Wet oxygen diffusion method for obtaining low-concentration BSG and high sheet resistance

Abstract

The invention discloses a high-sheet-resistance wet oxygen diffusion method for obtaining low-concentration BSG, and belongs to the technical field of solar cell preparation. A multi-step source introduction method is adopted, the source introduction time is shortened, the source introduction flow is increased, rapid heating promotion is achieved, and a wet oxygen oxidation method and a low-temperature deposition method are innovatively adopted; wherein the low-temperature deposition method can slow the reaction decomposition of an impurity source and reduce the concentration of the impurity source deposited on the surface of a silicon wafer, so that the content of impurities diffused into a silicon substrate is reduced, the effect of deep and shallow junctions is finally realized, and the method is an effective method for preparing low-concentration shallow junctions and obtaining high sheet resistance; according to the invention, high sheet resistance with excellent uniformity is realized while the BSG with low impurity concentration is obtained, the process time is shortened, the subsequent LECO process is ensured to be more ideally realized, and finally, the battery conversion efficiency is improved to the maximum extent and the process time is shortened to the maximum extent.

Description

Technical Field

[0001] The invention belongs to the technical field of solar cell preparation, and in particular relates to a wet oxygen diffusion method for obtaining low-concentration BSG with high square resistance. Background Art

[0002] At present, when conventional N-type single crystal diffusion technology and LECO technology are matched, the diffusion square resistance needs to be maintained at 450±200Ω to obtain maximum efficiency. However, the conventional diffusion process cannot achieve the goal of significantly improving efficiency, and the process time is too long, which seriously affects production capacity and increases production costs. Summary of the invention

[0003] In order to solve the problems raised in the above background technology, the present invention provides a wet oxygen diffusion method for obtaining low-concentration BSG and high square resistance, so as to solve the problem that the existing process cannot achieve the purpose of significantly improving efficiency, and the process time is too long, which seriously affects production capacity and increases production costs.

[0004] To achieve the above object, the present invention provides the following technical solutions: A wet oxygen diffusion method for obtaining low-concentration BSG and high square resistance comprises the following steps: S1: Place the boat with silicon wafers into the furnace tube, and evacuate and heat the furnace tube; S2: first pre-deposition; when the temperature in the furnace tube is stabilized at 825±2°C, boron trichloride, oxygen and nitrogen are continuously introduced into the furnace tube for 1-5 minutes, with a nitrogen flow rate of 2000-10000sccm, an oxygen flow rate of 200-2000sccm, and a boron trichloride flow rate of 50-600sccm; S3: first heating; stop the introduction of boron trichloride and oxygen, continue to introduce nitrogen at a flow rate of 2000-10000sccm into the furnace tube for 1-5 minutes, and heat the furnace tube to 835±2°C; S4: second pre-deposition; continue to introduce boron trichloride, oxygen and nitrogen into the furnace tube for 2-6 minutes, with a nitrogen flow rate of 2000-10000sccm, an oxygen flow rate of 200-2000sccm, and a boron trichloride flow rate of 50-600sccm; S5: heating for the second time; continue to introduce nitrogen into the furnace tube, while stopping the introduction of oxygen and boron trichloride, for 2-8 minutes, the nitrogen flow rate is 2000-10000sccm, and the furnace tube is heated to 845±2℃; S6: the third pre-deposition; when the temperature in the furnace tube is stabilized at 845±2°C, nitrogen, boron trichloride and oxygen are introduced for 2-6 minutes, with a nitrogen flow rate of 2000-10000sccm, an oxygen flow rate of 200-2000sccm, and a boron trichloride flow rate of 50-600sccm; S7: heating for the third time; stopping the introduction of boron trichloride and oxygen, continuing to introduce nitrogen at a flow rate of 2000-10000 sccm into the furnace tube for nitrogen purge, continuing for 2-8 minutes, and heating the furnace tube to 850±2°C; S8: The fourth heating; nitrogen is introduced at a flow rate of 2000-10000 sccm for 3-15 minutes, and the furnace temperature is raised to 895±5°C; S9: Constant temperature operation; nitrogen gas is introduced at a flow rate of 2000-10000 sccm for 3-15 minutes, and the furnace tube is kept at a constant temperature of 895±5°C; S10: Perform the first oxidation and the fifth heating; stop nitrogen introduction, introduce wet oxygen into the furnace tube for 15-30 minutes, the wet oxygen flow rate is 10000-30000 sccm, and the furnace tube is heated to 1000±10°C; S11: second oxidation; continue to introduce wet oxygen for 20-50 minutes, with a flow rate of wet oxygen of 10000-30000 sccm; S12: third oxidation; continue to introduce wet oxygen for 10-30 minutes, with a flow rate of wet oxygen of 10000-30000 sccm; S13: performing the first cooling and the fourth oxidation; continuing to introduce wet oxygen for 20-50 minutes, with a wet oxygen flow rate of 10000-30000 sccm, and cooling the furnace tube to 800±10°C; S14: second cooling; stop the wet oxygen introduction, introduce nitrogen into the furnace tube for 5-20 minutes, the nitrogen flow rate is 10000-30000 sccm, and the furnace tube is cooled to 750±10°C; S15: Perform vacuum breaking operation on the furnace tube and take out the boat.

[0005] Preferably, during the first pre-deposition, the temperature in the furnace tube is 825° C., the flow rates of boron trichloride, oxygen and nitrogen introduced into the furnace tube are 110 sccm, 400 sccm and 7000 sccm respectively, and the introduction time is 2 minutes.

[0006] Preferably, during the second pre-deposition, the temperature in the furnace tube is 835° C., the flow rates of boron trichloride, oxygen and nitrogen introduced into the furnace tube are 110 sccm, 400 sccm and 7000 sccm respectively, and the introduction time is 3.5 minutes.

[0007] Preferably, during the third pre-deposition, the temperature in the furnace tube is 845° C., the flow rates of boron trichloride, oxygen and nitrogen introduced into the furnace tube are 110 sccm, 400 sccm and 7000 sccm respectively, and the introduction time is 3.5 minutes.

[0008] Preferably, during the first oxidation and the fifth heating, the flow rate of wet oxygen introduced into the furnace tube is 18000 sccm, which lasts for 20 minutes, and the temperature of the furnace tube is raised to 1000°C.

[0009] Preferably, during the second and third oxidations, the flow rate of wet oxygen introduced into the furnace tube is 18000 sccm, wherein the second oxidation lasts for 35 minutes, and the third oxidation lasts for 20 minutes.

[0010] Preferably, during the first cooling and the fourth oxidation, the flow rate of wet oxygen introduced into the furnace tube is 15000 sccm, which lasts for 32 minutes, and the furnace tube is cooled to 800°C.

[0011] Preferably, during the second cooling, the flow rate of nitrogen introduced into the furnace tube is 18000 sccm, which lasts for 10 minutes, and the furnace tube is cooled to 750°C.

[0012] Compared with the prior art, the present invention has the following beneficial effects: The present application adopts a multi-step source passing method, reduces the source passing time, increases the source passing flow, rapidly heats up and advances, and innovatively adopts a wet oxygen oxidation method and a low-temperature deposition method. The low-temperature deposition method can slow down the decomposition of the impurity source reaction, and reduce the concentration of the deposited on the silicon wafer surface, thereby reducing the content of impurities diffused into the silicon substrate, and ultimately achieving the effect of shallow junction depth. It is an effective method for preparing low-concentration shallow junctions and obtaining high square resistance. The present application achieves high square resistance with excellent uniformity while obtaining low impurity concentration BSG, while shortening the process time, ensuring a more ideal implementation of the subsequent LECO process, and ultimately maximizing the battery conversion efficiency and compressing the process time. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the comparison of positive oxidation ECV. DETAILED DESCRIPTION

[0014] In order to facilitate those skilled in the art to understand the technical content of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not used to limit the present invention.

[0015] Embodiment 1: A wet oxygen diffusion method for obtaining low-concentration BSG and high square resistance comprises the following steps: S1: Place the boat with silicon wafers into the furnace tube, and evacuate and heat the furnace tube; S2: first pre-deposition; when the temperature in the furnace tube is stabilized at 825°C, boron trichloride, oxygen and nitrogen are continuously introduced into the furnace tube for 2 minutes, with a nitrogen flow rate of 7000 sccm, an oxygen flow rate of 400 sccm and a boron trichloride flow rate of 110 sccm; S3: first heating; stop the introduction of boron trichloride and oxygen, continue to introduce nitrogen at a flow rate of 7000 sccm into the furnace tube for 3 minutes, and heat the furnace tube to 835°C; S4: second pre-deposition; continue to introduce boron trichloride, oxygen and nitrogen into the furnace tube for 3.5 minutes, with a nitrogen flow rate of 7000 sccm, an oxygen flow rate of 400 sccm and a boron trichloride flow rate of 110 sccm; S5: second heating; continue to introduce nitrogen into the furnace tube, while stopping the introduction of oxygen and boron trichloride, for 3 minutes, the nitrogen flow rate is 7000sccm, and the furnace tube is heated to 845°C; S6: the third pre-deposition; when the temperature in the furnace tube is stabilized at 845°C, nitrogen, boron trichloride and oxygen are introduced for 3.5 minutes, with a nitrogen flow rate of 7000 sccm, an oxygen flow rate of 400 sccm and a boron trichloride flow rate of 110 sccm; S7: heating for the third time; stopping the introduction of boron trichloride and oxygen, continuing to introduce nitrogen at a flow rate of 7000 sccm into the furnace tube for nitrogen purge, continuing for 3 minutes, and heating the furnace tube to 850°C; S8: the fourth heating; nitrogen gas is introduced at a flow rate of 7000 sccm for 6 minutes, and the furnace temperature is raised to 895°C; S9: Constant temperature operation; nitrogen gas is introduced at a flow rate of 7000 sccm for 5.5 minutes, and the furnace tube is kept at a constant temperature of 895°C; S10: performing the first oxidation and the fifth heating; stopping the nitrogen supply, and supplying wet oxygen into the furnace tube for 20 minutes, with a wet oxygen flow rate of 18000 sccm, and heating the furnace tube to 1000° C.; S11: second oxidation; continue to introduce wet oxygen for 35 minutes, with a flow rate of 18000 sccm; S12: third oxidation; continue to introduce wet oxygen for 20 minutes, with a flow rate of 18000 sccm; S13: performing the first cooling and the fourth oxidation; continuing to introduce wet oxygen for 32 minutes, with a wet oxygen flow rate of 15000 sccm, and cooling the furnace tube to 800° C.; S14: second cooling; stop the wet oxygen introduction, introduce nitrogen into the furnace tube for 10 minutes, the nitrogen flow rate is 18000 sccm, and the furnace tube is cooled to 750°C; S15: Perform vacuum breaking operation on the furnace tube and take out the boat.

[0016] The present application adopts a multi-step source passing method, reduces the source passing time, increases the source passing flow, rapidly heats up and advances, and innovatively adopts a wet oxygen oxidation method and a low-temperature deposition method. The low-temperature deposition method can slow down the decomposition of the impurity source reaction, and reduce the concentration of the deposited on the silicon wafer surface, thereby reducing the content of impurities diffused into the silicon substrate, and ultimately achieving the effect of shallow junction depth. It is an effective method for preparing low-concentration shallow junctions and obtaining high square resistance. The present application achieves high square resistance with excellent uniformity while obtaining low impurity concentration BSG, while shortening the process time, ensuring a more ideal implementation of the subsequent LECO process, and ultimately maximizing the battery conversion efficiency and compressing the process time.

[0017] like Figure 1 As shown, Figure 1 The ECV curves of two different diffusion processes are shown, namely the EVC curve of wet oxygen diffusion with low BSG concentration and high square resistance involved in this application and the ECV curve of conventional B diffusion square resistance. This application obviously has high square resistance, low surface impurity concentration, and shallow junction depth. Therefore, this application is a highly efficient diffusion method. When the surface concentration is low, the surface defect density of the battery is low, the dead layer is small, and the carriers on the surface are reduced, thereby increasing the open circuit voltage of the battery; the junction depth is shallow, the natural light incident on the PN junction has a short optical path, and low-wavelength light can reach the built-in electric field area. The generated hole-electron pairs can be separated by the built-in electric field formed by the PN junction, which improves the battery light absorption and increases the battery short-circuit current. Finally, the LECO process is matched to improve the battery photoelectric conversion efficiency.

Claims

1. A wet oxygen diffusion method for obtaining low-concentration BSG and high square resistance, characterized in that: The following steps are involved: S1: Place the boat with silicon wafers into the furnace tube, and evacuate and heat the furnace tube; S2: first pre-deposition; when the temperature in the furnace tube is stabilized at 825±2°C, boron trichloride, oxygen and nitrogen are continuously introduced into the furnace tube for 1-5 minutes, with a nitrogen flow rate of 2000-10000sccm, an oxygen flow rate of 200-2000sccm, and a boron trichloride flow rate of 50-600sccm; S3: first heating; stop the introduction of boron trichloride and oxygen, continue to introduce nitrogen at a flow rate of 2000-10000sccm into the furnace tube for 1-5 minutes, and heat the furnace tube to 835±2°C; S4: second pre-deposition; continue to introduce boron trichloride, oxygen and nitrogen into the furnace tube for 2-6 minutes, with a nitrogen flow rate of 2000-10000sccm, an oxygen flow rate of 200-2000sccm, and a boron trichloride flow rate of 50-600sccm; S5: heating for the second time; continue to introduce nitrogen into the furnace tube, while stopping the introduction of oxygen and boron trichloride, for 2-8 minutes, the nitrogen flow rate is 2000-10000sccm, and the furnace tube is heated to 845±2℃; S6: the third pre-deposition; when the temperature in the furnace tube is stabilized at 845±2°C, nitrogen, boron trichloride and oxygen are introduced for 2-6 minutes, with a nitrogen flow rate of 2000-10000sccm, an oxygen flow rate of 200-2000sccm, and a boron trichloride flow rate of 50-600sccm; S7: heating for the third time; stopping the introduction of boron trichloride and oxygen, continuing to introduce nitrogen at a flow rate of 2000-10000 sccm into the furnace tube for nitrogen purge, continuing for 2-8 minutes, and heating the furnace tube to 850±2°C; S8: The fourth heating; nitrogen is introduced at a flow rate of 2000-10000 sccm for 3-15 minutes, and the furnace temperature is raised to 895±5°C; S9: Constant temperature operation; nitrogen gas is introduced at a flow rate of 2000-10000 sccm for 3-15 minutes, and the furnace tube is kept at a constant temperature of 895±5°C; S10: Perform the first oxidation and the fifth heating; stop nitrogen introduction, introduce wet oxygen into the furnace tube for 15-30 minutes, the wet oxygen flow rate is 10000-30000 sccm, and the furnace tube is heated to 1000±10°C; S11: second oxidation; continue to introduce wet oxygen for 20-50 minutes, with a flow rate of wet oxygen of 10000-30000 sccm; S12: third oxidation; continue to introduce wet oxygen for 10-30 minutes, with a flow rate of wet oxygen of 10000-30000 sccm; S13: performing the first cooling and the fourth oxidation; continuing to introduce wet oxygen for 20-50 minutes, with a wet oxygen flow rate of 10000-30000 sccm, and cooling the furnace tube to 800±10°C; S14: second cooling; stop the wet oxygen introduction, introduce nitrogen into the furnace tube for 5-20 minutes, the nitrogen flow rate is 10000-30000 sccm, and the furnace tube is cooled to 750±10°C; S15: Perform vacuum breaking operation on the furnace tube and take out the boat.

2. A wet oxygen diffusion method for obtaining low-concentration BSG and high square resistance according to claim 1, characterized in that: During the first pre-deposition, the temperature in the furnace tube was 825° C., and the flow rates of boron trichloride, oxygen and nitrogen introduced into the furnace tube were 110 sccm, 400 sccm and 7000 sccm, respectively, for 2 minutes.

3. A wet oxygen diffusion method for obtaining low-concentration BSG with high square resistance according to claim 1, characterized in that: During the second pre-deposition, the temperature in the furnace tube was 835° C., and the flow rates of boron trichloride, oxygen and nitrogen introduced into the furnace tube were 110 sccm, 400 sccm and 7000 sccm, respectively, for 3.5 minutes.

4. A wet oxygen diffusion method for obtaining low-concentration BSG and high square resistance according to claim 1, characterized in that: During the third pre-deposition, the temperature in the furnace tube was 845° C., and the flow rates of boron trichloride, oxygen and nitrogen introduced into the furnace tube were 110 sccm, 400 sccm and 7000 sccm, respectively, for 3.5 minutes.

5. A wet oxygen diffusion method for obtaining low-concentration BSG with high square resistance according to claim 1, characterized in that: During the first oxidation and the fifth heating, the flow rate of wet oxygen introduced into the furnace tube was 18000 sccm, which lasted for 20 minutes, and the temperature of the furnace tube was raised to 1000°C.

6. A wet oxygen diffusion method for obtaining low-concentration BSG with high square resistance according to claim 1, characterized in that: During the second and third oxidations, the flow rate of wet oxygen introduced into the furnace tube was 18000 sccm. The second oxidation lasted for 35 minutes, and the third oxidation lasted for 20 minutes.

7. A wet oxygen diffusion method for obtaining low-concentration BSG with high square resistance according to claim 1, characterized in that: During the first cooling and the fourth oxidation, the flow rate of wet oxygen introduced into the furnace tube was 15000 sccm, which lasted for 32 minutes, and the furnace tube was cooled to 800°C.

8. A wet oxygen diffusion method for obtaining low-concentration BSG with high square resistance according to claim 1, characterized in that: During the second cooling, the flow rate of nitrogen introduced into the furnace tube was 18000 sccm, which lasted for 10 minutes, and the temperature of the furnace tube was reduced to 750°C.

Images