Method for improving TopCon boron expanding furnace mouth rich source and serious flange rusting corrosion

Abstract

The invention provides a method for improving source enrichment of a TopCon boron expansion furnace mouth and serious rusting and corrosion of a flange, which comprises the following steps: in a boron diffusion process, before boron source gas is introduced for diffusion, firstly increasing the nitrogen introduction amount of the furnace mouth; three source introduction steps of the boron diffusion process are executed, and after each step is completed, the BCl3 gas purging step in the conventional process is canceled; after the three-step source diffusion is completed, a waste gas treatment mode is changed into a negative pressure reverse extraction mode; by modifying equipment control software, a function of reversely pumping the BCl3 pipeline immediately after the boron source is introduced every time is added; and according to the sheet resistance expression trend, the amount of the introduced boron source is reduced, and the oxygen / nitrogen ratio is optimized at the same time. According to the method, the problems of source enrichment of the furnace mouth and flange corrosion in the TopCon boron diffusion process are fundamentally solved, the service life of equipment is prolonged, the maintenance cost is reduced, the product quality is ensured, the production efficiency is improved, and remarkable economic benefits and application values are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of boron diffusion of TopCon batteries, and in particular to a method for improving the serious rust and corrosion of the boron diffusion source and flange of a TopCon boron expansion furnace. Background Art

[0002] In photovoltaic cell manufacturing, TopCon (Tunnel Oxide Passivated Contact) technology is a high-efficiency crystalline silicon solar cell structure. Its core structure includes an N-type silicon substrate, a P+ emitter formed by boron diffusion on the front side, and an ultra-thin tunnel oxide layer (SiO2) and doped polysilicon layer (Poly-Si) on the back side. Boron diffusion technology is primarily used to form the PN junction on the front side of the cell. Its quality directly affects the cell's open-circuit voltage (Voc) and conversion efficiency, making it a key process step in TopCon cell manufacturing.

[0003] However, the current Topcon boron diffusion process has numerous issues, including: 1. Boron has a low solubility in silicon, requiring traditional boron diffusion to be performed at high temperatures (>1000°C), which is time-consuming (approximately 150 minutes). 2. The furnace door suffers from severe corrosion from prolonged exposure to air leaks and high-temperature calcination. Furthermore, using a purge mode directly leads to air leaks at the furnace mouth, making exhaust difficult to remove. Airflow through the furnace door carries contaminants, leading to severe silicon wafer contamination.

[0004] These issues not only affect the stability and consistency of the boron diffusion process, but also negatively impact the equipment's lifespan and maintenance costs. They can also lead to product quality fluctuations and reduce battery conversion efficiency. Therefore, an improved method is urgently needed to address the severe rust and corrosion of the TopCon boron diffusion furnace's source and flange, thereby extending equipment life, ensuring process stability, and ensuring product quality. Summary of the Invention

[0005] Based on the problems existing in the background technology, the present invention provides a method for improving the serious rust and corrosion of the TopCon boron expansion furnace mouth and flange, aiming to solve the technical problems of serious furnace mouth rich source, serious rust and corrosion of the flange, short equipment life and high maintenance cost in the existing TopCon boron diffusion process.

[0006] The present invention is implemented through the following technical solutions:

[0007] A method for improving the serious rust and corrosion of the TopCon boron expansion furnace mouth source and flange, comprising the following steps:

[0008] S1. In the boron diffusion process, before the boron source gas is introduced for diffusion, the nitrogen gas flow rate at the furnace mouth is increased to form a high-velocity airflow barrier at the furnace mouth. The barrier prevents the boron reactant from back-diffusion and adhesion to the furnace mouth flange through the action of airflow dynamics;

[0009] S2 performs a three-step boron diffusion process through the source step, after each step is completed, cancel the conventional process BCl3 gas purge step;

[0010] S3. After completing the three-step source diffusion process, the waste gas treatment mode is changed to negative pressure backdraft mode. Negative pressure is applied through the equipment's tail exhaust system, causing the waste gas to flow in the opposite direction along the pipeline and be discharged from the tail exhaust system.

[0011] S4. By modifying the equipment control software, an additional function is added to the BCl3 pipeline for back-pumping immediately after each boron source is completed. This function automatically starts after the source is completed to avoid the residual BCl3 gas in the pipeline from diffusing to the furnace in subsequent processes;

[0012] S5. Based on the square resistance performance trend, reduce the amount of boron source introduced and optimize the oxygen / nitrogen ratio to promote the full formation of an oxide protective layer of SiO2 on the silicon wafer surface and inhibit the corrosive reaction of BCl3.

[0013] Preferably, the amount of nitrogen introduced in step S1 is 1.5-2 times the amount of nitrogen introduced into the furnace port in the original standard process, and the specific value is 700-1100 sccm.

[0014] Preferably, the negative pressure back-pumping mode in step S3 is to generate a negative pressure of 200-300 mbar in the exhaust system at the rear of the equipment, and the exhaust time is 90-120 s.

[0015] Preferably, in step S4, the back-pumping time of the BCl3 pipeline is 30-60s, and the back-pumping negative pressure value is 200-300mbar.

[0016] Preferably, step S1 also includes changing the nitrogen intake mode at the furnace mouth from single-point intake to multi-point annular distribution intake, so as to improve the distribution uniformity of nitrogen in the furnace mouth area and enhance the barrier effect.

[0017] Preferably, reducing the amount of boron source in step S5 means reducing the amount of BCl3 introduced from 120-130 sccm in the original process to 100-120 sccm, and optimizing the oxygen / nitrogen ratio, with an oxygen flow rate of 450-500 sccm and a nitrogen flow rate of 900-1100 sccm, to form an oxygen:nitrogen mixed gas with a volume ratio of 1:2 to 1:2.2.

[0018] Preferably, in step S5 , the standard square resistance is set to ±25Ω, and the on-chip uniformity is controlled within 3%.

[0019] Preferably, the method is applicable to the boron diffusion step in the TopCon cell manufacturing process of an N-type silicon substrate.

[0020] Beneficial effects of the present invention:

[0021] 1. Effectively reduce the enrichment of the furnace mouth: by increasing the nitrogen flow rate at the furnace mouth to form an airflow barrier, eliminating the BCl3 purge step and adopting the back-pumping mode, the enrichment of boron reactants at the furnace mouth is significantly reduced, thus avoiding the enrichment problem;

[0022] 2. Significantly reduce flange corrosion: Changing the nitrogen intake mode at the furnace mouth enhances the protective effect of nitrogen on the flange. At the same time, the back-pumping mode prevents corrosive gases from being discharged from the furnace mouth, effectively reducing the degree of flange corrosion. According to experimental results, the degree of flange corrosion can be reduced by more than 80%;

[0023] 3. Significantly extend equipment life: Reduce flange corrosion and furnace mouth corrosion, effectively extend the service life of quartz spare parts such as furnace tubes and flanges, reduce equipment maintenance frequency and costs, and the equipment service life is expected to be extended by more than 50%;

[0024] 4. Improved process stability: By optimizing the oxygen / nitrogen ratio and boron source dosage, we ensure that equipment problems are improved without affecting product quality. The square resistance standard is controlled within the range of ±25Ω, and the on-chip uniformity reaches 3%, which is conducive to the lateral transmission of current.

[0025] 5. Improve production efficiency: reduce equipment failures and downtime, improve equipment reliability and production efficiency, and reduce spare parts replacement and maintenance costs;

[0026] 6. Simple, feasible and easy to implement: The present invention does not require major changes to the hardware structure of the equipment. It can be achieved mainly through process parameter optimization and software modification. It has low implementation difficulty, low cost and high promotion value.

[0027] The present invention fundamentally solves the problems of furnace mouth rich source and flange corrosion in the TopCon boron diffusion process through a series of process optimization measures. It not only extends the equipment life and reduces maintenance costs, but also ensures product quality and improves production efficiency, with significant economic benefits and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to further explain the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 The method of the present invention improves the state of the furnace door;

[0030] Figure 2The method of the present invention improves the state of the front furnace door. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described in detail below with reference to specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0032] Example 1

[0033] This embodiment provides a method for improving the serious rust and corrosion of the TopCon boron expansion furnace source and flange. This method is applied to the boron diffusion step in the TopCon solar cell manufacturing process for N-type silicon substrates. The specific implementation steps are as follows:

[0034] Step 1: Wafer loading

[0035] Place the N-type silicon wafers on a quartz boat and send the boat containing the silicon wafers into the boron diffusion furnace to ensure that the silicon wafers are evenly arranged and avoid overlapping.

[0036] Step 2: Heating and pre-oxidation

[0037] The temperature in the furnace was raised to 848°C, the nitrogen flow rate was 900 sccm, the oxygen flow rate was 1500 sccm, the pressure was set to 230 mbar, and the pre-oxidation time lasted for 120 seconds. The purpose of this step was to form a thin oxide layer on the surface of the silicon wafer to prepare for subsequent boron diffusion.

[0038] Before the boron diffusion process begins, the nitrogen flow rate at the furnace inlet is increased from the standard 500 sccm to 900 sccm, an increase of approximately 1.8 times. Simultaneously, the nitrogen inlet method is changed from a single-point inlet to a four-point annular distribution, creating a uniform, high-velocity nitrogen barrier at the furnace inlet. This is accomplished by modifying the gas flow parameters in the equipment control system and installing an annular distributor.

[0039] The principle of forming a high-flow nitrogen barrier is to utilize the dynamic characteristics of the airflow to form a stable airflow field in the furnace mouth area, and prevent the boron reactant from diffusing back to the furnace mouth through momentum transfer and pressure gradient, thereby effectively preventing the boron reactant from adhering to the furnace mouth flange.

[0040] Step 3: Boron diffusion deposition (three times)

[0041] A standard three-step boron diffusion process was performed with the following parameters: temperature: 848°C, pressure: 230 mbar, BCl3 flow rate: 110 sccm, oxygen flow rate: 480 sccm, nitrogen flow rate: 1000 sccm, and source time: 175 s.

[0042] These parameters are optimized based on the square resistance performance trend, the boron source dosage and gas ratio: the BCl3 injection amount is reduced from 130sccm in the original process to 110sccm, the oxygen flow rate is set to 480sccm, and the nitrogen flow rate is set to 1000sccm, forming a mixed gas with an oxygen:nitrogen volume ratio of approximately 1:2.1.

[0043] By optimizing the gas ratio, we promote the formation of a protective oxide layer of SiO2 on the silicon wafer surface, inhibiting the corrosive reaction of BCl3. At the same time, we monitor and control the uniformity of square resistance to ensure that the standard is within ±25Ω and the uniformity within the wafer is controlled within 3%.

[0044] Unlike conventional processes, this embodiment eliminates the BCl3 purge step after each source opening. In conventional processes, pure BCl3 gas is introduced after the source opening for a purge at a flow rate of 50-100 sccm for 30-60 seconds to clean the pipeline. This embodiment eliminates this step, preventing additional BCl3 gas from entering the system and causing a furnace-mouth source enrichment.

[0045] By modifying the equipment control software, a function has been added to back-pump the BCl3 pipeline immediately after each source pass. This function starts immediately after each source pass, with a back-pump negative pressure of 250 mbar, a back-pump time of 45 seconds, and a back-pump temperature of 848°C, the same as the source pass temperature. This BCl3 pipeline back-pump function extracts any remaining BCl3 gas from the pipeline immediately after each source pass, preventing it from gradually diffusing to the furnace mouth during subsequent steps, thereby mitigating the problem of furnace mouth enrichment. The software modification primarily involves adding an automatic execution command for the back-pump step to the process control program.

[0046] Step 4: Use negative pressure backflow mode instead of traditional purge mode

[0047] After completing the three-step source, the exhaust gas is discharged using a negative pressure reverse extraction mode instead of the traditional forward purge mode. Specifically, a negative pressure of 250mbar is applied to the exhaust system at the rear of the equipment, the conventional exhaust valve at the furnace mouth is closed, and the reverse extraction valve in the pipeline is opened. The extraction time is set to 100 seconds, and the extraction temperature is maintained at 848°C.

[0048] The working principle of the negative pressure back-draw mode is to form a negative pressure area at the tail of the equipment, so that the airflow direction in the reaction chamber is directed from the furnace mouth to the tail, thereby discharging the waste gas from the tail exhaust system, effectively avoiding the corrosion of the flange caused by the waste gas discharged from the furnace mouth.

[0049] Step 5: Promoting Diffusion

[0050] The temperature rises to 885°C, the first push time is 270 seconds, the nitrogen flow rate is 3000sccm, the second push time is 130 seconds, the nitrogen flow rate is 3000sccm, and the pressure is maintained at 230mbar. The purpose of this step is to promote the further diffusion of boron atoms into the silicon wafer to form a PN junction of the required depth.

[0051] Step 6: Oxidation after heating

[0052] The temperature was raised to 1050°C, oxygen was introduced at a flow rate of 25,000 sccm, and the pressure was increased to 850 mbar. Post-oxidation was performed in two stages: the first, a temperature rise phase, lasting 800 seconds; the second, a constant temperature phase, lasting 3200 seconds. This step aims to form a glass layer, remove excess boron sources, and stabilize the PN junction structure.

[0053] Step 7: Cool down and get out of the boat

[0054] The temperature was slowly lowered to 820°C under oxygen flow for about 2300 seconds. The oxygen flow was stopped and nitrogen was introduced for protection. After the temperature was lowered to a safe temperature, the pressure was returned to atmospheric pressure and the silicon wafer boat was removed from the furnace tube.

[0055] Comparative Example 1

[0056] This comparative example represents the conventional technical solution before the improvement of the present invention.

[0057] Step 1: Wafer loading

[0058] Place the N-type silicon wafers on a quartz boat and send the boat containing the silicon wafers into the boron diffusion furnace to ensure that the silicon wafers are evenly arranged and avoid overlapping.

[0059] Step 2: Heating and pre-oxidation

[0060] The temperature in the furnace was raised to 848°C, the nitrogen flow rate was 500 sccm, the oxygen flow rate was 1500 sccm, the pressure was set to 230 mbar, and the pre-oxidation time lasted for 120 seconds. The purpose of this step was to form a thin oxide layer on the surface of the silicon wafer to prepare for subsequent boron diffusion.

[0061] Step 3: Boron diffusion deposition (three times)

[0062] The temperature was maintained at 848°C, BCl3 gas was introduced at a flow rate of 130 sccm, oxygen gas was introduced at a flow rate of 450 sccm, nitrogen gas was introduced at a flow rate of 900 sccm, the pressure was maintained at 220 mbar, and the deposition time was 175 seconds.

[0063] After the source is passed, BCl3 is introduced for purging: the BCl3 purge flow rate is 50-100 sccm, and the purge time is 30-45 seconds. The purpose of the purge is to clean the pipeline and reduce gas retention.

[0064] Nitrogen gas was introduced at 5000 sccm for 100 seconds to clean the pipeline.

[0065] Step 4: Heat and purge

[0066] The temperature was raised to 885°C, nitrogen was introduced at a flow rate of 4000 sccm, the pressure was maintained at 230 mbar, and the purge time was 150 seconds. The purpose of this step was to remove residual reactants and prepare for subsequent advancement.

[0067] Step 5: Promoting Diffusion

[0068] The temperature is maintained at 885°C, the first push time is 270 seconds, the nitrogen flow rate is 3000sccm, the second push time is 130 seconds, the nitrogen flow rate is 3000sccm, and the pressure is maintained at 230mbar. The purpose of this step is to encourage boron atoms to further diffuse into the silicon wafer to form a PN junction of the required depth.

[0069] Step 6: Oxidation after heating

[0070] The temperature was raised to 1050°C, oxygen was introduced at a flow rate of 25,000 sccm, and the pressure was increased to 850 mbar. Post-oxidation was performed in two stages: the first, a temperature rise phase, lasting 800 seconds; the second, a constant temperature phase, lasting 3200 seconds. This step aims to form a glass layer, remove excess boron sources, and stabilize the PN junction structure.

[0071] Step 7: Cool down and get out of the boat

[0072] The temperature was slowly lowered to 820°C under oxygen flow for about 2300 seconds. The oxygen flow was stopped and nitrogen was introduced for protection. After the temperature was lowered to a safe temperature, the pressure was returned to atmospheric pressure and the silicon wafer boat was removed from the furnace tube.

[0073] Test Example 1: Comparison of square resistance performance between conventional purge mode and back-pump mode

[0074] To fully verify the effectiveness of the present method, detailed comparative testing was conducted on the sheet resistance of silicon wafers in the conventional purge mode of Comparative Example 1 and the reverse pumping mode of Example 1. The test was conducted using six temperature zones, with nine test points in each zone. The specific test results are shown in Tables 1 and 2.

[0075] Table 1 Sheet resistance performance data under conventional purge mode (Comparative Example 1) (unit: Ω / □)

[0076]

[0077] Table 2 Sheet resistance performance data under the back-pulling mode (Example 1) (unit: Ω / □)

[0078]

[0079] From the comparison of the data in Table 1 and Table 2, it can be clearly seen that after adopting the back-pump mode, the silicon wafer resistance performance has been significantly improved compared with the conventional purge mode:

[0080] 1. Improved square resistance: The average square resistance in the reverse pumping mode (304Ω / □) is 8.57% higher than that in the conventional purge mode (280Ω / □).

[0081] 2. Significant improvement in intra-chip uniformity: The intra-chip average in the back-pump mode is 1.63%; the worst intra-chip uniformity of 2.53% in the back-pump mode is still better than the best intra-chip uniformity of 2.85% in the conventional purge mode.

[0082] 3. Reduced differences between points: In conventional purge mode, the maximum difference between points in the same temperature zone can reach 32.1Ω / □ (temperature zone 3: 266.2-298.3); in reverse pumping mode, the maximum difference between points in the same temperature zone is only 25Ω / □ (temperature zone 4: 301-317). The reduced difference between points indicates more uniform boron diffusion, which is beneficial to improving battery performance.

[0083] These detailed comparative data fully demonstrate that the back-pumping mode adopted in the present invention not only effectively solves the problems of furnace mouth rich source and flange corrosion, but also significantly improves the process stability of boron diffusion and the uniformity of silicon wafer square resistance, fundamentally improving product quality and consistency.

[0084] Test Example 2: Improvement effect of furnace door condition

[0085] To fully verify the effectiveness of the method of the present invention, a comparative experiment was conducted. The control group used the traditional process (Comparative Example 1), and the experimental group used the method of Example 1. Each group was operated continuously for 3 months, and the condition of the furnace door before and after improvement was recorded.

[0086] Figure 1 and Figure 2 The method of the present invention improves the state of the rear furnace door and the state of the front furnace door respectively.

[0087] Improve the condition of the front furnace door: The flange surface is covered with a large amount of yellow-brown deposits, mainly boron compound deposits. The flange sealing surface is severely corroded with obvious pits and oxidation marks. The bolt fixing parts are severely rusted, and some bolts are corroded and difficult to remove. The sealing performance of the furnace door is reduced, and there is air leakage. The service life of the flange is severely shortened, and it can only be used for an average of 2-3 months.

[0088] The condition of the furnace door after improvement: the flange surface remains basically clean, without obvious deposits, the flange sealing surface is intact, without corrosion pits, and there is no obvious rust on the bolt fixing parts. The furnace door has good sealing performance and no air leakage. The service life of the flange is significantly extended and is expected to be used for more than 9 months.

[0089] This comparison directly demonstrates the significant effectiveness of the method in reducing rust and corrosion at the furnace mouth and flange, significantly extending equipment life and reducing maintenance costs. Furthermore, because the back-drawing mode improves sheet resistance uniformity, the more uniform sheet resistance across the entire screen surface increases the sintering window when the metal grid contacts the silicon wafer during sintering, further enhancing cell performance.

[0090] While this invention primarily addresses the TopCon boron diffusion process, its fundamental principles and technical concepts can also be applied to other high-temperature processes involving corrosive gases, such as the boron diffusion process for PERC cells, surface treatment processes for HJT cells, and other diffusion processes using corrosive gases (e.g., POCl₃, BBr₃). By appropriately adjusting the airflow barrier parameters, negative pressure backflow mode parameters, and gas ratios, the technical concepts of this invention can be flexibly applied to diverse process requirements, achieving the dual goals of equipment protection and process optimization.

[0091] Finally, it should be noted that the above-described embodiments merely represent several implementation methods of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made by a person skilled in the art without departing from the spirit of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention should be based on the appended claims.

Claims

1. A method for improving the serious rust and corrosion of the TopCon boron expansion furnace mouth and flange, characterized in that: The following steps are involved: S1. In the boron diffusion process, before the boron source gas is introduced for diffusion, the nitrogen gas flow rate at the furnace is increased to form a high-velocity nitrogen gas flow barrier at the furnace mouth; S2 performs a three-step boron diffusion process through the source step, after each step is completed, cancel the conventional process BCl3 gas purge step; S3. After completing the three-step source diffusion process, the waste gas treatment mode is changed to negative pressure backdraft mode. Negative pressure is applied through the equipment's tail exhaust system, causing the waste gas to flow in the opposite direction along the pipeline and be discharged from the tail exhaust system. S4. By modifying the equipment control software, an additional function is added to the BCl3 pipeline for back-pumping immediately after each boron source is completed. This function automatically starts after the source is completed to avoid the residual BCl3 gas in the pipeline from diffusing to the furnace in subsequent processes; S5. Based on the square resistance performance trend, reduce the amount of boron source introduced and optimize the oxygen / nitrogen ratio to promote the full formation of an oxide protective layer of SiO2 on the silicon wafer surface and inhibit the corrosive reaction of BCl3.

2. The method according to claim 1, characterized in that The amount of nitrogen introduced in step S1 is 1.5-2 times the amount of nitrogen introduced into the furnace port in the original standard process, and the specific value is 700-1100 sccm.

3. The method according to claim 1, characterized in that The negative pressure back-pumping mode in step S3 generates a negative pressure of 200-300 mbar in the exhaust system at the rear of the equipment, and the exhaust time is 90-120 seconds.

4. The method according to claim 1, wherein In step S4, the back-pumping time of the BCl3 pipeline is 30-60s, and the back-pumping negative pressure value is 200-300mbar.

5. The method according to claim 1, wherein Step S1 also includes changing the nitrogen intake mode at the furnace mouth from single-point intake to multi-point annular distributed intake.

6. The method according to claim 1, characterized in that Reducing the amount of boron source in step S5 means reducing the BCl3 feed rate from 120-130 sccm in the original process to 100-120 sccm, and optimizing the oxygen / nitrogen ratio at the same time, with an oxygen flow rate of 450-500 sccm and a nitrogen flow rate of 900-1100 sccm, to form a mixed gas with an oxygen:nitrogen volume ratio of 1:2 to 1:2.

2.

7. The method according to claim 1, characterized in that In step S5, the standard square resistance is set to ±25Ω, and the on-chip uniformity is controlled within 3%.

8. The method according to claim 1, characterized in that The method is applicable to the boron diffusion step in the TopCon battery manufacturing process of an N-type silicon substrate.

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