A high temperature boron diffusion process to extend the life of quartz spare parts

Abstract

The present application proposes a high-temperature boron diffusion process for extending the life of quartz spare parts, and relates to the technical field of TOPCon battery preparation. The process includes: heating the silicon wafer for a pre-oxidation process; introducing oxygen and a boron source, adjusting the pressure for the first boron diffusion deposition, and purging with nitrogen after deposition; repeating the above steps for the second boron diffusion deposition and the third boron diffusion deposition; then purging and advancing, heating again and adjusting the pressure, introducing oxygen for post-oxidation treatment, and finally cooling and back-pressing out of the boat. The present application increases the oxygen intake during the deposition step, thereby increasing the amount of oxygen and the boron source reacting without increasing the BCL3 consumption; increasing the reaction pressure, reducing the pumping speed, and then increasing the deposition rate to obtain a higher concentration PN junction; reducing the temperature and oxygen intake in the post-oxidation stage, and increasing the oxidation time, so as to obtain a shallower PN junction, reduce the oxidation of quartz, and extend the life of quartz spare parts.

Description

Technical Field

[0001] The present application relates to the technical field of TOPCon battery preparation, and in particular to a high-temperature boron diffusion process for extending the life of quartz spare parts. Background Art

[0002] With the excessive exploitation and consumption of non-renewable energy such as oil, coal, and natural gas, it is difficult for such energy to meet human needs in the long run. Solar energy is favored by international energy development because of its wide coverage, less geographical restrictions, and inexhaustible supply. Solar photovoltaic power generation technology is more conducive to meeting the needs of human development. On the other hand, the traditional and most promising solar cells are still silicon-based solar cells. The main raw material for producing silicon-based solar cells is silicon (Si). Silicon accounts for 26.4% of the total mass in the earth's crust, second only to oxygen (49.4%), which ranks first. It is sufficient for the production of solar cells. Therefore, solar cells have developed rapidly in recent decades.

[0003] Tunnel Oxide Passivated Contact solar cell (TOPCon) is a high-efficiency crystalline silicon solar cell that has developed rapidly in recent years. The characteristics of this cell are that it uses high-quality ultra-thin silicon oxide plus doped polysilicon layer to achieve high-efficiency passivation and selective carrier collection on the back of the cell, and has no silicon / metal contact interface, which is conducive to improving the open circuit voltage, and collecting carriers over the entire area is conducive to improving the fill factor.

[0004] In the boron diffusion process, the method currently commonly used is to generate boron element by thermal decomposition of BCl3, and diffuse from the Si surface to the Si interior under the condition of concentration difference. The quartz spare parts of the N-type Topcon battery boron diffusion machine are affected by the boron diffusion oxidation temperature of 1040-1050℃ and the high oxygen content, resulting in a very short furnace life (generally less than 90 days), and the shallow PN junction that has troubled boron diffusion for a long time is also difficult to obtain from the existing process (for high-concentration shallow PN junction), so it is necessary to optimize the process. Summary of the invention

[0005] The purpose of the present application is to provide a high-temperature boron diffusion process for extending the life of quartz spare parts. This process can prepare a high-concentration shallow PN junction, reduce quartz oxidation, and increase the life of quartz spare parts.

[0006] In order to solve the above technical problems, the technical solution adopted in this application is:

[0007] The present application provides a high-temperature boron diffusion process for extending the life of quartz spare parts, comprising the following steps:

[0008] S1, placing the silicon wafer on a boat support, sending it into a boron diffusion furnace, and heating it for a pre-oxidation process;

[0009] S2, introducing oxygen and boron source, adjusting the pressure to perform the first boron diffusion deposition, and purging with nitrogen after deposition;

[0010] S3, repeating step S2 and introducing oxygen and boron source to perform a second boron diffusion deposition and a third boron diffusion deposition;

[0011] S4. After the third boron diffusion deposition, the temperature is raised for purging and pushing, the temperature is raised again and the pressure is adjusted, oxygen is introduced for post-oxidation treatment, and finally the temperature is lowered, the pressure is returned, and the boat is taken out.

[0012] Compared with the prior art, the embodiments of the present application have at least the following advantages or beneficial effects:

[0013] The present application increases the oxygen flow rate during the deposition step, thereby increasing the amount of oxygen and boron source reaction without increasing the BCL3 consumption; increases the reaction pressure, reduces the pumping speed, and thus increases the deposition rate to obtain a higher concentration PN junction; reduces the temperature and oxygen flow rate in the post-oxidation stage, and increases the oxidation time to obtain a shallower PN junction (the process concentration of the present application embodiment is 3.67E+18, and the junction depth is 0.67μm; the concentration of the conventional process before improvement is 1.97E+18, and the junction depth is 0.73μm), thereby obtaining the following advantages:

[0014] 1. Improve minority carrier lifetime: In the photovoltaic effect, minority carrier lifetime is one of the important factors affecting battery efficiency. Heavy doping can increase carrier concentration, reduce minority carrier diffusion length, thereby increasing minority carrier lifetime, and further increasing the short-circuit current and open-circuit voltage of photovoltaic cells, ultimately improving the conversion efficiency of the battery.

[0015] 2. Reduce series resistance: The existence of series resistance will lead to a decrease in current, affecting the fill factor and conversion efficiency of the battery. Heavy doping can significantly reduce the resistivity of semiconductor materials and reduce contact resistance, thereby reducing series resistance and increasing current output.

[0016] 3. Enhance the performance against light attenuation: Photovoltaic cells will be affected by factors such as light and ambient temperature during use, causing their performance to gradually decay. Heavy doping can improve the stability of photovoltaic cells, improve their performance against light attenuation, and extend the service life of the battery.

[0017] 4. Optimize spectral response characteristics: Heavy doping technology can optimize the spectral response characteristics of photovoltaic cells, increase their absorption rate within a specific wavelength range, and thus improve the conversion efficiency of the cells;

[0018] 5. Because quartz has a high melting point, its surface will gradually lose moisture under high-temperature oxidation, causing the quartz structure to become loose and eventually weathered. In addition, quartz is chemically unstable and easily reacts with oxygen at high temperatures to generate unstable sulfates, which causes the color to darken, the texture to become brittle, and it is easy to be worn away; based on the characteristics of quartz, this application reduces the oxygen and temperature of the high-temperature oxidation step, increases the extraction pressure, and greatly reduces the furnace tube load, which can extend the life of the furnace tube, thereby increasing the furnace tube quartz life and saving operating costs. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0020] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to specific embodiments.

[0021] A high temperature boron diffusion process for extending the life of quartz spare parts comprises the following steps:

[0022] S1, placing the silicon wafer on a boat support, sending it into a boron diffusion furnace, and heating it for a pre-oxidation process;

[0023] S2, introducing oxygen and boron source, adjusting the pressure to perform the first boron diffusion deposition, and purging with nitrogen after deposition;

[0024] S3, repeating step S2 and introducing oxygen and boron source to perform a second boron diffusion deposition and a third boron diffusion deposition;

[0025] S4. After the third boron diffusion deposition, the temperature is raised for purging and pushing, the temperature is raised again and the pressure is adjusted, oxygen is introduced for post-oxidation treatment, and finally the temperature is lowered, the pressure is returned, and the boat is taken out.

[0026] In some embodiments of the present application, in the above step S1, the pre-oxidation temperature is 845-850° C., the amount of nitrogen introduced is 900-1100 sccm, the amount of oxygen introduced is 1500 sccm, and the pre-oxidation time is 100-150 s.

[0027] In some embodiments of the present application, during the first boron diffusion deposition in the above step S2, the oxygen intake is 450-500 sccm, the boron source intake is 110-130 sccm, the pressure is 220-240 mbar, the deposition time is 170-200 s, and the purge time is 90-110 s.

[0028] In some embodiments of the present application, during the first boron diffusion deposition in the above step S2, the oxygen flow rate is 480 sccm, the boron source flow rate is 120 sccm, the pressure is 230 mbar, the deposition time is 200 s, and the purge time is 100 s.

[0029] In some embodiments of the present application, the purging temperature in the above-mentioned step S4 is 880-890° C., the amount of purging nitrogen is 3800-4200 sccm, and the purging time is 120-180 s.

[0030] In some embodiments of the present application, the advancement of the above-mentioned step S4 includes two advancement diffusions, and the advancement times are 260-280s and 110-150s respectively.

[0031] In some embodiments of the present application, in the above step S4, the post-oxidation temperature is 1020-1030° C., the oxygen flow rate is 16000-19000 sccm, the pressure is 820-880 mbar, and the total post-oxidation time is 3500-5000 s.

[0032] In some embodiments of the present application, in the above step S4, the post-oxidation temperature is 1025° C., the oxygen flow rate is 18000 sccm, the pressure is 850 mbar, and the total post-oxidation time is 4300 s.

[0033] The features and performance of the present application are further described in detail below in conjunction with the embodiments.

[0034] Example 1

[0035] A high-temperature boron diffusion process for extending the life of quartz spare parts, specifically comprising the following steps:

[0036] Preheating: Preheat the boron diffusion furnace at 843°C, with 2000 sccm of nitrogen, 1030 mbar pressure, and 10 seconds.

[0037] Entering the boat: placing the silicon wafer on the boat support and sending it into the boron diffusion furnace;

[0038] Pumping out pressure: stop nitrogen, raise the temperature to 848℃, gradually reduce the pressure to 700mbar, then reduce to 230mbar, pump for 300s; then introduce nitrogen and pump out pressure for 700s;

[0039] Leak detection: Stop nitrogen flow, and increase the pressure to 1060 mbar for 60 seconds;

[0040] Pre-oxidation: introduce nitrogen (DN2, the nitrogen at this time is mainly to make the oxygen more evenly distributed in the furnace tube, so that a layer of oxide layer is obtained on the surface of the silicon wafer) at 1000sccm, introduce 700sccm DoorN2 (to protect the flange from being corroded by the acid gas or substances remaining in the tube and extend the flange life); introduce 1500sccm oxygen, pressure 230mbar, temperature 848℃, time 120s;

[0041] Purge: nitrogen gas 5000 sccm, temperature 848°C, time 100 s;

[0042] First boron diffusion deposition: 5300sccm nitrogen (nitrogen introduced during deposition is mainly used as a source, indicating that the amount of bcl3 is very small, and a large amount of nitrogen needs to be introduced into the tube in order to evenly distribute it in the tube), 700sccm DoorN2 (to protect the flange from being corroded by residual acidic gases or substances in the tube and extend the flange life); temperature 848℃, 480sccm oxygen, 120sccm boron chloride, pressure 230mbar, deposition time 200s;

[0043] Purge: nitrogen gas 5000 sccm, pressure 230 mbar, temperature 848 °C, time 100 s;

[0044] Second boron diffusion deposition: nitrogen 5300 sccm, temperature 848°C, oxygen 480 sccm, boron chloride 120 sccm, pressure 230 mbar, deposition time 175 s;

[0045] Purge: nitrogen gas 5000 sccm, pressure 230 mbar, temperature 848 °C, time 100 s;

[0046] The third boron diffusion deposition: nitrogen 5300 sccm, temperature 848 ° C, oxygen 480 sccm, boron chloride 120 sccm, pressure 230 mbar, deposition time 200 s;

[0047] Temperature purge: nitrogen 4000 sccm, pressure 230 mbar, temperature 887 ° C, time 150 s;

[0048] Push diffusion: nitrogen 3000sccm, pressure 230mbar, temperature 887℃, time 270s;

[0049] Further diffusion: nitrogen gas 3000 sccm, pressure 230 mbar, temperature 887 ° C, time 130 s;

[0050] Heating: oxygen 18000sccm, pressure 850mbar, temperature 1000℃, time 800s;

[0051] Heating again: oxygen 18000sccm, pressure 850mbar, temperature 1025℃, time 500s;

[0052] Post-oxidation: oxygen 18000sccm, pressure 850mbar, temperature 1025℃, time 1100s;

[0053] Post-oxidation: oxygen 18000sccm, pressure 850mbar, temperature 1025℃, time 3200s;

[0054] Cooling: Slowly cool to 820℃ under oxygen flow for 2280s;

[0055] Finally, press back out of the boat and take out the silicon wafer.

[0056] Example 2

[0057] A high-temperature boron diffusion process for extending the life of quartz spare parts, specifically comprising the following steps:

[0058] Preheating: Preheat the boron diffusion furnace at 843°C, with 2000 sccm of nitrogen, 1030 mbar pressure, and 10 seconds.

[0059] Entering the boat: placing the silicon wafer on the boat support and sending it into the boron diffusion furnace;

[0060] Pumping down: stop nitrogen, raise the temperature to 848℃, gradually reduce the pressure to 700mbar, then reduce to 230mbar, pump for 300s; then introduce nitrogen and pump down for 700s;

[0061] Leak detection: Stop nitrogen flow, and increase the pressure to 1060 mbar for 60 seconds;

[0062] Pre-oxidation: 1000 sccm nitrogen, 1500 sccm oxygen, pressure 230 mbar, temperature 848°C, time 130 s;

[0063] Purge: nitrogen gas 5000 sccm, temperature 846°C, time 100 s;

[0064] The first boron diffusion deposition: nitrogen 5300sccm, temperature 850°C, oxygen 485sccm, boron chloride 120sccm, pressure 230mbar, deposition time 200s;

[0065] Purge: nitrogen gas 5000 sccm, pressure 230 mbar, temperature 850 °C, time 100 s;

[0066] Second boron diffusion deposition: nitrogen 5300 sccm, temperature 850°C, oxygen 485 sccm, boron chloride 120 sccm, pressure 230 mbar, deposition time 175 s;

[0067] Purge: nitrogen gas 5000 sccm, pressure 230 mbar, temperature 850 °C, time 100 s;

[0068] The third boron diffusion deposition: nitrogen 5300 sccm, temperature 850 ° C, oxygen 485 sccm, boron chloride 120 sccm, pressure 230 mbar, deposition time 200 s;

[0069] Temperature purge: nitrogen 4000 sccm, pressure 230 mbar, temperature 885 ° C, time 150 s;

[0070] Push diffusion: nitrogen 3000sccm, pressure 230mbar, temperature 885℃, time 270s;

[0071] Further diffusion: nitrogen gas 3000 sccm, pressure 230 mbar, temperature 885 ° C, time 130 s;

[0072] Heating: oxygen 18000sccm, pressure 850mbar, temperature 1000℃, time 800s;

[0073] Heating again: oxygen 185000sccm, pressure 850mbar, temperature 1022°C, time 500s;

[0074] Post-oxidation: oxygen 18500sccm, pressure 850mbar, temperature 1022℃, time 1100s;

[0075] Post-oxidation: oxygen 18500sccm, pressure 850mbar, temperature 1022℃, time 3200s;

[0076] Cooling: Slowly cool to 820℃ under oxygen flow for 2280s;

[0077] Finally, press back out of the boat and take out the silicon wafer.

[0078] Comparative Example

[0079] This comparative example is a conventional process, and the main differences between it and Example 1 are as follows: 1. The oxygen flow rate during the three boron diffusion depositions is 450 sccm and the pressure is 210 mbar; 2. The temperature during the two post-oxidation is 1040°C and the oxygen flow rate is 25000 sccm. The remaining steps and process conditions are the same.

[0080] Experimental Example 1

[0081] Table 1

[0082] Group Comparative example (before process) Example 1 Comparative example (after process) Number of experiments 1455 988 1267 Eff (efficiency) 26.649% 26.778% 26.750% Uoc (open circuit voltage, mV) 0.7361 0.7370 0.7366 Isc (short circuit current, mA) 14.0982 14.1235 14.1194 FF (fill factor) 85.95 86.11 86.09 Rs (series resistance, Ω) 0.0012 0.0012 0.0012 Rsh (parallel resistance, Ω) 1694 1603 1725 Irev2 (reverse current, mA) 0.033 0.029 0.033

[0083] From Table 1, it can be seen that the efficiency of the new boron expansion process is significantly improved compared with the original process (before the process) and the original process (after the process). Compared with before the experiment: Isc is 25mA higher, voltage is 0.9mV higher, FF is 0.16 higher. Compared with after the experiment: Isc is 4.1mA higher, voltage is 0.4mV higher, FF is 0.02 higher; it can be concluded that the new boron expansion process is better than the comparative process before the improvement in efficiency.

[0084] Experimental Example 2

[0085] This experimental example is a control experiment, in which the experimental group adopts the boron diffusion process of Example 1. The control group is the conventional process before, and the difference between it and the experimental group is mainly two points: 1. The oxygen flow rate during the three boron diffusion depositions is 450sccm and the pressure is 210mbar; 2. The temperature during the two post-oxidation is 1040℃ and the oxygen flow rate is 25000sccm. The rest of the steps and process conditions are the same.

[0086] The lifespan of the boron diffusion hidden furnace tubes in the experimental group and the control group was tested, and their average lifespans are shown in Table 2.

[0087] Table 2

[0088] Group Average life span (days) Control group 85 Experimental Group 124

[0089] It can be seen from Table 2 that by improving the process of the deposition step and the post-oxidation step of the boron diffusion, the influence of the quartz spare parts in the boron diffusion step can be reduced and the life of the furnace tube can be increased.

[0090] In summary, a high-temperature boron diffusion process for extending the life of quartz spare parts in an embodiment of the present application has the following advantages: the present application increases the oxygen intake during the deposition step, thereby increasing the reaction amount of oxygen and the boron source without increasing the BCL3 consumption; increases the reaction pressure, reduces the pumping speed, and thus increases the deposition rate to obtain a PN junction with a higher concentration; reduces the temperature and oxygen intake in the post-oxidation stage, and increases the oxidation time to obtain a shallower PN junction (the process concentration of the embodiment of the present application is 3.67E+18, and the junction depth is 0.67μm; the concentration of the conventional process before improvement is 1.97E+18, and the junction depth is 0.73μm), thereby obtaining the following advantages:

[0091] 1. Improve minority carrier lifetime: In the photovoltaic effect, minority carrier lifetime is one of the important factors affecting battery efficiency. Heavy doping can increase carrier concentration, reduce minority carrier diffusion length, thereby increasing minority carrier lifetime, and further increasing the short-circuit current and open-circuit voltage of photovoltaic cells, ultimately improving the conversion efficiency of the battery1.

[0092] 2. Reduce series resistance: The existence of series resistance will lead to a decrease in current, affecting the fill factor and conversion efficiency of the battery. Heavy doping can significantly reduce the resistivity of semiconductor materials, reduce contact resistance, thereby reducing series resistance and increasing current output.

[0093] 3. Enhance the performance against light attenuation: Photovoltaic cells will be affected by factors such as light and ambient temperature during use, causing their performance to gradually decay. Heavy doping can improve the stability of photovoltaic cells, improve their performance against light attenuation, and extend the battery's service life1.

[0094] 4. Optimize spectral response characteristics: Heavy doping technology can optimize the spectral response characteristics of photovoltaic cells, increase their absorption rate within a specific wavelength range, and thus improve the conversion efficiency of the cells;

[0095] 5. Reducing the oxygen and temperature in the high-temperature oxidation step and increasing the extraction pressure can greatly reduce the furnace tube load. Because quartz has a high melting point, its surface will gradually lose moisture under high-temperature oxidation, causing the quartz structure to become loose and eventually weathered. In addition, quartz is chemically unstable and easily reacts with oxygen at high temperatures to generate unstable sulfates, which darkens the color, becomes brittle, and is easily worn away. Based on the characteristics of quartz, reducing the temperature and oxygen intake can extend the life of the furnace tube, thereby increasing the furnace tube quartz life and saving operating costs.

[0096] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present application.

Claims

1. A high temperature boron diffusion process for extending the life of quartz spare parts, characterized in that: The following steps are involved: S1. Place the silicon wafer on a boat holder, send it into a boron diffusion furnace, heat it to 845-850°C for pre-oxidation process, introduce 900-1100sccm nitrogen and 1500sccm oxygen, and maintain for 100-150s; S2, introducing oxygen gas at 450-500 sccm and boron source at 110-130 sccm, adjusting the pressure to 220-240 mbar for the first boron diffusion deposition, and introducing nitrogen gas at 5000 sccm for 90-110 s after deposition for 170-200 s; S3, repeating step S2 to perform the second and third boron diffusion deposition; S4. After the third deposition, the temperature is raised to 880-890°C, and nitrogen is introduced at 3800-4200sccm for 120-180s. Then two push diffusions are performed, and the temperature is raised to 1020-1030°C for post-oxidation treatment. Oxygen is introduced at 16000-19000sccm and the pressure is 820-880mbar for 3500-5000s. Finally, the temperature is lowered and the pressure is returned to the boat.

2. A high temperature boron diffusion process for extending the life of quartz spare parts according to claim 1, characterized in that: During the first boron diffusion deposition in step S2, the oxygen flow rate is 480 sccm, the boron source flow rate is 120 sccm, the pressure is 230 mbar, the deposition time is 200 s, and the purge time is 100 s.

3. The high temperature boron diffusion process for extending the life of quartz spare parts according to claim 1, characterized in that: The advancement of the S4 step includes two advancement diffusions, and the advancement times are 260-280s and 110-150s respectively.

4. The high temperature boron diffusion process for extending the life of quartz spare parts according to claim 1, characterized in that: In the step S4, the post-oxidation temperature is 1025° C., the oxygen flow rate is 18000 sccm, the pressure is 850 mbar, and the total post-oxidation time is 4300 s.