Method for improving concentric circles of N-type TopCon battery and battery

Abstract

The invention discloses a method for improving concentric circles of an N-type TopCon battery. A boron diffusion process for preparing the battery comprises the steps of boat entering, vacuumizing, heating, constant temperature maintaining, leakage detecting, constant temperature maintaining, three-time diffusion deposition, boron source propelling, cooling oxidation, constant-temperature oxidation, cooling oxidation, cooling, vacuum breaking and boat exiting. The oxidation temperature of boron diffusion is controlled to be 800-900 DEG C, the pressure in the furnace tube is 850-900 mbar, and oxygen, nitrogen and wet oxygen are introduced at the same time. The BSG with the thickness of 80-120 nm can be formed on the boron-rich layer on the surface of the silicon wafer without prolonging the oxidation time even in a low-temperature state, and the sheet resistance of boron diffusion is controlled to be 500-600 omega / sq. The method is applied to preparation of the N-type TopCon battery, the thickness of the BSG is ensured, the influence of oxygen elements on a silicon wafer is reduced, and the concentric circle phenomenon is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a method for improving concentric circles of an N-type TopCon cell and a cell. Background Art

[0002] TOPCon cells are a type of photovoltaic crystalline silicon cells. In recent years, they have been gradually adopted by industry companies due to their obvious advantages such as high conversion efficiency, low attenuation performance, high mass production cost performance, etc. TOPCon is a tunnel oxide passivated contact (Tunnel Oxide Passivated Contact) solar cell technology based on the principle of selective carriers. Its cell structure is an N-type silicon substrate cell. An ultra-thin layer of silicon oxide is prepared on the back of the cell, and then a layer of doped silicon thin layer is deposited. The two together form a passivated contact structure, which effectively reduces surface recombination and metal contact recombination.

[0003] Concentric circles are the main factor affecting the yield of N-type silicon wafers / cells. Concentric circles are the phenomenon that when the cell is tested for EL, there are black circles spreading outward from the middle of the cell. The conversion efficiency of the cell is extremely low in the blackened area. The proportion of concentric circles in N-type TOPCon cells is significantly higher than that in P-type cells.

[0004] The process route for the front-side matching laser sintering of N-type TOPCon cells is: texturing - boron diffusion (forming doping layer and BSG layer) - back and edge BSG (boron silicon glass) removal - alkali polishing - LPCVD - phosphorus diffusion - front and edge PSG (phosphorus silicon glass) removal - RCA - ALD - front / back film PECVD - screen printing - sintering, annealing - laser sintering - testing.

[0005] The purpose of the boron diffusion process is to dope and form a BSG (boron silicon glass) protective layer. In order to form the BSG protective layer, a boron diffusion annealing step is required: oxygen is introduced to form BSG with the boron-rich layer on the surface of the silicon wafer, which plays a protective role in subsequent processes. If the BSG thickness is too thin, the protective effect will be lost. The BSG protective layer generally needs to be 80 to 120nm thick to meet the normal progress of subsequent processes.

[0006] In conventional methods, if you want to form a thicker BSG, you need to oxidize it at a high temperature of 1020-1050℃ for a long time. However, during the high temperature process, too much oxygen will be introduced into the silicon body, causing serious concentric circle anomalies and resulting in loss of cell efficiency and yield. If you only lower the temperature, although the introduction of oxygen is reduced, it is impossible to form a sufficiently thick BSG (80-120nm), and subsequent processes cannot proceed normally. Moreover, the oxidation time is longer, which is also prone to battery defects such as blackening of the center of the concentric circles. Summary of the invention

[0007] In order to overcome the above-mentioned deficiencies in the prior art, the present invention provides a method for improving the concentric circles of an N-type TopCon battery and a battery.

[0008] The present invention is achieved through the following technical solutions:

[0009] A method for improving the concentric circles of an N-type TopCon battery, wherein the boron diffusion process for preparing the battery comprises the following steps:

[0010] (S1) Entering the boat, controlling the pressure in the furnace tube of the boron expansion furnace to be consistent with the external air pressure, the temperature to be 800-820°C, introducing nitrogen, loading the silicon wafer after texturing in the quartz boat and sending it into the furnace tube;

[0011] (S2) evacuating the furnace, stopping the introduction of nitrogen, and reducing the pressure in the furnace tube to 650-750 mbar;

[0012] (S3) Heating, maintaining constant temperature, and checking for leaks. The pressure in the furnace tube is pumped down to 130-160 mbar, and the temperature is raised to 815-835° C. to confirm whether the leak rate is qualified.

[0013] (S4) maintaining a constant temperature, maintaining the pressure in the furnace tube at 130-160 mbar, and the temperature at 815-836° C., while introducing BCl 3 , nitrogen and oxygen;

[0014] (S5) First diffusion deposition, maintaining the pressure in the furnace tube at 130-160 mbar, the temperature at 815-837° C., and introducing BCl 3 , nitrogen and oxygen at the same time;

[0015] (S6) maintaining a constant temperature, maintaining the pressure in the furnace tube at 130-160 mbar, maintaining the temperature at 825-845° C., stopping the introduction of oxygen, and simultaneously introducing BCl 3 and nitrogen;

[0016] (S7) a second diffusion deposition, maintaining the pressure in the furnace tube at 130-160 mbar, maintaining the temperature at 825-846° C., and introducing BCl 3 , nitrogen and oxygen at the same time;

[0017] (S8) maintaining a constant temperature, maintaining the pressure in the furnace tube at 130-160 mbar, maintaining the temperature at 835-850° C., stopping the introduction of oxygen, and simultaneously introducing BCl 3 and nitrogen;

[0018] (S9) a third diffusion deposition, maintaining the pressure in the furnace tube at 130-160 mbar, the temperature at 835-851° C., and introducing BCl 3 , nitrogen and oxygen at the same time;

[0019] (S10) advancing the boron source, first maintaining the pressure in the furnace tube at 130-160 mbar, raising the temperature to 885-915° C., stopping the introduction of oxygen, and simultaneously introducing BCl3 and nitrogen; then stopping the introduction of BCl3, maintaining the pressure in the furnace tube at 380-420 mbar and the temperature at 885-915° C., and only introducing nitrogen to advance the deposited BCl3;

[0020] (S11) cooling and oxidizing, maintaining the pressure in the furnace tube at 850-900 mbar, reducing the temperature to 800-900° C., introducing oxygen, nitrogen and wet oxygen at the same time, and oxidizing for 680-720 seconds;

[0021] (S12) constant temperature oxidation, the pressure in the furnace tube is 850-900 mbar, the temperature is reduced to 800-900° C., oxygen, nitrogen and wet oxygen are introduced simultaneously, and oxidation is continued for 3800-4400 seconds;

[0022] (S13) cooling and oxidizing, maintaining the pressure in the furnace tube at 850-900 mbar, reducing the temperature to 800-830° C., and simultaneously introducing oxygen, nitrogen and wet oxygen, cooling and oxidizing for 1500-1900 seconds;

[0023] (S14) cooling, maintaining the pressure in the furnace tube at 850-900 mbar, reducing the temperature to 780-800° C., stopping the introduction of oxygen and wet oxygen, and introducing only nitrogen;

[0024] (S15) breaking the vacuum, removing the boat, returning to normal pressure, and continuing to introduce nitrogen, taking out the quartz boat containing the silicon wafers in the furnace tube.

[0025] Preferably, in step (S1), the nitrogen flow rate is 1800-2200 sccm, and the time is 350-450 seconds.

[0026] Preferably, in step (S4), the ventilation flow rate of BCl3 is 280-320sccm, the ventilation flow rate of nitrogen is 3400-3600sccm, the ventilation flow rate of oxygen is 190-210sccm, and the time is 260-340 seconds.

[0027] Preferably, in the first diffusion deposition in step (S5), the gas flow rate of BCl3 is 170-190 sccm, the gas flow rate of nitrogen is 3000-3400 sccm, the gas flow rate of oxygen is 240-260 sccm, and the time is 100-140 seconds.

[0028] Preferably, in the second diffusion deposition in step (S7) and the third diffusion deposition in step (S9), the ventilation flow rates and times of BCl3, nitrogen and oxygen are the same, the ventilation flow rate of BCl3 is 170-190sccm, the ventilation flow rate of nitrogen is 3000-3400sccm, the ventilation flow rate of oxygen is 490-510sccm, and the time is 220-260 seconds.

[0029] Preferably, in steps (S6) constant temperature and (S8) constant temperature, the ventilation flow rate and time of BCl3 and nitrogen are the same, the ventilation flow rate of BCl3 is 280-320sccm, the ventilation flow rate of nitrogen is 3000-3400sccm, and the time is 190-210 seconds.

[0030] Preferably, in the boron source advancement (S10), the temperature is first raised to 885-915°C, the introduction of oxygen is stopped, and BCl3 and nitrogen are introduced simultaneously, with a ventilation flow rate of BCl3 of 280-320sccm and a ventilation flow rate of nitrogen of 480-520sccm, for 100-140 seconds; then the introduction of BCl3 is stopped, and only nitrogen is introduced, with a ventilation flow rate of 3300-3600sccm, for 380-420 seconds; then the pressure in the furnace tube is 380-420mbar and the temperature is kept at 885-915°C, and only nitrogen is introduced to advance the deposited BCl3, with a ventilation flow rate of nitrogen of 4300-4600sccm, for 430-470 seconds.

[0031] Preferably, in step (S11) cooling oxidation, step (S12) constant temperature oxidation and step (S13) cooling oxidation, the ventilation flow rates of oxygen, nitrogen and wet oxygen are the same, the ventilation flow rate of oxygen is 1800-2200sccm, the ventilation flow rate of nitrogen is 580-620sccm, and the flow rate of wet oxygen is 1400-1600sccm.

[0032] Preferably, in step (S11) temperature reduction oxidation, step (S12) constant temperature oxidation and step (S13) temperature reduction oxidation, the wet oxygen is oxygen that passes through a water bath device (such as a water bottle) before entering the boron expansion furnace tube to increase the oxygen humidity.

[0033] On the other hand, the present invention provides an N-type TopCon battery, wherein the preparation method of the battery comprises the above-mentioned boron diffusion process, wherein the square resistance of the boron diffusion is controlled at 500-600Ω / sq, and the BSG thickness is 80-120nm.

[0034] By adopting the boron diffusion process of the present invention, it is possible to achieve a route to ensure good contact in the lightly doped mode without superimposing the laser SE process during the preparation of the N-type TOPCON battery, and clarify the process route of the front matching laser sintering of the N-type TOPCON battery as follows: texturing process-boron diffusion process (forming a doping layer and a BSG layer)-BSG removal-alkali polishing-LPCVD-phosphorus diffusion-PSG removal-RCA-ALD-front / back film PECVD-screen printing-sintering, annealing-laser sintering-testing. The boron diffusion process in this process route adopts the method provided by the present invention, and the remaining processes are conventional processes of the production line, and the mass production process formula can be used. Laser sintering is used to promote the mutual diffusion of silver and silicon, forming a contact effect equivalent to or better than laser SE doping, achieving the effect of further reducing the surface boron-rich layer. At the same time, the cancellation of the laser SE process can completely avoid damage to the battery surface.

[0035] The beneficial effects produced by the technical solution of the present invention are as follows:

[0036] In the oxidation process of the boron diffusion step, the oxidation temperature is controlled at 800-900°C, the pressure in the furnace tube is 850-900 mbar, and oxygen, nitrogen and wet oxygen are introduced at the same time. The pressure used for oxidation is 850-900 mbar, which is not much different from the normal pressure (1000 mbar), and the pressure requirement is not high.

[0037] The wet oxygen in the present invention is different from the wet oxidation in the prior art. The prior art uses liquid water to be directly passed while oxygen is introduced. If the prior art is used to directly pass liquid water into the boron expansion furnace tube, the uniformity will be particularly poor; because the liquid water enters the cavity, the silicon wafers close to the outlet of the substance will react violently, and the silicon wafers far away from the outlet will not react fully. This can only be solved by increasing the time. If the oxidation temperature is lowered, the oxidation time needs to be extended. Because only after the silicon wafers close to the outlet have fully reacted, the silicon wafers far away from the liquid water outlet will have reaction resources. The wet oxygen in the present invention is "oxygen" in the case of adding a water bath device (such as a water bottle), and it is still gaseous "oxygen" when it enters the boron expansion furnace tube. It will diffuse rapidly in the boron expansion furnace tube and will not cause uniformity problems. In this way, there is no need to extend the oxidation time even if the oxidation temperature is lowered.

[0038] The present invention simultaneously introduces oxygen, nitrogen and wet oxygen, which can reduce the boron diffusion oxidation temperature by 100-200°C. Wet oxygen is used to increase the humidity before oxygen enters the boron expansion furnace tube. Wet oxygen has strong oxidizing properties and is more conducive to improving the oxidation rate and oxidation efficiency. A BSG with a thickness of 80-120nm can be formed on the boron-rich layer on the surface of the silicon wafer, and the square resistance of boron diffusion is controlled at 500-600Ω / sq. In this way, the BSG thickness is guaranteed under low temperature conditions, the influence of oxygen elements on the silicon wafer is reduced, and the concentric circle phenomenon is reduced.

[0039] In addition, the present invention also combines three steps of gradual temperature rise deposition diffusion to overcome the problem of uneven doping during boron diffusion doping, which can significantly improve the uniformity of square resistance and further reduce the concentric circle phenomenon, which is beneficial to improving the electrical performance of the battery and obtaining a solar cell with excellent electrical performance. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0041] Therefore, the following detailed description of the embodiments provided by the present invention is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] This embodiment fully analyzes the prior art that the preparation of N-type TopCon batteries is prone to battery defects such as blackening of the center of the concentric circles due to high-temperature oxidation in the boron diffusion process, and provides a method for improving the concentric circles of N-type TopCon batteries. The boron diffusion process of the battery preparation includes the following steps:

[0043] (S1) Entering the boat, controlling the pressure in the furnace tube of the boron expansion furnace to be consistent with the external air pressure, the temperature to be 800-820°C, introducing nitrogen, loading the silicon wafer after texturing in the quartz boat and sending it into the furnace tube;

[0044] (S2) evacuating the furnace, stopping the introduction of nitrogen, and reducing the pressure in the furnace tube to 650-750 mbar;

[0045] (S3) Heating, maintaining constant temperature, and checking for leaks. The pressure in the furnace tube is pumped down to 130-160 mbar, and the temperature is raised to 815-835° C. to confirm whether the leak rate is qualified.

[0046] (S4) maintaining a constant temperature, maintaining the pressure in the furnace tube at 130-160 mbar, and the temperature at 815-836° C., while introducing BCl 3 , nitrogen and oxygen;

[0047] (S5) First diffusion deposition, maintaining the pressure in the furnace tube at 130-160 mbar, the temperature at 815-837° C., and introducing BCl 3 , nitrogen and oxygen at the same time;

[0048] (S6) maintaining a constant temperature, maintaining the pressure in the furnace tube at 130-160 mbar, maintaining the temperature at 825-845° C., stopping the introduction of oxygen, and simultaneously introducing BCl 3 and nitrogen;

[0049] (S7) a second diffusion deposition, maintaining the pressure in the furnace tube at 130-160 mbar, maintaining the temperature at 825-846° C., and introducing BCl 3 , nitrogen and oxygen at the same time;

[0050] (S8) maintaining a constant temperature, maintaining the pressure in the furnace tube at 130-160 mbar, maintaining the temperature at 835-850° C., stopping the introduction of oxygen, and simultaneously introducing BCl 3 and nitrogen;

[0051] (S9) a third diffusion deposition, maintaining the pressure in the furnace tube at 130-160 mbar, the temperature at 835-851° C., and introducing BCl 3 , nitrogen and oxygen at the same time;

[0052] (S10) advancing the boron source, first maintaining the pressure in the furnace tube at 130-160 mbar, raising the temperature to 885-915° C., stopping the introduction of oxygen, and simultaneously introducing BCl3 and nitrogen; then stopping the introduction of BCl3, maintaining the pressure in the furnace tube at 380-420 mbar and the temperature at 885-915° C., and only introducing nitrogen to advance the deposited BCl3;

[0053] (S11) cooling and oxidizing, maintaining the pressure in the furnace tube at 850-900 mbar, reducing the temperature to 800-900° C., introducing oxygen, nitrogen and wet oxygen at the same time, and oxidizing for 680-720 seconds;

[0054] (S12) isothermal oxidation, at a pressure of 850 to 900 mbar and a temperature of 800 to 900° C. in the furnace tube, oxygen, nitrogen and wet oxygen are introduced simultaneously, and oxidation is continued for 3800 to 4400 seconds;

[0055] (S13) cooling and oxidizing, maintaining the pressure in the furnace tube at 850-900 mbar, reducing the temperature to 800-830° C., and simultaneously introducing oxygen, nitrogen and wet oxygen, cooling and oxidizing for 1500-1900 seconds;

[0056] (S14) cooling, maintaining the pressure in the furnace tube at 850-900 mbar, reducing the temperature to 780-800° C., stopping the introduction of oxygen and wet oxygen, and introducing only nitrogen;

[0057] (S15) breaking the vacuum, removing the boat, returning to normal pressure, and continuing to introduce nitrogen, taking out the quartz boat containing the silicon wafers in the furnace tube.

[0058] As a preferred embodiment, in step (S1), the ventilation flow rate of nitrogen is 1800-2200 sccm, and the time is 350-450 seconds.

[0059] As a preferred embodiment, in step (S4), the ventilation flow rate of BCl3 is 280-320sccm, the ventilation flow rate of nitrogen is 3400-3600sccm, the ventilation flow rate of oxygen is 190-210sccm, and the time is 260-340 seconds.

[0060] As a preferred embodiment, in the first diffusion deposition in step (S5), the gas flow rate of BCl3 is 170-190 sccm, the gas flow rate of nitrogen is 3000-3400 sccm, the gas flow rate of oxygen is 240-260 sccm, and the time is 100-140 seconds.

[0061] As a preferred embodiment, in the second diffusion deposition in step (S7) and the third diffusion deposition in step (S9), the ventilation flow rates and times of BCl3, nitrogen and oxygen are the same, the ventilation flow rate of BCl3 is 170-190sccm, the ventilation flow rate of nitrogen is 3000-3400sccm, the ventilation flow rate of oxygen is 490-510sccm, and the time is 220-260 seconds.

[0062] As a preferred embodiment, in the constant temperature step (S6) and the constant temperature step (S8), the ventilation flow rate and time of BCl3 and nitrogen are the same, the ventilation flow rate of BCl3 is 280-320sccm, the ventilation flow rate of nitrogen is 3000-3400sccm, and the time is 190-210 seconds.

[0063] As a preferred embodiment, in the boron source advancement step (S10), the temperature is first raised to 885-915°C, the introduction of oxygen is stopped, and BCl3 and nitrogen are introduced at the same time, with a ventilation flow rate of BCl3 of 280-320sccm and a ventilation flow rate of nitrogen of 480-520sccm, for 100-140 seconds; then the introduction of BCl3 is stopped, and only nitrogen is introduced, with a ventilation flow rate of 3300-3600sccm, for 380-420 seconds; then the pressure in the furnace tube is 380-420mbar and the temperature is kept at 885-915°C, and only nitrogen is introduced to advance the deposited BCl3, with a ventilation flow rate of nitrogen of 4300-4600sccm, for 430-470 seconds.

[0064] As a preferred embodiment, in step (S11) cooling oxidation, step (S12) constant temperature oxidation and step (S13) cooling oxidation, the ventilation flow rates of oxygen, nitrogen and wet oxygen are the same, the ventilation flow rate of oxygen is 1800-2200sccm, the ventilation flow rate of nitrogen is 580-620sccm, and the flow rate of wet oxygen is 1400-1600sccm.

[0065] As a preferred embodiment, in step (S11) cooling oxidation, step (S12) constant temperature oxidation and step (S13) cooling oxidation, the wet oxygen is oxygen that passes through a water bath device (such as a water bottle) before entering the boron expansion furnace tube to increase the oxygen humidity.

[0066] On the other hand, the present invention provides an N-type TopCon battery, wherein the preparation method of the battery comprises the above-mentioned boron diffusion process, wherein the square resistance of the boron diffusion is controlled at 500-600Ω / sq, and the BSG thickness is 80-120nm.

[0067] In order to more clearly illustrate the technical solutions and advantages of the present invention, the present invention is further explained below in conjunction with embodiments and comparative examples.

[0068] In the following examples and comparative examples, the wet oxygen is oxygen that passes through a bottle filled with water before entering the boron expansion furnace tube to increase the humidity of the oxygen.

[0069] Example 1

[0070] (S1) Entering the boat, controlling the pressure in the furnace tube of the boron expansion furnace to be consistent with the external air pressure, the temperature is 800°C, nitrogen is introduced, and the silicon wafer after texturing is loaded into the quartz boat and sent into the furnace tube, the nitrogen ventilation flow rate is 1800sccm, and the time is 450 seconds;

[0071] (S2) evacuating the furnace, stopping the introduction of nitrogen, and reducing the pressure in the furnace tube to 650 mbar;

[0072] (S3) Heating, maintaining constant temperature, and checking for leaks. The pressure in the furnace tube is pumped down to 130 mbar, the temperature is raised to 820° C., the temperature is maintained constant, and the leak rate is confirmed to be qualified;

[0073] (S4) maintaining a constant temperature, maintaining the pressure in the furnace tube at 130 mbar, maintaining the temperature at 820-825° C., and introducing BCl 3 , nitrogen and oxygen at a flow rate of 280 sccm for BCl 3 , 3400 sccm for nitrogen, and 190 sccm for oxygen for 340 seconds;

[0074] (S5) First diffusion deposition, maintaining the pressure in the furnace tube at 130 mbar, maintaining the temperature at 821-826° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 170 sccm for BCl 3 , 3000 sccm for nitrogen and 240 sccm for oxygen, and the time is 140 seconds;

[0075] (S6) maintaining a constant temperature, maintaining the pressure in the furnace tube at 130 mbar, maintaining the temperature at 835-840° C., stopping the introduction of oxygen, and introducing BCl 3 and nitrogen at the same time, with a BCl 3 flow rate of 280 sccm and a nitrogen flow rate of 3000 sccm, for 210 seconds;

[0076] (S7) a second diffusion deposition, maintaining the pressure in the furnace tube at 130 mbar, maintaining the temperature at 836-841° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 170 sccm for BCl 3 , 3000 sccm for nitrogen and 490 sccm for oxygen, and the time is 260 seconds;

[0077] (S8) maintaining a constant temperature, maintaining the pressure in the furnace tube at 130 mbar, maintaining the temperature at 845-850° C., stopping the introduction of oxygen, and introducing BCl 3 and nitrogen at the same time, with a BCl 3 flow rate of 280 sccm and a nitrogen flow rate of 3000 sccm, for 210 seconds;

[0078] (S9) a third diffusion deposition, maintaining the pressure in the furnace tube at 130 mbar, the temperature at 846-851° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 170-190 sccm for BCl 3 , 3000 sccm for nitrogen and 490 sccm for oxygen, for 260 seconds;

[0079] (S10) the boron source is advanced, the pressure in the furnace tube is first maintained at 130 mbar, the temperature is raised to 885°C, oxygen is stopped, and BCl3 and nitrogen are introduced simultaneously, the ventilation flow rate of BCl3 is 280 sccm, and the ventilation flow rate of nitrogen is 480 sccm, and the time is 100 seconds; then the introduction of BCl3 is stopped, and only nitrogen is introduced, and the ventilation flow rate is 3300 sccm, and the time is 420 seconds; then the pressure in the furnace tube is 380 mbar, and the temperature is 885°C for insulation, and only nitrogen is introduced to advance the deposited BCl3, and the ventilation flow rate of nitrogen is 4300 sccm, and the time is 470 seconds;

[0080] (S11) cooling and oxidizing, maintaining the pressure in the furnace tube at 850 mbar, reducing the temperature to 850-855° C., introducing oxygen, nitrogen and wet oxygen at the same time, first oxidizing for 720 seconds, with the ventilation flow rate of oxygen being 1800 sccm, the ventilation flow rate of nitrogen being 580 sccm, and the flow rate of wet oxygen being 1400 sccm;

[0081] (S12) constant temperature oxidation, at a pressure of 850 mbar and a temperature of 850-855° C. in the furnace tube, oxygen, nitrogen and wet oxygen are introduced simultaneously, and oxidation is continued for 4400 seconds, with a ventilation flow rate of 1800 sccm for oxygen, 580 sccm for nitrogen and 1400 sccm for wet oxygen;

[0082] (S13) cooling and oxidizing, maintaining the pressure in the furnace tube at 850 mbar, reducing the temperature to 824-826° C., and simultaneously introducing oxygen, nitrogen and wet oxygen, cooling and oxidizing for 1900 seconds, with the ventilation flow rate of oxygen being 1800 sccm, the ventilation flow rate of nitrogen being 580 sccm, and the flow rate of wet oxygen being 1400 sccm;

[0083] (S14) cooling, maintaining the pressure in the furnace tube at 850 mbar, reducing the temperature to 780-800° C., stopping the introduction of oxygen and wet oxygen, and introducing only nitrogen, with a nitrogen flow rate of 15000 sccm;

[0084] (S15) Break the vacuum, take out the boat, introduce nitrogen at a flow rate of 18000 sccm for 50 seconds, restore to normal pressure, and the temperature is 760°C; keep introducing nitrogen for 900 seconds, with a nitrogen flow rate of 1800 sccm, and take out the quartz boat containing silicon wafers in the furnace tube.

[0085] Example 2

[0086] (S1) Entering the boat, controlling the pressure in the furnace tube of the boron expansion furnace to be consistent with the external pressure, the temperature is 820°C, nitrogen is introduced, and the silicon wafer after texturing is loaded into the quartz boat and sent into the furnace tube, the nitrogen ventilation flow rate is 2200sccm, and the time is 350 seconds;

[0087] (S2) evacuating the furnace, stopping the introduction of nitrogen, and reducing the pressure in the furnace tube to 750 mbar;

[0088] (S3) Heating, maintaining constant temperature, and checking for leaks. The pressure in the furnace tube is pumped down to 160 mbar, the temperature is raised to 830° C., the temperature is maintained constant, and the leak rate is confirmed to be qualified;

[0089] (S4) maintaining a constant temperature, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 830-835° C., and introducing BCl 3 , nitrogen and oxygen at a flow rate of 320 sccm for BCl 3 , 3600 sccm for nitrogen, and 210 sccm for oxygen for 260 seconds;

[0090] (S5) First diffusion deposition, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 831-836° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 190 sccm for BCl 3 , 3400 sccm for nitrogen and 260 sccm for oxygen, and the time is 100 seconds;

[0091] (S6) maintaining a constant temperature, maintaining the pressure in the furnace tube at 160 mbar, and maintaining the temperature at 840-845° C., stopping the introduction of oxygen, and introducing BCl 3 and nitrogen at the same time, with a BCl 3 flow rate of 320 sccm and a nitrogen flow rate of 3400 sccm, for 190 seconds;

[0092] (S7) a second diffusion deposition, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 841-846° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 190 sccm for BCl 3 , 3400 sccm for nitrogen and 510 sccm for oxygen, and the time is 220 seconds;

[0093] (S8) maintaining a constant temperature, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 846-850° C., stopping the introduction of oxygen, and introducing BCl 3 and nitrogen at the same time, with a BCl 3 flow rate of 320 sccm and a nitrogen flow rate of 3400 sccm, for 190 seconds;

[0094] (S9) a third diffusion deposition, maintaining the pressure in the furnace tube at 160 mbar, the temperature at 847-851° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 190 sccm for BCl 3 , 3400 sccm for nitrogen and 510 sccm for oxygen, and the time for 220 seconds;

[0095] (S10) boron source is advanced, first the pressure in the furnace tube is maintained at 160 mbar, the temperature is raised to 915 ° C, oxygen is stopped, and BCl3 and nitrogen are introduced simultaneously, the ventilation flow rate of BCl3 is 320 sccm, and the ventilation flow rate of nitrogen is 520 sccm, and the time is 140 seconds; then BCl3 is stopped, and only nitrogen is introduced, and the ventilation flow rate is 3600 sccm, and the time is 380 seconds; then the pressure in the furnace tube is 420 mbar, and the temperature is 915 ° C insulation, and only nitrogen is introduced to advance the deposited BCl3, and the ventilation flow rate of nitrogen is 4600 sccm, and the time is 430 seconds;

[0096] (S11) cooling and oxidizing, maintaining the pressure in the furnace tube at 900 mbar, reducing the temperature to 860-865° C., introducing oxygen, nitrogen and wet oxygen at the same time, first oxidizing for 680 seconds, with the ventilation flow rate of oxygen being 2200 sccm, the ventilation flow rate of nitrogen being 620 sccm, and the flow rate of wet oxygen being 1600 sccm;

[0097] (S12) constant temperature oxidation, at a furnace pressure of 900 mbar and a temperature of 860-865° C., oxygen, nitrogen and wet oxygen are introduced simultaneously, and oxidation is continued for 3800 seconds, with a ventilation flow rate of oxygen of 2200 sccm, a ventilation flow rate of nitrogen of 620 sccm and a flow rate of wet oxygen of 1600 sccm;

[0098] (S13) cooling and oxidizing, maintaining the pressure in the furnace tube at 900 mbar, reducing the temperature to 826-830° C., and simultaneously introducing oxygen, nitrogen and wet oxygen, cooling and oxidizing for 1500 seconds, with the ventilation flow rate of oxygen being 2200 sccm, the ventilation flow rate of nitrogen being 620 sccm, and the flow rate of wet oxygen being 1600 sccm;

[0099] (S14) cooling, maintaining the pressure in the furnace tube at 900 mbar, reducing the temperature to 780-800° C., stopping the introduction of oxygen and wet oxygen, and introducing only nitrogen, with a nitrogen flow rate of 20,000 sccm;

[0100] (S15) Break the vacuum, take out the boat, introduce nitrogen at a flow rate of 22000sccm for 30 seconds, restore to normal pressure, and keep the temperature at 760℃~800℃; keep introducing nitrogen for 750 seconds, with a nitrogen flow rate of 2200sccm, and take out the quartz boat containing silicon wafers in the furnace tube.

[0101] Example 3

[0102] (S1) Entering the boat, controlling the pressure in the furnace tube of the boron expansion furnace to be consistent with the external pressure, the temperature is 810°C, nitrogen is introduced, and the silicon wafer after texturing is loaded into the quartz boat and sent into the furnace tube, the nitrogen ventilation flow rate is 2000sccm, and the time is 410 seconds;

[0103] (S2) evacuating the furnace, stopping the introduction of nitrogen, and reducing the pressure in the furnace tube to 720 mbar;

[0104] (S3) Heating, maintaining constant temperature, and checking for leaks. The pressure in the furnace tube is pumped down to 150 mbar, the temperature is raised to 825° C., the temperature is maintained constant, and the leak rate is confirmed to be qualified;

[0105] (S4) maintaining a constant temperature, maintaining the pressure in the furnace tube at 150 mbar, maintaining the temperature at 825-828° C., and introducing BCl 3 , nitrogen and oxygen at a flow rate of 300 sccm for BCl 3 , 3500 sccm for nitrogen, and 200 sccm for oxygen for 350 seconds;

[0106] (S5) First diffusion deposition, maintaining the pressure in the furnace tube at 150 mbar, maintaining the temperature at 826-829° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 180 sccm for BCl 3 , 3200 sccm for nitrogen and 250 sccm for oxygen, and the time is 120 seconds;

[0107] (S6) maintaining a constant temperature, maintaining the pressure in the furnace tube at 150 mbar, maintaining the temperature at 835-840° C., stopping the introduction of oxygen, and introducing BCl 3 and nitrogen at the same time, with a BCl 3 flow rate of 300 sccm and a nitrogen flow rate of 3200 sccm, for 200 seconds;

[0108] (S7) a second diffusion deposition, maintaining the pressure in the furnace tube at 150 mbar, maintaining the temperature at 836-841° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 180 sccm for BCl 3 , 3200 sccm for nitrogen and 500 sccm for oxygen, and the time is 250 seconds;

[0109] (S8) maintaining a constant temperature, maintaining the pressure in the furnace tube at 150 mbar, maintaining the temperature at 846-850° C., stopping the introduction of oxygen, and introducing BCl 3 and nitrogen at the same time, with a BCl 3 flow rate of 300 sccm and a nitrogen flow rate of 3200 sccm, for 200 seconds;

[0110] (S9) a third diffusion deposition, maintaining the pressure in the furnace tube at 150 mbar, the temperature at 847-851° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 180 sccm for BCl 3 , 3200 sccm for nitrogen and 500 sccm for oxygen, for 250 seconds;

[0111] (S10) the boron source is advanced, the pressure in the furnace tube is first maintained at 150 mbar, the temperature is raised to 900° C., oxygen is stopped, and BCl3 and nitrogen are introduced simultaneously, the ventilation flow rate of BCl3 is 300 sccm, and the ventilation flow rate of nitrogen is 500 sccm, and the time is 120 seconds; then the introduction of BCl3 is stopped, and only nitrogen is introduced, and the ventilation flow rate is 3400 sccm, and the time is 400 seconds; then the pressure in the furnace tube is 400 mbar, and the temperature is 900° C. for insulation, and only nitrogen is introduced to advance the deposited BCl3, and the ventilation flow rate of nitrogen is 4500 sccm, and the time is 450 seconds;

[0112] (S11) cooling and oxidizing, maintaining the pressure in the furnace tube at 875 mbar, reducing the temperature to 880° C., introducing oxygen, nitrogen and wet oxygen at the same time, first oxidizing for 710 seconds, with the ventilation flow rate of oxygen being 1900 sccm, the ventilation flow rate of nitrogen being 610 sccm, and the flow rate of wet oxygen being 1450 sccm;

[0113] (S12) constant temperature oxidation, at a furnace pressure of 875 mbar and a temperature of 880-885° C., oxygen, nitrogen and wet oxygen are introduced simultaneously, and oxidation is continued for 4200 seconds, with a ventilation flow rate of oxygen of 1900 sccm, a ventilation flow rate of nitrogen of 610 sccm and a flow rate of wet oxygen of 1450 sccm;

[0114] (S13) cooling and oxidizing, maintaining the pressure in the furnace tube at 875 mbar, reducing the temperature to 821-825° C., and simultaneously introducing oxygen, nitrogen and wet oxygen for 1800 seconds, with the ventilation flow rate of oxygen being 1900 sccm, the ventilation flow rate of nitrogen being 610 sccm, and the flow rate of wet oxygen being 1450 sccm;

[0115] (S14) cooling, maintaining the pressure in the furnace tube at 875 mbar, reducing the temperature to 780-800° C., stopping the introduction of oxygen and wet oxygen, and introducing only nitrogen, with a nitrogen flow rate of 18000 sccm;

[0116] (S15) Break the vacuum, take out the boat, introduce nitrogen at a flow rate of 20,000 sccm for 35 seconds, restore to normal pressure, and keep the temperature at 760°C to 800°C; keep introducing nitrogen for 800 seconds at a nitrogen flow rate of 2,000 sccm, and take out the quartz boat containing silicon wafers in the furnace tube.

[0117] Example 4

[0118] (S1) Entering the boat, controlling the pressure in the furnace tube of the boron expansion furnace to be consistent with the external pressure, the temperature is 820°C, nitrogen is introduced, and the silicon wafer after texturing is loaded into the quartz boat and sent into the furnace tube, the nitrogen ventilation flow rate is 2000sccm, and the time is 400 seconds;

[0119] (S2) evacuating the furnace, stopping the introduction of nitrogen, and reducing the pressure in the furnace tube to 700 mbar;

[0120] (S3) Heating, maintaining constant temperature, and checking for leaks. The pressure in the furnace tube is pumped down to 130 mbar, the temperature is raised to 830° C., the temperature is maintained constant, and the leak rate is confirmed to be qualified;

[0121] (S4) maintaining a constant temperature, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 832-836° C., and introducing BCl 3 , nitrogen and oxygen at a flow rate of 300 sccm for BCl 3 , 3500 sccm for nitrogen, and 200 sccm for oxygen for 300 seconds;

[0122] (S5) First diffusion deposition, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 833-837° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 180 sccm for BCl 3 , 3200 sccm for nitrogen and 250 sccm for oxygen, for 120 seconds;

[0123] (S6) maintaining a constant temperature, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 840-845° C., stopping the introduction of oxygen, and introducing BCl 3 and nitrogen at the same time, with a BCl 3 flow rate of 300 sccm and a nitrogen flow rate of 3200 sccm, for 200 seconds;

[0124] (S7) a second diffusion deposition, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 841-846° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 180 sccm for BCl 3 , 3200 sccm for nitrogen and 500 sccm for oxygen, and the time is 240 seconds;

[0125] (S8) maintaining a constant temperature, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 846-850° C., stopping the introduction of oxygen, and introducing BCl 3 and nitrogen at the same time, with a BCl 3 flow rate of 300 sccm and a nitrogen flow rate of 3200 sccm, for 200 seconds;

[0126] (S9) a third diffusion deposition, maintaining the pressure in the furnace tube at 160 mbar, the temperature at 847-851° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 180 sccm for BCl 3 , 3200 sccm for nitrogen and 500 sccm for oxygen, and the time is 240 seconds;

[0127] (S10) boron source advancement, first maintaining the pressure in the furnace tube at 160 mbar, heating to 890°C, stopping the introduction of oxygen, and simultaneously introducing BCl3 and nitrogen, with a ventilation flow rate of 300 sccm for BCl3 and 500 sccm for nitrogen, for 120 seconds; then stopping the introduction of BCl3, only introducing nitrogen, with a ventilation flow rate of 3500 sccm, for 400 seconds; then the pressure in the furnace tube is 400 mbar, the temperature is 910°C for insulation, only introducing nitrogen to advance the deposited BCl3, with a ventilation flow rate of 4500 sccm for 450 seconds;

[0128] (S11) cooling and oxidizing, maintaining the pressure in the furnace tube at 865 mbar, reducing the temperature to 900° C., introducing oxygen, nitrogen and wet oxygen at the same time, first oxidizing for 700 seconds, with the ventilation flow rate of oxygen being 2000 sccm, the ventilation flow rate of nitrogen being 600 sccm, and the flow rate of wet oxygen being 1500 sccm;

[0129] (S12) constant temperature oxidation, the pressure in the furnace tube is 865 mbar, the temperature is reduced to 900° C., oxygen, nitrogen and wet oxygen are introduced simultaneously, and oxidation is continued for 4100 seconds, the ventilation flow rate of oxygen is 2000 sccm, the ventilation flow rate of nitrogen is 600 sccm, and the flow rate of wet oxygen is 1500 sccm;

[0130] (S13) cooling and oxidizing, maintaining the pressure in the furnace tube at 865 mbar, reducing the temperature to 825° C., and simultaneously introducing oxygen, nitrogen and wet oxygen, cooling and oxidizing for 1700 seconds, with the ventilation flow rate of oxygen being 2000 sccm, the ventilation flow rate of nitrogen being 600 sccm, and the flow rate of wet oxygen being 1500 sccm;

[0131] (S14) cooling, maintaining the pressure in the furnace tube at 865 mbar, reducing the temperature to 780-800° C., stopping the introduction of oxygen and wet oxygen, and introducing only nitrogen, with a nitrogen flow rate of 17000 sccm;

[0132] (S15) Break the vacuum, take out the boat, introduce nitrogen at a flow rate of 20,000 sccm for 40 seconds, restore to normal pressure, and keep the temperature at 760°C to 800°C; keep introducing nitrogen for 800 seconds at a nitrogen flow rate of 2,000 sccm, and take out the quartz boat containing silicon wafers in the furnace tube.

[0133] Example 5

[0134] (S1) Entering the boat, controlling the pressure in the furnace tube of the boron expansion furnace to be consistent with the external pressure, the temperature is 815°C, nitrogen is introduced, and the silicon wafer after texturing is loaded into the quartz boat and sent into the furnace tube. The nitrogen ventilation flow rate is 2000sccm, and the time is 390 seconds;

[0135] (S2) evacuating the furnace, stopping the introduction of nitrogen, and reducing the pressure in the furnace tube to 700 mbar;

[0136] (S3) Heating, maintaining constant temperature, and checking for leaks. The pressure in the furnace tube is pumped down to 130 mbar, the temperature is raised to 830° C., the temperature is maintained constant, and the leak rate is confirmed to be qualified;

[0137] (S4) maintaining a constant temperature, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 832-836° C., and introducing BCl 3 , nitrogen and oxygen at a flow rate of 300 sccm for BCl 3 , 3500 sccm for nitrogen, and 200 sccm for oxygen for 300 seconds;

[0138] (S5) First diffusion deposition, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 833-837° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 180 sccm for BCl 3 , 3200 sccm for nitrogen and 250 sccm for oxygen, for 120 seconds;

[0139] (S6) maintaining a constant temperature, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 840-845° C., stopping the introduction of oxygen, and introducing BCl 3 and nitrogen at the same time, with a BCl 3 flow rate of 300 sccm and a nitrogen flow rate of 3200 sccm, for 200 seconds;

[0140] (S7) a second diffusion deposition, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 841-846° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 180 sccm for BCl 3 , 3200 sccm for nitrogen and 500 sccm for oxygen, and the time is 240 seconds;

[0141] (S8) maintaining a constant temperature, maintaining the pressure in the furnace tube at 160 mbar, maintaining the temperature at 846-850° C., stopping the introduction of oxygen, and introducing BCl 3 and nitrogen at the same time, with a BCl 3 flow rate of 310 sccm and a nitrogen flow rate of 3100 sccm, for 208 seconds;

[0142] (S9) a third diffusion deposition, maintaining the pressure in the furnace tube at 160 mbar, the temperature at 847-851° C., introducing BCl 3 , nitrogen and oxygen at a flow rate of 185 sccm for BCl 3 , 3300 sccm for nitrogen and 490 sccm for oxygen, and the time is 250 seconds;

[0143] (S10) boron source advancement, first maintaining the pressure in the furnace tube at 160 mbar, heating to 890°C, stopping the introduction of oxygen, and simultaneously introducing BCl3 and nitrogen, with a ventilation flow rate of 300 sccm for BCl3 and 500 sccm for nitrogen, for 120 seconds; then stopping the introduction of BCl3, only introducing nitrogen, with a ventilation flow rate of 3500 sccm, for 400 seconds; then the pressure in the furnace tube is 400 mbar, the temperature is 910°C for insulation, only introducing nitrogen to advance the deposited BCl3, with a ventilation flow rate of 4500 sccm for 450 seconds;

[0144] (S11) cooling and oxidizing, maintaining the pressure in the furnace tube at 865 mbar, reducing the temperature to 900° C., introducing oxygen, nitrogen and wet oxygen at the same time, first oxidizing for 710 seconds, with the ventilation flow rate of oxygen being 1900 sccm, the ventilation flow rate of nitrogen being 590 sccm, and the flow rate of wet oxygen being 1400 sccm;

[0145] (S12) constant temperature oxidation, the pressure in the furnace tube is 865 mbar, the temperature is reduced to 900° C., oxygen, nitrogen and wet oxygen are introduced simultaneously, and oxidation is continued for 4000 seconds, the ventilation flow rate of oxygen is 2100 sccm, the ventilation flow rate of nitrogen is 610 sccm, and the flow rate of wet oxygen is 1600 sccm;

[0146] (S13) cooling and oxidizing, maintaining the pressure in the furnace tube at 865 mbar, reducing the temperature to 825° C., and simultaneously introducing oxygen, nitrogen and wet oxygen, cooling and oxidizing for 1700 seconds, with the ventilation flow rate of oxygen being 2000 sccm, the ventilation flow rate of nitrogen being 600 sccm, and the flow rate of wet oxygen being 1500 sccm;

[0147] (S14) cooling, maintaining the pressure in the furnace tube at 865 mbar, reducing the temperature to 780-800° C., stopping the introduction of oxygen and wet oxygen, and introducing only nitrogen, with a nitrogen flow rate of 17000 sccm;

[0148] (S15) Break the vacuum, take out the boat, introduce nitrogen at a flow rate of 20,000 sccm for 40 seconds, restore to normal pressure, and keep the temperature at 760°C to 800°C; keep introducing nitrogen for 800 seconds at a nitrogen flow rate of 2,000 sccm, and take out the quartz boat containing silicon wafers in the furnace tube.

[0149] Comparative Example 1

[0150] Comparative Example 1 includes most of the operating steps in Examples 1 to 5, except that: in step (S11) temperature reduction oxidation and step (S12) constant temperature oxidation, the oxidation temperature is 1020 to 1050° C., and no wet oxygen is introduced, but oxygen and nitrogen are introduced;

[0151] In step (S13) of temperature reduction oxidation, although the oxidation temperature is the same as that of Examples 1 to 5, wet oxygen is not introduced, but oxygen and nitrogen are introduced.

[0152] Comparative Example 2

[0153] Comparative Example 2 includes most of the operating steps in Examples 1 to 5, with the difference being that in steps (S11) cooling oxidation, (S12) constant temperature oxidation, and (S13) cooling oxidation, although the oxidation temperatures are the same as those in Examples 1 to 5, wet oxygen is not introduced, but oxygen and nitrogen are introduced.

[0154] Comparative Example 3

[0155] Comparative Example 3 includes most of the operating steps in Examples 1 to 5, with the difference being that in steps (S11) cooling oxidation, (S12) constant temperature oxidation, and (S13) cooling oxidation, the oxidation temperature is 1020 to 1050°C, and no wet oxygen is introduced, but oxygen and nitrogen are introduced.

[0156] Comparative Example 4

[0157] Comparative Example 4 includes most of the operating steps in Examples 1 to 5, except that, in steps (S5) to (S9), a single diffusion deposition is adopted: the pressure in the furnace tube is maintained at 160 mbar, the temperature is maintained at 860 to 880°C, and BCl3, nitrogen and oxygen are introduced at the same time, the ventilation flow rate of BCl3 is 180 to 300 sccm, the ventilation flow rate of nitrogen is 2500 to 3200 sccm, the ventilation flow rate of oxygen is 250 to 300 sccm, and the time is 800 to 1200 seconds.

[0158] Comparative Example 5

[0159] Comparative Example 5 includes most of the operating steps in Examples 1 to 5, except that there is no step (S10) of boron source advancement.

[0160] Performance Testing:

[0161] Five test positions (distributed at the four corners and the center of the square silicon wafer) were selected from the silicon wafers prepared in the above embodiments and comparative examples, and the BSG thickness was tested using a laser ellipsometer, and the square resistance was tested using a four-probe square resistance tester. The results are shown in Tables 1 and 2.

[0162] Table 1 BSG thickness test results (unit: nm)

[0163]

[0164]

[0165] Table 2 Square resistance test results (unit: Ω / sq)

[0166] center Position 1 Position 2 Location 3 Position 4 Mean Example 1 571.90 575.80 576.13 576.22 576.32 575.27 Example 2 558.56 566.73 567.40 567.75 566.12 565.31 Example 3 549.89 556.35 556.12 556.87 555.95 555.04 Example 4 542.68 546.65 547.61 547.19 546.17 546.06 Example 5 541.04 546.76 546.34 546.85 546.65 545.52 Comparative Example 1 361.55 366.11 366.05 366.95 367.14 365.56 Comparative Example 2 680.78 686.27 685.72 685.93 686.52 685.04 Comparative Example 3 361.04 366.66 366.68 366.69 367.28 365.67 Comparative Example 4 308.35 365.63 325.55 375.27 315.65 338.09 Comparative Example 5 701.03 707.04 706.68 706.66 706.41 705.56

[0167] From Tables 1 and 2, we can see that:

[0168] Comparing Examples 1 to 5 with Comparative Examples 1 and 3, the thickness of the BSG layer in Examples 1 to 5 increases and the square resistance increases significantly. This shows that lowering the oxidation temperature and simultaneously introducing oxygen, nitrogen and wet oxygen are conducive to the formation of BSG and reduce the entry of oxygen into the silicon body. Even at a relatively low temperature, a sufficiently thick BSG can be formed with the boron-rich layer on the surface of the silicon wafer without extending the oxidation reaction time.

[0169] Comparing Examples 1 to 5 with Comparative Example 2, in Comparative Example 2, the sheet resistance is significantly improved under low-temperature oxidation at 800 to 900°C without the introduction of wet oxygen, but the formed BSG is seriously thin, with a thickness of about 50 to 60 nm. This also shows that increasing wet oxygen is conducive to the formation of BSG, and lowering the oxidation temperature can also increase the sheet resistance.

[0170] Compared with comparative example 4, the square resistance of embodiments 1 to 5 is significantly increased. This shows that the problem of uneven doping during boron diffusion doping can be overcome by three times of gradual temperature increase deposition diffusion, and the uniformity of square resistance can be significantly improved.

[0171] Comparing Examples 1 to 5 with Comparative Example 5, the square resistance of Comparative Example 5 is significantly higher. This also shows that through the boron source advancement, the square resistance of the silicon wafer is moderate, and a thicker BSG can be formed. If the boron source advancement step is eliminated, the square resistance will be higher, at 600-800Ω / sq, and a normal PN junction cannot be formed, and the battery performance is seriously low.

[0172] The silicon wafers prepared in the above embodiments and comparative examples were tested with an EL tester for the concentric circles of the whole silicon wafer battery. The silicon wafers prepared in the above embodiments and comparative examples were used to prepare N-type TopCon batteries using the same process, and their conversion efficiency Eta (%), open circuit voltage Uoc (V), short circuit current Isc (A), fill factor FF (%), and series resistance Rser (Ω) were tested. The test results are shown in Table 3.

[0173] Table 3 Battery performance test results

[0174]

[0175]

[0176] From Table 3, we can see that:

[0177] Comparing Examples 1 to 5 with Comparative Examples 1 and 3, there is little difference in conversion efficiency Eta (%), open circuit voltage Uoc (V), short circuit current Isc (A), fill factor FF (%), and series resistance Rser (Ω); however, the concentric circle ratio of Examples 1 to 5 is significantly reduced. This shows that the present invention can not only reduce the oxidation temperature by 100 to 200°C without increasing the oxidation time by introducing oxygen, nitrogen and wet oxygen at the same time, but also greatly reduce the concentric circle ratio to meet the requirements of N-type TopCon batteries.

[0178] Comparing Examples 1 to 5 with Comparative Example 2, Comparative Example 2 uses low-temperature oxidation without introducing wet oxygen, resulting in a thin BSG that cannot play a protective role. Subsequent processes will damage the surface, resulting in a significant decrease in the conversion efficiency Eta (%), open circuit voltage Uoc (V), and fill factor FF (%) of the battery prepared in Comparative Example 2, a high series resistance Rser (Ω), and a significant increase in the concentric circle ratio, but slightly improved compared to other comparative examples. This shows that low-temperature oxidation can reduce the ratio of concentric circles, and adding wet oxygen can form a sufficiently thick BSG, thereby improving the electrical performance of the battery.

[0179] Comparing Examples 1 to 5 with Comparative Example 4, Comparative Example 4 uses one diffusion deposition, and the square resistance uniformity is poor, resulting in a low conversion efficiency Eta (%) of the battery prepared in Comparative Example 4, and a significant increase in the proportion of concentric circles. This shows that by three times of gradual temperature increase deposition diffusion and then oxidation at low temperature, the square resistance uniformity can be significantly improved, thereby reducing the concentric circle phenomenon, which is beneficial to improving the electrical performance of the battery and obtaining a solar cell with excellent electrical performance.

[0180] Comparing Examples 1 to 5 with Comparative Example 5, Comparative Example 5 lacks the step of advancing the boron source, and the boron source cannot be doped into the silicon body, and a complete PN junction cannot be formed, resulting in a significant decrease in the conversion efficiency Eta (%), open circuit voltage Uoc (V), and fill factor FF (%) of the battery prepared in Comparative Example 5, and a high series resistance Rser (Ω), and a significant increase in the proportion of concentric circles. This shows that advancing the boron source before low-temperature oxidation can not only greatly reduce the proportion of concentric circles, but also improve the electrical performance of the battery.

[0181] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the concentric circles of N-type TopCon batteries, characterized in that: The boron diffusion process of the battery preparation comprises the following steps: (S1) Entering the boat, controlling the pressure in the furnace tube of the boron expansion furnace to be consistent with the external air pressure, the temperature to be 800-820°C, introducing nitrogen, loading the silicon wafer after texturing in the quartz boat and sending it into the furnace tube; (S2) evacuating the furnace, stopping the introduction of nitrogen, and reducing the pressure in the furnace tube to 650-750 mbar; (S3) Heating, maintaining constant temperature, and checking for leaks. The pressure in the furnace tube is pumped down to 130-160 mbar, the temperature is raised to 815-835° C., the temperature is maintained constant, and the leak rate is confirmed to be qualified; (S4) maintaining a constant temperature, maintaining the pressure in the furnace tube at 130-160 mbar, and the temperature at 815-836° C., while introducing BCl 3 , nitrogen and oxygen; (S5) First diffusion deposition, maintaining the pressure in the furnace tube at 130-160 mbar, the temperature at 815-837° C., and introducing BCl 3 , nitrogen and oxygen at the same time; (S6) maintaining a constant temperature, maintaining the pressure in the furnace tube at 130-160 mbar, maintaining the temperature at 825-845° C., stopping the introduction of oxygen, and introducing BCl 3 and nitrogen at the same time; (S7) a second diffusion deposition, maintaining the pressure in the furnace tube at 130-160 mbar, maintaining the temperature at 825-846° C., and introducing BCl 3 , nitrogen and oxygen at the same time; (S8) maintaining a constant temperature, maintaining the pressure in the furnace tube at 130-160 mbar, maintaining the temperature at 835-850° C., stopping the introduction of oxygen, and simultaneously introducing BCl 3 and nitrogen; (S9) a third diffusion deposition, maintaining the pressure in the furnace tube at 130-160 mbar, the temperature at 835-851° C., and introducing BCl 3 , nitrogen and oxygen; (S10) advancing the boron source, first maintaining the pressure in the furnace tube at 130-160 mbar, raising the temperature to 885-915° C., stopping the introduction of oxygen, and simultaneously introducing BCl3 and nitrogen; then stopping the introduction of BCl3, maintaining the pressure in the furnace tube at 380-420 mbar and the temperature at 885-915° C., and only introducing nitrogen to advance the deposited BCl3; (S11) cooling and oxidizing, maintaining the pressure in the furnace tube at 850-900 mbar, reducing the temperature to 800-900° C., introducing oxygen, nitrogen and wet oxygen at the same time, and oxidizing for 680-720 seconds; (S12) isothermal oxidation, at a pressure of 850 to 900 mbar and a temperature of 800 to 900° C. in the furnace tube, oxygen, nitrogen and wet oxygen are introduced simultaneously, and oxidation is continued for 3800 to 4400 seconds; (S13) cooling and oxidizing, maintaining the pressure in the furnace tube at 850-900 mbar, reducing the temperature to 800-830° C., and simultaneously introducing oxygen, nitrogen and wet oxygen, cooling and oxidizing for 1500-1900 seconds; (S14) cooling, maintaining the pressure in the furnace tube at 850-900 mbar, reducing the temperature to 780-800° C., stopping the introduction of oxygen and wet oxygen, and introducing only nitrogen; (S15) breaking the vacuum, removing the boat, returning to normal pressure, and continuing to introduce nitrogen, taking out the quartz boat containing the silicon wafers in the furnace tube.

2. The method for improving the concentric circles of N-type TopCon batteries according to claim 1, characterized in that: In step (S1), the nitrogen gas flow rate is 1800 to 2200 sccm, and the time is 350 to 450 seconds.

3. The method for improving the concentric circles of N-type TopCon batteries according to claim 1, characterized in that: In step (S4), the flow rate of BCl3 is 280-320 sccm, the flow rate of nitrogen is 3400-3600 sccm, the flow rate of oxygen is 190-210 sccm, and the time is 260-340 seconds.

4. The method for improving the concentric circles of N-type TopCon batteries according to claim 1, characterized in that: In the first diffusion deposition of step (S5), the gas flow rate of BCl3 is 170-190 sccm, the gas flow rate of nitrogen is 3000-3400 sccm, the gas flow rate of oxygen is 240-260 sccm, and the time is 100-140 seconds.

5. The method for improving the concentric circles of N-type TopCon batteries according to claim 1, characterized in that: In the second diffusion deposition in step (S7) and the third diffusion deposition in step (S9), the ventilation flow rates and times of BCl3, nitrogen and oxygen are the same, the ventilation flow rate of BCl3 is 170-190sccm, the ventilation flow rate of nitrogen is 3000-3400sccm, the ventilation flow rate of oxygen is 490-510sccm, and the time is 220-260 seconds.

6. The method for improving the concentric circles of N-type TopCon batteries according to claim 1, characterized in that: In steps (S6) constant temperature and (S8) constant temperature, the ventilation flow rate and time of BCl3 and nitrogen are the same, the ventilation flow rate of BCl3 is 280-320sccm, the ventilation flow rate of nitrogen is 3000-3400sccm, and the time is 190-210 seconds.

7. The method for improving the concentric circles of N-type TopCon batteries according to claim 1, characterized in that: In the step (S10) of advancing the boron source, the temperature is first raised to 885-915°C, the introduction of oxygen is stopped, and BCl3 and nitrogen are introduced at the same time, with a ventilation flow rate of BCl3 of 280-320sccm and a ventilation flow rate of nitrogen of 480-520sccm, for 100-140 seconds; then the introduction of BCl3 is stopped, and only nitrogen is introduced, with a ventilation flow rate of 3300-3600sccm, for 380-420 seconds; then the pressure in the furnace tube is 380-420mbar and the temperature is kept at 885-915°C, and only nitrogen is introduced to advance the deposited BCl3, with a ventilation flow rate of nitrogen of 4300-4600sccm, for 430-470 seconds.

8. The method for improving the concentric circles of N-type TopCon batteries according to claim 1, characterized in that: In step (S11) cooling oxidation, step (S12) constant temperature oxidation and step (S13) cooling oxidation, the ventilation flow rates of oxygen, nitrogen and wet oxygen are the same, the ventilation flow rate of oxygen is 1800-2200sccm, the ventilation flow rate of nitrogen is 580-620sccm, and the flow rate of wet oxygen is 1400-1600sccm.

9. The method for improving the concentric circles of N-type TopCon batteries according to claim 1, characterized in that: In step (S11) temperature reduction oxidation, step (S12) constant temperature oxidation and step (S13) temperature reduction oxidation, the wet oxygen is oxygen that passes through a water bath device before entering the boron expansion furnace tube to increase the oxygen humidity.

10. An N-type TopCon battery, characterized in that: The preparation method of the battery comprises the boron diffusion process according to any one of claims 1 to 9, wherein the sheet resistance of the boron diffusion is controlled at 500 to 600 Ω / sq, and the BSG thickness is 80 to 120 nm.

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