0007] Based on this, the present invention discloses a laser-assisted etching and grooving method for preparing P+ polysilicon with a high doping concentration, including the following steps:

[0008] Step 1: Deposit and prepare a tunneling oxide layer and an intrinsic polysilicon layer on the back surface of the silicon wafer in sequence;

[0009] Step 2: Use a green picosecond laser to pattern-etch the intrinsic polysilicon layer to remove the intrinsic polysilicon layer and the tunneling oxide layer in the laser area, so that the back surface of the silicon wafer in the laser area is exposed;

[0010] Step 3: Perform single-sided pickling on the back surface of the silicon wafer to remove impurities in the laser area and the oxide layer generated by laser etching. The intrinsic polysilicon layer in the non-laser area is retained because it does not react with the pickling solution;

[0011] Step 4: Boron diffusion is carried out to make the intrinsic polysilicon layer in the non-laser area form P+ polysilicon with a doping concentration greater than 1e19 cm -3 , and a P+ emitter layer is formed on the exposed back surface of the silicon wafer in the laser area. Moreover, a borosilicate glass layer is formed on the back surfaces of both the P+ polysilicon and the P+ emitter layer;

[0012] Step 5: Use a green picosecond laser to pattern-etch the laser area again to remove the borosilicate glass layer and part of the P+ emitter layer in the laser area;

[0013] Step 6: Perform alkali wet etching on the silicon wafer to etch and remove the remaining P+ emitter layer in the laser area to form a notch. The P+ polysilicon in the non-laser area is not etched because it is protected by the borosilicate glass layer.

[0014] Preferably, in step 1, the process conditions for depositing and preparing the tunneling oxide layer include: the gas flow rate of O2 is 12000 - 30000 sccm, the temperature of the deposition reaction is 500 - 700 °C, and the time is 500 - 2000 s; the thickness of the tunneling oxide layer is 1.5 - 6 nm;

[0015] The process conditions for depositing the intrinsic polysilicon layer include: the gas flow rate of SiH4 is 400 - 1500 sccm, the temperature of the deposition reaction is 580 - 750 °C, the time is 1 - 3 h, and the air pressure is 150 - 450 mTorr; the thickness of the intrinsic polysilicon layer is 100 - 400 nm.

[0016] Further preferably, in the process of depositing the intrinsic polysilicon layer in step 1: after introducing SiH4, the temperature of the deposition reaction is 580 - 650 °C and the time is 1.5 - 2.8 h. By further optimizing and adjusting the temperature and time of the deposition reaction after introducing SiH4 (such as appropriately reducing the temperature of the deposition reaction after introducing SiH4 or appropriately reducing the time of the deposition reaction after introducing SiH4), the crystallization degree of the i - polysi layer is controlled, making its crystallization degree small and having more defects, which can further reduce the power requirement for the green - light picosecond laser used in patterning etching, and can further reduce the equipment cost. At the same time, the i - polysi layer has relatively more defects, which is more conducive to boron diffusion, can further increase the doping concentration of P+ polysilicon in the non - laser area, and is beneficial to further reducing the contact resistivity between the metal electrode prepared in the later metallization and P+ polysilicon.

[0017] Preferably, in steps 2 and 5, the process conditions for patterning and etching the intrinsic polysilicon layer with a green - light picosecond laser include: the power of the green - light picosecond laser is greater than or equal to 40 W and less than 100 W, the frequency is 500 - 1000 KHZ, the speed is 15000 - 20000 mm / s, and the line spacing is 0.2 - 0.5 mm.

[0018] Further preferably, in steps 2 and 5, the power of the green - light picosecond laser is 50 - 70 W.

[0019] Preferably, in step 3, the pickling solution is a mixed acid solution prepared by mixing HF solution and nitric acid solution according to a volume ratio of 1:3 - 1:5. The concentration of the HF solution is 50 - 75 wt%, the concentration of the nitric acid solution is 55 - 65 wt%, and the tape speed for single - side pickling is 2 - 5 m / min.

[0020] Preferably, in step 4, during the boron diffusion process, a mixed gas of BCl3 and O2 is first introduced, the diffusion temperature is 820 - 910 °C, the diffusion time is 1000 - 3000 s, the gas flow rate of BCl3 is 55 - 450 sccm, and the gas flow rate of O2 is 550 - 4000 sccm; then N2 is introduced to enter the propulsion stage, the propulsion temperature is 930 - 960 °C, the propulsion time is 1000 - 2000 s, and the gas flow rate of N2 is 3000 - 6000 sccm; then O2 is introduced to enter the oxidation stage, the oxidation temperature is 950 - 1050 °C, the oxidation time is 1000 - 3000 s, and the gas flow rate of O2 is 10000 - 30000 sccm; the thickness of the borosilicate glass layer is 30 - 75 nm.

[0021] Preferably, in step 6, the process conditions for the alkali wet etching include: using a polishing tank containing an alkali solution to perform the alkali wet etching on the silicon wafer, and the temperature of the alkali wet etching is 75 - 90 °C and the time is 2 - 4 min.

[0022] Preferably, a laser-assisted etching grooving method for preparing highly doped P+ polysilicon further includes: performing double-sided alkali polishing on the silicon wafer to remove impurities on the surface of the silicon wafer and form a flat morphology on the back surface of the silicon wafer.

[0023] The present invention also discloses an application of a laser-assisted etching grooving method for preparing highly doped P+ polysilicon, applying the laser-assisted etching grooving method for preparing highly doped P+ polysilicon to prepare a TBC battery.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] In the grooving method of the present invention, the i-polysi layer is patterned and etched by green picosecond laser, and then etched by single-sided pickling to the surface of the silicon wafer (the i-polysi layer in the non-laser area does not react with the pickling solution, so the i-polysi layer in the non-laser area can be retained without a mask), and then boron diffusion is carried out (the i-polysi layer in the non-laser area has more defects, and the diffusion rate of boron on the i-polysi layer is faster than that on the silicon wafer, so the boron doping concentration of the i-polysi layer in the non-laser area is higher, which is beneficial to the formation of higher doped P+ polysilicon), and then green picosecond laser patterning etching combined with alkali wet etching is carried out in the laser area (due to the protection of the BSG layer formed by boron diffusion, the highly doped P+ polysilicon in the non-laser area will not be etched by alkali); thus, the P+ polysilicon and P+ emitter layer in the laser area can be removed cleanly to form a notch with an ideal grooving depth, and the i-polysi layer in the non-laser area can form highly doped P+ polysilicon.

[0026] Compared with the existing method of directly performing laser grooving on P+ polysilicon, the present invention uses the above grooving method, which requires lower laser power and laser type for laser patterning etching of the i-polysi layer, solves the problem of difficult grooving of P+ polysilicon with high doping concentration in the prior art, and can retain the i-polysi layer in the non-laser area without a mask, greatly reducing the equipment investment cost and manufacturing cost. At the same time, the present invention can also form P+ polysilicon with a higher doping concentration in the non-laser area, without the need to reduce the doping concentration and thickness of P+ polysilicon as in CN118610280A, enabling good matching between P+ polysilicon and the metal electrodes fabricated by metallization, which is beneficial to reducing the contact resistivity between the metal electrodes prepared by subsequent metallization and P+ polysilicon, and thus contributing to improving the battery efficiency. Moreover, the grooving method of the present invention is easier to implement and is conducive to large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 FIG. is a schematic cross-sectional structure diagram after the laser-assisted etching grooving method for preparing P+ polysilicon with high doping concentration of the present invention is processed by step S2.

[0028] Figure 2 FIG. is a schematic cross-sectional structure diagram after the laser-assisted etching grooving method for preparing P+ polysilicon with high doping concentration of the present invention is processed by step S3.

[0029] Figure 3 FIG. is a schematic cross-sectional structure diagram after the laser-assisted etching grooving method for preparing P+ polysilicon with high doping concentration of the present invention is processed by step S5.

[0030] Figure 4 FIG. is a schematic cross-sectional structure diagram after the laser-assisted etching grooving method for preparing P+ polysilicon with high doping concentration of the present invention is processed by step S7.

[0031] Figure 5 FIG. is a schematic structure diagram of the back surface of a test sample fabricated by the laser-assisted etching grooving method for preparing P+ polysilicon with high doping concentration of the present invention.

[0032] Figure 6 FIG. is an ECV (current-voltage curve) data graph of P+ polysilicon in the non-laser area (corresponding to Figure 5 area 9) of the test sample fabricated after step S7 in Example 1.

[0033] Figure 7 FIG. is an ECV data graph of P+ polysilicon in the non-laser area of the test samples fabricated after step S7 in Examples 5-9 and Comparative Example 1.

[0034] Description of the reference numerals in the drawings: silicon wafer 1; tunneling SiOx layer 2; i-polysi layer 3; P+ polysilicon 31; laser region 4; P+ emitter layer 5; BSG layer 6; notch 7; square notch 8; non-laser region 9; linear notch 10. Detailed implementation manners

[0035] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific implementation manners.

[0036] A laser-assisted etching and grooving method for preparing P+ polysilicon 31 with a high doping concentration according to the present invention, referring to Figures 1-5 , specifically includes the following steps:

[0037] Step S1: Perform double-sided alkaline polishing on the silicon wafer 1 to remove impurities on the surface of the silicon wafer 1 and form a flat morphology on the back surface of the silicon wafer 1.

[0038] In step S1, the resistivity of the silicon wafer 1 is 1-1.6 Ω·cm, the sheet resistance is 80-95 Ω / sq, and the thickness is 130-150 μm. The silicon wafer 1 is subjected to double-sided alkaline polishing in a polishing tank containing an alkaline solution at 75-90 °C for 2-4 min.

[0039] Step S2: Sequentially deposit and prepare a tunneling SiOx layer 2 (tunneling silicon oxide layer) and an i-polysi layer 3 (intrinsic polysilicon layer) on the back surface of the silicon wafer 1. The structure after being processed by step S2 is as Figure 1 shown.

[0040] In step S2, the process parameters for depositing and preparing the tunneling SiOx layer 2 include: the gas flow rate of O2 is 12000-30000 sccm, the deposition reaction temperature is 500-700 °C, the time is 500-2000 s; the thickness of the prepared tunneling SiOx layer 2 is 1.5-6 nm. Then, an i-polysi layer 3 is deposited and prepared on the back surface of the tunneling SiOx layer 2, and its process parameters include: the gas flow rate of SiH4 is 400-1500 sccm, the deposition reaction temperature is 580-750 °C (preferably 580-650 °C), the time is 1-3 h, and the gas pressure is 150-450 mTorr; the thickness of the prepared i-polysi layer 3 is 100-400 nm.

[0041] Step S3: Pattern-etch the i-polysi layer 3 with green picosecond laser. The green picosecond laser has high energy and can remove the i-polysi layer 3 and the tunneling SiOx layer 2 in the laser region 4, forming a laser region 4 where the back surface of the silicon wafer 1 is locally exposed; while the non-laser region 9 (such as Figure 5As shown, the non-laser area, i.e., the area where the i-polysi layer 3 on the back side is not etched by the green picosecond laser, is used for subsequent preparation of P+ polysilicon 31. The structure after being processed in step S3 is as Figure 2 shown.

[0042] It should be noted that when etching the highly doped P+ polysilicon 31 (with a doping concentration of 6e19 - 2e20 cm -3 ) by traditional green picosecond laser etching, the process parameters are as follows: the power of the green picosecond laser is greater than or equal to 100 W, the rate is 3000 - 7000 mm / s, the frequency is 500 - 1000 KHz, and the line spacing is 1 - 30 μm. In this way, only a part of the P+ polysilicon 31 can be barely etched away with such high - requirement process parameters. The highly doped P+ polysilicon 31 is difficult to be removed by wet etching, which is not conducive to actual production. If the thickness (or doping concentration) of the P+ polysi (P+ polysilicon 31) is reduced, it will increase the matching difficulty of preparing metal electrodes in the later metallization process, resulting in an increase in the contact resistivity between the metal electrode and the P+ polysilicon 31 with a low doping concentration. In addition, replacing the laser equipment with a higher power is costly.

[0043] In step S3 of the present invention, instead, the i-polysi layer 3 is pattern - etched using a green picosecond laser, and its process parameters include: the power of the green picosecond laser is greater than or equal to 40 W and less than 100 W (preferably 50 W - 70 W), the frequency is 500 - 1000 KHZ, the rate is 15000 - 20000 mm / s, and the line spacing is 0.2 - 0.5 mm. In this way, the present invention can easily etch away the i-polysi layer 3 and the tunneling SiOx layer 2 with the above - mentioned lower - requirement process parameters. Therefore, the present invention will neither reduce the doping concentration (or thickness) of the P+ polysilicon 31 prepared using the i-polysi layer 3 later, can reduce the contact resistivity, and is helpful for improving the battery efficiency; nor does it need to use a laser device with a higher power, which can save costs.

[0044] Step S4: Perform single - side pickling on the back side of the silicon wafer 1 processed in step S3 to remove the impurities in the laser area 4 and the oxide layer generated after laser etching. The i-polysi layer 3 in the non - laser area 9 does not react with the pickling solution (such as a mixed acid solution of HF solution and nitric acid solution), so the i-polysi layer 3 and the tunneling SiOx layer 2 in the non - laser area 9 still remain.

[0045] In step S4, a chain etcher is used to remove impurities in the laser region 4 and the oxide layer generated after laser etching. The pickling solution is preferably a mixed acid solution prepared by mixing HF solution (hydrofluoric acid) and nitric acid solution in a volume ratio of 1:3 - 1:5, where the concentration of the HF solution is 50 - 75 wt%, the concentration of the nitric acid solution is 55 - 65 wt%, and the tape speed for single-sided pickling is 2 - 5 m / min.

[0046] Step S5: Boron diffusion is performed on the silicon wafer 1 processed in step S4 so that the i - polysi layer 3 in the non - laser region 9 forms a P+ polysilicon 31, and a P+ emitter layer 5 is formed on the back of the silicon wafer 1 exposed in the laser region 4, and a BSG layer 6 (borosilicate glass layer) is formed on the back of both the P+ polysilicon 31 and the P+ emitter layer 5. The structure after being processed by step S5 is as Figure 3 shown.

[0047] During the boron diffusion process in step S5, a mixed gas of BCl3 and O2 is first introduced, the diffusion temperature is 820 - 910 °C, the diffusion time is 1000 - 3000 s, the gas flow rate of BCl3 is 55 - 450 sccm, and the gas flow rate of O2 is 550 - 4000 sccm; then N2 is introduced to enter the push - in stage, the push - in temperature is 930 - 960 °C, the push - in time is 1000 - 2000 s, and the gas flow rate of N2 is 3000 - 6000 sccm; then O2 is introduced to enter the oxidation stage, the oxidation temperature is 950 - 1050 °C, the oxidation time is 1000 - 3000 s, and the gas flow rate of O2 is 10000 - 30000 sccm. Among them, the thickness of the BSG layer 6 is 30 - 75 nm.

[0048] Step S6: Then, green - light picosecond laser is used to pattern - etch the laser region 4 to remove the BSG layer 6 and part of the P+ emitter layer 5 in the laser region 4, while the non - laser region 9 still has the BSG layer 6 and P+ polysilicon 31. The process parameters of step S6 are the same as those of step S3, so they will not be elaborated here.

[0049] Step S7: Then, alkali wet etching is performed on the silicon wafer 1 (this alkali wet etching can adopt an alkali polishing process that only passes through the alkali solution but not the acid solution) to etch and remove the remaining P+ emitter layer 5 in the laser region 4, while the non - laser region 9 is not etched due to the protection of the BSG layer 6 and the high doping concentration of the P+ polysilicon 31. The structure after being processed by step S7 is as Figure 4 shown. The process parameters of the alkali wet etching in step S7 refer to the alkali polishing in step S1, so they will not be elaborated here.

[0050] After being processed by the above steps S1 - S7, a notch 7 with a depth of 1.8 - 3.5 μm can be formed. Subsequently, N+ polysilicon can be deposited and prepared in the notch 7, thereby realizing the preparation of the TBC battery.

[0051] The following presents a specific embodiment of a laser-assisted etching and grooving method for preparing highly doped P+ polysilicon 31 of the present invention:

[0052] Example 1

[0053] A laser-assisted etching and grooving method for preparing highly doped P+ polysilicon 31 in this embodiment refers to Figures 1-5 , and specifically includes the following steps:

[0054] Step S1: Select an N-type single-crystal silicon wafer 1 with a resistivity of 1.2 Ω·cm, a sheet resistance of 85 Ω / □, a thickness of 130 μm, and a width of 182.2 mm * 183.7 mm. Perform double-sided alkaline polishing on the silicon wafer 1, place it in a polishing tank with an alkaline solution at 85°C for 3 minutes, with a polishing thickness of 3 μm and a weight loss of 0.52 g.

[0055] Step S2: Adopt the LPCVD method (low-pressure chemical vapor deposition method). First, deposit and grow a tunneling SiOx layer 2 on the back surface of the silicon wafer 1. The gas flow rate of O2 is 22000 sccm, the deposition reaction temperature is 620°C, and the time is 830 s; the thickness of the prepared tunneling SiOx layer 2 is 1.8 nm. Then, continue to deposit and prepare an i-polysi layer 3 on the back surface of the tunneling SiOx layer 2. The gas flow rate of SiH4 is 550 sccm, the deposition reaction temperature is 630°C, the time is 2.8 h, and the pressure is 370 mToor; the thickness of the prepared i-polysi layer 3 is 300 nm. The structure after being processed by step S2 is as Figure 1 shown.

[0056] Step S3: Use a green picosecond laser to pattern-etch the i-polysi layer 3. The power of the green picosecond laser is 50 W, the frequency is 500 KHz, the rate is 15000 mm / s, and the line spacing is 0.33 mm; in this way, the local i-polysi layer 3 and the tunneling SiOx layer 2 can be removed, forming a laser area 4 that locally exposes the back surface of the silicon wafer 1. The structure after being processed by step S3 is as Figure 2 shown.

[0057] Step S4: Perform single-sided pickling using a chain etching machine. The pickling solution is a mixed acid solution prepared by mixing HF solution and nitric acid solution in a volume ratio of 1:4, where the concentration of the HF solution is 55 wt% and the concentration of the nitric acid solution is 60 wt%. The tape speed of the single-sided pickling is 4 m / min; in this way, the impurities in the laser area 4 and the oxide layer generated after laser etching can be removed.

[0058] Step S5: Perform boron diffusion. First, introduce a mixed gas of BCl3 and O2. The diffusion temperature is 850 °C, the diffusion time is 2000 s, the gas flow rate of BCl3 is 75 sccm, and the gas flow rate of O2 is 3000 sccm. Then, introduce N2 to enter the push stage. The push temperature is 930 °C, the push time is 1400 s, and the gas flow rate of N2 is 5400 sccm. Then, introduce O2 to enter the oxidation stage. The oxidation temperature is 980 °C, the oxidation time is 2100 s, and the gas flow rate of O2 is 16000 sccm. In this way, after the oxidation stage, the i - polysi layer 3 in the non - laser region 9 can form P+ polysilicon 31, and a P+ emitter layer 5 can be formed on the back of the silicon wafer 1 exposed in the laser region 4. Moreover, a 58 - nm - thick BSG layer 6 is formed on the backs of both the P+ polysilicon 31 and the P+ emitter layer 5. The structure after being processed by Step S5 is as Figure 3 shown.

[0059] Step S6: Then, use green - light picosecond laser to pattern - etch the laser region 4. The process parameters of the green - light picosecond laser are the same as those in Step S3, and the line - spacing deviation between the green - light picosecond laser in Step S6 and the green - light picosecond laser in Step S3 is controlled within 30 μm. In this way, the BSG layer 6 and part of the P+ emitter layer 5 in the laser region 4 can be removed.

[0060] Step S7: Then, perform alkaline wet etching (an alkaline polishing process that only passes through the alkaline solution and not the acidic solution). The process parameters of the alkaline wet etching refer to the alkaline polishing process parameters in Step S1. In this way, the remaining P+ emitter layer 5 in the laser region 4 can be removed, while the non - laser region 9 is not etched due to the protection of the BSG layer 6 and the high doping concentration of the P+ polysilicon 31. The structure after being processed by Step S7 is as Figure 4 shown.

[0061] After being processed by the above Steps S1 - S7, the notch 7 can be formed. Subsequently, N+ polysilicon can be deposited and prepared in the notch 7, thereby realizing the preparation of the TBC battery.

[0062] Example 2

[0063] A laser - assisted etching and grooving method for preparing P+ polysilicon with a high doping concentration in this example. The specific steps all refer to Example 1. The difference between this example and Example 1 is that:

[0064] In Step S3 and Step S6 of this example, only the power of the green - light picosecond laser is changed to 40 W; other process parameters are the same as those in Example 1.

[0065] Example 3

[0066] A laser - assisted etching and grooving method for preparing P+ polysilicon with a high doping concentration in this example. The specific steps all refer to Example 1. The difference between this example and Example 1 is that:

[0067] In steps S3 and S6 of this embodiment, only the power of the green picosecond laser is changed to 60 W; other process parameters are the same as those in Embodiment 1.

[0068] Embodiment 4

[0069] A laser-assisted etching and grooving method for preparing highly doped P+ polysilicon in this embodiment, the specific steps of which all refer to Embodiment 1, and the difference between it and Embodiment 1 is that:

[0070] In steps S3 and S6 of this embodiment, only the power of the green picosecond laser is changed to 80 W; other process parameters are the same as those in Embodiment 1.

[0071] Embodiment 5

[0072] A laser-assisted etching and grooving method for preparing highly doped P+ polysilicon in this embodiment, the specific steps of which all refer to Embodiment 1, and the difference between it and Embodiment 1 is that:

[0073] In step S2 of this embodiment during the preparation of the i-polysi layer, after introducing SiH4, only the deposition reaction temperature is changed to 580 °C; other process parameters are the same as those in Embodiment 1.

[0074] Embodiment 6

[0075] A laser-assisted etching and grooving method for preparing highly doped P+ polysilicon in this embodiment, the specific steps of which all refer to Embodiment 1, and the difference between it and Embodiment 1 is that:

[0076] In step S2 of this embodiment during the preparation of the i-polysi layer, after introducing SiH4, only the deposition reaction temperature is changed to 620 °C; other process parameters are the same as those in Embodiment 1.

[0077] Embodiment 7

[0078] A laser-assisted etching and grooving method for preparing highly doped P+ polysilicon in this embodiment, the specific steps of which all refer to Embodiment 1, and the difference between it and Embodiment 1 is that:

[0079] In step S2 of this embodiment during the preparation of the i-polysi layer, after introducing SiH4, only the deposition reaction temperature is changed to 650 °C; other process parameters are the same as those in Embodiment 1.

[0080] Embodiment 8

[0081] A laser-assisted etching and grooving method for preparing highly doped P+ polysilicon in this embodiment, the specific steps of which all refer to Embodiment 1, and the difference between it and Embodiment 1 is that:

[0082] In step S2 of this embodiment, during the preparation of the i-polysi layer, after introducing SiH4, only the deposition reaction time is changed to 1.5 h; other process parameters are the same as those in Embodiment 1.

[0083] Embodiment 9

[0084] A laser-assisted etching and grooving method for preparing highly doped P+ polysilicon in this embodiment, the specific steps of which are all referred to Embodiment 1, and the difference between it and Embodiment 1 lies in:

[0085] In step S2 of this embodiment, during the preparation of the i-polysi layer, after introducing SiH4, only the deposition reaction time is changed to 2.5 h; other process parameters are the same as those in Embodiment 1.

[0086] Comparative Example 1

[0087] A laser-assisted etching and grooving method for preparing highly doped P+ polysilicon in this comparative example, the specific steps of which are all referred to Embodiment 1, and the difference between it and Embodiment 1 lies in:

[0088] In step S2 of this comparative example, during the preparation of the i-polysi layer, after introducing SiH4, only the deposition reaction time is changed to 3.5 h; other process parameters are the same as those in Embodiment 1.

[0089] Performance test

[0090] For convenient performance testing, first, Embodiments 1-9 and Comparative Example 1 are made into test samples as Figure 5 shown; then, the test samples of Embodiments 1-9 and Comparative Example 1 are respectively subjected to the following performance tests. The test results are shown in Tables 1-3 and Figures 6-7 shown.

[0091] Figure 5 In the test sample of , 8 is a square notch (corresponding to the laser area, referred to as Area 8 for short); 9 is the non-laser area (referred to as Area 9 for short); 10 is a linear notch (corresponding to the laser area, referred to as Area 10 for short), and its line width is 500 μm. Among them, the shapes of Area 8 and Area 10 are different only for the convenience of separately testing the sheet resistance and the grooving depth.

[0092] Table 1

[0093]

[0094] Combined with Table 1 and Figure 6 the data, it can be known that:

[0095] (1) In the test samples of Examples 1-4, the sheet resistance of Region 8 is basically the same as that of the original silicon wafer in Step S1, indicating that after the treatment of Steps S1-S7 in Examples 1-4, the i-polysi layer and the P+ emitter layer in Region 8 have been removed; moreover, the grooving depth in Region 10 is basically greater than the sum of the thicknesses of the tunneling SiOx layer and the P+ polysilicon, further demonstrating the feasibility of the grooving method of the present invention.

[0096] (2) In the test samples of Examples 1-4, the sheet resistance of Region 9 is about 180 Ω / □. Combining with the ECV data of Region 9 in Example 1 as shown in Figure 6 , it can be seen that after the treatment of Steps S1-S7, the doping concentration and thickness of the P+ polysilicon in Region 9 are relatively high. The doping concentration of the P+ polysilicon in Region 9 of Example 1 is 7e19 cm -3 .

[0097] (3) As the power of the green picosecond laser used in laser patterning etching gradually increases, the grooving depth in Region 10 of the test sample after Step S7 also increases.

[0098] However, it should be noted that if the power of the green picosecond laser used in laser patterning etching is too high (such as greater than 100 W), the grooving depth in Region 10 will be too deep (Region 10 is used for depositing and preparing N+ polysilicon later), resulting in inconsistent heights of the metal electrodes prepared by metallization of the P region and the N region later, increasing the screen printing difficulty of the metal pastes in the P region and the N region, and also having an adverse impact on the passivation effect, recombination and cell efficiency of the battery. If the power of the green picosecond laser used in laser patterning etching is too small (such as less than 40 W), the i-polysi layer in the laser region is not easily etched and removed completely. After boron diffusion, high-doping-concentration P+ polysilicon still remains in the laser region, affecting the effect of the second laser patterning etching and resulting in insufficient grooving depth in Region 10.

[0099] Table 2

[0100]

[0101] Table 3

[0102]

[0103] Combining Tables 2-3 and Figure 7 , it can be known that:

[0104] (4) During the process of preparing the i-polysi layer in step S2, if the temperature of the deposition reaction after introducing SiH4 is relatively high (as shown in Example 7), or especially if the time of the deposition reaction after introducing SiH4 is too long (as shown in Comparative Example 1), the doping concentration of the P+ polysilicon in area 9 of the test sample after the treatment in step S7 is relatively low, which is not conducive to reducing the contact resistivity between the metal electrode prepared by later metallization and the P+ polysilicon.

[0105] Therefore, during the process of preparing the i-polysi layer in step S2, the temperature and time of the deposition reaction after introducing SiH4 can be further adjusted (such as appropriately reducing the temperature of the deposition reaction after introducing SiH4, or appropriately reducing the time of the deposition reaction after introducing SiH4) to control the crystallization degree of the i-polysi layer and make its crystallization degree small. In this way, the grooving depth in area 10 in Table 2-3 is deeper, so the power requirement for the green light picosecond laser used for patterning etching can be further reduced, and the equipment cost can be further reduced. At the same time, since the crystallization degree of the i-polysi layer is small and there are relatively more defects in the i-polysi layer, it is more conducive to boron diffusion. As a result, the doping concentration of the P+ polysilicon formed after boron diffusion of the i-polysi layer in the non-laser area is higher (as Figure 7 shown), which can further increase the doping concentration of the P+ polysilicon and is conducive to further reducing the contact resistivity between the metal electrode prepared by later metallization and the P+ polysilicon.

[0106] In addition, it should be noted that during the process of preparing the i-polysi layer in step S2, if the temperature of the deposition reaction after introducing SiH4 is too low (such as lower than 580 °C), or the time of the deposition reaction after introducing SiH4 is too short (such as shorter than 1 h), there will be too many defects in the i-polysi layer, which is not conducive to the uniformity of boron diffusion.

[0107] Although the preferred embodiments of the embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the embodiments of the present invention.

[0108] The technical solutions provided by the present invention have been introduced in detail above. Specific examples are used in this article to elaborate on the principles and implementation manners of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A laser-assisted etching and grooving method for preparing P+ polysilicon with a high doping concentration, characterized in that, It includes the following steps: Step 1: Deposit and prepare a tunneling oxide layer and an intrinsic polysilicon layer on the back of the silicon wafer in sequence; Step 2: Use green picosecond laser to pattern-etch the intrinsic polysilicon layer to remove the intrinsic polysilicon layer and the tunneling oxide layer in the laser area, exposing the back of the silicon wafer in the laser area; Step 3: Perform single-sided pickling on the back of the silicon wafer to remove impurities in the laser area and the oxide layer generated by laser etching. The intrinsic polysilicon layer in the non-laser area is retained because it does not react with the pickling solution; Step 4, boron diffusion, to form P+ polysilicon with a doping concentration greater than 1e19 cm -3 in the intrinsic polysilicon layer of the non-laser region, while a P+ emitter layer is formed on the back of the silicon wafer exposed in the laser region, and a borosilicate glass layer is formed on the back of both the P+ polysilicon and the P+ emitter layer; Step 5: Then use green picosecond laser to pattern-etch the laser area to remove the borosilicate glass layer and part of the P+ emitter layer in the laser area; Step 6: Perform alkaline wet etching on the silicon wafer to etch away the remaining P+ emitter layer in the laser area to form a notch. The P+ polysilicon in the non-laser area is not etched due to the protection of the borosilicate glass layer.

2. A laser-assisted etching and grooving method for preparing P+ polysilicon with a high doping concentration according to claim 1, wherein In the above Step 1, the process conditions for depositing and preparing the tunneling oxide layer include: the gas flow rate of O2 is 12000 - 30000 sccm, the temperature of the deposition reaction is 500 - 700 °C, and the time is 500 - 2000 s; the thickness of the tunneling oxide layer is 1.5 - 6 nm; The process conditions for depositing and preparing the intrinsic polysilicon layer include: the gas flow rate of SiH4 is 400 - 1500 sccm, the temperature of the deposition reaction is 580 - 750 °C, the time is 1 - 3 h, and the air pressure is 150 - 450 mTorr; the thickness of the intrinsic polysilicon layer is 100 - 400 nm.

3. A laser-assisted etching and grooving method for preparing highly doped P+ polysilicon according to claim 2, characterized in that In the process of depositing and preparing the intrinsic polysilicon layer in Step 1: after introducing SiH4, the temperature of the deposition reaction is 580 - 650 °C, and the time is 1.5 - 2.8 h.

4. A laser-assisted etching and grooving method for preparing P+ polysilicon with a high doping concentration according to claim 1, characterized in that In the above Step 2 and Step 5, the process conditions for using green picosecond laser to pattern-etch the intrinsic polysilicon layer include: the power of the green picosecond laser is greater than or equal to 40 W and less than 100 W, the frequency is 500 - 1000 KHZ, the speed is 15000 - 20000 mm / s, and the line spacing is 0.2 - 0.5 mm.

5. A laser-assisted etching and grooving method for preparing high-doping-concentration P+ polysilicon according to claim 4, characterized in that, In the above Step 2 and Step 5, the power of the green picosecond laser is 50 - 70 W.

6. A laser-assisted etching and grooving method for preparing P+ polysilicon with a high doping concentration according to claim 1, characterized in that, In the above Step 3, the pickling solution is a mixed acid solution prepared by mixing HF solution and nitric acid solution according to a volume ratio of 1:3 - 1:

5. The concentration of the HF solution is 50 - 75 wt%, the concentration of the nitric acid solution is 55 - 65 wt%, and the tape speed of single-sided pickling is 2 - 5 m / min.

7. A laser-assisted etching and grooving method for preparing P+ polysilicon with a high doping concentration according to claim 1, characterized in that, In the step 4, during the boron diffusion process, a mixed gas of BCl3 and O2 is first introduced, the diffusion temperature is 820 - 910 °C, the diffusion time is 1000 - 3000 s, the gas flow rate of BCl3 is 55 - 450 sccm, and the gas flow rate of O2 is 550 - 4000 sccm; then N2 is introduced to enter the push stage, the push temperature is 930 - 960 °C, the push time is 1000 - 2000 s, and the gas flow rate of N2 is 3000 - 6000 sccm; then O2 is introduced to enter the oxidation stage, the oxidation temperature is 950 - 1050 °C, the oxidation time is 1000 - 3000 s, and the gas flow rate of O2 is 10000 - 30000 sccm; the thickness of the borosilicate glass layer is 30 - 75 nm.

8. A laser-assisted etching and grooving method for preparing P+ polysilicon with a high doping concentration according to claim 1, characterized in that, In the step 6, the process conditions of the alkaline wet etching include: using a polishing tank containing an alkaline solution to perform the alkaline wet etching on the silicon wafer, the temperature of the alkaline wet etching is 75 - 90 °C, and the time is 2 - 4 min.

9. A laser-assisted etching and grooving method for preparing P+ polysilicon with a high doping concentration according to claim 1, characterized in that Before the step 1, it further includes: performing double-sided alkaline polishing on the silicon wafer to remove impurities on the surface of the silicon wafer and form a flat morphology on the back surface of the silicon wafer.

10. Use of a laser-assisted etching and grooving method for preparing high-doping-concentration P+ polysilicon according to any one of claims 1-9, characterized in that, Apply the laser-assisted etching and grooving method for preparing high-doping-concentration P+ polysilicon to prepare a TBC battery.

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