Oxidation annealing method of solar cell silicon wafer, silicon wafer and cell

Abstract

The embodiment of the invention provides an oxidation annealing method for a solar cell silicon wafer, the silicon wafer and a cell, and the method comprises the steps: sequentially carrying out the alkali polishing of the silicon wafer, and carrying out the heating of the silicon wafer in an oxygen-free environment; and after the heating treatment, carrying out step-by-step annealing and oxidation treatment on the silicon wafer. The embodiment of the invention can effectively solve the problem that the oxidation layer formed on the surface of the silicon wafer in the existing oxidation annealing process has a poor improvement effect on the hydrophilicity of the surface of the silicon wafer, so that a winding plating black edge is easy to appear when aluminum oxide is deposited by ALD (Atomic Layer Deposition).

Description

Technical Field

[0001] The invention relates to the technical field of solar cells, and in particular to an oxidation annealing method for a solar cell silicon wafer, a silicon wafer and a battery. Background Art

[0002] In the process of preparing solar cells, oxidation and annealing steps are generally added after the alkaline polishing process to improve the cell's resistance to potential induced degradation. At the same time, it can remove the surface damage layer, repair lattice damage, and activate the action of phosphorus atoms, thereby improving the efficiency of the cell.

[0003] At the same time, because the oxidation annealing process is carried out after the alkaline polishing process, and the alkaline polishing will cause the acid tank chemicals to adsorb on the surface of the silicon wafer, the silicon wafer becomes hydrophobic, and the oxide layer formed after the oxidation annealing can improve the surface hydrophobicity and passivate the oxide layer.

[0004] However, in the manufacturing process of PERC cells or shingled cell silicon wafers, the oxide layer formed on the surface of the silicon wafer by the existing oxidation annealing process is not effective in improving the hydrophilicity of the silicon wafer surface, resulting in the problem of edge black plating when atomic layer deposition (ALD) is used to deposit aluminum oxide.

[0005] Therefore, the prior art needs to be improved. Summary of the invention

[0006] The technical problem to be solved by the embodiments of the present invention is to provide an oxidation annealing method for solar cell silicon wafers, silicon wafers and batteries, so as to solve the technical problem that the oxide layer formed on the surface of the silicon wafer by the existing oxidation annealing process is not effective in improving the hydrophilicity of the silicon wafer surface, resulting in the occurrence of black edges when ALD deposits aluminum oxide.

[0007] In order to solve the above problems, the present invention is achieved through the following technical solutions:

[0008] The present invention provides an oxidation annealing method for a solar cell silicon wafer, which comprises:

[0009] After the silicon wafers are subjected to alkali polishing treatment in sequence, the silicon wafers are subjected to a temperature increase treatment in an oxygen-free environment;

[0010] After the temperature raising treatment, the silicon wafer is subjected to step-wise annealing and oxidation treatment.

[0011] Optionally, in the oxidation annealing method, the silicon wafer is subjected to step-by-step annealing and oxidation treatment, including:

[0012] The silicon wafer is subjected to low temperature annealing and oxidation treatment for multiple times.

[0013] Optionally, in the oxidation annealing method, the silicon wafer is subjected to a temperature-raising treatment in an oxygen-free environment, comprising:

[0014] The target temperature is set at 670-690° C., and 10,000-20,000 sccm of nitrogen is introduced at a pressure of 900-1,060 mbar and maintained for 5-10 minutes.

[0015] Optionally, in the oxidation annealing method, the annealing treatment includes:

[0016] Under the conditions of gas pressure of 900-1060 mbar and temperature of 650-670° C., nitrogen gas with a flow rate of 10000-15000 sccm is introduced and maintained for 10-15 minutes.

[0017] Optionally, in the oxidation annealing method, the oxidation treatment includes:

[0018] Under the conditions of gas pressure of 900-1060 mbar and temperature of 650-670° C., nitrogen gas with a flow rate of 20000-25000 sccm and oxygen gas with a flow rate of 1000-2000 sccm are introduced and maintained for 10-15 minutes.

[0019] Optionally, in the oxidation annealing method, before heating, the method further comprises:

[0020] After the furnace tube enters the boat, the temperature is set at 670-690° C., nitrogen is introduced at 5000-10000 sccm, and maintained at normal pressure of 900-1060 mbar for 3-5 minutes.

[0021] Optionally, in the oxidation annealing method, after the step-down annealing treatment, the method further comprises:

[0022] The silicon wafer was heated back to 690°C and nitrogen was introduced for purging during the heating process.

[0023] Optionally, in the oxidation annealing method, the silicon wafer is a single crystal silicon wafer.

[0024] The present invention also provides a solar cell silicon wafer, which is obtained by the oxidation annealing method as described above.

[0025] The present invention also provides a solar cell, which includes the solar cell silicon wafer as described above.

[0026] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0027] In an embodiment of the present invention, after the silicon wafer is subjected to alkali polishing treatment in sequence, the silicon wafer is subjected to a temperature treatment in an oxygen-free environment, and after the temperature treatment, the silicon wafer is subjected to a step-by-step annealing and oxidation treatment, wherein the step-by-step annealing and the step-by-step oxidation treatment can slowly deposit a more uniform and dense oxide layer, thereby achieving a better annealing and oxidation passivation effect, so that the difference in hydrophilicity between tubes can also be improved, and the subsequent ALD deposited aluminum oxide edge deposition difference resulting in the black edge of the plating is significantly improved, which can effectively solve the problem that the oxide layer formed on the surface of the silicon wafer by the existing oxidation annealing process has a poor effect on improving the hydrophilicity of the silicon wafer surface, resulting in the problem of the black edge of the plating being easily generated when the ALD deposits aluminum oxide.

[0028] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart of an oxidation annealing method for a solar cell silicon wafer provided by an embodiment of the present invention;

[0030] Figure 2 The overall process flow chart of oxidation annealing of solar cell silicon wafers in the embodiment of the present invention is 。 DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] The manufacturing process of solar cells such as PERC cells or shingled cells includes texturing, diffusion doping, SE, thermal oxidation, chain-type dephosphorus silicon glass layer (PSG), alkali polishing, annealing, ALD, front coating, back coating, back laser grooving, grid line printing and testing. Since the annealing process is carried out after the alkali polishing process, and the alkali polishing will make the acid tank chemicals adsorb on the surface of the silicon wafer, and the oxide layer formed on the surface of the silicon wafer by the existing oxidation annealing process is not effective in improving the hydrophilicity of the silicon wafer surface in the above process, it is easy to cause the problem of black edge plating when ALD deposits aluminum oxide, so the silicon wafer is hydrophobic, and the oxide layer formed after oxidation annealing can improve the hydrophilicity of the surface and passivate the oxide layer.

[0033] Figure 1 FIG. 1 is a flow chart of an oxidation annealing method for a solar cell silicon wafer provided by an embodiment of the present invention, such as Figure 1 As shown, the method may include steps 101 to 102:

[0034] Step 101: After the silicon wafers are subjected to alkali polishing treatment in sequence, the silicon wafers are subjected to a temperature-raising treatment in an oxygen-free environment.

[0035] In the above step 101, the alkali-polished silicon wafer is placed in a boat. After the silicon wafer is placed in the boat through the furnace tube, the temperature of the silicon wafer is increased under normal pressure and oxygen-free conditions. Specifically, the silicon wafer may be a single crystal silicon wafer.

[0036] Specifically, the silicon wafer is a silicon wafer that has been subjected to alkali polishing and is to be subjected to ALD treatment. In actual use, the silicon wafer is a silicon wafer that has been subjected to texturing treatment, diffusion doping treatment, SE, thermal oxidation treatment, chain PSG removal and alkali polishing in sequence.

[0037] The atmospheric pressure condition is 900-1060 mbar. The atmospheric pressure environment in this pressure range can reduce the time of depressurization before oxidation and back pressure after oxidation, so that the whole process has enough time for slow cooling, avoiding the situation where the annealing temperature is not uniform due to subsequent large-span rapid cooling.

[0038] Optionally, in one embodiment, the above-mentioned temperature increase treatment specifically includes:

[0039] The target temperature is set at 670-690° C., and 10,000-20,000 sccm of nitrogen is introduced at a pressure of 900-1,060 mbar and maintained for 5-10 minutes.

[0040] Among them, after the furnace tube enters the boat, the heating temperature control system automatically controls the temperature to the target temperature, and at the same time, 10,000 to 20,000 sccm of nitrogen is introduced into the furnace tube and continued for 5 to 10 minutes to complete the heating process.

[0041] Optionally, in the above-mentioned temperature increase treatment, the target temperature may be specifically 680° C., the gas pressure may be 1060 mbar, the nitrogen flow rate may be 15000 sccm, and the maintenance time may be 4 minutes.

[0042] Step 102: After the temperature rise treatment, the silicon wafer is subjected to step-by-step annealing and oxidation treatment.

[0043] In the above step 102, after the silicon wafer is heated, it is subjected to annealing and oxidation treatment in sequence, and the process is repeated multiple times, that is, the annealing and oxidation treatment is divided into multiple cycles to achieve the above step-by-step annealing and oxidation treatment. Specifically, the above cycles can be 3, 4 or 5.

[0044] Optionally, the above step 102 specifically includes: performing step-wise annealing and oxidation treatment on the silicon wafer, that is, through low-temperature step-wise annealing and step-wise oxidation, a denser oxide layer can be slowly deposited to achieve better annealing and oxidation passivation effects.

[0045] For example, when the annealing and oxidation treatments are divided into three cycles, after the silicon wafer is heated, a first low-temperature annealing treatment is performed, followed by a first normal-pressure aerobic oxidation treatment; then a second low-temperature annealing treatment is performed, followed by a second normal-pressure aerobic oxidation treatment; then a third low-temperature annealing treatment is performed, followed by a third normal-pressure aerobic oxidation treatment.

[0046] In an embodiment of the present invention, after the silicon wafer is subjected to alkali polishing treatment in sequence, the silicon wafer is subjected to a temperature treatment in an oxygen-free environment, and after the temperature treatment, the silicon wafer is subjected to a step-by-step annealing and oxidation treatment, wherein the step-by-step annealing and the step-by-step oxidation treatment change the solid solubility of oxygen in the semiconductor silicon material, and can slowly deposit a more uniform and dense oxide layer, thereby achieving a better annealing and oxidation passivation effect, so that the difference in hydrophilicity between tubes can also be improved, and the subsequent ALD deposited aluminum oxide edge deposition difference resulting in the black edge of the plating is significantly improved, which can effectively solve the problem that the oxide layer formed on the surface of the silicon wafer by the existing oxidation annealing process has a poor effect on improving the hydrophilicity of the silicon wafer surface, resulting in the problem of the black edge of the plating being easily generated when the ALD deposits aluminum oxide.

[0047] Optionally, in one embodiment, in the above step 102, the annealing treatment includes:

[0048] Under the conditions of gas pressure of 900-1060 mbar and temperature of 650-670° C., nitrogen gas with a flow rate of 10000-15000 sccm is introduced and maintained for 10-15 minutes.

[0049] In this embodiment, nitrogen is mainly used as a protective gas during the cooling annealing process, which can reduce the introduction of impurities in the air, and at the same time purge impurities condensed from oxidation to reduce residual impurities on the surface; the nitrogen amount is set at 10,000 to 15,000 sccm to provide sufficient heat conduction, reduce the difference in cooling rate, improve the uniformity of annealing temperature in each temperature zone, effectively repair the lattice defects of the silicon wafer, fully improve the stacking faults and dislocated lattices caused by SE laser, repair lattice damage, make the disordered lattice order more orderly, reduce recombination centers, increase minority carrier lifetime, improve filling factor, and at the same time activate more phosphorus sources, reduce the content of phosphorus atoms deposited on the surface of the silicon wafer in the diffusion section, reduce the "dead layer", reduce the interface state density between silicon and silicon dioxide, and further improve the passivation effect of the oxide layer, thereby significantly improving the conversion efficiency of the battery cell.

[0050] Optionally, in one embodiment, in the above step 102, the oxidation treatment specifically includes:

[0051] Under the conditions of gas pressure of 900-1060 mbar and temperature of 650-670° C., nitrogen gas with a flow rate of 20000-25000 sccm and oxygen gas with a flow rate of 1000-2000 sccm are introduced and maintained for 10-15 minutes.

[0052] In this step, under the conditions of gas pressure of 900-1060 mbar and temperature of 650-670°C, oxygen atoms are filled into the dangling bonds on the surface of the silicon wafer or enter the interior of the silicon wafer to fill in vacancies, dislocations, stacking faults and other defective positions, thereby forming a dense and uniform silicon dioxide layer on the surface of the silicon wafer, repairing the lattice defects on the surface of the silicon wafer, filling the dangling bonds, and at the same time achieving a passivation effect on the surface of the silicon wafer.

[0053] In an embodiment of the present invention, the above-mentioned oxidation treatment is a constant temperature oxidation process, and when performing the oxidation treatment, the temperature is controlled to be the temperature corresponding to the lowest solid solubility state of oxygen in the silicon matrix, that is, the oxidation is controlled at the lowest solid solubility state of oxygen in the silicon matrix to reduce the darkening of impurity complex centers formed by the infiltration of excessive oxygen during the oxidation process.

[0054] Optionally, the oxidation treatment temperature may be 650° C., 660° C. or 670° C., and the oxidation treatment time may be 10 min or 15 min. For example, the oxidation treatment temperature is 660° C., and the oxidation treatment time is 12 min.

[0055] Optionally, in one implementation manner, the oxidation annealing method provided in the embodiment of the present invention further includes step 100 before the above step 101:

[0056] Step 100, after the furnace tube enters the boat, the temperature is set to 670-690°C, nitrogen is introduced at 5000-10000 sccm, and maintained at normal pressure of 900-1060 mbar for 3-5 minutes.

[0057] In the above step 100, if there are impurities on the surface of the silicon wafer during the process of entering the boat, it is very easy to cause white spots in the subsequent coating; and when entering the boat, 5000-10000sccm of nitrogen is introduced, which can effectively increase the purge of the silicon wafer surface and significantly reduce the adsorption of impurities on the silicon wafer surface.

[0058] Optionally, in one implementation, the oxidation annealing method provided in the embodiment of the present invention further includes step 103 after the above step 102:

[0059] Step 103, returning the temperature of the silicon wafer to 690°C, and introducing nitrogen gas for purging during the temperature return process.

[0060] In the above step 103, that is, after the step temperature reduction annealing is completed, the silicon wafer is heated back to 690°C, and nitrogen gas is introduced at 25000-40000 sccm to purge, and the process is terminated and the wafer is taken out of the boat.

[0061] Among them, returning the silicon wafer to 690°C before leaving the boat can shorten the time for heating the next tube and improve production capacity.

[0062] See also Figure 2, shows the overall process flow chart of an embodiment of the present invention. Figure 2 As shown, including:

[0063] (1) Entering the boat: After the furnace tube enters the boat, the temperature is set at 670-690°C, and nitrogen is introduced at a flow rate of 5000-10000 sccm, and maintained at a normal pressure of 900-1060 mbar for 3-5 minutes;

[0064] (2) Temperature purge: Set the target temperature to 670-690°C, introduce 10,000-20,000 sccm of nitrogen at a pressure of 900-1,060 mbar, and maintain for 5-10 minutes;

[0065] (3) First low-temperature annealing: nitrogen gas with a flow rate of 10,000 to 15,000 sccm is introduced at a pressure of 900 to 1,060 mbar and a temperature of 650 to 670°C and maintained for 10 to 15 minutes;

[0066] (4) First aerobic oxidation: Under the conditions of a gas pressure of 900-1060 mbar and a temperature of 650-670°C, nitrogen gas with a flow rate of 20,000-25,000 sccm and oxygen gas with a flow rate of 1,000-2,000 sccm are introduced and maintained for 10-15 minutes;

[0067] (5) Second low-temperature annealing: nitrogen gas with a flow rate of 10,000 to 15,000 sccm is introduced at a pressure of 900 to 1,060 mbar and a temperature of 650 to 670°C and maintained for 10 to 15 minutes;

[0068] (6) Second aerobic oxidation: Under the conditions of a gas pressure of 900-1060 mbar and a temperature of 650-670°C, nitrogen with a flow rate of 20,000-25,000 sccm and oxygen with a flow rate of 1,000-2,000 sccm are introduced and maintained for 10-15 min;

[0069] (7) Third low-temperature annealing: nitrogen gas with a flow rate of 10,000 to 15,000 sccm is introduced at a pressure of 900 to 1,060 mbar and a temperature of 650 to 670°C and maintained for 10 to 15 minutes;

[0070] (8) Third aerobic oxidation: Under the conditions of a gas pressure of 900-1060 mbar and a temperature of 650-670°C, nitrogen gas with a flow rate of 20,000-25,000 sccm and oxygen gas with a flow rate of 1,000-2,000 sccm are introduced and maintained for 10-15 min;

[0071] (9) Exit the boat: Return the temperature to 690°C, introduce nitrogen gas at 25,000-40,000 sccm for purging, and end the process.

[0072] In summary, in the oxidation annealing method for solar cell silicon wafers provided in the embodiment of the present invention, a step-by-step annealing and step-by-step oxidation treatment process is adopted, which can slowly deposit a more uniform and dense oxide layer, achieve better annealing and oxidation passivation effects, and improve the hydrophilicity difference between tubes. The subsequent ALD deposited aluminum oxide edge deposition difference resulting in the black edge of the surrounding plating is significantly improved, and the problem of the oxide layer formed on the surface of the silicon wafer by the existing oxidation annealing process is not good for improving the hydrophilicity of the silicon wafer surface, resulting in the problem of the black edge of the surrounding plating being easy to appear when the ALD deposits aluminum oxide.

[0073] An embodiment of the present invention further provides a PERC cell silicon wafer, which is obtained by the oxidation annealing method as described above.

[0074] An embodiment of the present invention further provides a solar cell, which includes the PERC cell silicon wafer as described above.

[0075] The present invention is described in detail below by way of examples.

[0076] After the alkali polishing process is completed, 2400 silicon wafers are taken for testing. Since two adjacent silicon wafers have similar or close characteristics, in order to ensure the fairness of the data, the 2400 silicon wafers are selected alternately in odd order and even order and divided into two even groups, each with 1200 wafers, so that one group uses the normal pressure oxidation annealing method provided by the present invention, and the other group uses the conventional normal pressure oxidation annealing process, and the remaining processes are completed using the same conditions.

[0077] Example 1

[0078] (1) Entering the boat: After the furnace tube enters the boat, the temperature is set to 680°C, nitrogen gas is introduced at a flow rate of 7000 sccm, and maintained at a normal pressure of 1000 mbar for 4 minutes;

[0079] (2) Temperature purge: Set the target temperature to 680°C, introduce 20,000 sccm of nitrogen at a pressure of 1,000 mbar, and maintain for 10 min;

[0080] (3) First low-temperature annealing: nitrogen gas with a flow rate of 15000 sccm was introduced at a pressure of 900 mbar and a temperature of 660°C and maintained for 15 min;

[0081] (4) First aerobic oxidation: Under the conditions of gas pressure of 900 mbar and temperature of 660°C, nitrogen with a flow rate of 25000 sccm and oxygen with a flow rate of 2000 sccm were introduced and maintained for 15 min;

[0082] (5) Second low-temperature annealing: nitrogen gas with a flow rate of 15000 sccm was introduced at a pressure of 900 mbar and a temperature of 660°C and maintained for 10 min;

[0083] (6) Second aerobic oxidation: Under the conditions of a gas pressure of 900 mbar and a temperature of 660°C, nitrogen with a flow rate of 25,000 sccm and oxygen with a flow rate of 2,000 sccm were introduced and maintained for 10 min;

[0084] (7) Third low-temperature annealing: nitrogen gas with a flow rate of 15000 sccm was introduced at a pressure of 900 mbar and a temperature of 660°C and maintained for 15 min;

[0085] (8) Third aerobic oxidation: Under the conditions of a gas pressure of 900 mbar and a temperature of 660°C, nitrogen with a flow rate of 25000 sccm and oxygen with a flow rate of 2000 sccm were introduced and maintained for 15 min;

[0086] (9) Exit the boat: Return the temperature to 690°C, introduce nitrogen gas at 40,000 sccm for purging, and end the process.

[0087] According to the above-mentioned Example 1, a silicon wafer A1 having an oxide layer is obtained.

[0088] Comparative Example 1

[0089] (1) Entering the boat: After the furnace tube enters the boat, the temperature is set to 730°C, nitrogen is introduced at 25000 sccm, and the atmospheric pressure is 1060 mbar, and maintained for 5 minutes;

[0090] (2) Heating: set the temperature to 730°C, introduce nitrogen at 25000 sccm, atmospheric pressure at 1060 mbar, and maintain for 5 min;

[0091] (3) Oxidation: Oxidation was maintained for 10 to 15 minutes at a normal pressure of 1060 mbar and a temperature of 730°C. During the oxidation process, 15,000 sccm of nitrogen and 5,000 sccm of oxygen were introduced.

[0092] (4) Cooling annealing: maintain oxygen-free annealing for 15 min at atmospheric pressure 1060 mbar and temperature 650°C, and introduce 25000 sccm of nitrogen during the process;

[0093] (5) Boat exit: The boat exit temperature of the furnace tube is set at 730°C, and nitrogen gas is introduced at 25,000 sccm for purging to end the process.

[0094] According to the test of the comparative example 1 above, a silicon wafer B1 with an oxide layer was obtained.

[0095] The above silicon wafer A1 and silicon wafer B1 were tested for edge black edge yield respectively. The results showed that the battery cell after atmospheric pressure oxidation annealing provided by the embodiment of the present invention had no edge black edge phenomenon, while the edge black edge ratio of the battery cell after ordinary atmospheric pressure cooling annealing was 0.13%.

[0096] In summary, in the present embodiment, in the oxidation annealing method for solar cell silicon wafers provided by the embodiment of the present invention, a step-by-step annealing and step-by-step oxidation treatment process is adopted, which can slowly deposit a more uniform and dense oxide layer, achieve better annealing and oxidation passivation effects, so that the difference in hydrophilicity between tubes can also be improved, and the subsequent ALD deposited aluminum oxide edge deposition difference resulting in the black edge of the surrounding plating is significantly improved, which can effectively solve the problem that the oxide layer formed on the surface of the silicon wafer by the existing oxidation annealing process has a poor effect on improving the hydrophilicity of the silicon wafer surface, resulting in the problem of the black edge of the surrounding plating being easy to appear when the ALD deposits aluminum oxide.

[0097] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concept. Therefore, the claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0098] The above is a detailed introduction to the oxidation annealing method for a solar cell silicon wafer, a silicon wafer and a battery provided by the present invention. Specific examples are used herein to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for a person skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and the scope of application. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for oxidation annealing of a solar cell silicon wafer, characterized in that: include: After the silicon wafers are subjected to alkali polishing treatment in sequence, the silicon wafers are subjected to a temperature-raising treatment in an oxygen-free environment; After the temperature raising treatment, the silicon wafer is subjected to step-wise annealing and oxidation treatment.

2. The oxidation annealing method according to claim 1, characterized in that: The silicon wafer is subjected to step-wise annealing and oxidation treatment, including: The silicon wafer is subjected to low temperature annealing and oxidation treatment for multiple times.

3. The oxidation annealing method according to claim 1, characterized in that: The silicon wafer is subjected to a temperature-raising treatment in an oxygen-free environment, comprising: The target temperature is set at 670-690° C., and 10,000-20,000 sccm of nitrogen is introduced at a pressure of 900-1,060 mbar and maintained for 5-10 minutes.

4. The oxidation annealing method according to claim 1, characterized in that: The annealing treatment comprises: Under the conditions of gas pressure of 900-1060 mbar and temperature of 650-670° C., nitrogen gas with a flow rate of 10000-15000 sccm is introduced and maintained for 10-15 minutes.

5. The oxidation annealing method according to claim 1, characterized in that: The oxidation treatment comprises: Under the conditions of gas pressure of 900-1060 mbar and temperature of 650-670° C., nitrogen gas with a flow rate of 20000-25000 sccm and oxygen gas with a flow rate of 1000-2000 sccm are introduced and maintained for 10-15 minutes.

6. The oxidation annealing method according to claim 1, characterized in that: Before heating, the method further comprises: After the furnace tube enters the boat, the temperature is set at 670-690° C., nitrogen is introduced at 5000-10000 sccm, and maintained at normal pressure of 900-1060 mbar for 3-5 minutes.

7. The oxidation annealing method according to any one of claims 1 to 6, characterized in that: After the step-down annealing treatment, the method further comprises: The silicon wafer was heated back to 690°C and nitrogen was introduced for purging during the heating process.

8. The oxidation annealing method according to claim 7, characterized in that: The silicon wafer is a single crystal silicon wafer.

9. A solar cell silicon wafer, characterized in that: The method is obtained by the oxidation annealing method according to any one of claims 1 to 8.

10. A solar cell, characterized in that: Comprising the solar cell silicon wafer as claimed in claim 9.

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