A method of manufacturing a back contact solar cell using laser superposition exposure ablation

Abstract

The application relates to a back contact solar cell manufacturing method, which comprises the following steps: dividing a second main surface of a semiconductor substrate into a first semiconductor area and a second semiconductor area; sequentially forming a first conductive type film layer, a first insulating film layer and a laser absorption sacrifice layer on the second main surface of the semiconductor substrate; the laser absorption sacrifice layer comprises a silicon-based laser absorption film layer, a second insulating film layer and a protective film layer which are sequentially formed on the first insulating film layer; removing part of the film layer of the laser absorption sacrifice layer on the second semiconductor area by using a first laser to expose the second semiconductor area by using a laser exposure ablation process; sequentially removing the laser absorption sacrifice layer, the first insulating film layer and the first conductive type film layer remaining in the first laser exposure area by using a chemical etching process to form an opening of the second semiconductor area; and then performing chemical cleaning to expose the silicon-based laser absorption film layer of the first semiconductor area. The application aims to ensure production efficiency and prevent the problem of heterojunction film thermal decay.

Description

TECHNICAL FIELD

[0001] The application relates to a back contact solar cell manufacturing method adopting laser overlapping exposure ablation. BACKGROUND

[0002] Heterojunction solar cell technology has the characteristics of low surface recombination rate and high open circuit voltage, but surface mechanical damage and subsequent chemical corrosion affect the average electrical performance level of mass production. Therefore, the laser opening process is widely used in back contact solar cell technology to reduce efficiency damage and improve production efficiency. However, since the heterojunction itself is a low-temperature process (lower than 200 DEG C), the film layer is sensitive to the thermal effect of laser, and thermal decay effect is easy to occur. Therefore, under the premise of considering production efficiency and production quality, how to use laser to ablate the film layer is an important research topic for laser application in heterojunction solar cell production. SUMMARY

[0003] The application aims to provide a back contact solar cell manufacturing method adopting laser overlapping exposure ablation, which can ensure production efficiency and prevent thermal decay of the heterojunction film layer.

[0004] The application achieves the above-mentioned purpose by the following technical scheme:

[0005] A back contact solar cell manufacturing method adopting laser overlapping exposure ablation, a semiconductor substrate second main surface is divided into a first semiconductor region and a second semiconductor region; a first conductive type film layer, a first insulating film layer and a laser absorption sacrificial layer are sequentially formed on the semiconductor substrate second main surface; the laser absorption sacrificial layer comprises a silicon-based laser absorption film layer, a second insulating film layer and a protective film layer which are sequentially formed on the first insulating film layer; a laser exposure ablation process is used to remove part of the film layer of the laser absorption sacrificial layer on the second semiconductor region by using a first laser, and a chemical etching process is used to sequentially remove the laser absorption sacrificial layer, the first insulating film layer and the first conductive type film layer remaining in the first laser exposure area to form an opening of the second semiconductor region, and then chemical cleaning is performed to expose the silicon-based laser absorption film layer of the first semiconductor region.

[0006] Compared with the prior art, the application has the following advantages:

[0007] (1) The laser exposure ablation process and the chemical etching process are combined, the target film layer is selectively ablated by using the standing wave interference mechanism and the laser absorption sacrificial layer design, the thermal decay problem of the first conductive type film layer in the subsequent process due to high temperature is prevented, the semiconductor substrate in the first laser exposure area is prevented from being damaged by laser, and the production efficiency is effectively improved.

[0008] (2) The silicon-based adhesion-enhancing film layer, as an intermediate between the insulating film layer and other film layers, ensures the adhesion between the film layers and the firm combination of the film layers, and prevents delamination.

[0009] (3) The cooperation of the second insulating film layer and the protective film layer can mask the area where the silicon-based adhesion-enhancing film layer needs to be reserved in chemical corrosion, preventing the silicon-based adhesion-enhancing film layer from being damaged. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is a schematic sectional view of the process of opening the second semiconductor region after the first conductive type film layer, the first insulating film layer and the laser absorption sacrificial layer are made on the back surface of the silicon wafer in an embodiment of the present application. Figure 1a is a schematic sectional view formed after the first conductive type film layer, the first insulating film layer and the laser absorption sacrificial layer are made on the back surface of the silicon wafer. Figure 1b is a schematic sectional view formed after the protective film layer is removed in the first exposure area. Figure 1c is a schematic sectional view formed after the second insulating film layer, the amorphous silicon laser absorption layer and the silicon-based adhesion-enhancing film layer are further removed in the second exposure area. Figure 1d1 is a schematic sectional view of the first exposure area formed after the second insulating film layer in the first exposure area and part of the first insulating film layer in the second exposure area are removed using an acid etching solution containing fluoride ions. Figure 1d2 is a schematic sectional view of the second exposure area formed after the second insulating film layer in the first exposure area and part of the first insulating film layer in the second exposure area are removed using an acid etching solution containing fluoride ions. Figure 1e1 is a schematic sectional view of the first exposure area formed after the exposed amorphous silicon laser absorption layer and the silicon-based adhesion-enhancing film layer are removed using a weak alkaline solution. Figure 1e2 is a schematic sectional view of the second exposure area formed after the exposed amorphous silicon laser absorption layer and the silicon-based adhesion-enhancing film layer are removed using a weak alkaline solution. Figure 1f is a schematic sectional view formed after the exposed first insulating film layer is removed using an acid etching solution containing fluoride ions.

[0011] Figure 1g is a schematic sectional view formed after chemical etching and chemical cleaning are performed to remove the exposed first conductive type film layer, expose the silicon substrate and remove the protective film layer and the second insulating film layer remaining on the surface of the first conductive region.

[0012] Figure 2 is a schematic sectional view formed after the opening area of the second conductive region is formed and chemical cleaning is performed in an embodiment of the present application.

[0013] Figure 3This is a schematic cross-sectional view of a silicon wafer after a third intrinsic amorphous silicon layer, an amorphous film layer or an oxygen-containing microcrystalline film layer and a silicon nitride antireflection film layer are formed on the front side of the wafer using a PECVD device, and a second semiconductor film layer is formed on the back side of the wafer.

[0014] Figure 4 This is a schematic cross-sectional view formed after a portion of the second conductive film layer in the first conductive region is ablated using a laser ablation process, and the exposed insulating film layer is removed by a chemical etching process to expose the first conductive film layer and complete the opening of the first conductive region.

[0015] Figure 5 This is a schematic cross-sectional view of the conductive film layer and electrode formed in one embodiment of the present invention.

[0016] Figure 6 Is Figure 1a The image shows a silicon wafer with a 355nm wavelength laser incident on its back side. The resulting laser standing wave has an E0 at the location of each film layer. 2 Distribution diagram of (square value of electric field strength).

[0017] Figure 7 Is Figure 1b The image shows a silicon wafer with a 355nm wavelength laser incident on its back side. The resulting laser standing wave has an E0 at the location of each film layer. 2 Distribution diagram of (square value of electric field strength).

[0018] Figure 8a to Figure 8c yes Figure 1b The top view shows the film state after scanning with different laser beam spots during the laser exposure ablation process. The shaded areas in laser spot 24 represent overlapping areas. Figure 8a In the process, the laser spot is nearly circular, with adjacent spots partially overlapping, while the next adjacent spots do not overlap; Figure 8b In the process, the laser spot is nearly square, with adjacent spots partially overlapping, while the next adjacent spots do not overlap. Figure 8c In the process, the laser spot is a crystalline square. The first column of scanning spots does not overlap, and the second column of retrace spots does not overlap in the direction of the moving trajectory, but the first column of spots and the second column of spots partially overlap. Detailed Implementation

[0019] A back contact solar cell manufacturing method using laser overlapping exposure ablation, a semiconductor substrate second main surface is divided into a first semiconductor region and a second semiconductor region; a first conductive type film layer, a first insulating film layer and a laser absorption sacrificial layer are sequentially formed on the semiconductor substrate second main surface; the laser absorption sacrificial layer comprises a silicon-based laser absorption film layer, a second insulating film layer and a protective film layer sequentially formed on the first insulating film layer; a part of the film layer of the laser absorption sacrificial layer on the second semiconductor region is removed by a first laser using a laser exposure ablation process, and the remaining laser absorption sacrificial layer, the first insulating film layer and the first conductive type film layer in the first laser exposure area are sequentially removed by a chemical etching process to form an opening of the second semiconductor region, and then chemical cleaning is performed to expose the silicon-based laser absorption film layer of the first semiconductor region.

[0020] The first laser is a laser with a wavelength of 354-356 nm formed by a laser.

[0021] The first laser is a laser obtained by tripling a yttrium aluminum garnet laser.

[0022] The laser exposure ablation process is to expose the film layer on the second semiconductor region more than twice by the first laser, the overlapping area is exposed twice, and the remaining exposure area is exposed only once; or the laser exposure ablation process is to expose the film layer on the second semiconductor region once by the first laser, the adjacent exposure spots partially overlap, the next adjacent exposure spots do not overlap, the overlapping part is exposed twice, and the non-overlapping part is exposed only once.

[0023] The first conductive type film layer is an N-type semiconductor film layer, and the second conductive type film layer is a P-type semiconductor film layer.

[0024] After forming the opening of the second semiconductor region, a second conductive type film layer is deposited on the semiconductor substrate second main surface; a laser non-continuous ablation process is used to remove the film layer covering the internal partial area of the first semiconductor region and located on the first insulating film layer, and a chemical etching process is used to remove the exposed first insulating film layer; the laser non-continuous ablation process is to expose the film layer on the internal partial area of the first semiconductor region by the second laser, the exposure spots do not overlap, and there is a gap between the adjacent exposure spots in part or all of the exposure spots.

[0025] The second laser is a laser with a wavelength of 531-533 nm formed by a laser.

[0026] The second laser is a pulsed laser with a pulse width of less than 20 nanoseconds.

[0027] The second laser is a laser obtained by doubling a yttrium aluminum garnet laser.

[0028] The first conductive type film layer is an N-type semiconductor film layer; and the second conductive type film layer is a P-type semiconductor film layer.

[0029] The preparation method of the laser absorption sacrifice layer is as follows: forming an amorphous silicon laser absorption layer on the first insulating film layer, forming a second insulating film layer on the amorphous silicon laser absorption layer, and forming a protective film layer on the second insulating film layer.

[0030] Before forming the amorphous silicon laser absorption layer, a silicon-based adhesion-enhancing layer is formed on the first insulating film layer by using a high-power density deposition process (generally, PECVD or PVD process is used for high-power density deposition).

[0031] The amorphous silicon laser absorption layer is prepared by using a plasma enhanced chemical vapor deposition method.

[0032] The protective film layer is prepared by using a plasma enhanced chemical vapor deposition method to deposit a microcrystalline cover layer or an amorphous cover layer on the second insulating film layer.

[0033] The content of the present application will be described in detail below in combination with the drawings and examples of the present application:

[0034] As Figure 1 FIG. 8 shows an embodiment of a back contact solar cell manufacturing method using laser overlapping exposure ablation according to the present application.

[0035] A Czochralski or ingot single crystal ingot is cut by a diamond wire or slurry to form a silicon wafer 00 with a thickness of 100-250 microns. Although the single crystal ratio of the ingot single crystal is higher, there are still a large proportion of polycrystalline grain boundaries and lattice defects in the cell. If the substrate used is an ingot single crystal silicon wafer, it needs to be pretreated at different temperature stages before being introduced into the heterojunction production process to achieve the effect of gettering and saturation of dangling bonds. The pretreated silicon wafer is first subjected to tank solution pre-cleaning to remove surface organic contamination and large particles. Then, it is damaged and textured with alkali solution to form a roughened light-trapping structure, and then subjected to RCA cleaning (or a solution formula equivalent to RCA cleaning), and finally, HF solution to remove the surface oxide layer, deionized water cleaning and surface drying process. In the process flow, the structure of front surface texturing and back surface polishing can be formed by first double-sided texturing and then single-sided alkali polishing, or by single-sided plating of an anti-alkali etching film on the surface of a double-sided polished silicon wafer and then texturing.

[0036] After solution cleaning, the first conductive type film layer, i.e. the surface passivation film layer (non-doped type) (e.g. the first intrinsic amorphous silicon layer 11) and the doped film layer (e.g. the N-type semiconductor film layer 12) are prepared by PECVD equipment. The PECVD equipment power source uses 13.56 MHz, 26 MHz or 40 MHz, preferably 13.56 MHz. The process gas for the first intrinsic amorphous silicon layer 11 includes all or several combinations of silane (SiH4), hydrogen (H2), carbon dioxide (CO2) and methane (CH4). The process gas for the preparation of the N-type semiconductor film layer 12 includes all or several combinations of silane (SiH4), hydrogen (H2), carbon dioxide (CO2) and phosphine (PH3). In order to improve the selectivity ratio of laser ablation (effective laser absorption ratio of the film layer to be ablated and the underlying functional layer to be protected), the N-type semiconductor film layer 12 can use an oxygen-containing microcrystalline film layer, which includes three stages of processes: (1) the first is a non-oxygen-containing incubation layer with a high H2 / SiH4 ratio, which aims to promote the formation of microcrystalline state; (2) an oxygen-containing microcrystalline layer, which includes an oxygen-containing microcrystalline μc-SiO x :H(N) with a film formation speed controlled at 0.2-2 angstroms / second, preferably at 0.6-0.8 angstroms / second; the thickness of the oxygen-containing microcrystalline μc-SiO x :H(N) on the film formation surface is 40-200 angstroms, preferably 60-120 angstroms; (3) a non-oxygen-containing contact layer, which aims to reduce the contact resistance between the TCO film layer.

[0037] Between the first conductive type film layer (11, 12) and the second conductive type film layer (26, 27) is an insulating film layer deposited by PECVD to prevent leakage of the device. The insulating film layer 14 is all or several combinations of silicon nitride, silicon dioxide, silicon oxide, silicon oxynitride. In order to achieve the requirements of the laser overlapping exposure ablation, an additional laser absorption sacrificial layer is required, which includes a silicon-based adhesion enhancement layer 15 with silicon as the main component to enhance adhesion, an amorphous silicon optical absorption layer 16 (i.e. an amorphous silicon laser absorption layer), a second insulating film layer 18, a P-type doped semiconductor layer 19 (i.e. a protective film layer) on the top layer. Figure 1a A cross-sectional view showing the completion of the deposition of the above-mentioned film layers is shown. A pulsed light source with a wavelength of 355 nm is used, as shown in Figure 6 Due to the optical interference maximum design near the topmost layer, after the first exposure, only the P-type doped semiconductor layer 19 is removed, and then the same source of pulsed laser is used, as shown in Figure 7 The interference effect of the remaining film layers ensures that the energy absorbed near the silicon-based adhesion enhancement layer 15 and the amorphous silicon optical absorption layer 16 is maximum, and the silicon-based adhesion enhancement layer 15 and the amorphous silicon optical absorption layer 16 are correspondingly removed. After the above-mentioned process steps, a cross-sectional structure as shown in Figure 1c is formed. Subsequently, an acidic solution containing fluoride ions is applied for etching, forming a cross-sectional structure as shown inFigure 1d1 and Figure 1d2 The structure is shown. By designing the optical film layer or fine-tuning the coating process, the etching time of the second insulating film layer 18 is made shorter than that of the first insulating film layer 14. A weakly alkaline solution can selectively remove the silicon-based reinforcing adhesion layer 15 and the amorphous silicon optical absorption layer 16 without affecting the first insulating film layer 14 and the top p-type doped semiconductor layer 19 (e.g., Figure 1e1 and Figure 1e2 (As shown). Further corrosion with an acidic solution containing fluoride ions results in a formation as shown. Figure 1f The structure is shown. The purpose of the openings is to remove the exposed first conductive films (11, 12), so that in subsequent processes (in one embodiment, the exposed first conductive films 11, 12 and the p-type doped semiconductor layer 19 are removed using an alkaline solution, followed by chemical cleaning before depositing the second conductive film to remove the second insulating film 18), the desired result can be achieved. Figure 1g The structure shown forms a P-type electrode opening region (i.e., the second conductive region, the region where the second conductive film layer contacts the silicon wafer) on the back of the battery. Figure 2 As shown), in the secondary coating, a second conductive film layer (26, 27) is used instead.

[0038] The table below shows the results of applying silicon nitride with the first insulating layer 14 being 50 nm and the second insulating layer 18 being 30 nm. Figure 1a The absorption of the first conductive film layer (11 and 12), the amorphous silicon optical absorption layer 16, and the topmost capping layer when a 355nm wavelength laser is incident on the back of the battery cell is shown.

[0039]

[0040] The table below shows the results for the first insulating layer being 50 nm silicon nitride. Figure 1b The back of the battery cell is illuminated by a 355nm wavelength laser. The optical absorption of the first conductive film layer (11+12), the silicon-based reinforced adhesion layer 15, and the amorphous silicon optical absorption layer 16 caused by the pulsed laser, as well as their relative selectivity, are shown. The higher the selectivity, the easier it is to remove the upper layer without damaging the lattice structure near the substrate surface.

[0041]

[0042] After chemical cleaning, the back surface of the silicon wafer is deposited with a second conductive film layer (second intrinsic amorphous silicon layer 26 and P-type semiconductor film layer 27) by PECVD, which includes RCA1 and RCA2 cleaning, removal of intrinsic oxide layer with low-concentration hydrofluoric acid, slow pulling with deionized water, etc. The power supply of the PECVD equipment uses 13.56 MHz, 26 MHz or 40 MHz, preferably 13.56 MHz. The process gas for the second intrinsic amorphous silicon layer 26 includes all or several combinations of silane (SiH4), hydrogen (H2), carbon dioxide (CO2) and methane (CH4). The process gas for preparing the P-type semiconductor film layer 27 includes all or several combinations of silane (SiH4), hydrogen (H2), carbon dioxide (CO2) and diborane (B2H6) or TMB. As shown in Figure 3 The front surface of the silicon wafer 00 is coated in the order of the third intrinsic amorphous silicon layer 21, the amorphous film layer or oxygen-containing microcrystalline film layer 22 and the silicon nitride anti-reflection film layer 23. The process gas for the third intrinsic amorphous silicon layer 26 on the front surface (light-receiving surface) includes all or several combinations of silane (SiH4), hydrogen (H2), carbon dioxide (CO2) and methane (CH4).

[0043] As shown in Figure 4 The second conductive film layer (26, 27), the amorphous silicon optical absorption layer 16 and the silicon-based adhesion-enhancing layer 15 in the first conductive region are removed by laser ablation, and then the exposed first insulating film layer 14 is removed by chemical etching with hydrofluoric acid to form the N-type electrode opening region 28. The laser for opening is spatially shaped into a flat-top laser to ensure uniform energy in the processing region. The laser for opening is a pulsed laser, preferably a green laser with a pulse width of less than 100 picoseconds. To avoid the decrease in power generation efficiency caused by laser damage, the N-type electrode opening region 28 is formed by non-continuous ablation of laser processing spots (i.e., using a laser non-continuous ablation process).

[0044] As shown in Figure 5 After the laser opening process, a conductive film layer and an electrode are prepared by PVD magnetron sputtering.

[0045] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for manufacturing a back-contact solar cell using laser exposure ablation, characterized in that: The second main surface of the semiconductor substrate is divided into a first semiconductor region and a second semiconductor region. A first conductive film layer, a first insulating film layer, and a laser-absorbing sacrificial stack are sequentially formed on the second main surface of a semiconductor substrate. The first conductive film layer includes intrinsic amorphous silicon and a doped semiconductor layer. The laser-absorbing sacrificial stack includes a silicon-based laser-absorbing film layer, a second insulating film layer, and a protective film layer sequentially formed on the first insulating film layer. A laser exposure ablation process is used to remove part of the laser-absorbing sacrificial stack layer on the second semiconductor region using a first laser. A chemical etching process is used to sequentially remove the remaining laser-absorbing sacrificial stack layer, the first insulating film layer, and the first conductive film layer in the first laser-exposed area to form an opening in the second semiconductor region. Then, chemical cleaning is performed to expose the silicon-based laser-absorbing film layer in the first semiconductor region. The laser exposure ablation process includes a single exposure area and a double exposure area. The single exposure area only removes the protective film layer, while the double exposure area removes all layers above the first insulating film layer, thereby exposing the first insulating film layer.

2. The method for manufacturing a back-contact solar cell using laser exposure ablation according to claim 1, characterized in that: The first laser is a laser with a wavelength of 354-356nm generated by a laser.

3. The method for manufacturing a back-contact solar cell using laser exposure ablation according to claim 2, characterized in that: The first laser is a laser obtained by third harmonicization of a yttrium aluminum garnet laser.

4. The method for manufacturing a back-contact solar cell using laser exposure ablation according to claim 1, characterized in that: The laser exposure ablation process involves using a first laser to expose the film layer on the second semiconductor region in two or more rounds, with some exposed areas receiving two exposures and the remaining exposed areas receiving only one exposure; or, the laser exposure ablation process involves using a first laser to expose the film layer on the second semiconductor region in one round, with adjacent exposure spots partially overlapping and the next adjacent exposure spots not overlapping, the overlapping parts receiving two exposures and the non-overlapping parts receiving only one exposure.

5. The method for manufacturing a back-contact solar cell using laser exposure ablation according to claim 1, characterized in that: After forming the opening of the second semiconductor region, a second conductive film layer is deposited on the second main surface of the semiconductor substrate; a laser discontinuous ablation process is used to remove the film layer covering a portion of the first semiconductor region and located on the first insulating film layer, and a chemical etching process is used to remove the exposed first insulating film layer; the laser discontinuous ablation process involves using a second laser to expose the film layer on a portion of the first semiconductor region, with the exposure spots not overlapping, and gaps left between adjacent exposure spots in some or all of the exposure spots.

6. The method for manufacturing a back-contact solar cell using laser exposure ablation according to claim 5, characterized in that: The first conductive film is an N-type semiconductor film, and the second conductive film is a P-type semiconductor film.

7. The method for manufacturing a back-contact solar cell using laser exposure ablation according to claim 5, characterized in that: The second laser is a laser with a wavelength of 531-533nm generated by a laser.

8. The method for manufacturing a back-contact solar cell using laser exposure ablation according to claim 7, characterized in that: The second laser is a pulsed laser with a pulse width of less than 20 nanoseconds.

9. The method for manufacturing a back-contact solar cell using laser exposure ablation according to claim 5, characterized in that: The second laser is a laser obtained by frequency doubling of a yttrium aluminum garnet laser.

10. The method for manufacturing a back-contact solar cell using laser exposure ablation according to any one of claims 1-9, characterized in that: The method for preparing the silicon-based laser absorption film is to form an amorphous silicon laser absorption layer on a first insulating film layer.

11. The method for manufacturing a back-contact solar cell using laser exposure ablation according to claim 10, characterized in that: Before forming the amorphous silicon laser absorption layer, a silicon-based reinforcement adhesion layer is formed on the first insulating film layer using a high power density deposition process.

12. The method for manufacturing a back-contact solar cell using laser exposure ablation according to claim 10, characterized in that: The amorphous silicon laser absorption layer is fabricated by depositing an amorphous silicon layer using plasma-enhanced chemical vapor deposition.

13. The method for manufacturing a back-contact solar cell using laser exposure ablation according to claim 10, characterized in that: The protective film is fabricated by depositing a P-type doped microcrystalline capping layer or a P-type doped amorphous capping layer on the second insulating film layer using plasma-enhanced chemical vapor deposition.

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