PECVD process for improving membrane explosion of TOPCON battery

Abstract

The invention specifically discloses a PECVD (Plasma Enhanced Chemical Vapor Deposition) process for improving membrane explosion of a TOPCON battery. The PECVD process comprises the following steps: (1) placing a graphite boat filled with silicon wafers in a furnace tube; (2) filling nitrogen into the furnace tube for protection; (3) step-by-step heating and constant-temperature hydrogen passivation treatment are carried out; (4) vacuumizing in the furnace tube; (5) NH3 and N2O are introduced into the furnace tube for ionization; (6) depositing silicon nitride; (7) carrying out vacuumizing and nitrogen charging to atmospheric pressure treatment; and (8) transporting the graphite boat out of the furnace tube. According to the preparation method, the membrane explosion ratio of the TOPCon battery in the preparation process is effectively reduced, and the efficiency of the battery is improved; in particular, through step-by-step heating and increase of laughing gas and ammonia ionization in front of the silicon nitride film layer, N-H bonds are formed in the film layer, so that hydrogen overflow is reduced, film explosion is improved, and a better hydrogen passivation effect is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of solar cells, and in particular to a PECVD process for improving film explosion of TOPCON cells. Background Art

[0002] TOPCon (tunneling silicon oxide passivation contact technology) cells have been widely used in the photovoltaic field due to their excellent performance. However, in the preparation process, the atomic layer deposition (ALD) process is usually used to deposit aluminum oxide in TOPCon cells. The batteries prepared by the existing deposition process contain more hydrogen in the aluminum oxide deposits. After sintering, they are prone to large-area film explosions on the front and local film explosions on the back, resulting in poor battery appearance and poor passivation effect. In addition, the market demands high-efficiency TOPCon battery products, which need to be further improved through hydrogen passivation. However, the traditional hydrogen passivation method is prone to rapid hydrogen overflow during the rapid temperature rise sintering process, resulting in the risk of film explosion, thereby reducing the passivation effect. Summary of the invention

[0003] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a PECVD process for improving the film explosion of TOPCON batteries. By performing step-by-step temperature increase in the coating section and forming NH bonds inside the film layer before silicon nitride deposition, slow hydrogen overflow is achieved, effectively reducing the film explosion phenomenon and improving the hydrogen passivation effect.

[0004] In order to achieve the above object, the present invention adopts the following technical solution:

[0005] A PECVD process for improving TOPCON cell film explosion includes the following steps:

[0006] (1) Entering the furnace tube: placing the graphite boat filled with silicon wafers into the furnace tube;

[0007] (2) Nitrogen filling protection: fill the furnace tube with nitrogen;

[0008] (3) Step-by-step heating: The furnace tube is heated in stages, and the temperature is kept constant after each stage reaches the temperature, and then it is heated to the next stage temperature;

[0009] (4) Vacuuming: Vacuuming the furnace tube;

[0010] (5) Improve the treatment of film explosion: introduce NH3 and N2O into the furnace tube for ionization;

[0011] (6) Silicon nitride deposition: performing multiple silicon nitride deposition steps;

[0012] (7) Evacuate and fill with nitrogen to atmospheric pressure: evacuate the excess reaction residual gas in the furnace tube and fill with nitrogen to atmospheric pressure;

[0013] (8) Out of the furnace tube: transport the graphite boat out of the furnace tube.

[0014] Among them, in the step-by-step heating process, when each heating temperature is reached, a certain time is maintained for constant temperature treatment. The silicon wafer is kept at a constant temperature through heat conduction, so that the hydrogen deposited by the aluminum oxide can overflow separately and can combine with some broken bonds of the silicon-silicon covalent bonds to passivate the internal defects of the silicon wafer. The present invention reduces the heating rate by performing a distributed heating method of heating and maintaining a constant temperature in the coating section, so that the hydrogen passivation overflows slowly and the overflow speed is reduced; and nitrous oxide and ammonia are added in front of the silicon nitride film layer for ionization. Nitrogen has a strong electrical load and adsorption force on hydrogen, and forms NH bonds inside the film layer. The NH bond energy is higher and more stable than the Si-H bond energy, which can slow down the nitrogen overflow speed. In addition, NH3 can also provide a large amount of hydrogen to further passivate the defects inside the silicon wafer, and can achieve a better hydrogen passivation effect, thereby improving the explosion of the film.

[0015] Furthermore, in step (1), the furnace tube temperature is 400±50° C. and the pressure is 10000±100 mtorr.

[0016] Furthermore, in the step (2), nitrogen is charged at a flow rate of 20000±100sccm.

[0017] Furthermore, in step (3), the step-by-step heating process specifically includes the following steps:

[0018] ① The first temperature is raised to 430±50℃, the heating time is 2±0.2min, the pressure is set to 10000±100mtorr, the nitrogen flow rate is 2000±50sccm, and the temperature is kept constant for 3±0.2min for hydrogen passivation;

[0019] ② The second temperature is raised to 460±50°C, the heating time is 2±0.2min, the pressure is set to 10000±100mtorr, the nitrogen flow rate is 2000±50sccm, and the temperature is kept constant for 3±0.2min for hydrogen passivation;

[0020] ③ The temperature was raised to 500±50°C for the third time, the heating time was 3±0.2min, the pressure was set to 10000±100mtorr, the nitrogen flow rate was 2000±50sccm, and the temperature was kept constant for 3±0.2min for hydrogen passivation.

[0021] It should be noted that the third heating temperature cannot exceed 550°C, as too high a temperature will affect the formation of the film layer.

[0022] Furthermore, in step (4), the furnace temperature is 500±50°C, the nitrogen flow rate is 0, the pressure is set to 50±30mtorr, and the vacuum time is 2±0.2min.

[0023] Furthermore, in the step (5), NH3 and N2O are introduced in a ratio of 1:1, the gas flow rate is 6000±500sccm, the RF power is 12000±1000W, the pressure is 1500±50mtor, and the process time is 1.5±0.2min.

[0024] Furthermore, in step (6), three silicon nitride deposition steps are performed, specifically:

[0025] ① The first silicon nitride deposition step: in the furnace tube, the temperature is set to 500±50°C, ammonia and silane are introduced, the ammonia flow rate is 9000±1000sccm, the silane flow rate is 2300±500sccm, the pressure is 1500±50mtorr, the RF power is 15000±1000W, and the process time is 2.2±0.2min;

[0026] ② The second silicon nitride deposition step: in the furnace tube, the temperature is set to 500±50°C, ammonia and silane are introduced, the ammonia flow rate is 10500±1000sccm, the silane flow rate is 1800±500sccm, the pressure is 1500±50mtorr, the RF power is 15000±1000W, and the process time is 3.2±0.2min;

[0027] ③The third silicon nitride deposition step: in the furnace tube, the temperature is set to 500±50°C, ammonia and silane are introduced, the ammonia flow rate is 14500±1000sccm, the silane flow rate is 1500±500sccm, the pressure is 1500±50mtorr, the RF power is 15000±1000W, and the process time is 6±0.5min.

[0028] Furthermore, in step (7), the specific operation of the evacuation treatment is: in the furnace tube, the pressure is set to 0, the gas flow rate is set to 0, the temperature is set to 400±50°C, and the excess reaction residual gas in the furnace tube is evacuated, and the evacuation time is 1±0.2min.

[0029] Furthermore, in step (7), the specific operation of filling nitrogen back to atmospheric pressure is as follows: in the furnace tube, the pressure is set to 10000±100 mtorr, the nitrogen gas flow rate is set to 30000±100 sccm, the temperature is set to 400±50°C, and the excess reaction residual gas in the furnace tube is evacuated for 90 seconds.

[0030] Furthermore, in step (8), the furnace tube temperature is set to 400±50° C., the heating time is 2±0.2 min, and the pressure is set to 10000±100 mtorr.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention effectively reduces the overflow of hydrogen during the deposition of aluminum oxide, improves the hydrogen passivation effect, significantly reduces the risk of film explosion, and improves battery efficiency through a step-by-step heating process and a method of forming NH bonds inside the film layer before the silicon nitride film layer. Specifically, during the film coating process, the present invention controls the temperature through step-by-step heating, and adds nitrous oxide and ammonia ionization to introduce N elements to form NH bonds inside the film layer before the silicon nitride deposition step, so as to achieve a better hydrogen passivation effect, reduce the film explosion ratio to 0.005%, and at the same time, the conversion efficiency can reach 25.948%, with better electrical performance. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the protection scope of the present invention.

[0034] Example 1

[0035] This embodiment provides a PECVD process for improving the film explosion of TOPCON cells, including the following steps:

[0036] (1) Entering the furnace tube: Place the graphite boat filled with silicon wafers in the furnace tube; set the furnace tube temperature to 400°C for 2 min and the pressure to 10,000 mtorr;

[0037] (2) Nitrogen filling protection: nitrogen is filled into the furnace tube; the nitrogen filling rate is set to 20,000 sccm, which is used to clean the air in the furnace tube and to clean the graphite boat and the reaction furnace tube. The furnace tube temperature is maintained at 400°C and the pressure is 10,000 mtorr;

[0038] (3) Step-by-step heating process:

[0039] ① The first temperature was raised to 430°C for 2 minutes, the pressure was set to 10000 mtorr, the nitrogen flow rate was 2000 sccm, and the temperature was kept constant for 3 minutes for hydrogen passivation;

[0040] ② The second temperature was raised to 460°C for 2 minutes, the pressure was set to 10,000 mtorr, the nitrogen flow rate was 2,000 sccm, and the temperature was kept constant for 3 minutes for hydrogen passivation;

[0041] ③ The temperature was raised to 500°C for the third time, the heating time was 3 min, the pressure was set to 10000 mtorr, the nitrogen flow rate was 2000 sccm, and the temperature was kept constant for 3 min for hydrogen passivation.

[0042] (4) Vacuuming: Vacuum the furnace tube; the furnace tube temperature is still set to 500°C, the nitrogen flow rate is set to 0, the pressure is set to 50 mtorr, and the vacuuming time is 2 min.

[0043] (5) Improvement of film explosion treatment: NH3 and N2O are introduced into the furnace tube for ionization; the process time is set to 1.5 min, the temperature is still set to 500 °C, NH3 and N2O are introduced in a 1:1 ratio, the gas flow rate is 6000 sccm, the RF power is 12000 W, the pressure is set to 1500 mtor, and the process time is 1.5 min; N2O and NH3 are bombarded into N and H plasma groups by the RF power supply, some of which are attached to the surface and some are pumped into the exhaust gas treatment device. Nitrogen has a strong electrical load and has an adsorption force on hydrogen. The NH bond energy formed is higher than the Si-H bond energy and is more stable, which can slow down the nitrogen overflow rate. In addition, NH3 provides a large amount of hydrogen to further passivate the defects inside the silicon wafer; on the other hand, plasma can clean the dust on the surface of the silicon wafer, making the silicon wafer surface cleaner, which can improve the yield.

[0044] (6) Silicon nitride deposition process: multiple silicon nitride deposition steps are performed, specifically:

[0045] ① The first silicon nitride deposition step: the temperature in the furnace tube is set to 500°C, ammonia and silane are introduced, the ammonia flow rate is 9000sccm, the silane flow rate is 2300sccm, the pressure is 1500mtorr, the RF power is 15000W, and the process time is 2.2min;

[0046] ② Second silicon nitride deposition step: In the furnace tube, the temperature is set to 500°C, ammonia and silane are introduced, the ammonia flow rate is 10500sccm, the silane flow rate is 1800sccm, the pressure is 1500mtorr, the RF power is 15000W, and the process time is 3.2min;

[0047] ③The third silicon nitride deposition step: in the furnace tube, the temperature is set to 500°C, ammonia and silane are introduced, the ammonia flow rate is 145000sccm, the silane flow rate is 1500sccm, the pressure is 1500mtorr, the RF power is 15000W, and the process time is 6min.

[0048] (7) Evacuate and fill with nitrogen to return to atmospheric pressure: ① Evacuate: set the pressure to 0, the gas flow rate to 0, the temperature to 400°C, and exhaust the excess reaction residual gas in the furnace tube. The evacuation time is 60 seconds; ② Fill with nitrogen to return to atmospheric pressure: set the pressure to 10,000 mtorr, the nitrogen gas flow rate to 30,000 sccm, the temperature to 400°C, and exhaust the excess reaction residual gas in the furnace tube. The evacuation time is 90 seconds.

[0049] (8) Out of the furnace tube: transport the graphite boat out of the furnace tube. The furnace tube temperature is set to 400°C, the time is 2 minutes, and the pressure is set to 10000 mtorr.

[0050] Example 2

[0051] Compared with Example 1, the difference between this embodiment and Example 1 is that the step-by-step heating of step (3) is as follows:

[0052] ① The first temperature was raised to 380°C for 2 minutes, the pressure was set to 10000 mtorr, the nitrogen flow rate was 2000 sccm, and the temperature was kept constant for 3 minutes for hydrogen passivation;

[0053] ② The second temperature was raised to 410°C for 2 minutes, the pressure was set to 10000 mtorr, the nitrogen flow rate was 2000 sccm, and the temperature was kept constant for 3 minutes for hydrogen passivation;

[0054] ③ The temperature was raised to 450°C for the third time, the heating time was 3 min, the pressure was set to 10000 mtorr, the nitrogen flow rate was 2000 sccm, and the temperature was kept constant for 3 min for hydrogen passivation.

[0055] The remaining steps and parameters remain the same as those in Example 1.

[0056] Example 3

[0057] Compared with Example 1, the difference between this embodiment and Example 1 is that the step-by-step heating of step (3) is specifically as follows:

[0058] ① The first temperature was raised to 480°C for 2 minutes, the pressure was set to 10000 mtorr, the nitrogen flow rate was 2000 sccm, and the temperature was kept constant for 3 minutes for hydrogen passivation;

[0059] ② The second temperature was raised to 510°C for 2 minutes, the pressure was set to 10000 mtorr, the nitrogen flow rate was 2000 sccm, and the temperature was kept constant for 3 minutes for hydrogen passivation;

[0060] ③ The temperature was raised to 550°C for the third time, the heating time was 3 min, the pressure was set to 10000 mtorr, the nitrogen flow rate was 2000 sccm, and the temperature was kept constant for 3 min for hydrogen passivation.

[0061] The remaining steps and parameters remain the same as those in Example 1.

[0062] Example 4

[0063] The difference between this embodiment and embodiment 1 is that the third heating temperature in the step-by-step heating process of step (3) is 580° C., and the remaining steps and parameters are consistent with those of embodiment 1.

[0064] Comparative Example 1

[0065] Compared with Example 1, the difference between this comparative example is as follows: The difference is that the constant temperature hydrogen passivation treatment time in the step-by-step heating process of step (3) is insufficient, specifically:

[0066] ① The first temperature was raised to 430°C for 2 minutes, the pressure was set to 10000 mtorr, the nitrogen flow rate was 2000 sccm, and the temperature was kept constant for 2.5 minutes for hydrogen passivation;

[0067] ② The second temperature was raised to 460°C for 2 minutes, the pressure was set to 10,000 mtorr, the nitrogen flow rate was 2,000 sccm, and the temperature was kept constant for 2.5 minutes for hydrogen passivation;

[0068] ③ The temperature was raised to 500°C for the third time, the heating time was 3 min, the pressure was set to 10000 mtorr, the nitrogen flow rate was 2000 sccm, and the temperature was kept constant for 2.5 min for hydrogen passivation.

[0069] The remaining steps and parameters remain the same as those in Example 1.

[0070] Comparative Example 2

[0071] The difference between this comparative example and Example 1 is that the constant temperature hydrogen passivation treatment time in the step-by-step heating process of step (3) is too long, specifically:

[0072] ① The first temperature was raised to 430°C for 2 minutes, the pressure was set to 10000 mtorr, the nitrogen flow rate was 2000 sccm, and the temperature was kept constant for 3.5 minutes for hydrogen passivation;

[0073] ② The second temperature was raised to 460°C for 2 minutes, the pressure was set to 10,000 mtorr, the nitrogen flow rate was 2,000 sccm, and the temperature was kept constant for 3.5 minutes for hydrogen passivation;

[0074] ③ The temperature was raised to 500°C for the third time, the heating time was 3 min, the pressure was set to 10000 mtorr, the nitrogen flow rate was 2000 sccm, and the temperature was kept constant for 3.5 min for hydrogen passivation.

[0075] The remaining steps and parameters remain the same as those in Example 1.

[0076] Comparative Example 3

[0077] Compared with Example 1, the difference between this comparative example and Example 1 is that there is no constant temperature hydrogen passivation treatment in the step-by-step heating process of step (3), specifically:

[0078] ① The first temperature was raised to 430°C, the heating time was 2 min, the pressure was set to 10000 mtorr, and the nitrogen flow rate was 2000 sccm;

[0079] ② The second heating was to 460°C, the heating time was 2 min, the pressure was set to 10000 mtorr, and the nitrogen flow rate was 2000 sccm;

[0080] ③ The temperature was raised to 500°C for the third time, the heating time was 3 min, the pressure was set to 10000 mtorr, and the nitrogen flow rate was 2000 sccm.

[0081] The remaining steps and parameters remain the same as those in Example 1.

[0082] Comparative Example 4

[0083] The difference between this comparative example and Example 1 is that the improved film explosion treatment process in step (5) is to only introduce NH3 into the furnace tube for ionization, and the remaining steps and parameters are consistent with Example 1.

[0084] Comparative Example 5

[0085] The difference between this comparative example and Example 1 is that the improved film explosion treatment process in step (5) is to only introduce N2O into the furnace tube for ionization, and the remaining steps and parameters are consistent with Example 1.

[0086] Comparative Example 6

[0087] The difference between this comparative example and Example 1 is that there is no step (5) for improving the film bursting treatment process, and the remaining steps and parameters are consistent with those of Example 1.

[0088] Performance Testing

[0089] The electrical performance of the TOPCon solar cells prepared in Examples 1-4 and Comparative Examples 1-6 was tested.

[0090] The test method is: using an IV tester to measure various parameters of the solar cell, and the results are shown in Table 1.

[0091] Table 1 Test results of battery of embodiment and comparative example

[0092]

[0093]

[0094] Performance test data conclusion analysis:

[0095] As can be seen from the above table, the present invention improves the film explosion through a step-by-step temperature increase process and a method of forming NH bonds inside the film layer before the silicon nitride film layer. The film explosion ratio can be reduced to below 0.012%, and the conversion efficiency can reach more than 25.936%, with better electrical performance.

[0096] First, compared with Example 4 in which the third heating temperature is too high, Example 1 can fully allow the hydrogen generated by aluminum oxide to overflow better than Example 4, and the film quality is better; while Example 4 has a slightly worse film thickness and density due to the excessively high heating temperature, but has a good effect on improving film explosion.

[0097] Secondly, by comparing Example 1 with Comparative Example 1.3, the present invention uses constant temperature heat conduction to allow the H bond to have more H outer electron activity, thereby obtaining more energy greater than the bond energy, being able to break free from the constraints of the silicon lattice, and being able to combine with some broken bonds of silicon-silicon covalent bonds to make up for defects and perform passivation, thereby preventing minority carriers from being captured by defects during directional movement; in Comparative Example 1, the constant temperature passivation hydrogen treatment time is insufficient, resulting in insufficient energy and failure to achieve the movement effect; in Comparative Example 2, the constant temperature hydrogen passivation treatment time is too long, resulting in excessive H overflow, failure to achieve slow release, and the passivation effect will also deteriorate; and in Comparative Example 3, there is no constant temperature hydrogen passivation treatment, resulting in poor hydrogen passivation effect, indicating that constant temperature heat conduction can allow more hydrogen to overflow.

[0098] Again, by comparing Example 1 with Comparative Examples 4-6, step (5) in Comparative Example 4 improves the film explosion treatment process by only introducing nitrogen for ionization, resulting in fewer NH bonds formed. In the subsequent screen sintering, the hydrogen passivation effect will be slightly worse than that of Comparative Example 1; step (5) in Comparative Example 5 improves the film explosion treatment process by only introducing nitrous oxide for ionization, which will also result in fewer NH bonds. This shows that simply introducing nitrogen or nitrous oxide for ionization will form NH bonds, but in smaller quantities, affecting the hydrogen passivation effect; and in Comparative Example 6, there is no step (5) to improve the film explosion treatment process, resulting in an increased film explosion ratio and a poor passivation effect; this shows that the method of forming NH bonds inside the film layer effectively reduces the overflow of hydrogen during the alumina deposition process, thereby reducing the film explosion, and at the same time, hydrogen overflow passivation defects during the subsequent sintering improves the hydrogen passivation effect.

[0099] The principle of improving the film explosion treatment process is: the bond energy of Si-H is 354.7 kJ / mol, which is less than the bond energy of NH 391 kJ / mol. The lower the bond energy, the easier it is to break. The higher the bond energy, the more stable it is and can achieve slow release. The main reason for film explosion is that the film layer is broken from the inside by gas due to the rapid release of a large amount of hydrogen, thus the purpose of the present invention to introduce NH3 and N2O into the furnace tube for ionization is to form high bond energy and slowly release hydrogen, thereby achieving the effect of improving film explosion.

[0100] The present invention adopts a distributed heating method of heating and maintaining a constant temperature in the coating section, which can not only reduce the heating rate, so that the hydrogen passivation overflows slowly and slows down the hydrogen overflow speed, but also achieve a preheating effect, and the uniformity of the deposited film layer is better during the process; by adding nitrous oxide and ammonia ionization in front of the silicon nitride film layer and forming NH bonds inside the film layer, the overflow of hydrogen in the aluminum oxide deposition process is effectively reduced, and a better hydrogen passivation effect is achieved, thereby significantly reducing the risk of film explosion and improving battery efficiency.

[0101] The present invention is further described above with the aid of specific embodiments. However, it should be understood that the specific description here should not be construed as limiting the essence and scope of the present invention. Various modifications made to the above embodiments by ordinary technicians in the field after reading this specification are all within the scope of protection of the present invention.

Claims

1. A PECVD process for improving TOPCON battery film explosion, characterized in that: The following steps are involved: (1) Entering the furnace tube: placing the graphite boat filled with silicon wafers into the furnace tube; (2) Nitrogen filling protection: fill the furnace tube with nitrogen; (3) Step-by-step heating: The furnace tube is heated in stages, and the temperature is kept constant after each stage reaches the temperature, and then it is heated to the next stage temperature; (4) Vacuuming: Vacuuming the furnace tube; (5) Improve the treatment of film explosion: introduce NH3 and N2O into the furnace tube for ionization; (6) Silicon nitride deposition: performing multiple silicon nitride deposition steps; (7) Evacuate and fill with nitrogen to atmospheric pressure: evacuate the excess reaction residual gas in the furnace tube and fill with nitrogen to atmospheric pressure; (8) Out of the furnace tube: transport the graphite boat out of the furnace tube.

2. The PECVD process according to claim 1, characterized in that In the step (1), the temperature of the furnace tube is 400±50° C. and the pressure is 10000±100 mtorr.

3. The PECVD process according to claim 1, characterized in that: In the step (2), nitrogen gas is introduced at a flow rate of 20000±100 sccm.

4. The PECVD process according to claim 1, characterized in that In step (3), the step-by-step heating process specifically includes the following steps: ① The first temperature is raised to 430±50℃, the heating time is 2±0.2min, the pressure is set to 10000±100mtorr, the nitrogen flow rate is 2000±50sccm, and the temperature is kept constant for 3±0.2min for hydrogen passivation; ② The second temperature is raised to 460±50°C, the heating time is 2±0.2min, the pressure is set to 10000±100mtorr, the nitrogen flow rate is 2000±50sccm, and the temperature is kept constant for 3±0.2min for hydrogen passivation; ③ The temperature was raised to 500±50°C for the third time, the heating time was 3±0.2min, the pressure was set to 10000±100mtorr, the nitrogen flow rate was 2000±50sccm, and the temperature was kept constant for 3±0.2min for hydrogen passivation.

5. The PECVD process according to claim 1, characterized in that: In the step (4), the furnace temperature is 500±50° C., the nitrogen flow rate is 0, the pressure is set to 50±30 mtorr, and the vacuum time is 2±0.2 min.

6. The PECVD process according to claim 1, characterized in that In the step (5), NH3 and N2O are introduced in a ratio of 1:1, the gas flow rate is 6000±500sccm, the RF power is 12000±1000W, the pressure is 1500±50mtor, and the process time is 1.5±0.2min.

7. The PECVD process according to claim 1, characterized in that: In the step (6), three silicon nitride deposition steps are performed, specifically: ① The first silicon nitride deposition step: in the furnace tube, the temperature is set to 500±50°C, ammonia and silane are introduced, the ammonia flow rate is 9000±1000sccm, the silane flow rate is 2300±500sccm, the pressure is 1500±50mtorr, the RF power is 15000±1000W, and the process time is 2.2±0.2min; ② The second silicon nitride deposition step: in the furnace tube, the temperature is set to 500±50°C, ammonia and silane are introduced, the ammonia flow rate is 10500±1000sccm, the silane flow rate is 1800±500sccm, the pressure is 1500±50mtorr, the RF power is 15000±1000W, and the process time is 3.2±0.2min; ③The third silicon nitride deposition step: in the furnace tube, the temperature is set to 500±50°C, ammonia and silane are introduced, the ammonia flow rate is 14500±1000sccm, the silane flow rate is 1500±500sccm, the pressure is 1500±50mtorr, the RF power is 15000±1000W, and the process time is 6±0.5min.

8. The PECVD process according to claim 1, characterized in that In the step (7), the specific operation of the evacuation treatment is: in the furnace tube, the pressure is set to 0, the gas flow rate is set to 0, the temperature is set to 400±50°C, and the excess reaction residual gas in the furnace tube is evacuated, and the evacuation time is 1±0.2min.

9. The PECVD process according to claim 1, characterized in that: In the step (7), the specific operation of filling nitrogen back to atmospheric pressure is as follows: the pressure in the furnace tube is set to 10000±100 mtorr, the nitrogen gas flow rate is set to 30000±100 sccm, the temperature is set to 400±50°C, and the excess reaction residual gas in the furnace tube is evacuated for 90 seconds.

10. The PECVD process according to claim 1, characterized in that: In the step (8), the furnace temperature is set to 400±50° C., the heating time is 2±0.2 min, and the pressure is set to 10000±100 mtorr.

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