Preparation method of back contact battery anti-reflection film for improving silicon nitride dust

Abstract

The invention belongs to the technical field of back contact batteries, and discloses a preparation method of a back contact battery anti-reflection film for improving silicon nitride dust. The method comprises the following steps: feeding a silicon wafer into PECVD (Plasma Enhanced Chemical Vapor Deposition) equipment, sequentially heating, keeping constant temperature, vacuumizing and keeping constant pressure, introducing ammonia gas for ionization, vacuumizing after ionization is finished, and completing pre-film cleaning of the silicon wafer; sequentially depositing three layers of silicon nitride films; and finally, nitrogen is introduced for membrane back-blowing. Before the silicon nitride film layer is deposited, the ionized ammonia gas is used for performing pre-film cleaning on the silicon wafer, so that the problem of dust particulate matter pollution before deposition can be effectively improved; after the three silicon nitride film layers are deposited, nitrogen is introduced to perform post-film purging and cleaning on the silicon wafer, so that the post-film dust particulate matter pollution problem can be effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of back contact cells, and in particular to a method for preparing a back contact cell anti-reflection film for improving silicon nitride dust. Background Art

[0002] Back contact cells are an advanced design for improving the efficiency of solar cells. The core design concept is to place all the metal electrodes of the cell on the back of the cell, thereby ensuring that the front of the cell is not blocked by any metal grid lines, thereby maximizing the area of ​​the cell that absorbs sunlight, reducing optical losses, and improving photoelectric conversion efficiency. After the concept of back contact cells was proposed in 1975, after continuous research and development and technological improvements, it has now become one of the recognized technical routes with high conversion efficiency in the solar photovoltaic industry. Its front appearance not only has no grid lines to maximize the light-receiving area, but also has a higher appearance. This structure can be used as a platform technology combined with a variety of cell routes to highlight the uniqueness of back contact cells.

[0003] The preparation of the emitter in the back passivation contact battery has become a key technology. Considering the contact between the metal and the conductor, there are direct contact and passivation contact. If the passivation contact method is used to achieve a higher doping level and passivation effect, it is inseparable from the better passivation layer preparation and ion doping method. The existing technology generally uses the tubular PECVD method to deposit the silicon nitride anti-reflection film, and accelerates the chemical reaction by glow discharge. The film formation rate is usually adjusted by changing the process parameters such as power, temperature, time, and pressure. In the PECVD process, the reaction gas (such as silane and ammonia) is excited by the radio frequency power supply to generate high-energy plasma. The ions and neutral particles in these plasmas collide with gas molecules, causing the gas to decompose into electrons, ions, and active groups. These decomposition products react chemically on the substrate surface to generate solid silicon nitride film. At the same time, some particulate substances may also be produced. These particles form dust under certain conditions, which seriously affects the surface passivation effect and the appearance of the battery cell.

[0004] Therefore, how to improve the influence of dust during the deposition of silicon nitride anti-reflection film is of great significance for the in-depth research and development of back-contact batteries. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a back contact anti-reflection film for a battery with improved silicon nitride dust, so as to solve the problem that dust affects the surface passivation effect and the appearance of the battery cell during the preparation of the silicon nitride anti-reflection film in the prior art.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a back contact cell anti-reflection film for improving silicon nitride dust, comprising the following steps:

[0008] (1) Pre-membrane cleaning: The silicon wafer is sent to the PECVD equipment, and the temperature is raised, the temperature is kept constant, the vacuum is evacuated, and the pressure is kept constant. Ammonia gas is introduced for ionization. After the ionization is completed, the vacuum is evacuated to complete the pre-membrane cleaning of the silicon wafer;

[0009] (2) Depositing the first silicon nitride film: introducing silane and ammonia gases, and depositing the first silicon nitride film by PECVD on the silicon wafer after pre-film cleaning;

[0010] (3) Depositing a second silicon nitride film: introducing silane and ammonia gas to deposit a second silicon nitride film on the first silicon nitride film by PECVD method;

[0011] (4) Depositing a third silicon nitride film: introducing silane and ammonia gas to deposit a third silicon nitride film on the second silicon nitride film by a PECVD method;

[0012] (5) Post-film purging: After the deposition of the third layer of silicon nitride film is completed, the vacuum is evacuated and nitrogen is introduced for purging, thereby completing the preparation of the back contact cell anti-reflection film for improving silicon nitride dust.

[0013] Preferably, in the above-mentioned method for preparing a back contact cell anti-reflection film for improving silicon nitride dust, the silicon wafer in step (1) is N-type single crystal silicon.

[0014] Preferably, in the above-mentioned method for preparing a back contact battery anti-reflection film for improving silicon nitride dust, the heating temperature in step (1) is 500-550°C; the constant temperature time is 500-600s; and the constant pressure time is 20-30s.

[0015] Preferably, in the above-mentioned method for preparing a back-contact battery anti-reflection film for improving silicon nitride dust, the process parameters of the pre-membrane cleaning in step (1) are: ammonia flow rate of 10000-13000sccm; pressure of 1500-1700mtorr; power of 15000-18000W; duty cycle of 6:125; and ionization time of 30-60s.

[0016] Preferably, in the above-mentioned method for preparing a back-contact battery anti-reflection film for improving silicon nitride dust, the process parameters for depositing the first layer of silicon nitride film in step (2) are: silane flow rate is 2000-3000sccm; ammonia flow rate is 7500-9000sccm; temperature is 500-560°C; pressure is 1600-1700mtorr; power is 10000-14000W; and deposition time is 100-150s.

[0017] Preferably, in the above-mentioned method for preparing a back-contact battery anti-reflection film for improving silicon nitride dust, the process parameters for depositing the second layer of silicon nitride film in step (3) are: silane flow rate is 1200-1900sccm; ammonia flow rate is 10000-13000sccm; temperature is 500-560°C; pressure is 1700-2000mtorr; power is 13000-15000W; and deposition time is 200-280s.

[0018] Preferably, in the above-mentioned method for preparing a back-contact battery anti-reflection film for improving silicon nitride dust, the process parameters for depositing the third layer of silicon nitride film in step (4) are: silane flow rate is 900-1200sccm; ammonia flow rate is 10000-13000sccm; temperature is 500-560°C; pressure is 1800-2100mtorr; power is 15000-17000W; and deposition time is 300-370s.

[0019] Preferably, in the above-mentioned method for preparing a back-contact battery anti-reflection film for improving silicon nitride dust, the process parameters of the post-membrane purge in step (5) are: nitrogen flow rate of 10000-15000sccm; pressure of 1700mtorr; purge time of 20-50s.

[0020] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention uses ionized ammonia to clean the silicon wafer before depositing the silicon nitride film layer, which can effectively improve the dust particle pollution problem before deposition; after depositing three layers of silicon nitride film, nitrogen is introduced to purge and clean the silicon wafer after film deposition, which can effectively improve the dust particle pollution problem generated after coating. The present invention uses a method of introducing special gas to clean the anti-reflection film before and after deposition, improves the passivation effect and appearance of the cell affected by silicon nitride dust pollution, and thus effectively improves the electrical performance of the back contact cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the description of the embodiments or the prior art are briefly introduced below.

[0023] Figure 1 The present invention is a flow chart for preparing the anti-reflection film for the back contact cell for improving silicon nitride dust;

[0024] Figure 2 Schematic diagram of the structure of the anti-reflection film of the back contact battery obtained in Example 1; wherein 1 is a silicon wafer, 2 is a first layer of silicon nitride film, 3 is a second layer of silicon nitride film, and 4 is a third layer of silicon nitride film;

[0025] Figure 3This is an appearance diagram of a back contact battery prepared by the preparation method of Comparative Example 1;

[0026] Figure 4 This is the appearance of the back contact battery prepared by the preparation method of Example 1. DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing a back contact cell anti-reflection film for improving silicon nitride dust, comprising the following steps:

[0028] (1) Pre-membrane cleaning: The silicon wafer is sent to the PECVD equipment, and the temperature is raised, the temperature is kept constant, the vacuum is evacuated, and the pressure is kept constant. Ammonia gas is introduced for ionization. After the ionization is completed, the vacuum is evacuated to complete the pre-membrane cleaning of the silicon wafer;

[0029] (2) Depositing the first silicon nitride film: introducing silane and ammonia gases, and depositing the first silicon nitride film by PECVD on the silicon wafer after pre-film cleaning;

[0030] (3) Depositing a second silicon nitride film: introducing silane and ammonia gas to deposit a second silicon nitride film on the first silicon nitride film by PECVD method;

[0031] (4) Depositing a third silicon nitride film: introducing silane and ammonia gas to deposit a third silicon nitride film on the second silicon nitride film by a PECVD method;

[0032] (5) Post-film purging: After the deposition of the third layer of silicon nitride film is completed, the vacuum is evacuated and nitrogen is introduced for purging, thereby completing the preparation of the back contact cell anti-reflection film for improving silicon nitride dust.

[0033] In the present invention, the silicon wafer in step (1) is preferably N-type single crystal silicon.

[0034] In the present invention, the method of feeding the silicon wafer into the PECVD device in step (1) is: inserting the silicon wafer into a graphite boat, and feeding the graphite boat into the PECVD furnace tube.

[0035] In the present invention, the temperature of the heating in step (1) is preferably 500-550°C, more preferably 510-540°C, and more preferably 520°C; the constant temperature time is preferably 500-600s, more preferably 520-580s, and more preferably 550s; the constant pressure time is preferably 20-30s, more preferably 22-26s, and more preferably 24s.

[0036] In the present invention, the process parameters of the pre-membrane cleaning in step (1) are as follows: the ammonia flow rate is preferably 10000-13000sccm, more preferably 11000-12500sccm, and more preferably 12000sccm; the pressure is preferably 1500-1700mtorr, more preferably 1550-1650mtorr, and more preferably 1600mtorr; the power is preferably 15000-18000W, more preferably 16000-17500W, and more preferably 17000W; the duty cycle is preferably 6:125; the ionization time is preferably 30-60s, more preferably 40-60s, and more preferably 50s.

[0037] In the present invention, the process parameters for depositing the first layer of silicon nitride film in step (2) are as follows: the silane flow rate is preferably 2000-3000sccm, more preferably 2200-2800sccm, and more preferably 2500sccm; the ammonia flow rate is preferably 7500-9000sccm, more preferably 7800-8500sccm, and more preferably 8000sccm; the temperature is preferably 500-560°C, more preferably 520-550°C, and more preferably 550°C; the pressure is preferably 1600-1700mtorr, more preferably 1650-1700mtorr, and more preferably 1700mtorr; the power is preferably 10000-14000W, more preferably 11000-13000W, and more preferably 13000W; the deposition time is preferably 100-150s, more preferably 120-140s, and more preferably 140s.

[0038] In the present invention, the process parameters for depositing the second layer of silicon nitride film in step (3) are as follows: the silane flow rate is preferably 1200-1900sccm, more preferably 1400-1700sccm, and more preferably 1600sccm; the ammonia flow rate is preferably 10000-13000sccm, more preferably 11000-12300sccm, and more preferably 12000sccm; the temperature is preferably 500-560°C, more preferably 520-560°C, and more preferably 550°C; the pressure is preferably 1700-2000mtorr, more preferably 1800-1900mtorr, and more preferably 1800mtorr; the power is preferably 13000-15000W, more preferably 14000-15000W, and more preferably 15000W; the deposition time is preferably 200-280s, more preferably 230-260s, and more preferably 250s.

[0039] In the present invention, the process parameters for depositing the third layer of silicon nitride film in step (4) are as follows: the silane flow rate is preferably 900-1200sccm, more preferably 950-1100sccm, and more preferably 1000sccm; the ammonia flow rate is preferably 10000-13000sccm, more preferably 11000-12500sccm, and more preferably 12000sccm; the temperature is preferably 500-560°C, more preferably 520-560°C, and more preferably 550°C; the pressure is preferably 1800-2100mtorr, more preferably 1850-2000mtorr, and more preferably 1900mtorr; the power is preferably 15000-17000W, more preferably 15500-16500W, and more preferably 16000W; the deposition time is preferably 300-370s, more preferably 310-350s, and more preferably 320s.

[0040] In the present invention, the process parameters of the post-membrane purge in step (5) are: the nitrogen flow rate is preferably 10000-15000sccm, more preferably 11000-14000sccm, and more preferably 12000sccm; the pressure is preferably 1700mtorr; the purge time is preferably 20-50s, more preferably 30-50s, and more preferably 40s.

[0041] In the present invention, after the purging in step (5) is completed, it also includes evacuating the air, introducing nitrogen to break the vacuum, and leaving the boat at normal pressure.

[0042] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] Example 1

[0044] This embodiment provides a method for preparing a back contact cell anti-reflection film for improving silicon nitride dust. The preparation process is as follows: Figure 1 As shown, the following steps are included:

[0045] (1) Pre-membrane cleaning: N-type single crystal silicon wafers are selected as substrates, and the silicon wafers are inserted into a graphite boat. The graphite boat is sent into a PECVD furnace tube for heating. The temperature is raised to 530°C and kept constant for 600 seconds. After vacuuming and constant pressure for 30 seconds, ammonia is introduced. Ionization is carried out under the conditions of an ammonia flow rate of 12500sccm, a pressure of 1650mtorr, a power of 16000W, a duty cycle of 6:125, and an ionization time of 60 seconds. After ionization, vacuuming is performed to complete the pre-membrane cleaning of the silicon wafer;

[0046] (2) Deposition of the first silicon nitride film: silane (SiH4) and ammonia are introduced, the silane flow rate is 2500sccm, the ammonia flow rate is 8000sccm, the temperature is controlled at 530°C, the pressure is 1700mtorr, the power is 13000W, the deposition time is 140s, and the first silicon nitride film is deposited on the silicon wafer after pre-film cleaning;

[0047] (3) Deposition of a second silicon nitride film: introducing silane (SiH4) and ammonia gas, with a silane flow rate of 1600 sccm and an ammonia flow rate of 12000 sccm, the temperature being controlled at 530°C, the pressure being 1800 mtorr, the power being 15000 W, and the deposition time being 250 s, to deposit a second silicon nitride film on the first silicon nitride film;

[0048] (4) Deposition of a third silicon nitride film: introducing silane (SiH4) and ammonia gas, with a silane flow rate of 1000 sccm and an ammonia flow rate of 12000 sccm, the temperature being controlled at 530°C, the pressure being 1900 mtorr, the power being 16000 W, and the deposition time being 320 s, to deposit a third silicon nitride film on the second silicon nitride film;

[0049] (5) Post-film purging: After the deposition of the third layer of silicon nitride film is completed, vacuum is evacuated and nitrogen is introduced for purging. The nitrogen flow rate is 15000 sccm, the pressure is 1700 mtorr, and the introduction time is 50 s. After the completion, vacuum is evacuated and nitrogen is introduced to break the vacuum. The film is taken out of the boat at normal pressure, thus completing the preparation of the back contact cell anti-reflection film for improving silicon nitride dust. The obtained back contact cell anti-reflection film structure is as shown in FIG. Figure 2 shown.

[0050] Example 2

[0051] This embodiment provides a method for preparing a back contact cell anti-reflection film for improving silicon nitride dust. The preparation process is as follows: Figure 1 As shown, the following steps are included:

[0052] (1) Pre-membrane cleaning: N-type single crystal silicon wafers are selected as substrates, and the silicon wafers are inserted into a graphite boat. The graphite boat is sent into a PECVD furnace tube for heating. The temperature is raised to 520°C and kept constant for 550 seconds. After vacuuming and constant pressure for 20 seconds, ammonia is introduced. Ionization is carried out under the conditions of an ammonia flow rate of 10,000 sccm, a pressure of 1,500 mtorr, a power of 15,000 W, a duty cycle of 6:125, and an ionization time of 30 seconds. After ionization, vacuuming is performed to complete the pre-membrane cleaning of the silicon wafer;

[0053] (2) Deposition of the first silicon nitride film: silane (SiH4) and ammonia are introduced, the silane flow rate is 2300sccm, the ammonia flow rate is 7800sccm, the temperature is controlled at 520°C, the pressure is 1600mtorr, the power is 11000W, the deposition time is 130s, and the first silicon nitride film is deposited on the silicon wafer after pre-film cleaning;

[0054] (3) Deposition of a second silicon nitride film: introducing silane (SiH4) and ammonia gas, with a silane flow rate of 1400 sccm and an ammonia flow rate of 10000 sccm, the temperature being controlled at 520°C, the pressure being 1700 mtorr, the power being 13000 W, and the deposition time being 210 s, to deposit a second silicon nitride film on the first silicon nitride film;

[0055] (4) Deposition of a third silicon nitride film: introducing silane (SiH4) and ammonia gas, with a silane flow rate of 900 sccm and an ammonia flow rate of 10,000 sccm, the temperature being controlled at 520°C, the pressure being 1,800 mtorr, the power being 15,000 W, and the deposition time being 300 s, to deposit a third silicon nitride film on the second silicon nitride film;

[0056] (5) Post-film purge: After the deposition of the third layer of silicon nitride film is completed, evacuate the vessel and introduce nitrogen for purging. The nitrogen flow rate is 10,000 sccm and the pressure is 1,700 mtorr. The introduction time is 20 s. After completion, evacuate the vessel and introduce nitrogen to break the vacuum. The vessel is then taken out of the boat at normal pressure, thus completing the preparation of the back contact anti-reflection film for improving silicon nitride dust.

[0057] Example 3

[0058] This embodiment provides a method for preparing a back contact cell anti-reflection film for improving silicon nitride dust. The preparation process is as follows: Figure 1 As shown, the following steps are included:

[0059] (1) Pre-membrane cleaning: N-type single crystal silicon wafers are selected as substrates, and the silicon wafers are inserted into a graphite boat. The graphite boat is sent into a PECVD furnace tube for heating. The temperature is raised to 550°C and kept constant for 500 seconds. After vacuuming and constant pressure for 24 seconds, ammonia is introduced. Ionization is carried out under the conditions of an ammonia flow rate of 13000sccm, a pressure of 1700mtorr, a power of 18000W, a duty cycle of 6:125, and an ionization time of 60 seconds. After ionization, vacuuming is performed to complete the pre-membrane cleaning of the silicon wafer;

[0060] (2) Deposition of the first silicon nitride film: silane (SiH4) and ammonia are introduced, the silane flow rate is 2800sccm, the ammonia flow rate is 9000sccm, the temperature is controlled at 550°C, the pressure is 1700mtorr, the power is 14000W, the deposition time is 150s, and the first silicon nitride film is deposited on the silicon wafer after pre-film cleaning;

[0061] (3) Deposition of a second silicon nitride film: introducing silane (SiH4) and ammonia gas, with a silane flow rate of 1900 sccm and an ammonia flow rate of 13000 sccm, the temperature being controlled at 550°C, the pressure being 2000 mtorr, the power being 14000 W, and the deposition time being 280 s, to deposit a second silicon nitride film on the first silicon nitride film;

[0062] (4) Deposition of a third silicon nitride film: introducing silane (SiH4) and ammonia gas, with a silane flow rate of 1200 sccm and an ammonia flow rate of 13000 sccm, the temperature being controlled at 550°C, the pressure being 2100 mtorr, the power being 17000 W, and the deposition time being 370 s, to deposit a third silicon nitride film on the second silicon nitride film;

[0063] (5) Post-film purge: After the deposition of the third layer of silicon nitride film is completed, evacuate the vessel and introduce nitrogen for purging. The nitrogen flow rate is 15,000 sccm and the pressure is 1,700 mtorr. The introduction time is 50 s. After completion, evacuate the vessel and introduce nitrogen to break the vacuum. The vessel is then taken out of the boat at normal pressure, thus completing the preparation of the back contact anti-reflection film for improving silicon nitride dust.

[0064] Comparative Example 1

[0065] This comparative example provides a method for preparing an anti-reflection film for a back contact battery, comprising the following steps:

[0066] (1) Deposition of the first layer of silicon nitride film: N-type single crystal silicon wafer is selected as the substrate, and the silicon wafer is inserted into a graphite boat, and the graphite boat is sent into a PECVD furnace tube for heating, and the temperature is raised to 530°C and kept constant for 600 seconds. After vacuuming and constant pressure for 30 seconds, silane (SiH4) and ammonia are introduced, and the silane flow rate is 2500sccm, and the ammonia flow rate is 8000sccm. The temperature is controlled at 530°C, the pressure is 1700mtorr, the power is 13000W, and the deposition time is 140s. The first layer of silicon nitride film is deposited on the silicon wafer after pre-film cleaning;

[0067] (2) Deposition of a second silicon nitride film: introducing silane (SiH4) and ammonia gas, with a silane flow rate of 1600 sccm and an ammonia flow rate of 12000 sccm, the temperature being controlled at 530°C, the pressure being 1800 mtorr, the power being 15000 W, and the deposition time being 250 s, to deposit a second silicon nitride film on the first silicon nitride film;

[0068] (3) Deposition of the third silicon nitride film: silane (SiH4) and ammonia gas were introduced, with a silane flow rate of 1000 sccm and an ammonia flow rate of 12000 sccm. The temperature was controlled at 530°C, the pressure was 1900 mtorr, the power was 16000 W, and the deposition time was 320 s. The third silicon nitride film was deposited on the second silicon nitride film. After the deposition of the third silicon nitride film was completed, the film was evacuated and returned to normal pressure before leaving the boat.

[0069] The back contact battery prepared according to the preparation method of Example 1 and Comparative Example 1 has electrical performance test results as shown in Table 1. Figure 3 and Figure 4 As shown. Figure 3 and Figure 4 It can be seen that the surface of the cell obtained without the cleaning operation before and after the anti-reflection film deposition as described in the present invention has dust, while the surface of the cell obtained by the method of the embodiment of the present invention is smooth and dust-free.

[0070] Table 1 Electrical performance test results of back contact cells prepared by the preparation methods of Example 1 and Comparative Example 1

[0071] index Comparative Example 1 Example 1 Conversion efficiency Eta (%) 25.47 25.53 Open circuit voltage Uoc(V) 0.7282 0.7302 Short circuit current Isc(A) 13.850 13.931 Filling factor FF(%) 84.88 85.05 Series resistance Rs(Ω) 0.00086 0.00083 Parallel resistance Rsh(Ω) 2683.06 2996.11 Reverse current 2Irev2(A) 0.0107 0.0174

[0072] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a back contact cell anti-reflection film for improving silicon nitride dust, characterized in that: The following steps are involved: (1) Pre-membrane cleaning: The silicon wafer is sent into the PECVD equipment, and the temperature is raised, the temperature is kept constant, the vacuum is evacuated, and the pressure is kept constant. Ammonia gas is introduced for ionization. After the ionization is completed, the vacuum is evacuated to complete the pre-membrane cleaning of the silicon wafer; (2) Depositing the first silicon nitride film: introducing silane and ammonia gases, and depositing the first silicon nitride film by PECVD on the silicon wafer after pre-film cleaning; (3) Depositing a second silicon nitride film: introducing silane and ammonia gas to deposit a second silicon nitride film on the first silicon nitride film by PECVD method; (4) Depositing a third silicon nitride film: introducing silane and ammonia gas to deposit a third silicon nitride film on the second silicon nitride film by a PECVD method; (5) Post-film purging: After the deposition of the third layer of silicon nitride film is completed, the vacuum is evacuated and nitrogen is introduced for purging, thereby completing the preparation of the back contact cell anti-reflection film for improving silicon nitride dust.

2. The method for preparing a back contact cell anti-reflection film for improving silicon nitride dust according to claim 1, characterized in that: The silicon wafer in step (1) is N-type single crystal silicon.

3. The method for preparing a back contact cell anti-reflection film for improving silicon nitride dust according to claim 1, characterized in that: The temperature of the heating in step (1) is 500-550° C.; the time of the constant temperature is 500-600 seconds; and the time of the constant pressure is 20-30 seconds.

4. The method for preparing a back contact cell anti-reflection film for improving silicon nitride dust according to claim 2, characterized in that: The process parameters of the pre-membrane cleaning in step (1) are: ammonia flow rate of 10000-13000sccm; pressure of 1500-1700mtorr; power of 15000-18000W; duty cycle of 6:125; and ionization time of 30-60s.

5. The method for preparing a back contact cell anti-reflection film for improving silicon nitride dust according to claim 1 or 4, characterized in that: The process parameters for depositing the first layer of silicon nitride film in step (2) are: silane flow rate of 2000-3000sccm; ammonia flow rate of 7500-9000sccm; temperature of 500-560°C; pressure of 1600-1700mtorr; power of 10000-14000W; and deposition time of 100-150s.

6. The method for preparing a back contact cell anti-reflection film for improving silicon nitride dust according to claim 5, characterized in that: The process parameters for depositing the second layer of silicon nitride film in step (3) are: silane flow rate of 1200-1900sccm; ammonia flow rate of 10000-13000sccm; temperature of 500-560°C; pressure of 1700-2000mtorr; power of 13000-15000W; and deposition time of 200-280s.

7. The method for preparing a back contact cell anti-reflection film for improving silicon nitride dust according to claim 6, characterized in that: The process parameters for depositing the third layer of silicon nitride film in step (4) are: silane flow rate is 900-1200sccm; ammonia flow rate is 10000-13000sccm; temperature is 500-560°C; pressure is 1800-2100mtorr; power is 15000-17000W; and deposition time is 300-370s.

8. The method for preparing a back contact cell anti-reflection film for improving silicon nitride dust according to claim 6 or 7, characterized in that: The process parameters of the post-membrane purge in step (5) are: nitrogen flow rate of 10000-15000 sccm; pressure of 1700 mtorr; and purge time of 20-50 s.

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