CN113571602B - Secondary diffusion selective emitter and preparation method and application thereof - Google Patents

Secondary diffusion selective emitter and preparation method and application thereof Download PDF

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CN113571602B
CN113571602B CN202110835667.3A CN202110835667A CN113571602B CN 113571602 B CN113571602 B CN 113571602B CN 202110835667 A CN202110835667 A CN 202110835667A CN 113571602 B CN113571602 B CN 113571602B
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diffusion
phosphorus source
source
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oxidation treatment
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CN113571602A (en
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贾松燕
何悦
任永伟
任勇
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Hengdian Group DMEGC Magnetics Co Ltd
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    • H01—ELECTRIC ELEMENTS
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    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
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    • 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
    • H01L21/223—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 gaseous phase
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    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/547—Monocrystalline silicon PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
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Abstract

The invention provides a selective emitter for secondary diffusion, and a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) Performing constant-temperature oxidation on the selective emitter for the first time, and performing diffusion propulsion after the phosphorus source is introduced for the first time to obtain a silicon wafer for the first time; (2) Washing the silicon wafer subjected to the first diffusion obtained in the step (1) by using an HF solution to obtain a silicon wafer subjected to the phosphorus-removed silicon glass, performing secondary constant-temperature oxidation on the silicon wafer subjected to the phosphorus-removed silicon glass, and secondarily introducing a phosphorus source to obtain a secondary diffusion product; (3) And (3) carrying out laser doping and etching on the secondary diffusion product to obtain a selective emitter product with low surface concentration. The method optimizes the problem that a large amount of phosphorus sources are required to be deposited on the surface of the battery in the diffusion process due to the introduction of the current laser doping process, and can be matched with the current mainstream laser doping process and achieve low surface concentration so as to obtain the selective emitter with higher open voltage and efficiency.

Description

Secondary diffusion selective emitter and preparation method and application thereof
Technical Field
The invention belongs to the technical field of crystalline silicon solar cells, and relates to a secondary diffusion selective emitter, a preparation method and application thereof.
Background
The iteration of the crystalline silicon solar cell technology is a main power for promoting the development of the industry, and in recent two years, PERC cells are widely popularized in the photovoltaic field due to the advantage of conversion efficiency. The process of the selective emitter (SE for short) is further efficiency improvement on PERC batteries and pushes the batteries into PERC+ age.
CN110164759a discloses a regional layered deposition diffusion process comprising the steps of: (1) pretreatment of a silicon wafer; (2) pre-oxidation; (3) low temperature low concentration phosphorus source deposition; (4) high temperature medium concentration phosphorus source deposition; (5) forming a PN junction; (6) low-temperature high-concentration phosphorus source deposition; and (7) cooling, pushing out the quartz boat, and taking out the silicon wafer. The method of forming the phosphosilicate glass layer by superposition, cooling and deposition on the basis of the conventional PERC technology is adopted to realize the purposes of high sheet resistance and high phosphorus source of the phosphosilicate glass layer, but the problems of low conversion efficiency of the battery caused by higher phosphorus concentration and shallower PN junction on the surface of the silicon wafer still exist.
CN110190153a discloses a high efficiency selective emitter solar cell diffusion process comprising: boat feeding, temperature rising, constant temperature, oxidation, deposition 1, deposition 2, oxidation, deposition 3, temperature rising, temperature reducing, deposition 4, temperature reducing and boat taking. The method adopts three-stage deposition propulsion and then cooling deposition to promote the phosphorus content in the phosphorosilicate glass layer, and the process basically achieves the requirements of high junction depth and high sheet resistance and promotes short wave correspondence; however, four steps of deposition are still carried out at a higher temperature, and part of phosphorus in PSG enters the silicon wafer, so that the surface phosphorus concentration is reduced; the minority carrier lifetime is affected, resulting in a problem of low open circuit voltage and short circuit current.
The above scheme has the problem that the conversion efficiency of the prepared pole piece is low or the open-circuit voltage and the short-circuit current are low, so that the development of a selective emitter with high conversion efficiency and high open-circuit voltage and short-circuit current is necessary.
Disclosure of Invention
The invention aims to provide a selective emitter for secondary diffusion, a preparation method and application thereof, and the selective emitter can ensure good diffusion effect of a light receiving area and better control of lower sheet resistance and conductivity of a printing area through low-concentration phosphorus source diffusion, high-temperature propulsion, phosphorus-removed silicon glass, low Wen Tonggao-concentration phosphorus source deposition, annealing, laser doping and etching, so that the aim of improving the efficiency of a battery piece optimally is achieved.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for preparing a secondarily diffused selective emitter, the preparation comprising the steps of:
(1) Performing constant-temperature oxidation treatment on the silicon wafer once, and performing diffusion propulsion once after introducing a phosphorus source once to obtain a first-time diffusion silicon wafer;
(2) Washing the silicon wafer subjected to the first diffusion obtained in the step (1) by using an HF solution to obtain a silicon wafer subjected to phosphorus-removed silicon glass, performing secondary constant-temperature oxidation treatment on the silicon wafer subjected to phosphorus-removed silicon glass, and secondarily introducing a phosphorus source to obtain a secondary source product;
(3) The secondary through source product in the step (2) is doped and etched by laser to obtain a secondary diffusion selective emitter;
wherein the speed of the secondary phosphorus source is higher than that of the primary phosphorus source;
wherein the temperature of the secondary introduced phosphorus source is lower than that of the primary introduced phosphorus source.
According to the invention, the first round of low-concentration phosphorus source diffusion and high-temperature propulsion are adopted, after phosphosilicate glass is removed, the second round of high-concentration phosphorus source deposition and annealing are carried out, and finally, the laser doping and etching are carried out, so that the good diffusion effect of a light receiving area is ensured, the lower sheet resistance and conductivity of a printing area can be well controlled, and the conversion efficiency of the solar cell is further improved.
The step (1) is characterized by high-temperature propulsion, low-surface concentration phosphorus source and dead layer of the descending surface, and the step (2) is characterized by adopting low-temperature deposition, wherein the phosphorus source required by laser doping is deposited on the surface of the battery in the low-temperature process, but the propulsion is not generated, and the PN structure of the step (1) is not changed.
Preferably, the step (1) is preceded by a vacuum-pumping treatment.
Preferably, the temperature of the primary constant temperature oxidation treatment is 780-800 ℃, for example: 780 ℃, 785 ℃, 790 ℃, 795 ℃ or 800 ℃ and the like.
Preferably, the time of the one constant temperature oxidation treatment is 5 to 15min, for example: 5min, 8min, 10min, 12min or 15min, etc.
Preferably, the pressure of the primary constant temperature oxidation treatment is 100 to 200mbar, for example: 100mbar, 120mbar, 140mbar, 180mbar or 200mbar etc.
Preferably, the speed of oxygen gas introduced in the primary constant temperature oxidation treatment is 500-4000 sccm, for example: 500sccm, 800sccm, 1000sccm, 2000sccm, 3000sccm, 4000sccm, or the like.
Preferably, the temperature of the primary introduced phosphorus source in the step (1) is 790-820 ℃, for example: 790 ℃, 795 ℃, 800 ℃, 810 ℃ or 820 ℃ and the like.
Preferably, the speed of the primary introducing phosphorus source is 500-1000 sccm, for example: 500sccm, 600sccm, 700sccm, 800sccm, 900sccm, 1000sccm, or the like.
Preferably, the time for one-time charging of the phosphorus source is 5-10 min, for example: 5min, 6min, 7min, 8min or 10min, etc.
Preferably, the pressure of the primary feed phosphorus source is from 100 to 200mbar, for example: 100mbar, 120mbar, 140mbar, 180mbar or 200mbar etc.
Preferably, the phosphorus source of the one-pass phosphorus source comprises a carried POCl 3 Small nitrogen of the source.
Preferably, oxygen is introduced at the same time as the phosphorus source is introduced at one time.
Preferably, the speed of oxygen is 500-4000 sccm, for example: 500sccm, 800sccm, 1000sccm, 2000sccm, 3000sccm, 4000sccm, or the like.
Preferably, the temperature of the primary diffusion promotion in the step (1) is 830-870 ℃, for example: 830 ℃, 840 ℃, 850 ℃, 860 ℃ or 870 ℃ and the like.
Preferably, the time of the one diffusion propulsion is 10-20 min, for example: 10min, 12min, 14min, 16min, 18min or 20min, etc.
Preferably, after the primary diffusion in the step (1), cooling, back pressure and measurement are carried out on the silicon wafer subjected to the primary diffusion before the washing in the step (2), so as to obtain the silicon wafer qualified in the primary diffusion.
Preferably, the temperature of the cooling is 680 ℃ or lower.
Preferably, the back pressure is normal pressure.
Preferably, the measurement is to take 1 piece of silicon wafer which completes the first diffusion according to the temperature area to measure the square resistance.
Preferably, the standard of measurement is a square resistance of 90 to 150Ω, for example: 90 Ω, 110 Ω, 130 Ω, 140 Ω, 150 Ω, etc.
Preferably, the mass concentration of the HF solution in step (2) is 5-20%, for example: 5%, 10%, 12%, 15% or 20%, etc.
The high-efficiency silicon wafer brought by low surface concentration is reserved by the first diffusion, and the superfluous phosphosilicate glass on the surface layer is washed off by HF (high-frequency) washing, so that the second diffusion is avoided.
Preferably, the secondary constant temperature oxidation treatment is preceded by a vacuum-pumping treatment.
Preferably, the temperature of the secondary constant temperature oxidation treatment is 720-760 ℃, for example: 720 ℃, 730 ℃, 740 ℃, 750 ℃, 760 ℃ or 760 ℃ and the like.
Preferably, the time of the secondary constant temperature oxidation treatment is 1 to 5 minutes, for example: 1min, 2min, 3min, 4min or 5min, etc.
Preferably, the pressure of the secondary constant temperature oxidation treatment is 100-200 mbar, for example: 100mbar, 120mbar, 140mbar, 180mbar or 200mbar etc.
Preferably, the oxygen is introduced into the secondary constant temperature oxidation treatment at a speed of 500-4000 sccm, for example: 500sccm, 800sccm, 1000sccm, 2000sccm, 3000sccm, 4000sccm, or the like.
Preferably, the temperature of the secondary introduced phosphorus source in the step (2) is 740-760 ℃, for example: 740 ℃, 745 ℃, 750 ℃, 755 ℃ or 760 ℃ and the like.
Preferably, the speed of the secondary introducing phosphorus source is 800-1500sccm, for example: 800sccm, 900sccm, 1000sccm, 1200sccm, 1500sccm, or the like.
Preferably, the time for secondary charging of the phosphorus source is 10-20 min, for example: 10min, 12min, 14min, 16min, 18min or 20min, etc.
Preferably, the pressure of the secondary inlet phosphorus source is 100-200 mbar, for example: 100mbar, 120mbar, 140mbar, 180mbar or 200mbar etc.
Preferably, the phosphorus source of the secondary inlet phosphorus source comprises a carried POCl 3 Small nitrogen of the source.
Preferably, oxygen is introduced while the phosphorus source is introduced secondarily.
Preferably, the speed of oxygen is 500-4000 sccm, for example: 500sccm, 800sccm, 1000sccm, 2000sccm, 3000sccm, 4000sccm, or the like.
The secondary diffusion adopts a low-temperature high-concentration source for deposition, so that preparation is carried out for laser doping in the subsequent process, and the secondary diffusion has the advantages of not only retaining the high-efficiency level of low surface concentration of diffusion, but also achieving good surface phosphorus source deposition for the subsequent laser doping.
Preferably, the temperature reduction and back pressure are performed before the laser doping in the step (3).
Preferably, the temperature of the cooling is 680 ℃ or lower.
Preferably, the back pressure is normal pressure.
Preferably, the laser doping in step (3) includes passing the secondary source product through a laser SE device to form heavy doping in the printed area.
Preferably, the square resistance of the secondary diffusion product is 90 to 150Ω, for example: 90 Ω, 100 Ω, 110 Ω, 120 Ω, 150 Ω, etc.
Preferably, the square resistance of the secondary diffusion product after passing through the laser SE device is 40 to 80 omega, for example: 40 Ω, 45 Ω, 50 Ω, 55 Ω, 60 Ω, 70 Ω, 80 Ω, etc.
Preferably, the etching includes etching the laser doped product to remove the edge and back P-N junctions.
Preferably, the etched product is cleaned after the etching.
Preferably, the cleaning agent is an HF solution.
Preferably, the mass concentration of the HF solution is 5-20%, for example: 5%, 10%, 12%, 15% or 20%, etc.
As a preferred embodiment of the present invention, the secondary diffusion method includes the steps of:
(1) Performing constant-temperature oxidation treatment on the selective emitter for 5-15 min at 780-800 ℃ and 100-200 mbar at the speed of 500-4000 sccm, performing diffusion promotion for 10-20 min at 830-870 ℃ after performing primary phosphorus source introduction at 500-1000 sccm at 790-820 ℃ and 100-200 mbar for 5-10 min, and obtaining a silicon wafer for primary diffusion;
(2) Washing the silicon wafer subjected to the first diffusion obtained in the step (1) by using an HF solution with the mass concentration of 5-20% to obtain a silicon wafer subjected to phosphorus removal glass, carrying out secondary constant temperature oxidation treatment on the silicon wafer subjected to phosphorus removal glass under the conditions of 720-760 ℃ and the speed of introducing oxygen of 500-4000 sccm, and carrying out secondary introduction of a phosphorus source with the speed of 800-1500sccm for 5-10 min at the temperature of 740-760 ℃ and the speed of introducing oxygen of 100-200 mbar to obtain a secondary introduction product;
(3) The secondary through source product in the step (2) is doped and etched by laser to obtain a secondary diffusion selective emitter;
wherein the speed of the secondary phosphorus source is greater than the speed of the primary phosphorus source.
In a second aspect, the present invention provides a secondarily diffused selective emitter produced by the production method as described in the first aspect.
In a third aspect, the present invention provides a crystalline silicon solar cell comprising a secondarily diffused selective emitter as described in the second aspect.
Compared with the prior art, the invention has the following beneficial effects:
(1) The secondary diffusion method of the selective emitter ensures good diffusion effect of the light receiving area, and can well control low sheet resistance and conductivity of the printing area, thereby achieving the purpose of improving the efficiency of the battery piece optimally.
(2) The method optimizes the problem that a large amount of phosphorus sources are required to be deposited on the surface of the battery in the diffusion process due to the introduction of the current laser doping process, and the problems of more dead layers and more composites on the surface and affecting the open pressure of the whole battery are easily caused in the one-time diffusion process. The secondary diffusion process is a method which can be matched with the currently mainstream laser doping process and can reach low surface concentration so as to obtain higher open pressure and efficiency.
(3) In the method, the first diffusion ensures good diffusion effect of the light receiving area, and laser doping is performed after the secondary power supply so as to better control the lower sheet resistance and conductivity of the printing area, thereby improving the efficiency, open-circuit voltage and short-circuit current of the battery piece.
Drawings
Fig. 1 is a flow chart of a process for preparing a secondarily diffused selective emitter according to example 1 of the present invention.
Detailed Description
Example 1
The embodiment provides a selective emitter for secondary diffusion, and the preparation method of the selective emitter comprises the following steps:
(1) Inserting the silicon wafer subjected to texturing and cleaning into a quartz boat by an automatic inserting machine, placing the quartz boat on a paddle of a diffusion furnace, sending the quartz boat into the diffusion furnace tube heated to 780 ℃, vacuumizing to set pressure of 120mbar, introducing 1000sccm oxygen for 10min to form an oxide layer on the surface of the silicon wafer, heating to 800 ℃, setting pressure of 120mbar, and introducing 800sccm carried POCl into the furnace 3 Depositing a phosphorus source on the silicon wafer oxide layer for 8min by using small nitrogen of the source and 1000sccm of oxygen, heating to 860 ℃ and keeping for 15min to diffuse the phosphorus source into the surface layer of the silicon wafer to form a P-N junction, thereby obtaining a silicon wafer for the first diffusion; cooling to below 680 ℃ after diffusion is completed, back pressing to normal pressure, preparing a boat, opening a furnace door, taking 1 piece of silicon wafer subjected to first diffusion according to a temperature zone to measure square resistance, wherein the temperature is required to be 100-110 omega, and unloading other products by using an automatic inserting machine;
(2) Removing surface phosphosilicate glass from silicon wafers subjected to primary diffusion by using 10% HF, drying for secondary deposition, inserting the silicon wafers subjected to phosphosilicate glass removal into a quartz boat by using an automatic inserting machine, placing the quartz boat on a paddle of a diffusion furnace, sending the quartz boat into a furnace tube heated to 730 ℃, vacuumizing to set pressure of 160mbar, introducing 800sccm of oxygen for 2min, and introducing carried POCl into the furnace again 3 Small nitrogen of the source, flow 1200sccm, deposition 20min; setting pressure to 130mbar, introducing 800sccm oxygen, setting temperature to 750 ℃ to obtain a secondary power supply product, cooling to below 680 ℃ after finishing secondary power supply, back pressing to normal pressure, opening a furnace door, and discharging the product with the finished secondary power supply by an automatic inserting machine;
(3) And (3) forming heavy doping on a product of the secondary through source in a printing area through a laser SE (selective emitter) device, wherein square resistance is required to be 40-80 omega, removing an edge and a back P-N junction through etching after laser doping is finished, and cleaning through 10% HF to obtain the secondary diffusion selective emitter.
The preparation process flow chart of the secondary diffusion selective emitter is shown in figure 1.
Example 2
(1) Inserting the silicon wafer subjected to texturing and cleaning into a quartz boat by an automatic inserting machine, placing the quartz boat on a paddle of a diffusion furnace, sending the quartz boat into the diffusion furnace tube heated to 790 ℃, vacuumizing to set pressure of 120mbar, introducing 1100sccm oxygen for 10min to form an oxide layer on the surface of the silicon wafer, heating to 800 ℃, setting pressure of 120mbar, and introducing 850sccm carried POCl into the furnace 3 Depositing a phosphorus source on a silicon wafer oxide layer for 8min by using small nitrogen of the source and 1000sccm of oxygen, heating to 870 ℃, and keeping for 15min to diffuse the phosphorus source into the surface layer of the silicon wafer to form a P-N junction, so as to obtain a silicon wafer for first diffusion; cooling to below 680 ℃ after diffusion is completed, back pressing to normal pressure, preparing a boat, opening a furnace door, taking 1 piece of silicon wafer subjected to first diffusion according to a temperature zone to measure square resistance, wherein the temperature is required to be 110-120 omega, and unloading other products by an automatic inserting machine;
(2) Removing surface phosphosilicate glass from silicon wafers subjected to primary diffusion through 15% HF, drying for secondary deposition, inserting the silicon wafers subjected to phosphosilicate glass removal into a quartz boat by an automatic inserting machine, placing the quartz boat on a paddle of a diffusion furnace, sending the quartz boat into a furnace tube heated to 750 ℃, vacuumizing to set pressure of 160mbar, introducing 800sccm of oxygen for 2min, and introducing carried POCl into the furnace again 3 Small nitrogen of the source, flow 1000sccm, deposition 20min; setting pressure to 120mbar, introducing 800sccm oxygen, setting temperature to 750 ℃ to obtain a secondary power supply product, cooling to below 680 ℃ after finishing secondary power supply, back pressing to normal pressure, opening a furnace door, and discharging the product with the finished secondary power supply by an automatic inserting machine;
(3) And (3) forming heavy doping on a product of the secondary through source in a printing area through a laser SE (selective emitter) device, wherein square resistance is required to be 40-80 omega, removing an edge and a back P-N junction through etching after laser doping is finished, and cleaning through 15% HF to obtain the secondary diffusion selective emitter.
Example 3
This embodiment differs from embodiment 1 only in that step (1) the carry-over POCl is described 3 The flow rate of the small nitrogen of the source was 500sccm, and other conditions and parameters were exactly the same as in example 1.
Example 4
This embodiment differs from embodiment 1 only in that step (1) the carry-over POCl is described 3 The flow rate of the small nitrogen of the source was 1000sccm, and other conditions and parameters were exactly the same as in example 1.
Example 5
This example differs from example 1 only in that the diffusion advancing temperature in step (1) is 830 ℃, and other conditions and parameters are exactly the same as example 1.
Example 6
This example differs from example 1 only in that the diffusion advancing temperature in step (1) is 870 ℃, and other conditions and parameters are exactly the same as example 1.
Example 7
This embodiment differs from embodiment 1 only in that step (2) the carry-over POCl is described 3 The flow rate of the small nitrogen of the source was 800sccm, and other conditions and parameters were exactly the same as in example 1.
Example 8
This embodiment differs from embodiment 1 only in that step (2) the carry-over POCl is described 3 The flow rate of the small nitrogen of the source was 1500sccm, and the other conditions and parameters were exactly the same as in example 1.
Comparative example 1
This comparative example differs from example 1 only in that step (1) the carry-over POCl is described 3 The flow rate of the small nitrogen of the source is 1200sccm, and POCl is carried by the introducing in the step (2) 3 The flow rate of the small nitrogen of the source was 800sccm, and other conditions and parameters were exactly the same as in example 1.
Performance test:
the selective emitters obtained in examples 1 to 8 and comparative example 1 were used to prepare batteries, and the diffusion sheet resistance, SE sheet resistance, conversion efficiency, open circuit voltage and short circuit current were tested, and the test results are shown in table 1:
TABLE 1
Figure BDA0003176854220000101
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Figure BDA0003176854220000111
As can be seen from Table 1, the conversion efficiency of the batteries prepared by the selective emitter prepared by the method of the present invention can reach 22.7% or more, the open circuit voltage can reach 0.6810V or more, and the short circuit current can reach 10.45A or more, as can be obtained from examples 1 to 8.
As can be seen from a comparison of example 1 and examples 3-4, the carry-over POCl introduced in step (1) 3 The small nitrogen flow of the source can affect the performance of the selective emitter, and the POCl is carried in the step (1) 3 The speed of the small nitrogen of the source is controlled between 500 and 1000sccm, a selective emitter with better effect can be obtained, if the POCl is carried in the step (1) 3 If the flow of the small nitrogen of the source is too high, the surface concentration is high, the sheet resistance is low, the open voltage and the current are comprehensively low, if the step (1) is that the POCl is carried 3 The small nitrogen flow of the source is too small, so that the surface concentration is low, the open voltage and the current have advantages, but the sheet resistance is higher, and the overall efficiency is lower.
As can be seen from the comparison of the embodiment 1 and the embodiments 5-6, the diffusion advancing temperature in the step (1) affects the performance of preparing the selective emitter, the diffusion advancing temperature in the step (1) is controlled between 830 and 870 ℃, the selective emitter with better effect can be prepared, if the diffusion advancing temperature in the step (1) is too high, the overall sheet resistance is reduced, the efficiency is lower, but the open pressure has advantages; if the diffusion advancing temperature in the step (1) is too low, the overall sheet resistance is higher, the overall efficiency is lower, and the open-circuit current advantage is not obvious.
As can be seen from a comparison of example 1 and examples 7-8, the carry-over POCl introduced in step (2) 3 The small nitrogen flow of the source can affect the performance of the selective emitter, and the POCl is carried in the step (2) 3 The flow rate of the small nitrogen of the source is controlled between 800 and 1500sccm, a selective emitter with better effect can be prepared, if the POCl is carried in the step (2) 3 The flow of the small nitrogen of the source is overlarge, the change of the rear resistance of the whole SE is not obvious, and the phosphorus source is wasted; if the step (2) is that the carried POCl is introduced 3 The flow of small nitrogen of the source is too small, the wholeThe sheet resistance after the body SE cannot be reduced to below 80 omega, the local performance advantage of the SE cannot be reflected, and the overall efficiency is low.
From example 1 and comparison 1, it is possible to carry POCl if step (1) is carried out by passing 3 The flow of small nitrogen of the source is larger than that of the incoming carrying POCl 3 The flow of small nitrogen of the source has insignificant change of the sheet resistance after the whole SE, the phosphorus source is wasted, the surface concentration is high, the sheet resistance is low, and the open voltage and the current are comprehensively low.
The applicant declares that the above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be apparent to those skilled in the art that any changes or substitutions that are easily conceivable within the technical scope of the present invention disclosed by the present invention fall within the scope of the present invention and the disclosure.

Claims (45)

1. A method for preparing a selective emitter by secondary diffusion, the method comprising the steps of:
(1) Performing constant-temperature oxidation treatment on the silicon wafer once, and performing diffusion propulsion once after introducing a phosphorus source once to obtain a first-time diffusion silicon wafer;
(2) Washing the silicon wafer subjected to the first diffusion obtained in the step (1) by using an HF solution to obtain a silicon wafer subjected to phosphorus-removed silicon glass, performing secondary constant-temperature oxidation treatment on the silicon wafer subjected to phosphorus-removed silicon glass, and secondarily introducing a phosphorus source to obtain a secondary source product;
(3) The secondary through source product in the step (2) is doped and etched by laser to obtain a secondary diffusion selective emitter;
wherein the speed of the secondary phosphorus source is higher than that of the primary phosphorus source;
wherein the temperature of the secondary introduced phosphorus source is lower than that of the primary introduced phosphorus source.
2. The method according to claim 1, wherein the one constant temperature oxidation treatment in step (1) is preceded by a vacuum-pumping treatment.
3. The method according to claim 1, wherein the temperature of the primary constant temperature oxidation treatment is 780 to 800 ℃.
4. The method according to claim 1, wherein the time of the one constant temperature oxidation treatment is 5 to 15 minutes.
5. The process according to claim 1, wherein the pressure of the primary constant temperature oxidation treatment is 100 to 200mbar.
6. The method according to claim 1, wherein the speed of introducing oxygen in the primary constant temperature oxidation treatment is 500 to 4000sccm.
7. The method of claim 1, wherein the temperature of the one-pass phosphorus source in step (1) is 790 to 820 ℃.
8. The method of claim 1, wherein the one-pass phosphorus source is at a rate of 500-1000 sccm.
9. The method of claim 1, wherein the one-pass introduction of the phosphorus source is for 5 to 10 minutes.
10. The method according to claim 1, wherein the pressure of the primary phosphorus source is 100 to 200mbar.
11. The method of claim 1, wherein the one-pass phosphorus source comprises a carrier POCl 3 Small nitrogen of the source.
12. The method of claim 1, wherein oxygen is introduced simultaneously with the primary introduction of the phosphorus source.
13. The method of claim 12, wherein the oxygen is introduced at a rate of 500 to 4000sccm.
14. The method of claim 1, wherein the temperature of the primary diffusion advance is 830-870 ℃.
15. The method of claim 1, wherein the time for one diffusion advance is 10 to 20 minutes.
16. The method of claim 1 wherein after said one diffusion step of step (1), said first diffusion step of step (2) is followed by a temperature reduction, back pressure and measurement of said first diffusion step prior to said washing step to obtain a first diffusion qualified silicon wafer.
17. The method of claim 16, wherein the reduced temperature is 680 ℃ or less.
18. The method of claim 16, wherein the back pressure is at atmospheric pressure.
19. The method of claim 16 wherein the measuring is to measure the sheet resistance of 1 piece each per temperature zone of the wafer after the first diffusion is completed.
20. The method of claim 16, wherein the standard for measurement is a sheet resistance of 90 to 150 Ω.
21. The method according to claim 1, wherein the HF solution in step (2) has a mass concentration of 5 to 20%.
22. The method according to claim 1, wherein the secondary constant temperature oxidation treatment is preceded by a vacuum-pumping treatment.
23. The method according to claim 1, wherein the secondary constant temperature oxidation treatment is carried out at a temperature of 720 to 760 ℃.
24. The method according to claim 1, wherein the time of the secondary constant temperature oxidation treatment is 1 to 5 minutes.
25. The process according to claim 1, wherein the pressure of the secondary constant temperature oxidation treatment is 100 to 200mbar.
26. The method according to claim 1, wherein the oxygen is introduced at a rate of 500 to 4000sccm in the secondary constant temperature oxidation treatment.
27. The method of claim 1, wherein the temperature of the secondary phosphorus source in step (2) is 740-760 ℃.
28. The method of claim 1, wherein the secondary phosphorus source is introduced at a rate of 800-1500 sccm.
29. The method of claim 1, wherein the secondary charging of phosphorus source is for 10 to 20 minutes.
30. The process according to claim 1, wherein the pressure of the secondary phosphorus source is between 100 and 200mbar.
31. The method of claim 1, wherein the secondary phosphorus source comprises a carrier POCl 3 Small nitrogen of the source.
32. The method of claim 1, wherein oxygen is introduced simultaneously with the secondary introduction of the phosphorus source.
33. The method of claim 32, wherein the oxygen is introduced at a rate of 500 to 4000sccm.
34. The method of claim 1, wherein the laser doping in step (3) is preceded by a temperature reduction and back pressure.
35. The method of claim 34, wherein the reduced temperature is 680 ℃ or less.
36. The method of claim 34, wherein the back pressure is at atmospheric pressure.
37. The method of claim 1, wherein the laser doping in step (3) comprises passing the secondarily diffused product through a laser SE device to form a heavy doping in the printed area.
38. The method of claim 37, wherein the secondary diffusion product has a sheet resistance of 90 to 150 Ω.
39. The method of claim 37, wherein the sheet resistance of the secondarily diffused product is 40 to 80 Ω after passing through the laser SE apparatus.
40. The method of claim 1, wherein the etching comprises etching the laser doped product to remove edge and backside P-N junctions.
41. The method of claim 1, wherein the etched product is cleaned after the etching.
42. The process of claim 41 wherein the washed detergent is an HF solution.
43. The method according to claim 42, wherein the HF solution has a mass concentration of 5 to 20%.
44. A secondarily diffused selective emitter manufactured by the manufacturing method according to any one of claims 1 to 43.
45. A crystalline silicon solar cell comprising a secondarily diffused selective emitter according to claim 44.
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Denomination of invention: A selective emitter with secondary diffusion and its preparation method and application

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