A PECVD coating process for monocrystalline silicon cells

Abstract

The present invention discloses a PECVD coating process for monocrystalline silicon cells, belonging to the technical field of monocrystalline silicon solar cells. The process includes the following steps: Step 1, pretreatment of the silicon substrate; Step 2, formation of the buffer layer; Step 3, formation of the high-refractive-index layer; Step 4, generation of the intermediate layer; Step 5, generation of the outermost layer. In the present invention, an extremely thin low-refractive-index silicon nitride buffer layer is inserted between the multilayer film or infinitely graded film of the conventional silicon nitride antireflection and passivation film and the substrate. The relatively thin silicon nitride buffer layer grown under low tube voltage and low radio frequency power has the advantages of small surface bombardment damage, good H passivation effect, and no influence on optical properties, playing a role in strengthening the H passivation of the substrate, reducing the number of recombination centers, and improving the minority carrier lifetime.

Description

Technical Field

[0001] The present invention belongs to the technical field of monocrystalline silicon solar cells, and particularly relates to a PECVD coating process for monocrystalline silicon cells. Background Art

[0002] Currently, the existence of impurities and defects in crystalline silicon cells seriously reduces the lifetime of minority carriers and restricts the photoelectric conversion efficiency of crystalline silicon solar cells. At present, for various impurities and crystal defects, the main method at the cell end is to inject H atoms into the silicon body through electrical injection and optical injection to passivate the impurities and defects.

[0003] Conventional tube PECVD is a direct coating method, that is, the plasma bombards the surface of the silicon wafer, so that the hydrogen atoms in it penetrate into the silicon wafer, playing a passivation role on the surface and inside of the silicon wafer. However, since the source of H mainly relies on SiH4 and NH3 in the PECVD coating process, their content is far from enough to passivate a large number of impurities and defects.

[0004] Currently, the surface of the cell often has passivation film layers such as silicon oxide and aluminum oxide superimposed. In this coating method, since the plasma bombards the surface of the silicon wafer, it will cause serious damage to the surface passivation film layer and form more surface defects. Summary of the Invention

[0005] Object of the Invention: In order to solve the above problems, the present invention provides a PECVD coating process for monocrystalline silicon cells.

[0006] Technical Solution: A PECVD coating process for monocrystalline silicon cells includes the following steps:

[0007] Step 1, pretreatment of the silicon substrate: Insert the silicon substrate on the carrier and send it into the furnace tube; set the temperature in the furnace tube to 400 - 550 °C and keep it constant for 150 - 210 s; evacuate and leak-check the furnace tube.

[0008] Step 2, formation of the buffer layer: Introduce special gases into the furnace tube and maintain the pressure and flow rate of the special gases in the furnace tube. The pressure in the furnace tube is 1450 - 1700 mTorr; turn on the radio frequency to deposit the buffer layer, the radio frequency power is 7000 - 11000 W, and the deposition time is 40 - 100 s.

[0009] Step 3, formation of the high refractive index layer: Adjust the flow rate of the special gases to obtain the pressure required for depositing the high refractive index layer. The pressure in the furnace tube is 1700 - 2000 mTorr; turn on the radio frequency to deposit the high refractive index layer, the radio frequency power is 11000 - 15000 W, and the deposition time is 100 - 200 s.

[0010] Step 4, Generation of the intermediate layer: Adjust the flow rate of the special gas to obtain the pressure required for depositing the intermediate layer, with the pressure inside the furnace tube being 1700 - 2000 mTorr; Turn on the RF deposition for the high-refractive-index layer, with the RF power being 11000 - 16000 W and the deposition time being 100 - 200 s;

[0011] Step 5, Generation of the outermost layer: Adjust the flow rate of the special gas to obtain the pressure required for depositing the outermost layer, with the pressure inside the furnace tube being 1800 - 2100 mTorr; Turn on the RF deposition for the outermost layer, with the RF power being 11000 - 16000 W and the deposition time being 400 - 560 s.

[0012] In a further embodiment, in Step 1, evacuate the bottom pressure of the furnace tube to below 50 mTorr; During the leak detection process, the leak rate is less than 30 mTorr / min.

[0013] In a further embodiment, the special gas components introduced into the furnace tube in Step 2 at least include: SiH4, NH3; The flow rate ratio of SiH4 to NH3 is 1:(10 - 12).

[0014] In a further embodiment, the off / on value of the duty cycle of the RF deposition in Step 2 is 10 - 15.

[0015] In a further embodiment, the flow rate ratio of SiH4 to NH3 in Step 3 is 1:(4 - 6).

[0016] In a further embodiment, the flow rate ratio of SiH4 to NH3 in Step 4 is 1:(7 - 9).

[0017] In a further embodiment, the flow rate ratio of SiH4 to NH3 in Step 5 is 1:(9 - 10).

[0018] In a further embodiment, the off / on values of the duty cycle of the RF deposition in Steps 3 to 5 are respectively: 10 - 16, 10 - 14, 10 - 14.

[0019] In Step 1, set the temperature inside the tube to raise the temperature inside the tube to the deposition process requirement temperature of 400 - 550 °C, and keep it at a constant temperature for a period of time to make the graphite boat and the silicon wafers inside the boat reach a constant temperature state. The constant temperature is beneficial to the uniform thickness of the grown film layer.

[0020] In Step 2, the selection of the radio frequency power is directly proportional to the boat length and the wafer loading amount, but not higher than the radio frequency power in the subsequent film formation step. Compared with the process with a relatively low radio frequency power, the bombardment damage to the silicon wafer surface is small. The duty cycle off / on value is between 10 and 15, the process time is between 40 and 100 s, the deposition time is short, and the buffer layer film thickness is thin, meeting the advantages of small surface damage, good H passivation effect, and taking into account not affecting the optical properties. The actual setting of the tube voltage is directly proportional to the tube diameter and the wafer loading amount, but not higher than the tube voltage in the subsequent film formation step. Within this pressure range, as the pressure decreases, the concentration of H bonds increases and the concentration of Si-N bonds decreases, resulting in a slight decrease in the refractive index of the thin film while reducing the concentration of silicon dangling bonds. The SiH4:NH3 flow ratio is 1:(10 - 12), and the flow values of SiH4 and NH3 are set according to the actual situation, which is directly proportional to the tube diameter and the wafer loading amount.

[0021] According to the actual situation, after Step 2, continue to deposit the multi-layer film or the infinitely graded film of Steps 3 to 5. After the film deposition is completed, purge and then take out the tube. In this solution, an extremely thin low-refractive-index silicon nitride buffer layer is inserted between the multi-layer film or the infinitely graded film of the conventional silicon nitride antireflection passivation film and the substrate, which is convenient to operate.

[0022] An extremely thin low-refractive-index silicon nitride buffer layer is inserted between the multi-layer film or the infinitely graded film of the conventional silicon nitride antireflection passivation film and the substrate. This buffer layer grows in an atmosphere with a relatively small radio frequency power and a relatively small SiH4:NH3 flow ratio. The relatively small radio frequency power reduces the bombardment damage to the substrate surface. At the same time, in an atmosphere with a relatively small SiH4:NH3 flow ratio, it plays a role in strengthening the H passivation of the substrate, reducing the number of recombination centers, and increasing the minority carrier lifetime. Under the film layer structure conditions of a hydrogen-rich state, superimposing subsequent passivation processes such as light injection / electrical injection, the short-circuit current and open-circuit voltage are further improved, resulting in a better conversion efficiency. This process can be carried out under the existing production conditions, is simple and effective, and has good practicability. The buffer layer is applicable to any one of the multi-layer film or the infinitely graded film structures. When growing the antireflection passivation film, the buffer layer is preferentially grown, and then the multi-layer film or the infinitely graded film structure is grown.

[0023] In the PECVD coating process of a monocrystalline silicon cell described above, the silicon nitride layer grown on the surface of the substrate is, from the inside to the outside, a buffer layer, a high-refractive-index layer, an intermediate layer, and an outermost layer.

[0024] Beneficial effects: (1) An extremely thin low-refractive silicon nitride buffer layer is inserted between the multilayer film or infinite gradient film of the conventional silicon nitride anti-reflection passivation film and the substrate. The thinner silicon nitride buffer layer grown under low tube pressure (1450~1700mTorr) and low RF power (7000~11000W) meets the advantages of small surface bombardment damage, good H passivation effect, and no influence on optical properties, plays a role in strengthening the H passivation substrate, reduces the number of recombination centers, and improves the minority carrier lifetime.

[0025] (2) Under the condition of hydrogen-rich film structure, the subsequent passivation processes such as light injection / electric injection are superimposed, so that the short-circuit current and open-circuit voltage are further improved, thereby achieving better conversion efficiency. This process can be produced under existing production conditions, which is simple, effective and practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a process flow chart of this preparation method.

[0027] Figure 2 This is the single crystal silicon battery structure prepared in Example 1.

[0028] Figures 1 to 2 The markings in the figure are: buffer layer 1, high fold layer 2, middle layer 3, outermost layer 4. DETAILED DESCRIPTION Example

[0029] A PECVD coating process for a single crystal silicon cell comprises the following steps:

[0030] (1) Use a graphite boat as a carrier, insert the silicon wafers into the graphite boat, and send it into the PECVD furnace tube.

[0031] (2) The temperature inside the tube is set. The temperature from the furnace mouth to the furnace tail shows a downward trend. The heating time is 660s, the overall temperature rises to about 500℃, and the temperature is kept constant for 180s.

[0032] (3) Evacuate the tube and check for leaks. The bottom pressure is reduced to below 50 mTorr. During the leak detection process, the leakage rate is less than 30 mTorr / min.

[0033] (4) Pass special gas and stabilize the pressure. The flow rate of special gas SiH4 is 800sccm, the flow rate of NH3 is 8000sccm, the pressure in the tube is controlled at 1600 mTorr, and the pressure is stabilized for 10s;

[0034] (5) Maintain the tube pressure at 1600 mTorr and the special gas SiH4 flow rate at 800 sccm, NH3 flow rate at 8000 sccm, turn on the RF deposition buffer layer, RF power at 9000 W, duty cycle off / on value at 15, process time at 40 s, and grow the buffer layer.

[0035] (6)Stabilize the special gases. The flow rate of the special gas SiH4 is 1300 sccm, the flow rate of NH3 is 7500 sccm, the pressure inside the tube is controlled at 1750 mTorr, and stabilize for 10 s.

[0036] (7)Maintain the tube pressure at 1750 mTorr, the flow rate of the special gas SiH4 at 1300 sccm, and the flow rate of NH3 at 7500 sccm. Turn on the radio frequency deposition of the high refractive index layer. The radio frequency power is 12500 W, the off / on value of the duty cycle is 16, and the process time is 150 s.

[0037] (8)Stabilize the special gases. The flow rate of the special gas SiH4 is 950 sccm, the flow rate of NH3 is 7850 sccm, the pressure inside the tube is controlled at 1800 mTorr, and stabilize for 10 s.

[0038] (9)Maintain the tube pressure at 1800 mTorr, the flow rate of the special gas SiH4 at 950 sccm, and the flow rate of NH3 at 7850 sccm. Turn on the radio frequency deposition of the intermediate layer. The radio frequency power is 13000 W, the off / on value of the duty cycle is 14, and the process time is 150 s.

[0039] (10)Stabilize the special gases. The flow rate of the special gas SiH4 is 800 sccm, the flow rate of NH3 is 8000 sccm, the pressure inside the tube is controlled at 1850 mTorr, and stabilize for 10 s.

[0040] (11)Maintain the tube pressure at 1850 mTorr, the flow rate of the special gas SiH4 at 800 sccm, and the flow rate of NH3 at 8000 sccm. Turn on the radio frequency deposition of the outermost layer. The radio frequency power is 13000 W, the off / on value of the duty cycle is 14, and the process time is 480 s.

[0041] (12)After the film deposition is completed, turn off the special gases, set the pressure inside the tube to 0 for vacuum pumping, and set the time to 30 s.

[0042] (13)After using N2 to break the vacuum and purge the furnace tube, the process is completed and the tube is taken out. Example

[0043] A PECVD coating process for monocrystalline silicon cells, comprising the following steps:

[0044] (1)Use a graphite boat as a carrier, insert the silicon wafers full into the graphite boat, and send them into the PECVD furnace tube.

[0045] (2)Set the temperature inside the tube. The temperature from the furnace mouth to the furnace tail shows a downward trend. The heating time is 660 s, the overall heating is about 400 °C, and keep it at a constant temperature for 180 s.

[0046] (3) Vacuum pumping and leak detection are carried out inside the tube. The pressure is pumped down to below 50 mTorr. During the leak detection process, the leak rate is less than 30 mTorr / min.

[0047] (4) Special gases are introduced for pressure stabilization. The flow rate of special gas SiH4 is 750 sccm, the flow rate of NH3 is 8250 sccm, and the pressure inside the tube is controlled at 1450 mTorr for 10 s of pressure stabilization.

[0048] (5) Maintain a tube pressure of 1450 mTorr, a SiH4 flow rate of 600 sccm, and an NH3 flow rate of 8400 sccm. Turn on the RF deposition of the buffer layer. The RF power is 7000 W, the off / on duty cycle value is 12, and the process time is 50 s to grow the buffer layer.

[0049] (6) Special gases are introduced for pressure stabilization. The flow rate of special gas SiH4 is 1300 sccm, the flow rate of NH3 is 7500 sccm, and the pressure inside the tube is controlled at 1750 mTorr for 10 s of pressure stabilization.

[0050] (7) Maintain a tube pressure of 1750 mTorr, a SiH4 flow rate of 1300 sccm, and an NH3 flow rate of 7500 sccm. Turn on the RF deposition of the high-refractive-index layer. The RF power is 12500 W, the off / on duty cycle value is 16, and the process time is 150 s.

[0051] (8) Special gases are introduced for pressure stabilization. The flow rate of special gas SiH4 is 950 sccm, the flow rate of NH3 is 7850 sccm, and the pressure inside the tube is controlled at 1800 mTorr for 10 s of pressure stabilization.

[0052] (9) Maintain a tube pressure of 1800 mTorr, a SiH4 flow rate of 950 sccm, and an NH3 flow rate of 7850 sccm. Turn on the RF deposition of the intermediate layer. The RF power is 13000 W, the off / on duty cycle value is 14, and the process time is 150 s.

[0053] (10) Special gases are introduced for pressure stabilization. The flow rate of special gas SiH4 is 800 sccm, the flow rate of NH3 is 8000 sccm, and the pressure inside the tube is controlled at 1850 mTorr for 10 s of pressure stabilization.

[0054] (11) Maintain a tube pressure of 1850 mTorr, a SiH4 flow rate of 800 sccm, and an NH3 flow rate of 8000 sccm. Turn on the RF deposition of the outermost layer. The RF power is 13000 W, the off / on duty cycle value is 14, and the process time is 480 s.

[0055] (12) After the film deposition is completed, turn off the special gases. Set the pressure inside the tube to 0 for vacuum pumping, and the time is set to 30 s.

[0056] After using N2 to break the vacuum and purge the furnace tubes, the process ends and the tubes are taken out. Example

[0057] A PECVD coating process for monocrystalline silicon cells includes the following steps:

[0058] (1) Using a graphite boat as a carrier, insert silicon wafers full into the graphite boat and send them into the PECVD furnace tube.

[0059] (2) Set the temperature inside the tube. The temperature from the furnace mouth to the furnace tail shows a downward trend. The heating time is 660 s, the overall temperature rise is about 450 °C, and keep the temperature constant for 180 s.

[0060] (3) Evacuate the tube and check for leaks. Pump down to below 50 mTorr at low pressure. During the leak detection process, the leak rate is less than 30 mTorr / min.

[0061] (4) Pass special gases to stabilize the pressure. The flow rate of special gas SiH4 is 700 sccm, the flow rate of NH3 is 8400 sccm, control the pressure inside the tube at 1700 mTorr, and stabilize the pressure for 10 s;

[0062] (5) Keep the tube pressure at 1700 mTorr, the flow rate of special gas SiH4 at 700 sccm, and the flow rate of NH3 at 8400 sccm. Turn on the radio frequency deposition buffer layer. The radio frequency power is 11000 W, the off / on duty cycle value is 14, and the process time is 60 s to grow the buffer layer.

[0063] (6) Pass special gases to stabilize the pressure. The flow rate of special gas SiH4 is 1300 sccm, the flow rate of NH3 is 7500 sccm, control the pressure inside the tube at 1750 mTorr, and stabilize the pressure for 10 s;

[0064] (7) Keep the tube pressure at 1750 mTorr, the flow rate of special gas SiH4 at 1300 sccm, and the flow rate of NH3 at 7500 sccm. Turn on the radio frequency deposition high refractive index layer. The radio frequency power is 12500 W, the off / on duty cycle value is 16, and the process time is 150 s.

[0065] (8) Pass special gases to stabilize the pressure. The flow rate of special gas SiH4 is 950 sccm, the flow rate of NH3 is 7850 sccm, control the pressure inside the tube at 1800 mTorr, and stabilize the pressure for 10 s;

[0066] (9) Keep the tube pressure at 1800 mTorr, the flow rate of special gas SiH4 at 950 sccm, and the flow rate of NH3 at 7850 sccm. Turn on the radio frequency deposition intermediate layer. The radio frequency power is 13000 W, the off / on duty cycle value is 14, and the process time is 150 s.

[0067] (10)Stabilize the general special gas pressure. The flow rate of special gas SiH4 is 800 sccm, the flow rate of NH3 is 8000 sccm, control the pressure inside the tube at 1850 mTorr, and stabilize the pressure for 10 s;

[0068] (11)Maintain the tube pressure of 1850 mTorr, the flow rate of special gas SiH4 at 800 sccm, and the flow rate of NH3 at 8000 sccm. Turn on the radio frequency deposition for the outermost layer. The radio frequency power is 13000 W, the off / on value of the duty cycle is 14, and the process time is 480 s.

[0069] (12)After the film layer deposition is completed, turn off the special gas, set the pressure inside the tube to 0 for vacuum pumping, and set the time to 30 s.

[0070] (13)After using N2 to break the vacuum and purge the furnace tube, the process is completed and the tube is taken out.

[0071] (1)Use a graphite boat as a carrier, insert the silicon wafers full into the graphite boat, and send them into the PECVD furnace tube;

[0072] (2)Set the temperature inside the tube. The temperature from the furnace mouth to the furnace tail shows a downward trend. The heating time is 660 s, the overall temperature rise is about 500 °C, and keep the temperature constant for 180 s.

[0073] (3)Perform vacuum pumping and leak detection inside the tube. Pump the low pressure to below 50 mTorr. During the leak detection process, the leak rate is less than 30 mTorr / min;

[0074] (4)Stabilize the general special gas pressure. The flow rate of special gas SiH4 is 1300 sccm, the flow rate of NH3 is 7500 sccm, control the pressure inside the tube at 1750 mTorr, and stabilize the pressure for 10 s;

[0075] (5)Maintain the tube pressure of 1750 mTorr, the flow rate of special gas SiH4 at 1300 sccm, and the flow rate of NH3 at 7500 sccm. Turn on the radio frequency deposition for the high refractive index layer. The radio frequency power is 12500 W, the off / on value of the duty cycle is 16, and the process time is 150 s;

[0076] (6)Stabilize the general special gas pressure. The flow rate of special gas SiH4 is 950 sccm, the flow rate of NH3 is 7850 sccm, control the pressure inside the tube at 1800 mTorr, and stabilize the pressure for 10 s;

[0077] (7)Maintain the tube pressure of 1800 mTorr, the flow rate of special gas SiH4 at 950 sccm, and the flow rate of NH3 at 7850 sccm. Turn on the radio frequency deposition for the intermediate layer. The radio frequency power is 13000 W, the off / on value of the duty cycle is 14, and the process time is 150 s;

[0078] (8)Stabilize the general special gas pressure. The flow rate of the special gas SiH4 is 800 sccm, the flow rate of NH3 is 8000 sccm, the pressure inside the tube is controlled at 1850 mTorr, and stabilize for 10 s;

[0079] (9)Maintain the tube pressure of 1850 mTorr, the flow rate of the special gas SiH4 at 800 sccm, and the flow rate of NH3 at 8000 sccm. Open the outermost layer of radio frequency deposition, the radio frequency power is 13000 W, the off / on value of the duty cycle is 14, and the process time is 500 s;

[0080] (10)After the film layer deposition is completed, turn off the special gas, set the pressure inside the tube to 0 for vacuum pumping, and set the time to 30 s;

[0081] (11)After using N2 to break the vacuum and purge the furnace tube, the process ends and the tube is taken out.

[0082] Perform data detection on the single-crystalline silicon obtained in Examples 1 to 3 and the comparative examples. The detection results are as follows:

[0083] (I)Comparison of test data:

[0084] Before annealing

[0085] Minority carrier lifetime before the film (microseconds) Wafer 1 Wafer 2 Wafer 3 Average value Example 1 57 72 63 64 Example 2 58 73 64 65 Example 3 60 71 62 64 Comparative example 62 69 73 68

[0086] After film coating

[0087] Film thickness (nm) Wafer 1 Wafer 2 Wafer 3 Average value Example 1 80.25 79.33 79.48 79.69 Example 2 80.10 80.21 79.65 79.99 Example 3 79.77 80.35 80.20 80.11 Comparative example 78.56 79.85 79.29 79.23

[0088] After annealing

[0089] Minority carrier lifetime after the film (microseconds) Wafer 1 Wafer 2 Wafer 3 Average value Example 1 113 98 105 105 Example 2 115 101 99 105 Example 3 99 97 112 103 Comparative example 85 94 110 96

[0090] (II)Comparison of electrical data:

[0091] ITEM Eta (%) Voc (V) Isc (A) Rs (mΩ) Rsh (Ω) FF Example 1 23.12 0.693 11.273 1.182 749 81.46 Example 2 23.10 0.694 11.288 1.180 745 80.33 Example 3 23.12 0.395 11.275 1.184 732 81.76 Comparative example 23.06 0.690 11.264 1.179 688 81.42

[0092] From the above data comparison, Examples 1 to 3 have obvious advantages in terms of Eta (%). This shows that the addition of the buffer layer not only satisfies the small surface bombardment damage, but also plays a role in strengthening the H passivation of the matrix, reducing the number of recombination centers, and increasing the minority carrier lifetime; it further improves the short-circuit current and open-circuit voltage, resulting in a better conversion efficiency. The efficiency gain of the examples is about 0.05% higher than that of the comparative examples.

[0093] For the comparison data of the minority carrier lifetime after annealing, Examples 1 to 3 have an increase in the minority carrier lifetime compared to the comparative examples. The increase in the minority carrier lifetime indicates a decrease in the number of recombination centers. Especially when comparing the minority carrier lifetime after annealing, it represents the effect of H passivation during the preparation of the buffer layer.

Claims

1. A PECVD coating process for monocrystalline silicon cells, characterized in that, It includes the following steps: Step 1, silicon substrate pretreatment: Insert the silicon substrate on a carrier and send it into the furnace tube; set the temperature in the furnace tube to 400 - 550 °C and keep it constant for 150 - 210 s; evacuate and leak-check the inside of the furnace tube; Step 2, formation of the buffer layer: Introduce special gases into the furnace tube and maintain the pressure and gas flow rate in the furnace tube. The pressure in the furnace tube is 1450 - 1700 mTorr; Turn on the radio frequency deposition of the buffer layer. The radio frequency power is 7000 - 11000 W and the deposition time is 40 - 100 s. The special gases introduced into the furnace tube include at least SiH4 and NH3. The flow rate ratio of SiH4 to NH3 is 1:(10 - 12); Step 3, formation of the high refractive index layer: Adjust the gas flow rate to obtain the pressure required for depositing the high refractive index layer. The pressure in the furnace tube is 1700 - 2000 mTorr; turn on the radio frequency deposition of the high refractive index layer. The radio frequency power is 11000 - 15000 W and the deposition time is 100 - 200 s. The flow rate ratio of SiH4 to NH3 is 1:(4 - 6); Step 4, generation of the intermediate layer: Adjust the gas flow rate to obtain the pressure required for depositing the intermediate layer. The pressure in the furnace tube is 1700 - 2000 mTorr; turn on the radio frequency deposition of the high refractive index layer. The radio frequency power is 11000 - 16000 W and the deposition time is 100 - 200 s. The flow rate ratio of SiH4 to NH3 is 1:(7 - 9); Step 5, generation of the outermost layer: Adjust the gas flow rate to obtain the pressure required for depositing the outermost layer. The pressure in the furnace tube is 1800 - 2100 mTorr; turn on the radio frequency deposition of the outermost layer. The radio frequency power is 11000 - 16000 W and the deposition time is 400 - 560 s. The flow rate ratio of SiH4 to NH3 is 1:(9 - 10).

2. The PECVD coating process for monocrystalline silicon cells according to claim 1, wherein, In Step 1, evacuate the bottom pressure of the furnace tube to below 50 mTorr; in the leak-check process, the leak rate is less than 30 mTorr / min.

3. A PECVD coating process for monocrystalline silicon cells as described in claim 1, characterized in that, In Step 2, the off / on value of the duty cycle of the radio frequency deposition is 10 - 15.

4. A PECVD coating process for monocrystalline silicon cells according to claim 1, characterized in that, The off / on values of the duty cycle of the radio frequency deposition in Steps 3 to 5 are 10 - 16, 10 - 14, and 10 - 14 respectively.

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