CN117423774A - Selective boron doping diffusion method for solar cell - Google Patents
Selective boron doping diffusion method for solar cell Download PDFInfo
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- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 title claims abstract description 134
- 229910052796 boron Inorganic materials 0.000 title claims abstract description 134
- 238000009792 diffusion process Methods 0.000 title claims abstract description 85
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 92
- 239000010703 silicon Substances 0.000 claims abstract description 92
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 91
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims abstract description 38
- 238000000034 method Methods 0.000 claims abstract description 38
- 229910021417 amorphous silicon Inorganic materials 0.000 claims abstract description 28
- 238000011282 treatment Methods 0.000 claims abstract description 20
- 229910052757 nitrogen Inorganic materials 0.000 claims abstract description 18
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 14
- 239000001301 oxygen Substances 0.000 claims abstract description 14
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 14
- 238000006243 chemical reaction Methods 0.000 claims abstract description 13
- 238000004050 hot filament vapor deposition Methods 0.000 claims abstract description 10
- 238000000151 deposition Methods 0.000 claims abstract description 9
- BLRPTPMANUNPDV-UHFFFAOYSA-N Silane Chemical compound [SiH4] BLRPTPMANUNPDV-UHFFFAOYSA-N 0.000 claims abstract description 8
- 239000001257 hydrogen Substances 0.000 claims abstract description 8
- 229910052739 hydrogen Inorganic materials 0.000 claims abstract description 8
- 229910000077 silane Inorganic materials 0.000 claims abstract description 8
- 238000007599 discharging Methods 0.000 claims abstract description 7
- 125000004435 hydrogen atom Chemical class [H]* 0.000 claims abstract 2
- 230000003647 oxidation Effects 0.000 claims description 8
- 238000007254 oxidation reaction Methods 0.000 claims description 8
- 230000001590 oxidative effect Effects 0.000 claims description 8
- 238000007664 blowing Methods 0.000 claims description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 abstract description 34
- 239000010453 quartz Substances 0.000 abstract description 10
- 238000010926 purge Methods 0.000 abstract description 8
- 238000004804 winding Methods 0.000 abstract description 8
- 239000006227 byproduct Substances 0.000 abstract description 6
- 150000002500 ions Chemical class 0.000 abstract description 5
- 235000012431 wafers Nutrition 0.000 description 57
- 230000000052 comparative effect Effects 0.000 description 21
- 238000010438 heat treatment Methods 0.000 description 16
- 238000004519 manufacturing process Methods 0.000 description 12
- 229910052814 silicon oxide Inorganic materials 0.000 description 12
- 235000012239 silicon dioxide Nutrition 0.000 description 11
- 239000000463 material Substances 0.000 description 7
- 239000003153 chemical reaction reagent Substances 0.000 description 6
- 239000000377 silicon dioxide Substances 0.000 description 6
- 239000000758 substrate Substances 0.000 description 6
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 5
- 229910021419 crystalline silicon Inorganic materials 0.000 description 5
- 230000008439 repair process Effects 0.000 description 5
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- 239000002184 metal Substances 0.000 description 3
- 239000007787 solid Substances 0.000 description 3
- FAQYAMRNWDIXMY-UHFFFAOYSA-N trichloroborane Chemical compound ClB(Cl)Cl FAQYAMRNWDIXMY-UHFFFAOYSA-N 0.000 description 3
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- 238000000137 annealing Methods 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 229910001873 dinitrogen Inorganic materials 0.000 description 2
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- 238000005516 engineering process Methods 0.000 description 2
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- 230000002035 prolonged effect Effects 0.000 description 2
- 239000002253 acid Substances 0.000 description 1
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- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
- H01L31/1804—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof comprising only elements of Group IV of the Periodic Table
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- H—ELECTRICITY
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/22—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities
- H01L21/225—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities using diffusion into or out of a solid from or into a solid phase, e.g. a doped oxide layer
- H01L21/2251—Diffusion into or out of group IV semiconductors
- H01L21/2252—Diffusion into or out of group IV semiconductors using predeposition of impurities into the semiconductor surface, e.g. from a gaseous phase
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- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/22—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities
- H01L21/225—Diffusion of impurity materials, e.g. doping materials, electrode materials, into or out of a semiconductor body, or between semiconductor regions; Interactions between two or more impurities; Redistribution of impurities using diffusion into or out of a solid from or into a solid phase, e.g. a doped oxide layer
- H01L21/2251—Diffusion into or out of group IV semiconductors
- H01L21/2254—Diffusion into or out of group IV semiconductors from or through or into an applied layer, e.g. photoresist, nitrides
- H01L21/2257—Diffusion into or out of group IV semiconductors from or through or into an applied layer, e.g. photoresist, nitrides the applied layer being silicon or silicide or SIPOS, e.g. polysilicon, porous silicon
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Abstract
The invention provides a selective boron doping diffusion method of a solar cell, which comprises the following steps: (1) Placing a silicon wafer in a reaction chamber of hot wire chemical vapor deposition equipment, vacuumizing, introducing silane, diborane and hydrogen, depositing a boron-doped amorphous silicon layer with the thickness of 10-30 nm, and discharging the silicon wafer from the chamber; (2) performing laser selective heavy doping treatment; (3) Placing the silicon wafer in a boron diffusion furnace tube, vacuumizing, and introducing nitrogen to perform oxygen-free boron diffusion; (4) Vacuumizing, purging with nitrogen, and introducing oxygen to oxidize and push the silicon wafer to finish the selective boron doping diffusion of the silicon wafer. The boron-doped amorphous silicon is adopted, so that ions can be diffused to a larger depth by adopting lower laser power in the selective heavy doping of laser; the boron-doped amorphous silicon layer is prepared by adopting a hot wire chemical vapor deposition method, so that the phenomenon of winding and expanding does not occur; adopts an oxygen-free boron source, and has no B in the whole process 2 O 3 Byproducts are generated, and the quartz piece is not damaged.
Description
Technical Field
The invention relates to the technical field of solar cells, in particular to a selective boron doping diffusion method for a solar cell.
Background
Solar energy is a clean, efficient and inexhaustible new energy source. The photovoltaic power generation has the advantages of safety, reliability, environmental protection, no pollution and the like. At present, silicon solar cells occupy an important place in the photovoltaic field because silicon materials have extremely abundant reserves in the crust, while silicon solar cells have excellent electrical and mechanical properties compared to other types of solar cells.
Boron diffusion doping is critical to achieving high conversion efficiency of a solar cell during the fabrication of a silicon solar cell. At present, the boron diffusion of the mass-produced silicon solar cell adopts a uniform junction process with a low-concentration shallow junction structure. The low concentration shallow junction structure can present new challenges to the metal electrode paste, low concentration doping can easily cause poor contact resistance, high series resistance of the battery and low fill factor FF. Meanwhile, shallow junction diffusion is easy to increase the probability of electrode metal penetrating into a PN junction region, so that the conversion efficiency of the battery is reduced.
In order to obtain higher cell conversion efficiency, a selective doping boron diffusion technology is inoculated. The low-concentration shallow junction is adopted in the non-metal contact area, the high-concentration deep junction is adopted in the metal contact area, the series resistance of the battery is reduced while the open-circuit voltage and the short-circuit current of the battery are improved, and the filling factor of the battery is improved, so that the conversion efficiency of the battery is effectively improved.
At present, the selective doped boron diffusion is mainly carried out by adopting the traditional CVD boron diffusion mode, namely, the deposition mode is that a proper amount of boron chloride and oxygen are introduced into a high-temperature quartz furnace tube, and the boron chloride and the oxygen react chemically to generate B 2 O 3 And a layer of boron doped silicon oxide (BSG) is formed on the silicon surface, and then boron is diffused into the silicon surface by high temperature nitrogen gas to a certain depth. After the boron source is deposited, carrying out laser selective heavy doping treatment on the crystalline silicon battery piece, then putting the crystalline silicon battery piece into a high-temperature oxidation furnace tube to carry out high-temperature push junction to push boron deeper into silicon, and repairing lattice damage of a silicon substrate generated by laser treatment by utilizing high temperature.
The above-mentioned selective boron-doped diffusion process has at least the following drawbacks:
(1) The CVD reaction occurring in the boron diffusion mode is isotropic, i.e.: the boron source is deposited at the position of the battery piece which needs to be exposed, and boron diffusion occurs at the subsequent high temperature, in order to remove the winding and expanding of the non-diffusion surface, the non-diffusion surface is required to be subjected to alkaline washing/acid washing in a subsequent cleaning process to etch the silicon wafer with a certain thickness so as to achieve the purpose of winding and expanding removal, and the chemical consumption and the silicon wafer cost are increased in the winding and expanding removal process;
(2) The pyramid structure of the crystalline silicon can be damaged by high-temperature oxidation in the high-temperature junction pushing process of the aerobic boron source, so that the reflectivity of the crystalline silicon is increased, and the light absorption capacity of the crystalline silicon is reduced;
(3) The source of oxygen-containing boron causes a large amount of B to be produced in the process 2 O 3 The byproducts have strong corrosiveness on quartz devices (such as a diffusion cavity quartz tube, a silicon wafer carrier quartz boat, a quartz furnace door and the like), and the service life is reduced (3-6 months);
(4) Boron doped silicon oxide (BSG) is used as a selective boron source dopant material because the solid solubility of boron in silicon dioxide is higher than that in silicon, so that if boron in silicon dioxide is to be diffused into silicon, a high laser energy is required and too high laser energy will destroy the lattice structure of the silicon substrate. In order to repair the lattice structure damaged by laser, a long-time high-temperature repair process is needed after the selective heavy doping treatment of the laser, the production efficiency is low, the energy consumption is high, the service life of key components of a machine is reduced, and the maintenance cost is increased.
The invention discloses a selective laser doping method and a device of a solar cell, wherein the publication number of the selective laser doping method and the device is CN116598375A, and the selective laser doping is carried out in liquid, namely doping source solution, so that the PSG/BSG deposition step is not required to be added, the integral diffusion time of a diffusion sheet can be shortened, the production efficiency is improved, and the doping source is saved, namely the production cost is saved; the laser acts on the surface of the silicon chip through the solution, so that the damage of the laser thermal effect can be further reduced. However, the process conditions of the invention are more severe, the doping source solution needs to ensure a certain content of doping source on one hand, and provides enough doping source for laser SE, and on the other hand, the doping solution needs to keep rheological property, ensure continuous circulation of liquid and maintain the uniformity and stability of the doping source concentration of the surface solution; in addition, the doping source solution also needs to have a certain transmittance of a wavelength band selected by laser during doping, so that the laser can be ensured to effectively act on the surface of the silicon wafer, and the controllability of the doping effect is poor.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, an object of the present invention is to provide a method for selectively doping boron in a solar cell, which is used to solve the problems that the existing selective doping boron diffusion process based on an aerobic boron source is easy to generate a coiling and expanding layer, which needs to consume a large amount of chemical reagent to remove a non-diffusion surface, the required laser energy is too high, the lattice structure of a silicon substrate is damaged, and a large amount of B is generated 2 O 3 And the by-product corrodes the quartz device.
To achieve the above and other related objects, the present invention is achieved by including the following technical means.
The invention provides a selective boron doping diffusion method for a solar cell, which comprises the following steps:
step (1): placing a silicon wafer in a reaction chamber of hot wire chemical vapor deposition equipment, vacuumizing, introducing silane, diborane and hydrogen, depositing a boron-doped amorphous silicon layer on one surface of the silicon wafer, and discharging the silicon wafer from the chamber; the thickness of the boron-doped amorphous silicon layer is 10-30 nm;
step (2): carrying out laser selective heavy doping treatment on the surface of the silicon wafer which is treated in the step (1) and is deposited with the boron-doped amorphous silicon layer;
step (3): placing the silicon wafer treated in the step (2) in a boron diffusion furnace tube, vacuumizing, and introducing nitrogen to perform oxygen-free boron diffusion;
step (4): and (3) vacuumizing the boron diffusion furnace tube, blowing nitrogen, introducing oxygen, and oxidizing and pushing the silicon wafer treated in the step (3) to finish the selective boron doping diffusion of the silicon wafer.
The invention creatively adopts the boron-doped amorphous silicon layer with the same property as silicon to replace the traditional boron-doped silicon oxide (BSG) as the selective boron source doping material, the amorphous silicon and the silicon have no solid solubility difference, and boron is easier to diffuse into the silicon under the driving of boron concentration gradient, so the boron-doped amorphous silicon has higher ion diffusion speed relative to the boron-doped silicon oxide (BSG), on one hand, the boron-doped amorphous silicon can be adopted in the laser selective heavy dopingIons can be diffused to a larger depth by low laser power, so that the lattice damage of laser to a silicon substrate is reduced, the repair time of subsequent high-temperature annealing is reduced, the energy consumption of battery manufacturing is reduced, and the equipment cost is reduced; on the other hand, the time of the boron diffusion process can be shortened, and the mass production efficiency can be improved. The boron-doped amorphous silicon layer is prepared by adopting a hot wire chemical vapor deposition method, a winding and expanding phenomenon can not occur, a large amount of chemical reagent is not consumed for etching and removing the winding and expanding layer process, the dosage of the chemical reagent is reduced, and the wet process cost is reduced. Adopts an oxygen-free boron source, and has no B in the whole process 2 O 3 The byproduct is generated, so that the quartz piece is not damaged, the equipment maintenance cost is reduced, and the service cycle of the equipment is prolonged.
Preferably, in the step (2), the laser selective heavy doping treatment uses a green laser.
More preferably, the pulse width of the green laser is 500 ps-2 ns, and the scanning speed is 15000-35000 m/s.
Preferably, in the step (3), the oxygen-free boron diffusion pressure is 300-500 mbar, the temperature is 900-930 ℃ and the time is 50-150 s.
Preferably, in the step (4), the pressure of the oxidation pushing junction is 600-820mbar, the temperature is 1000-1050 ℃ and the time is 40-80 min.
As described above, the solar cell selective boron doping diffusion method of the present invention has the following beneficial effects:
(1) The boron-doped amorphous silicon layer is prepared by adopting a hot wire chemical vapor deposition method, so that a winding and expanding phenomenon does not occur, a large amount of chemical reagent is not consumed, the winding and expanding layer removing process is not needed, the dosage of chemical reagent is reduced, and the wet process cost is reduced;
(2) The boron-doped amorphous silicon layer is adopted as a selective boron source doping material, so that the transmittance of green laser is low, advanced high-temperature oxygen-free boron diffusion is not needed, laser selective heavy doping treatment can be directly carried out before the boron-doped amorphous silicon layer enters a boron diffusion furnace tube, continuous production can be realized by oxygen-free boron diffusion and oxidation push-out, the boron diffusion process is not needed to be interrupted, the situation that a silicon wafer is polluted due to repeated cavity outlet and cavity inlet is avoided, and mass production is more facilitated;
(3) The boron-doped amorphous silicon layer with the same property as silicon is adopted to replace the traditional boron-doped silicon oxide (BSG) as a selective boron source doping material, the amorphous silicon and silicon have no solid solubility difference, boron is easier to diffuse into the silicon under the driving of boron concentration gradient, so that the boron-doped amorphous silicon has higher ion diffusion speed relative to the boron-doped silicon oxide (BSG), on one hand, ions can be diffused to a larger depth by adopting lower laser power in the selective heavy doping of laser, thereby reducing the lattice damage of laser to the silicon substrate, reducing the repair time of subsequent high-temperature annealing, reducing the energy consumption of battery manufacturing and simultaneously reducing the equipment cost; on the other hand, the time of the boron diffusion process can be shortened, and the mass production efficiency is improved;
(4) Adopts an oxygen-free boron source, and has no B in the whole process 2 O 3 The byproduct is generated, so that the quartz piece is not damaged, the equipment maintenance cost is reduced, and the service cycle of the equipment is prolonged.
Detailed Description
Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention.
It should be understood that the process equipment or devices not specifically identified in the examples below are all conventional in the art.
Furthermore, it is to be understood that the reference to one or more method steps in this disclosure does not exclude the presence of other method steps before or after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise indicated; it should also be understood that the combined connection between one or more devices/means mentioned in the present invention does not exclude that other devices/means may also be present before and after the combined device/means or that other devices/means may also be interposed between these two explicitly mentioned devices/means, unless otherwise indicated. Moreover, unless otherwise indicated, the numbering of the method steps is merely a convenient tool for identifying the method steps and is not intended to limit the order of arrangement of the method steps or to limit the scope of the invention in which the invention may be practiced, as such changes or modifications in their relative relationships may be regarded as within the scope of the invention without substantial modification to the technical matter.
The active boron concentration and junction depth of the PN junction of the silicon wafers in the following examples and comparative examples are tested by adopting an ECV electrochemical test method commonly used in industry.
In a specific embodiment, in step (1), the flow ratio of silane, diborane and hydrogen is 1: (2-2.85): (0.5-1).
In a more specific embodiment, in the step (1), the flow rate of silane is 1300-160 sccm; the flow rate of diborane is 3200-3700 sccm; the flow rate of the hydrogen is 800-1000 sccm.
In a specific embodiment, in the step (1), the reaction pressure is 2 to 10Pa.
In a specific embodiment, in the step (1), the hot filament chemical vapor deposition equipment adopts hot filament heating, and the temperature of the hot filament heating is 1750-1950 ℃.
In a specific embodiment, in the step (2), the laser selective heavy doping treatment adopts green laser, the pulse width of the green laser is 500 ps-2 ns, and the scanning speed is 15000-35000 m/s.
In a more specific embodiment, the power of the green laser is 10-20% lower than that of a conventional boron doped silica source.
In a specific embodiment, in the step (3), the flow rate of the nitrogen gas is 2500-3000 sccm.
In a specific embodiment, in the step (4), the flow rate of the oxygen is 15000-20000 sccm.
Example 1
The embodiment of the application provides a selective boron doping diffusion method for a solar cell, which comprises the following steps:
step (1): placing a silicon wafer in a reaction chamber of hot wire chemical vapor deposition equipment, vacuumizing, heating to 1950 ℃ by adopting a hot wire, introducing 1500sccm silane, 3700 sccm diborane and 900 sccm hydrogen to form a pressure of 3Pa, depositing a boron doped amorphous silicon layer with the thickness of 10nm on one surface of the silicon wafer, and discharging the silicon wafer from the chamber;
step (2): carrying out laser selective heavy doping treatment on the surface of the silicon wafer which is treated in the step (1) and is deposited with the boron-doped amorphous silicon layer; the laser selective doping treatment adopts green laser with the pulse width of 1ns, the power is 25.5W, and compared with the laser power taking the traditional boron-doped silicon oxide as a source, the laser power is 15 percent lower, and the scanning speed is 15000m/s;
step (3): placing the silicon wafer treated in the step (2) in a boron diffusion furnace tube, vacuumizing, purging, heating to 930 ℃, introducing 3000 sccm of nitrogen to form a pressure of 450mbar, and performing oxygen-free boron diffusion for 100 seconds;
step (4): and (3) vacuumizing a boron diffusion furnace tube, purging nitrogen, introducing 20000sccm of oxygen to form 800mbar pressure, heating to 1050 ℃, and oxidizing and pushing the silicon wafer treated in the step (3) for 40min to finish the selective boron doping diffusion of the silicon wafer.
The boron-expanded region of the silicon wafer obtained in this embodiment includes a non-laser heavily doped region and a laser heavily doped region, wherein the surface active boron concentration of the non-laser heavily doped region is 7.8E18/cm 3 At an active boron concentration of 1E17/cm 3 The junction depth of the non-laser heavily doped region is 0.63 mu m by taking the position as a reference; the surface active boron concentration of the laser heavily doped region is 1.2E19/cm 3 At an active boron concentration of 1E17/cm 3 The junction depth of the laser heavily doped region was 1.51 μm, as a reference.
Example 2
The embodiment of the application provides a selective boron doping diffusion method for a solar cell, which comprises the following steps:
step (1): placing a silicon wafer in a reaction chamber of hot wire chemical vapor deposition equipment, vacuumizing, heating to 1950 ℃ by adopting a hot wire, introducing 1300sccm silane, 3500 sccm diborane and 800sccm hydrogen to form a pressure of 2Pa, depositing a boron doped amorphous silicon layer with the thickness of 20nm on one surface of the silicon wafer, and discharging the silicon wafer from the chamber;
step (2): carrying out laser selective heavy doping treatment on the surface of the silicon wafer which is treated in the step (1) and is deposited with the boron-doped amorphous silicon layer; the laser selective doping treatment adopts green laser with the pulse width of 2ns and the power of 24W, which is 20 percent lower than the laser power of the traditional boron-doped silicon oxide as a source, and the scanning speed is 25000m/s;
step (3): placing the silicon wafer treated in the step (2) in a boron diffusion furnace tube, vacuumizing, purging, heating to 915 ℃, introducing 2500sccm of nitrogen to form 400mbar pressure, and performing anaerobic boron diffusion for 50s;
step (4): and (3) vacuumizing a boron diffusion furnace tube, purging nitrogen, introducing 15000sccm of oxygen to form pressure of 750mbar, heating to 1025 ℃, and oxidizing and pushing the silicon wafer treated in the step (3) for 60min to finish the selective boron doping diffusion of the silicon wafer.
The boron-expanded region of the silicon wafer obtained in this embodiment includes a non-laser heavily doped region and a laser heavily doped region, wherein the surface active boron concentration of the non-laser heavily doped region is 7.7E18/cm 3 At an active boron concentration of 1E17/cm 3 The junction depth of the non-laser heavily doped region is 0.62 mu m by taking the position as a reference; the surface active boron concentration of the laser heavily doped region is 1.1E19/cm 3 At an active boron concentration of 1E17/cm 3 The junction depth of the laser heavily doped region was 1.47 μm, as a reference.
Example 3
The embodiment of the application provides a selective boron doping diffusion method for a solar cell, which comprises the following steps:
step (1): placing a silicon wafer in a reaction chamber of hot wire chemical vapor deposition equipment, vacuumizing, heating to 1950 ℃ by adopting a hot wire, introducing 1600sccm of silane, 3200 sccm of diborane and 1000 sccm of hydrogen to form a pressure of 10Pa, depositing a boron doped amorphous silicon layer with the thickness of 30nm on one side of the silicon wafer, and discharging the silicon wafer from the chamber;
step (2): carrying out laser selective heavy doping treatment on the surface of the silicon wafer which is treated in the step (1) and is deposited with the boron-doped amorphous silicon layer; the laser selective doping treatment adopts green laser with the pulse width of 500ps, the power is 27W, and compared with the laser power taking the traditional boron-doped silicon oxide as a source, the laser selective doping treatment has the scanning speed of 35000m/s;
step (3): placing the silicon wafer treated in the step (2) in a boron diffusion furnace tube, vacuumizing, purging, heating to 900 ℃, introducing 2800sccm of nitrogen to form a pressure of 500mbar, and performing oxygen-free boron diffusion for 100 seconds;
step (4): and (3) vacuumizing a boron diffusion furnace tube, purging nitrogen, introducing 18000sccm of oxygen to form 820mbar pressure, heating to 1000 ℃, and oxidizing and pushing the silicon wafer treated in the step (3) for 80 minutes to finish the selective boron doping diffusion of the silicon wafer.
The boron-expanded region of the silicon wafer obtained in this embodiment includes a non-laser heavily doped region and a laser heavily doped region, wherein the surface active boron concentration of the non-laser heavily doped region is 7.7E18/cm 3 At an active boron concentration of 1E17/cm 3 The junction depth of the non-laser heavily doped region is 0.62 mu m by taking the position as a reference; the surface active boron concentration of the laser heavily doped region is 1.02E19/cm 3 At an active boron concentration of 1E17/cm 3 The junction depth of the laser heavily doped region was 1.39 μm, as a reference.
Comparative example 1
The comparative example of the present application provides a selectively doped boron diffusion method comprising the steps of:
step (1): placing a silicon wafer in a boron diffusion furnace tube, vacuumizing, introducing 2500sccm nitrogen, 230sccm boron trichloride and 800sccm oxygen, heating to 890 ℃ under 150Pa pressure, and depositing a boron-doped silicon oxide layer with the thickness of 15-20nm on the silicon wafer for 400s;
step (2): vacuumizing the boron diffusion furnace tube, purging nitrogen, heating to 930 ℃, introducing 3000 sccm nitrogen to form a pressure of 400mbar, performing oxygen-free boron diffusion for 400s, and discharging from the cavity;
step (3): carrying out laser selective heavy doping treatment on the silicon wafer treated in the step (2); the laser of the laser selective doping treatment adopts green laser with the pulse width of 1ns, the laser power is 30W, and the scanning speed is 25000m/s;
step (4): and (3) putting the silicon wafer treated in the step (3) into a boron diffusion furnace tube again, vacuumizing, blowing nitrogen, introducing 20000sccm of oxygen to form 800mbar pressure, heating to 1050 ℃, oxidizing and pushing the silicon wafer treated in the step (3) for 60 minutes, and completing the selective boron doping diffusion of the silicon wafer.
The boron-expanded region of the silicon wafer obtained in this comparative example comprises a non-laser heavily doped region and a laser heavily doped region, wherein the surface active boron concentration of the non-laser heavily doped region is 8.1E18/cm 3 At an active boron concentration of 1E17/cm 3 The junction depth of the non-laser heavily doped region is 0.72 mu m by taking the position as a reference; the surface active boron concentration of the laser heavily doped region is 1.1E18/cm 3 At an active boron concentration of 1E17/cm 3 The junction depth of the laser heavily doped region was 1.48 μm, as a reference.
Comparative example 2
Comparative example 2 differs from comparative example 1 in that step (4) is different, and the rest of the process is identical. The method comprises the following steps:
step (4): and (3) putting the silicon wafer treated in the step (3) into a boron diffusion furnace tube again, vacuumizing, blowing nitrogen, introducing 20000sccm of oxygen to form 800mbar pressure, heating to 1025 ℃, oxidizing and pushing the silicon wafer treated in the step (3) for 80 minutes, and completing the selective boron doping diffusion of the silicon wafer.
The boron-expanded region of the silicon wafer obtained in this comparative example comprises a non-laser heavily doped region and a laser heavily doped region, wherein the surface active boron concentration of the non-laser heavily doped region is 8.5E18/cm 3 At an active boron concentration of 1E17/cm 3 The junction depth of the non-laser heavily doped region is 0.68 μm by taking the position as a reference; the surface active boron concentration of the laser heavily doped region is 1.2E19/cm 3 At an active boron concentration of 1E17/cm 3 The junction depth of the laser heavily doped region was 1.4 μm, as a reference.
Comparative example 3
Comparative example 3 differs from comparative example 1 in that step (4) is different, and the rest of the process is identical. The method comprises the following steps:
step (4): and (3) putting the silicon wafer treated in the step (3) into a boron diffusion furnace tube again, vacuumizing, blowing nitrogen, introducing 20000sccm of oxygen to form 800mbar pressure, heating to 1000 ℃, oxidizing and pushing the silicon wafer treated in the step (3) for 100 minutes, and completing the selective boron doping diffusion of the silicon wafer.
The boron-expanded region of the silicon wafer obtained in this comparative example comprises a non-laser heavily doped region and a laser heavily doped region, wherein the surface active boron concentration of the non-laser heavily doped region is 8.9E18/cm 3 At an active boron concentration of 1E17/cm 3 The junction depth of the non-laser heavily doped region is 0.61 μm by taking the place as a reference; the surface active boron concentration of the laser heavily doped region is 1.35E19/cm 3 At an active boron concentration of 1E17/cm 3 The junction depth of the laser heavily doped region was 1.31 μm, as a reference.
Comparative examples 1-3 use conventional boron doped silica (BSG) as the selective boron source dopant material, and since the boron doped silica (BSG) has a high transmittance to green laser light, the direct use of green laser light does not allow selective boron diffusion of boron doped silica, and therefore high temperature oxygen-free boron diffusion is required before selective boron diffusion of green laser light. The process flow of the comparative example is complex, the boron diffusion process is required to be interrupted, and the silicon wafer is easy to pollute due to the fact that the cavity is discharged and fed for multiple times, and continuous production is not facilitated.
In the embodiments 1-3, the boron-doped amorphous silicon layer is used as the selective boron source doping material, so that the transmittance of green laser is low, high-temperature oxygen-free boron diffusion is not needed, laser selective heavy doping treatment can be directly performed before the boron diffusion furnace tube is entered, continuous production is realized by oxygen-free boron diffusion and oxidation promotion, the boron diffusion process is not needed to be interrupted, the situation of pollution of silicon wafers caused by repeated cavity exit and cavity entry is avoided, and mass production is more facilitated.
As can be seen from comparing experimental data of each example and each comparative example, the technical scheme can realize that the non-laser heavily doped region of the silicon wafer has relatively lower boron doping concentration, can reduce Auger recombination in the silicon caused by high-concentration boron doping, and does not influence the junction depth of the laser heavily doped region.
In addition, the laser power adopted in the laser selective heavy doping treatment procedure of the embodiments 1-3 is 10-20% lower than that of the comparative example, the lattice structure of the silicon substrate is free from loss, when the junction depth of the laser heavy doping region is similar, no further high-temperature long-time repair is needed, the energy consumption is lower, and the production efficiency is improved. Examples 1-3 Whole Process Using an anaerobic boron Source without B 2 O 3 The by-product does not have the problem of corroding the quartz furnace tube in comparative examples 1-3. In the embodiments 1-3, the boron doped amorphous silicon layer is used for replacing boron doped silicon oxide (BSG) of the comparative examples 1-3 as a selective boron source doping material, so that the ion diffusion speed is high, the oxygen-free boron diffusion time is shortened by 350-250 s compared with that of the comparative examples, and the production efficiency is greatly improved. After boron diffusion, oxidation and junction pushing of the silicon wafer prepared in the embodiment 1-3, no boron coiling and expansion are generated, and further alkali washing is not needed to remove a coiling and expansion layer; the silicon wafer prepared in the comparative examples 1-3 needs to consume a large amount of chemical reagents to remove the back side around plating silicon oxide around expansion and polishing in the next link of solar cell preparation after boron diffusion oxidation pushing junction. In summary, the photoelectric conversion efficiency of the solar cell obtained in examples 1 to 3 can be improved by 0.07 to 0.15% relative to that of the solar cell obtained in comparative examples 1 to 3.
While the invention has been described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that various modifications and additions may be made without departing from the scope of the invention. Equivalent embodiments of the present invention will be apparent to those skilled in the art having the benefit of the teachings disclosed herein, when considered in the light of the foregoing disclosure, and without departing from the spirit and scope of the invention; meanwhile, any equivalent changes, modifications and evolution of the above embodiments according to the essential technology of the present invention still fall within the scope of the technical solution of the present invention.
Claims (5)
1. The selective boron doping diffusion method for the solar cell is characterized by comprising the following steps of:
step (1): placing a silicon wafer in a reaction chamber of hot wire chemical vapor deposition equipment, vacuumizing, introducing silane, diborane and hydrogen, depositing a boron-doped amorphous silicon layer on one surface of the silicon wafer, and discharging the silicon wafer from the chamber; the thickness of the boron-doped amorphous silicon layer is 10-30 nm;
step (2): carrying out laser selective heavy doping treatment on the surface of the silicon wafer which is treated in the step (1) and is deposited with the boron-doped amorphous silicon layer;
step (3): placing the silicon wafer treated in the step (2) in a boron diffusion furnace tube, vacuumizing, and introducing nitrogen to perform oxygen-free boron diffusion;
step (4): and (3) vacuumizing the boron diffusion furnace tube, blowing nitrogen, introducing oxygen, and oxidizing and pushing the silicon wafer treated in the step (3) to finish the selective boron doping diffusion of the silicon wafer.
2. The method of claim 1, wherein the selectively boron-doped diffusion of the solar cell is characterized by: in the step (2), green laser is adopted for the laser selective heavy doping treatment.
3. The method of claim 2, wherein the selectively boron-doped diffusion of the solar cell is characterized by: the pulse width of the green laser is 500 ps-2 ns, and the scanning speed is 15000-35000 m/s.
4. The method of claim 1, wherein the selectively boron-doped diffusion of the solar cell is characterized by: in the step (3), the oxygen-free boron diffusion pressure is 300-500 mbar, the temperature is 900-930 ℃ and the time is 50-150 s.
5. The method of claim 1, wherein the selectively boron-doped diffusion of the solar cell is characterized by: in the step (4), the pressure of the oxidation pushing junction is 600-820mbar, the temperature is 1000-1050 ℃ and the time is 40-80 min.
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