Interface passivation method of solar cell silicon wafer and passivated silicon wafer

Abstract

The embodiment of the invention provides an interface passivation method of a solar cell silicon wafer and a passivated silicon wafer, and the preparation method provided by the embodiment of the invention comprises the following steps: placing a silicon wafer to be passivated in a furnace tube, and depositing a plurality of layers of aluminum oxide films on the back surface of the silicon wafer step by step by adopting a plasma enhanced chemical vapor deposition technology; and depositing a plurality of layers of aluminum oxide films on the back surface of the silicon wafer step by step, and depositing at least one layer of silicon nitride film on the surface of the silicon wafer by adopting a plasma enhanced chemical vapor deposition technology to obtain the passivated silicon wafer. The two-in-one furnace tube is used for depositing passivation films, namely aluminum oxide and silicon nitride, so that the space utilization rate and the coating efficiency are ensured, and meanwhile, multiple layers of aluminum oxide films are deposited on the back surface of the silicon wafer step by step, so that the aluminum oxide films are more uniformly deposited, and the surface passivation effect is improved; the problem that the difference of the photoelectric conversion efficiency of the prepared solar cell is large due to the fact that the uniformity of an aluminum oxide film formed by an existing coating passivation mode is poor is solved.

Description

Technical Field

[0001] The invention relates to the technical field of crystalline silicon solar cell manufacturing, and in particular to an interface passivation method for a solar cell silicon wafer and a passivated silicon wafer. Background Art

[0002] At present, due to the higher space occupation, the interface passivation of solar cell silicon wafers is gradually achieved by using plasma enhanced chemical vapor deposition (PECVD) aluminum oxide and SiNx as the back passivation film layer.

[0003] However, the aluminum oxide film formed by the passivation coating method of the two-in-one furnace tube has poor uniformity, resulting in large differences in the photoelectric conversion efficiency of the prepared solar cells and unstable performance. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an interface passivation method for solar cell silicon wafers and a passivated silicon wafer, so as to solve the problem that the aluminum oxide film formed by the existing coating passivation method has poor uniformity, resulting in large differences in the photoelectric conversion efficiency of the prepared solar cells.

[0005] In order to solve the above problems, the present invention is achieved through the following technical solutions:

[0006] The present invention provides a method for interface passivation of a solar cell silicon wafer, which comprises:

[0007] The silicon wafer to be passivated is placed in a furnace tube, and a multi-layer aluminum oxide film is deposited step by step on the back of the silicon wafer using a plasma enhanced chemical vapor deposition technique;

[0008] After depositing multiple layers of aluminum oxide films on the back of the silicon wafer in steps, at least one layer of silicon nitride film is deposited on the surface of the silicon wafer using plasma enhanced chemical vapor deposition technology to obtain a passivated silicon wafer.

[0009] Furthermore, in the interface passivation method, a multilayer aluminum oxide film is deposited step by step on the back side of the silicon wafer, comprising:

[0010] A multilayer aluminum oxide film with increasing thickness is deposited step by step at low temperature and low pressure on the back side of the silicon wafer.

[0011] Furthermore, in the interface passivation method, the multilayer aluminum oxide film includes a first aluminum oxide film with a thickness of 1 to 3 nm, a second aluminum oxide film with a thickness of 3 to 5 nm, and a third aluminum oxide film with a thickness of 5 to 10 nm.

[0012] Furthermore, in the interface passivation method, the thickness of the third aluminum oxide film is greater than or equal to the sum of the thicknesses of the first aluminum oxide film and the second aluminum oxide film.

[0013] Furthermore, in the interface passivation method, a multilayer aluminum oxide film with increasing thickness is deposited step by step on the back side of the silicon wafer, comprising:

[0014] Under the conditions of a temperature of 270 to 370° C. and a pressure of 1300 to 1700 mTor, nitrous oxide with a flow rate of 4500 to 8000 sccm and trimethylaluminum gas with a flow rate of 50 to 100 sccm are introduced for deposition for 30 to 50 seconds to form a first aluminum oxide film on the back of the silicon wafer;

[0015] Under the conditions of a temperature of 270 to 370° C. and a pressure of 1300 to 1700 mTor, nitrous oxide with a flow rate of 4500 to 8000 sccm and trimethylaluminum gas with a flow rate of 50 to 100 sccm are introduced for deposition for 50 to 80 seconds to form a second aluminum oxide film on the surface of the first aluminum oxide film;

[0016] Under the conditions of temperature of 270-370°C and pressure of 1300-1700 mTor, nitrous oxide with a flow rate of 4500-8000 sccm and trimethylaluminum gas with a flow rate of 50-100 sccm are introduced for deposition for 80-100 seconds to form a third aluminum oxide film on the surface of the second aluminum oxide film.

[0017] Furthermore, in the interface passivation method, after the step of forming a first aluminum oxide film on the back side of the silicon wafer and before the step of forming a second aluminum oxide film on the surface of the first aluminum oxide film, the method further includes:

[0018] The furnace tube is purged with protective gas.

[0019] Furthermore, in the interface passivation method, before the step of depositing multiple layers of aluminum oxide film on the back of the silicon wafer in steps and depositing at least one layer of silicon nitride film on the surface of the silicon wafer, the method further comprises:

[0020] The furnace tube is purged with protective gas.

[0021] Furthermore, in the interface passivation method, the furnace tube is purged with protective gas, comprising:

[0022] Under the conditions of gas pressure of 1300-1700 mbar and temperature of 270-370° C., nitrogen gas with a flow rate of 9000-15000 sccm is introduced and maintained for 10-20 seconds.

[0023] Furthermore, in the interface passivation method, at least one layer of silicon nitride film is deposited on the surface of the silicon wafer, comprising:

[0024] A multilayer silicon nitride film with a refractive index decreasing in sequence is deposited step by step on the surface of the silicon wafer.

[0025] An embodiment of the present invention further provides a passivated silicon wafer, which is passivated by the above-mentioned method.

[0026] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0027] In the interface passivation method of solar cell silicon wafer provided in the embodiment of the present invention, the silicon wafer to be passivated is first placed in a furnace tube, and a plasma enhanced chemical vapor deposition technique is used to deposit a multi-layer aluminum oxide film on the back of the silicon wafer in steps, and then a plasma enhanced chemical vapor deposition technique is used to deposit at least one layer of silicon nitride film on the surface of the silicon wafer to obtain a passivated silicon wafer. Because a two-in-one furnace tube is used to deposit the passivation film aluminum oxide and silicon nitride, the space utilization rate and coating efficiency are guaranteed. At the same time, because a multi-layer aluminum oxide film is deposited in steps on the back of the silicon wafer, the aluminum oxide film is deposited more uniformly, thereby improving the surface passivation effect, and improving the poor uniformity of the aluminum oxide film formed by the existing coating passivation method, resulting in a large difference in the photoelectric conversion efficiency of the prepared solar cell.

[0028] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a flowchart of a method for interface passivation of a solar cell silicon wafer provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] The embodiment of the present invention provides a method for interface passivation of a solar cell silicon wafer, such as Figure 1 As shown, it includes steps 101 to 102:

[0032] Step 101: placing a silicon wafer to be passivated in a furnace tube, and using plasma enhanced chemical vapor deposition technology to deposit a multi-layer aluminum oxide film on the back side of the silicon wafer in steps.

[0033] In the above step 101, the silicon wafer to be passivated is first cleaned, then loaded into a graphite boat and sent into a furnace tube; wherein the above silicon wafer is a semi-finished silicon wafer, specifically a cell with a PN junction, which can be a P-type silicon wafer or an N-type silicon wafer, and can be used to make a perc solar cell and a shingled solar cell. The above graphite boat is a graphite boat that has been cleaned in advance.

[0034] In the above step 101, after the silicon wafer is fed into the furnace tube, the temperature is increased and the furnace is evacuated to remove impurity gases; then the first reaction gas is introduced, and plasma enhanced chemical vapor deposition technology is used to stepwise deposit a multi-layer aluminum oxide film on the back of the silicon wafer as a passivation film.

[0035] Step 102: after depositing multiple layers of aluminum oxide films step by step on the back side of the silicon wafer, at least one layer of silicon nitride film is deposited on the surface of the silicon wafer using plasma enhanced chemical vapor deposition technology to obtain a passivated silicon wafer.

[0036] In the above step 103, after the passivation film is deposited, the second reaction gas is introduced, and plasma enhanced chemical vapor deposition technology is used to deposit at least one layer of silicon nitride film on the surface of the silicon wafer as an anti-reflection film. After completion, the tail gas is treated and extracted, and the protective gas is filled and back-pressurized out of the boat to obtain a passivated silicon wafer.

[0037] The protective gas is a stable gas that is not easy to react with aluminum oxide and silicon nitride, such as nitrogen, inert gas, etc.

[0038] In the interface passivation method of solar cell silicon wafer provided by the embodiment of the present invention, the silicon wafer to be passivated is first placed in a furnace tube, and a plasma enhanced chemical vapor deposition technique is used to deposit a multi-layer aluminum oxide film on the back of the silicon wafer in steps, and then a plasma enhanced chemical vapor deposition technique is used to deposit at least one layer of silicon nitride film on the surface of the silicon wafer to obtain a passivated silicon wafer. Because a two-in-one furnace tube is used to deposit the passivation film aluminum oxide and silicon nitride, the space utilization rate and coating efficiency are guaranteed. At the same time, because a multi-layer aluminum oxide film is deposited in steps on the back of the silicon wafer, the aluminum oxide film is deposited more uniformly, thereby improving the surface passivation effect, and improving the poor uniformity of the aluminum oxide film formed by the existing coating passivation method, resulting in a large difference in the photoelectric conversion efficiency of the prepared solar cell.

[0039] Optionally, in one embodiment, before the plasma enhanced chemical vapor deposition technology is used to deposit a multi-layer aluminum oxide film on the back side of the silicon wafer in steps, the method includes:

[0040] The furnace tube is cleaned with protective gas.

[0041] In this embodiment, by introducing protective gas to clean the furnace tube before depositing the aluminum oxide film, the acid gas, graphite powder and gas impurities in the furnace tube and the graphite boat can be extracted and removed to ensure the cleanliness of the tube.

[0042] The protective gas is a stable gas that is not easy to react with the graphite boat, such as nitrogen, inert gas, etc.

[0043] Optionally, in a specific embodiment, the furnace tube is cleaned with a protective gas, comprising:

[0044] At 270-370° C., nitrogen gas is introduced into the furnace tube at a flow rate of 20,000-40,000 sccm, and the pressure in the furnace tube is controlled at 1,500-2,000 mTor for 200-500 seconds.

[0045] In this embodiment, by reaching a temperature of 270-370°C and maintaining it for 200-500s, nitrogen is introduced at a flow rate of 20,000-40,000sccm, and the pressure in the furnace tube is slowly increased to 1,500-2,000mTor and continued for 200-500s, for example, 200s, 300s or 500s, so that the introduced nitrogen can fully extract the impurities remaining in the furnace tube and on the graphite boat to ensure the cleanliness of the furnace tube.

[0046] In some embodiments, the furnace tube is cleaned with protective gas, including: introducing nitrogen into the furnace tube at a flow rate of 25,000 to 35,000 sccm at 300 to 350° C., controlling the pressure in the furnace tube to 1,700 mTor, and continuing for 300 seconds.

[0047] Optionally, in one embodiment, before the furnace tube is cleaned with protective gas, the method further comprises:

[0048] The furnace tube is emptied.

[0049] In this embodiment, before the protective gas cleaning is performed, the furnace tube is first evacuated to remove impurities such as water vapor and oxygen in the furnace tube, so that the subsequent protective gas can clean the furnace tube and the graphite boat more thoroughly.

[0050] Optionally, in a specific implementation, the furnace tube is emptied, comprising:

[0051] Raise the temperature inside the furnace tube to 270-370°C and control the pressure to drop to 0 mTor.

[0052] In this specific implementation, a method of increasing temperature and pumping pressure is adopted, that is, the temperature in the furnace tube is increased to 270-370°C, and the pressure is controlled to drop to 0 mTor, so that the furnace tube is in a low pressure state and lasts for a predetermined time to complete the emptying of the furnace tube. The predetermined time can be 300-600s; in some implementations, the predetermined time can be 400-500s; in some implementations, the predetermined time can be 424-475s.

[0053] Optionally, in one embodiment, a multilayer aluminum oxide film is deposited stepwise on the back side of the silicon wafer, comprising:

[0054] A multilayer aluminum oxide film with increasing thickness is deposited step by step at low temperature and low pressure on the back side of the silicon wafer.

[0055] In this embodiment, a two-in-one furnace tube is used for low-temperature and low-pressure deposition, and a multi-layer aluminum oxide film with successively increasing thickness is formed, so that the aluminum oxide deposition is more compact, which can further improve the passivation effect.

[0056] Optionally, in a specific embodiment, the multilayer aluminum oxide film includes a first aluminum oxide film with a thickness of 1 to 3 nm, a second aluminum oxide film with a thickness of 3 to 5 nm, and a third aluminum oxide film with a thickness of 5 to 10 nm.

[0057] In this implementation, gradient differences are made on the multi-layer aluminum oxide film to further improve the deposition density.

[0058] Optionally, in a more specific embodiment, the thickness of the third aluminum oxide film is greater than or equal to the sum of the thickness of the first aluminum oxide film and the second aluminum oxide film, that is, the thickness of the top aluminum oxide film covers the thickness of the lower two films, which can achieve a better passivation effect.

[0059] For example, a first aluminum oxide film with a thickness of 2 nm and a second aluminum oxide film with a thickness of 4 nm are first deposited, and then a third aluminum oxide film with a thickness of 6 nm is deposited.

[0060] Optionally, in a specific embodiment, a multilayer aluminum oxide film is deposited stepwise on the back side of the silicon wafer, comprising:

[0061] Under the conditions of a temperature of 270 to 370° C. and a pressure of 1300 to 1700 mTor, nitrous oxide with a flow rate of 4500 to 8000 sccm and trimethylaluminum gas with a flow rate of 50 to 100 sccm are introduced for deposition for 30 to 50 seconds to form a first aluminum oxide film on the back of the silicon wafer;

[0062] Under the conditions of a temperature of 270 to 370° C. and a pressure of 1300 to 1700 mTor, nitrous oxide with a flow rate of 4500 to 8000 sccm and trimethylaluminum gas with a flow rate of 50 to 100 sccm are introduced for deposition for 50 to 80 seconds to form a second aluminum oxide film on the surface of the first aluminum oxide film;

[0063] Under the conditions of temperature of 270-370°C and pressure of 1300-1700 mTor, nitrous oxide with a flow rate of 4500-8000 sccm and trimethylaluminum gas with a flow rate of 50-100 sccm are introduced for deposition for 80-100 seconds to form a third aluminum oxide film on the surface of the second aluminum oxide film.

[0064] In this embodiment, under the conditions of a temperature of 270 to 370°C, a nitrous oxide (N2O) flow rate of 4500 to 8000 sccm, and a trimethylaluminum (TMA) flow rate of 50 to 100 sccm, the pressure is controlled to be 1300 to 1700 mTor, and by controlling the deposition time, low-temperature, low-pressure, slow deposition can be performed, and aluminum oxide protection of different thicknesses can be uniformly and densely formed on the back of the silicon wafer.

[0065] In this embodiment, under the conditions of a temperature of 270 to 370° C., a nitrous oxide (N 2 O) flow rate of 4500 to 8000 sccm, and a trimethylaluminum (TMA) flow rate of 50 to 100 sccm, the pressure is controlled to be 1300 to 1700 mTor and the deposition is performed for 30 to 50 seconds to form a first aluminum oxide film with a thickness of 1 to 3 nm on the back of the silicon wafer.

[0066] In this embodiment, under the conditions of a temperature of 270 to 370°C, a nitrous oxide (N2O) flow rate of 4500 to 8000 sccm, and a trimethylaluminum (TMA) flow rate of 50 to 100 sccm, the pressure is controlled to be 1300 to 1700 mTor and the deposition is performed for 50 to 80 seconds to form a second aluminum oxide film with a thickness of 3 to 5 nm on the surface of the first aluminum oxide film.

[0067] In this embodiment, under the conditions of a temperature of 270 to 370°C, a nitrous oxide (N2O) flow rate of 4500 to 8000 sccm, and a trimethylaluminum (TMA) flow rate of 50 to 100 sccm, the pressure is controlled to be 1300 to 1700 mTor and the deposition time is 80 to 100 s to form a third aluminum oxide film with a thickness of 5 to 10 nm on the surface of the second aluminum oxide film.

[0068] Optionally, in a specific implementation manner, the interface passivation method provided in the embodiment of the present invention, after the step of forming the first aluminum oxide film on the back side of the silicon wafer and before the step of forming the second aluminum oxide film on the surface of the first aluminum oxide film, further comprises:

[0069] The furnace tube is purged with protective gas.

[0070] In this specific embodiment, by passing a protective gas to clean the furnace tube after depositing the first aluminum oxide film and before depositing the second aluminum oxide film, the exhaust gas and the generated aluminum oxide powder inside the furnace tube can be removed to ensure the cleanliness of the tube, making the subsequently deposited aluminum oxide film purer.

[0071] Optionally, in a specific implementation manner, the interface passivation method provided in the embodiment of the present invention further comprises: before the step of depositing multiple layers of aluminum oxide film on the back side of the silicon wafer in steps and depositing at least one layer of silicon nitride film on the surface of the silicon wafer:

[0072] The furnace tube is purged with protective gas.

[0073] In this specific embodiment, by passing a protective gas to clean the furnace tube after depositing the third aluminum oxide film and before depositing the silicon nitride film, the exhaust gas and the generated aluminum oxide powder inside the furnace tube can be removed to ensure the cleanliness of the tube, making the subsequently deposited silicon oxide film purer.

[0074] The protective gas is a stable gas that is not easy to react with the graphite boat, such as nitrogen, inert gas, etc.

[0075] Optionally, in a specific implementation, the furnace tube is purged with protective gas, comprising:

[0076] Under the conditions of gas pressure of 1300-1700 mbar and temperature of 270-370° C., nitrogen gas with a flow rate of 9000-15000 sccm is introduced and maintained for 10-20 seconds.

[0077] In this embodiment, when the temperature reaches 270-370°C and the pressure in the furnace tube is increased to 1300-1700 mTor, nitrogen is introduced at a flow rate of 9000-15000 sccm for 10-20 seconds, for example, one or two of 10 seconds, 15 seconds or 20 seconds, so that the introduced nitrogen can fully extract the impurities remaining in the furnace tube and on the graphite boat, thereby ensuring the cleanliness of the furnace tube.

[0078] Optionally, in one embodiment, at least one layer of silicon nitride film is deposited on the surface of the silicon wafer, comprising:

[0079] A multilayer silicon nitride film with a refractive index decreasing in sequence is deposited step by step on the surface of the silicon wafer.

[0080] In this embodiment, a two-in-one furnace tube is used to deposit a multi-layer silicon nitride film with successively increasing thickness and successively decreasing refractive index, which can further enhance the anti-reflection effect.

[0081] In this embodiment, the multilayer silicon nitride film can be a three-layer coating. Under the condition of an RF power of 13000~17000w, the first silicon nitride film is first deposited at a silane to ammonia flow ratio of 1:4, and then the second silicon nitride film is deposited at a silane to ammonia flow ratio of 1:7, and finally the third silicon nitride film is deposited at a silane to ammonia flow ratio of 1:12, so that three-layer silicon nitride films with decreasing refractive indices can be formed.

[0082] For example, under the conditions of a temperature of 450-550° C., a silane flow rate of 1530 sccm, and an ammonia flow rate of 6300 sccm, the pressure is controlled to be 1500-1800 mTor, and low-temperature, low-flow and slow deposition can be performed, which can better deposit the first silicon nitride film on the surface of the silicon wafer;

[0083] Under the conditions of temperature of 450-550°C, silane flow rate of 1000sccm, ammonia flow rate of 7000sccm, and controlled pressure of 1500-1800mTor, low-temperature, low-flow and slow deposition can be performed, which can better deposit the second silicon nitride film on the surface of the silicon wafer;

[0084] Under the conditions of temperature of 450-550°C, silane flow of 700sccm, and ammonia flow of 8400sccm, the pressure is controlled at 1500-1800mTor, and low-temperature, low-flow slow deposition can be performed, which can better deposit the third silicon nitride film on the surface of the silicon wafer.

[0085] In the embodiment of the present invention, the thickness of the silicon nitride film may be 80-100 nm, for example, a range of one or any two of 80 nm, 85 nm, 90 nm, 95 nm, and 100 nm.

[0086] Optionally, in one implementation, after depositing at least one layer of silicon nitride film on the surface of the silicon wafer, the interface passivation method provided in the embodiment of the present invention further includes step 103:

[0087] Step 103, cleaning the furnace tube with protective gas.

[0088] In this embodiment, a protective gas such as nitrogen is introduced into the furnace tube to carry away the waste gas in the tube, thereby achieving further cleaning of the furnace tube.

[0089] Optionally, in a specific implementation, the above step 103 includes:

[0090] At 450-550° C., nitrogen gas is introduced into the furnace tube at a flow rate of 10000-30000 sccm, and the pressure in the furnace tube is controlled to be 0 mTor, and the process lasts for 50-100 seconds.

[0091] In this specific implementation, the temperature is firstly reached to 450-550°C, and the vacuum pump is kept running at a pumping speed to control the pressure in the furnace tube to 0 mTor, and maintained for 10-30 seconds to perform tail gas cleaning and extraction, and then nitrogen is introduced at a flow rate of 10,000-30,000 sccm, and the vacuum pump is controlled to keep running at a pumping speed, and the furnace tube is controlled at 0 mTor and maintained for 50-100 seconds, so that the exhaust gas in the furnace tube can be taken away, thereby achieving further cleaning of the furnace tube.

[0092] In some embodiments, the furnace tube is cleaned with a protective gas, including: controlling the pressure in the furnace tube to 0 mTor at 450-550°C and maintaining it for 20 seconds to clean and extract the tail gas; then introducing nitrogen at a flow rate of 10,000-30,000 sccm, and controlling the pressure in the furnace tube to 1,600 mTor, and maintaining it for 90 seconds, to achieve further cleaning of the furnace tube after deposition.

[0093] In this specific implementation, after further cleaning of the furnace tube is completed, protective gas is introduced to control the back pressure of the furnace tube to reach the external air pressure, and then the furnace door is opened to end the passivation process, that is, to obtain a passivated silicon wafer.

[0094] Optionally, in a specific embodiment, 30,000 to 50,000 sccm nitrogen can be introduced at 450° C. to 550° C. and the pressure in the furnace tube can be controlled to be 10,000 mTor, so that the internal pressure reaches the external air pressure to open the furnace door, and then the passivation process can be terminated.

[0095] An embodiment of the present invention further provides a passivated silicon wafer, which is passivated by the above method.

[0096] For the above passivated silicon wafer embodiment, it is passivated by the above method and can achieve the same technical effect. To avoid repetition, it will not be described here. For relevant details, please refer to the partial description of the embodiment of the interface passivation method for solar cell silicon wafer.

[0097] The present invention is described in detail below by way of examples.

[0098] Example 1

[0099] (1) Loading the boat: Place the PERC cell silicon wafers with formed PN junction into the boat, set the temperature to 300°C, and the pressure to 10000mTor for 60 seconds.

[0100] (2) Heating: After the boat is loaded, close the furnace door, set the temperature to 300°C, introduce nitrogen at 20,000 sccm, and maintain for 10 minutes.

[0101] (3) Check for leaks: Set the pressure to 0mTor, maintain the temperature at 300℃, and set the time to 230s to perform vacuum check for leaks and confirm that the furnace tube is properly sealed.

[0102] (4) Deposition of the first aluminum oxide film: Under the conditions of a temperature of 300°C, a pressure of 1300 mTor, and an RF power of 3500 W, nitrous oxide with a flow rate of 5000 sccm and trimethylaluminum gas with a flow rate of 55 sccm were introduced for deposition for 30 seconds to form a first aluminum oxide film on the back side of the silicon wafer.

[0103] (5) Furnace tube cleaning: nitrogen gas with a flow rate of 9000 sccm was introduced at a pressure of 1300 mbar and a temperature of 300°C for 10 seconds to purge the deposited alumina waste gas and the generated alumina powder.

[0104] (6) Deposition of the second aluminum oxide film: Under the conditions of a temperature of 300°C and a pressure of 1300 mTor, nitrous oxide with a flow rate of 6000 sccm and trimethylaluminum gas with a flow rate of 60 sccm were introduced for deposition for 50 seconds to form a second aluminum oxide film on the surface of the first aluminum oxide film.

[0105] (7) Deposition of the third aluminum oxide film: Under the conditions of a temperature of 300°C, a pressure of 1300 mTor, and an RF power of 3500 W, nitrous oxide with a flow rate of 7000 sccm and trimethylaluminum gas with a flow rate of 70 sccm were introduced for 80 seconds to form a third aluminum oxide film on the surface of the second aluminum oxide film.

[0106] (8) Furnace tube cleaning: nitrogen gas with a flow rate of 10,000 sccm was introduced at a pressure of 13,000 mbar and a temperature of 300°C for 20 seconds to purge the deposited alumina waste gas and the generated alumina powder.

[0107] (9) Silicon nitride film deposition: under the conditions of a temperature of 550° C., a silane flow rate of 1530 sccm, an ammonia flow rate of 6300 sccm, and a radio frequency power supply discharge power of 15000 watts, the pressure is controlled to be 1500 mTor and maintained for 120 s to deposit a first silicon nitride film on the surface of the silicon wafer;

[0108] Under the conditions of a temperature of 550° C., a silane flow rate of 1000 sccm, an ammonia flow rate of 7000 sccm, and a radio frequency power supply discharge power of 15000 watts, the pressure is controlled to be 1500 mTor and maintained for 130 seconds, and a second silicon nitride film is deposited on the surface of the silicon wafer;

[0109] Under the conditions of temperature of 550°C, silane flow rate of 700sccm, ammonia flow rate of 8400sccm, RF power supply discharge power of 15000W, the pressure was controlled to be 1500mTor and maintained for 140s to deposit the third silicon nitride film on the surface of the silicon wafer.

[0110] (10) Tail gas treatment: The temperature is controlled at 550°C, the pressure is set to 0 mTor and maintained for 20 seconds to clean and extract the tail gas;

[0111] (11) Furnace tube cleaning: The temperature was controlled at 550°C, the pressure was set to 0 mTor, and nitrogen gas with a flow rate of 20,000 sccm was introduced and maintained for 20 seconds to clean the furnace tube;

[0112] (12) Back pressure: nitrogen is introduced at a flow rate of 40,000 sccm until the pressure reaches 10,000 mTor, and the furnace door is opened when the internal pressure reaches the external pressure;

[0113] (13) Unloading the boat: The temperature is controlled at 450℃~550℃, the pressure is set to 10000mTor, the time is set to 120s, the furnace door is opened to unload the boat, and the passivated silicon wafer is obtained.

[0114] Comparative Example 1

[0115] (1) Loading the boat: Place the PERC cell silicon wafers with PN junction formed into the boat, set the temperature to 250-370℃, normal pressure to 10000mTor, and maintain for 60s.

[0116] (2) Heating: After the boat is loaded, close the furnace door, set the temperature to 370°C, introduce nitrogen at 20,000 sccm, and maintain for 10 min.

[0117] (3) Check for leaks: Set the pressure to 0mTor, maintain the temperature at 370°C, and set the time to 230s to perform vacuum check for leaks and confirm that the furnace tube is properly sealed.

[0118] (4) Aluminum oxide film deposition: Under the conditions of a temperature of 370°C, a pressure of 1700 mTor, and an RF power supply discharge power of 5000 W, nitrous oxide with a flow rate of 8000 sccm and trimethylaluminum gas with a flow rate of 100 sccm were introduced for 160 s to form an aluminum oxide film on the back of the silicon wafer.

[0119] (5) Furnace tube cleaning: Under the conditions of gas pressure of 1700 mbar and temperature of 370°C, nitrogen gas with a flow rate of 15000 sccm was introduced and maintained for 20 seconds to purge the deposited alumina waste gas and the generated alumina powder.

[0120] (6) Silicon nitride film deposition: under the conditions of a temperature of 550° C., a silane flow rate of 1530 sccm, an ammonia flow rate of 6300 sccm, and an RF power of 15,000 watts, the pressure was controlled to be 1500 mTor and maintained for 120 seconds to deposit a first silicon nitride film on the surface of the silicon wafer;

[0121] Under the conditions of a temperature of 550° C., a silane flow rate of 1000 sccm, an ammonia flow rate of 7000 sccm, and a radio frequency power supply discharge power of 15000 watts, the pressure is controlled to be 1500 mTor and maintained for 130 seconds, and a second silicon nitride film is deposited on the surface of the silicon wafer;

[0122] Under the conditions of temperature of 550°C, silane flow rate of 700sccm, ammonia flow rate of 8400sccm, RF power of 15000W, the pressure was controlled to be 1500mTor and maintained for 140s to deposit the third silicon nitride film on the surface of the silicon wafer.

[0123] (7) Tail gas treatment: The temperature is controlled at 550°C, the pressure is set to 0 mTor and maintained for 20 seconds to clean and extract the tail gas;

[0124] (8) Furnace tube cleaning: The temperature was controlled at 550°C, the pressure was set to 0 mTor, and nitrogen gas with a flow rate of 20,000 sccm was introduced and maintained for 20 seconds to clean the furnace tube;

[0125] (9) Back pressure: nitrogen is introduced at a flow rate of 40,000 sccm until the pressure reaches 10,000 mTor, and the furnace door is opened when the internal pressure reaches the external pressure;

[0126] (10) Unloading the boat: The temperature is controlled at 550°C, the pressure is set to 10000 mTor, the time is set to 120 s, the furnace door is opened to unload the boat, and the passivated silicon wafer is obtained.

[0127] Experimental data tracking was performed on the silicon wafers in Example 1 and Comparative Example 1, respectively, to measure the total thickness of the aluminum oxide film. The results are shown in Table 1.

[0128] Table 1

[0129]

[0130] The silicon wafers obtained in Example 1 and Comparative Example 1 were used to manufacture PERC solar cells, and the electrical performance of the manufactured cells was tested and the average electrical performance parameters were calculated. The results are shown in Table 2.

[0131] Table 2

[0132]

[0133] In Table 2, Eta represents the test conversion efficiency, Isc represents the short-circuit current, Uoc represents the open-circuit voltage, FF represents the fill factor, Rs represents the series resistance, Rsh represents the parallel resistance, and IRev1 represents the dark current.

[0134] Experiments show that the interface passivation method provided in the embodiment of the present invention deposits multiple layers of aluminum oxide film on the back of the silicon wafer in steps, which can make the aluminum oxide film deposited more uniformly, thereby improving the surface passivation effect and effectively improving the problem of poor uniformity of the aluminum oxide film formed by the existing coating passivation method.

[0135] In summary, in this embodiment, the silicon wafer to be passivated is first placed in a furnace tube, and a plasma enhanced chemical vapor deposition technique is used to deposit a multi-layer aluminum oxide film on the back of the silicon wafer in steps, and then a plasma enhanced chemical vapor deposition technique is used to deposit at least one layer of silicon nitride film on the surface of the silicon wafer to obtain a passivated silicon wafer. Because a two-in-one furnace tube is used to deposit the passivation film aluminum oxide and silicon nitride, the space utilization rate and coating efficiency are guaranteed. At the same time, because the multi-layer aluminum oxide film is deposited in steps on the back of the silicon wafer, the aluminum oxide film is deposited more uniformly, thereby improving the surface passivation effect, and improving the poor uniformity of the aluminum oxide film formed by the existing coating passivation method, resulting in a large difference in the photoelectric conversion efficiency of the prepared solar cell.

[0136] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concept. Therefore, the claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0137] The above is a detailed introduction to the interface passivation method of a solar cell silicon wafer and the passivated silicon wafer provided by the present invention. Specific examples are used in this article to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for a person skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A method for interface passivation of a solar cell silicon wafer, characterized in that: include: The silicon wafer to be passivated is placed in a furnace tube, and a multi-layer aluminum oxide film is deposited step by step on the back of the silicon wafer using a plasma enhanced chemical vapor deposition technique; After depositing multiple layers of aluminum oxide films on the back of the silicon wafer in steps, at least one layer of silicon nitride film is deposited on the surface of the silicon wafer using plasma enhanced chemical vapor deposition technology to obtain a passivated silicon wafer.

2. The interface passivation method according to claim 1, characterized in that: Depositing a multilayer aluminum oxide film on the back of the silicon wafer in steps, comprising: A multilayer aluminum oxide film with increasing thickness is deposited step by step at low temperature and low pressure on the back side of the silicon wafer.

3. The interface passivation method according to claim 1, characterized in that: The multi-layer aluminum oxide film includes a first aluminum oxide film with a thickness of 1 to 3 nm, a second aluminum oxide film with a thickness of 3 to 5 nm, and a third aluminum oxide film with a thickness of 5 to 10 nm.

4. The interface passivation method according to claim 3, characterized in that: The thickness of the third aluminum oxide film is greater than or equal to the sum of the thicknesses of the first aluminum oxide film and the second aluminum oxide film.

5. The interface passivation method according to claim 3, characterized in that: Depositing multiple layers of aluminum oxide films with increasing thicknesses step by step on the back side of the silicon wafer, comprising: Under the conditions of a temperature of 270 to 370° C. and a pressure of 1300 to 1700 mTor, nitrous oxide with a flow rate of 4500 to 8000 sccm and trimethylaluminum gas with a flow rate of 50 to 100 sccm are introduced for deposition for 30 to 50 seconds to form a first aluminum oxide film on the back of the silicon wafer; Under the conditions of a temperature of 270 to 370° C. and a pressure of 1300 to 1700 mTor, nitrous oxide with a flow rate of 4500 to 8000 sccm and trimethylaluminum gas with a flow rate of 50 to 100 sccm are introduced for deposition for 50 to 80 seconds to form a second aluminum oxide film on the surface of the first aluminum oxide film; Under the conditions of temperature of 270-370°C and pressure of 1300-1700 mTor, nitrous oxide with a flow rate of 4500-8000 sccm and trimethylaluminum gas with a flow rate of 50-100 sccm are introduced for deposition for 80-100 seconds to form a third aluminum oxide film on the surface of the second aluminum oxide film.

6. The interface passivation method according to claim 5, characterized in that: After the step of forming a first aluminum oxide film on the back side of the silicon wafer and before the step of forming a second aluminum oxide film on the surface of the first aluminum oxide film, the method further includes: The furnace tube is purged with protective gas.

7. The interface passivation method according to claim 1, characterized in that: Before the steps of depositing multiple layers of aluminum oxide film on the back of the silicon wafer in steps and depositing at least one layer of silicon nitride film on the surface of the silicon wafer, the method further comprises: The furnace tube is purged with protective gas.

8. The interface passivation method according to claim 6 or 7, characterized in that: The furnace tube is purged with protective gas, comprising: Under the conditions of gas pressure of 1300-1700 mbar and temperature of 270-370° C., nitrogen gas with a flow rate of 9000-15000 sccm is introduced and maintained for 10-20 seconds.

9. The interface passivation method according to claim 1, characterized in that: Depositing at least one layer of silicon nitride film on the surface of the silicon wafer comprises: A multilayer silicon nitride film with a refractive index decreasing in sequence is deposited step by step on the surface of the silicon wafer.

10. A passivated silicon wafer, characterized in that: The silicon wafer is passivated by the method according to any one of claims 1 to 9.

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