An ald multilayer film deposition method for improving photoelectric conversion efficiency

Abstract

The application relates to an ALD multilayer film deposition method for improving photoelectric conversion efficiency, which uses trimethylaluminum (Al(CH3)3) as an aluminum source, uses O3 or H2O as an oxygen source precursor, alternately introduces the aluminum source and the oxygen source into an atomic layer deposition plating film equipment, sequentially forms loose deposition layers, dense deposition layers and hydrogen-rich deposition layers on a silicon surface to form an ALD multilayer film, adjusts the introduction time length of Al(CH3)3, O3 or H2O to control the state of the deposition layers, improves the negative electricity carrying capacity, physical passivation effect and chemical passivation effect of the deposition layers, and further improves the photoelectric conversion efficiency of a solar cell.

Description

Technical Field

[0001] This invention relates to the field of crystalline silicon solar cell manufacturing, and more specifically to an ALD multilayer film deposition method for improving photoelectric conversion efficiency. Background Technology

[0002] Atomic layer deposition (ALD) is an ordered vapor phase coating technique that can prepare fully conformal and pinhole-free thin films. Atomic layer deposited alumina has the characteristics of high dielectric constant, good thermal stability, low preparation temperature, and high fixed negative charge density. Based on the good performance of ALD technology in improving the conversion efficiency of crystalline silicon solar cells through surface passivation, ALD technology has developed rapidly in the photovoltaic industry. These conditions also determine the advantages of alumina as a passivation film.

[0003] In existing technologies, alumina is deposited by atomic layer deposition using trimethylaluminum (Al(CH3)3) as the aluminum source and O3 or H2O as the oxygen precursor, which is alternately introduced into a cavity to prepare alumina thin films on the silicon wafer surface. The alumina films prepared by existing technologies are single-layer or double-layer films, which play a certain role in improving the photoelectric conversion efficiency of high-efficiency crystalline silicon solar cells, but the improvement is limited. Therefore, a new technology is needed to overcome these shortcomings and further improve the photoelectric conversion efficiency of solar cells. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an ALD multilayer film deposition method to improve photoelectric conversion efficiency. The aim is to further enhance the photoelectric conversion efficiency of solar cells by improving the deposition method.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for depositing ALD multilayer films to improve photoelectric conversion efficiency uses trimethylaluminum (Al(CH3)3) as the aluminum source and O3 and H2O as oxygen source precursors. The specific deposition method includes the following steps:

[0007] Step 1): Silicon wafer pretreatment;

[0008] Typically, after the cleaning process, a layer of atoms terminated by hydroxyl groups is formed on the surface of the silicon wafer. However, this layer of atoms terminated by hydroxyl groups does not cover the entire surface; there will be some defects where dangling bonds are formed, as shown in the attached diagram. Figure 1 As shown;

[0009] In the figure, the black vertical bonds on the silicon atoms on the silicon surface that are not connected to hydroxyl groups are dangling bonds. Dangling bonds are prone to minority carrier recombination, which reduces photoelectric conversion efficiency. The present invention can eliminate these dangling bonds by pre-treating the silicon wafer, making up for the defects of the hydroxyl termination layer and improving the passivation effect.

[0010] Step 2): Al(CH3)3 and O3 are alternately introduced onto the pretreated surface of the silicon wafer. The Al(CH3)3 introduction time is 1-3s and the O3 introduction time is 2-4s. Inert gas is used to purge between the alternations to generate an aluminum oxide layer. This process is repeated 3-6 times to obtain a loose deposition layer.

[0011] Specifically, Al(CH3)3 is introduced for 2 seconds, and O3 is introduced for 2 seconds, alternating between the two for purging with inert gas, for a total of 6 alternations. When Al(CH3)3 is introduced, it adsorbs onto the hydroxyl groups on the silicon surface or onto the hydroxyl groups on the surface of the already deposited alumina layer, undergoing adsorption substitution with the hydroxyl groups. This forms an atomic layer terminated with -O-Al(CH3)2 on the previous surface, generating CH4 gas. N2 is then introduced for purging, and excess Al(CH3)3 and CH4 gas that did not undergo adsorption substitution on the surface are removed by vacuum. The reaction equation is as follows:

[0012] Si-OH * →Si-O-Al(CH3)2 * +CH4

[0013] Or Al-OH * +Al(CH3)3 * →Al-O-Al(CH3)2 * +CH4

[0014] The asterisk (*) indicates a group that can participate in the reaction; when Al(CH3)3 is first introduced, it is Si-OH. * With Al(CH3)3 * An adsorption-substitution reaction occurs, and when Al(CH3)3 is subsequently introduced, it becomes Al-OH. * With Al(CH3)3 * An adsorption-substitution reaction occurs.

[0015] Its structure is shown in the attached diagram. Figure 2 As shown;

[0016] When O3 is introduced, it causes the methyl groups on the surface of -O-Al(CH3)2 to become Al-O bonds and atomic layers terminated with -OH, releasing oxygen and ethylene gas. The purge gas carries away excess O3 and byproducts from the reaction chamber. The reaction equation is as follows:

[0017] 2AlCH3 * +3O3→2Al(OH) * +C2H4+2O2

[0018] Its structure is shown in the attached diagram. Figure 3 As shown;

[0019] The above steps alternately form one layer of alumina each time, repeating 3-6 times to obtain a loose deposited layer. The structure of the loose deposited layer (partially) is shown in the attached figure. Figure 4 As shown;

[0020] The upper part of the figure is the open structure, and the lower part is the substrate. Because the Al(CH3)3 and O3 are introduced for a shorter time, Al(CH3)3 cannot completely adsorb and replace the hydroxyl groups on the silicon wafer surface. This leaves unadsorbed hydroxyl groups on SiO2, making the grown alumina film structure more open and enhancing its ability to fix negative charges.

[0021] Step 3): Al(CH3)3 and O3 are alternately introduced onto the loose deposited layer surface. The Al(CH3)3 introduction time is 4-8s and the O3 introduction time is 5-10s. Inert gas is used to purge between the alternations to generate an alumina layer. This alternation is repeated 7-10 times to obtain a dense deposited layer.

[0022] When Al(CH3)3 is introduced, it adsorbs onto the hydroxyl groups on the surface of the alumina layer and undergoes adsorption substitution with the hydroxyl groups on the silicon surface, forming an atomic layer terminated with -O-Al(CH3)2 on the silicon surface and generating CH4 gas. Excess Al(CH3)3 and CH4 gas that did not undergo the adsorption substitution reaction are removed by purging with N2 and vacuuming out. The reaction equation is as follows:

[0023] Al-OH * +Al(CH3)3 * →Si-O-Al(CH3)2 * +CH4

[0024] The asterisk (*) indicates a group that can participate in the reaction.

[0025] When O3 is introduced, it causes the methyl groups on the surface of -O-Al(CH3)2 to become Al-O bonds and atomic layers terminated with -OH, releasing oxygen and ethylene gas. The purge gas carries away excess O3 and byproducts from the reaction chamber. The reaction equation is as follows:

[0026] 2AlCH3 * +3O3→2Al(OH) * +C2H4+2O2

[0027] The above steps are repeated 7-10 times, alternating layers of alumina to form one layer at a time, resulting in a dense deposition layer. The structure of this dense deposition layer (partial) is shown in the attached figure. Figure 5 As shown;

[0028] The upper part of the figure is a dense deposition layer, and the lower part is a loose deposition layer. The extended Al(CH3)3 and O3 introduction time, with sufficient Al(CH3)3 and O3, can prepare a relatively dense film layer, ensuring complete coverage of the silicon wafer surface and having a good step coverage rate.

[0029] Step 4): Al(CH3)3 and H2O are alternately introduced onto the surface of the dense deposition layer. The Al(CH3)3 introduction time is 3-8s and the H2O introduction time is 5-10s. Inert gas is used to purge between the alternations to generate an alumina layer. This process is repeated 10-20 times to obtain a hydrogen-rich deposition layer.

[0030] When Al(CH3)3 is introduced, it adsorbs onto the hydroxyl groups on the surface of the alumina layer and undergoes adsorption substitution with the hydroxyl groups on the silicon surface, forming an atomic layer terminated with -O-Al(CH3)2 on the silicon surface and generating CH4 gas. Excess Al(CH3)3 and CH4 gas that did not undergo the adsorption substitution reaction are removed by purging with N2 and vacuuming out. The reaction equation is as follows:

[0031] Al-OH * +Al(CH3)3 * →AL-O-Al(CH3)2 * +CH4

[0032] The asterisk (*) indicates a group that can participate in the reaction.

[0033] When H2O is introduced, it causes the methyl groups on the surface of -O-Al(CH3)2 to become Al-O bonds and atomic layers terminated with -OH, releasing CH4 gas. The purge gas carries away excess H2O and byproducts from the reaction chamber. The reaction equation is as follows:

[0034] AlCH3 * +H₂O→Al(OH) * +CH4

[0035] The above steps alternately form one layer of alumina each time, repeated 10-20 times, to obtain a hydrogen-rich deposition layer. The structure of the hydrogen-rich deposition layer (partial) is shown in the attached figure. Figure 6 As shown;

[0036] Using H2O as the oxygen source, the prepared alumina film is rich in Al-OH. During annealing, H atoms in the Al-OH structure are released during the annealing process. Some H atoms remain in the Al2O3 lattice or at the interface of different deposition layers, or combine with dangling bonds, which reduces the interface defect state density, which is beneficial to hydrogen passivation and enhances the chemical passivation effect of alumina. Furthermore, the physical passivation effect is ensured through the gradually thickened deposition layer.

[0037] Step 5): The loose deposited layer, dense deposited layer and hydrogen-rich deposited layer obtained in Steps 2), 3), and 4) together form an ALD multilayer film.

[0038] Furthermore, the silicon wafer pretreatment process in step 1) is based on the alternating introduction of O3 and N2 onto the cleaned silicon wafer surface. The O3 introduction time is 3-10s, the N2 introduction time is 5-15s, and the temperature inside the atomic layer deposition coating equipment is 230℃-250℃, alternating 3-10 times.

[0039] The present invention pretreats silicon wafers with ozone, which enables oxygen to bond with the dangling bond, forming a Si-O structure at this point, compensating for the defects of the hydroxyl termination layer, and forming SiO2 after the subsequent annealing process, thereby improving the passivation effect.

[0040] Furthermore, the temperature inside the cavity of the atomic layer deposition coating equipment in steps 2)-4) is 190-250℃.

[0041] Furthermore, the temperature inside the cavity of the atomic layer deposition coating equipment in steps 2)-4) is 210-230℃.

[0042] When the chamber temperature is set relatively high, the adsorption and substitution reaction between Al(CH3)3 and silanol groups is accelerated, leading to a decrease in photoelectric conversion efficiency. When the chamber temperature is set relatively low, the adsorption and substitution reaction between Al(CH3)3 and silanol groups can be suppressed. An appropriate process temperature can hinder the physical adsorption of molecules on the surface. However, when the chamber temperature is too low, the production state is unstable and the photoelectric conversion efficiency of the product fluctuates greatly. Therefore, this invention optimizes the temperature range to achieve the best photoelectric conversion efficiency and ensure stable production.

[0043] Furthermore, the inert gas in steps 2) to 4) is nitrogen.

[0044] Furthermore, the O3 concentration in steps 1)-3) is 300 g / m³. 3 In steps 2)-4), the temperature of the Al(CH3)3 storage tank is 40℃-70℃, the temperature of the Al(CH3)3 pipeline is 50℃-80℃, the pressure of the Al(CH3)3 pipeline is 20-40 Torr, and the purging flow rate in steps 1)-4) is 10000-15000 sccm.

[0045] Furthermore, in step 4), the temperature of the H2O storage tank is 40℃-60℃, the temperature of the H2O pipeline is 50℃-70℃, and the pressure of the H2O pipeline is 40-70 Torr.

[0046] By setting specific parameters, hydrogen-rich deposition layers can be grown stably and rapidly, enhancing the passivation effect.

[0047] The beneficial effects of the present invention through the above technical solution are as follows:

[0048] The ALD multilayer film deposition method disclosed in this invention can significantly improve the passivation effect of alumina and enhance the photoelectric conversion efficiency of crystalline silicon solar cells, thus having good economic and social benefits.

[0049] This invention uses O3 and H2O as oxygen source precursors to prepare ALD multilayer films. First, O3 is used to oxidize the silicon wafer surface, which helps to eliminate defects on the silicon wafer surface. On the one hand, it is beneficial to enhance the field passivation effect of alumina; on the other hand, the SiO2 formed after annealing will also reduce the interface defect density and play a role in chemical passivation.

[0050] The growth of the ALD multilayer film of this invention is carried out in three steps. The first two layers use O3 as the oxygen source, and different Al(CH3)3 and O3 introduction times are designed. The loose deposition layer uses a shorter Al(CH3)3 and O3 introduction time, and the cavity temperature is set relatively lower than that of the ozone pretreatment process. The grown alumina layer has a more open structure to enhance its ability to fix negative charges. The dense deposition layer uses a longer Al(CH3)3 and O3 introduction time to prepare a denser film layer, ensuring complete coverage of the silicon wafer surface and good step coverage. The hydrogen-rich deposition layer uses H2O as the oxygen source. The prepared alumina layer is rich in H, which is beneficial for hydrogen passivation and enhances the chemical passivation effect of the alumina layer.

[0051] This invention employs ozone pretreatment of silicon wafers followed by the deposition of loose, dense, and hydrogen-rich deposition layers. This combination of layers significantly enhances photoelectric conversion efficiency. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the silicon pretreatment structure of the present invention;

[0053] Figure 2 This is a schematic diagram of the structure of Al(CH3)3 undergoing adsorption and substitution with hydroxyl groups according to the present invention;

[0054] Figure 3 This is a schematic diagram of the structure of the O3 oxidation of the methyl group on the surface of -O-Al(CH3)2 according to the present invention;

[0055] Figure 4 This is a schematic diagram of the connection between the unblocking structure and the substrate of the present invention;

[0056] Figure 5 This is a schematic diagram of the structure connecting the dense deposition layer and the loose deposition layer of the present invention;

[0057] Figure 6 This is a partial schematic diagram of the structure of the hydrogen-rich deposition layer of the present invention. Detailed Implementation

[0058] An ALD multilayer film deposition method for improving photoelectric conversion efficiency uses trimethylaluminum (Al(CH3)3) as the aluminum source, O3 or H2O as the oxygen source precursor, and high-purity nitrogen as the purge gas. The method involves depositing an ALD multilayer film on a silicon wafer within an atomic layer deposition equipment, forming an ALD multilayer film on the silicon surface consisting of a loose deposition layer, a dense deposition layer, and a hydrogen-rich deposition layer, arranged sequentially from bottom to top. The invention is further described below with reference to the accompanying drawings and specific embodiments:

[0059] Example 1:

[0060] 1. The silicon wafers that have completed the previous process are placed into the aluminum boat of the ALD process through the wafer insertion machine. The furnace door of the ALD machine is opened, and the aluminum boat filled with silicon wafers to be processed is transported into the process chamber by the boat transfer mechanism. The furnace door is then closed.

[0061] 2. Evacuate the process chamber to a low pressure of 0.015 Torr; then heat the process chamber to a temperature range of 230℃; finally, check for leaks in the process chamber, with the leak rate controlled within 0.1 Torr / min.

[0062] 3: Purge the process chamber with nitrogen gas before the process begins. The nitrogen purging flow rate is 12000 sccm and the purging time is 120s.

[0063] 4. Silicon wafer pretreatment: The chamber temperature is set to 230℃, the O3 flow rate is set to 8000 sccm, the O3 vent valve is opened for a pulse duration of 3 seconds, and the O3 vent valve is closed for a waiting time of 5 seconds; then nitrogen purging is performed, the nitrogen flow rate is set to 12000 sccm, the nitrogen purging valve is opened for a purging duration of 8 seconds, and the nitrogen purging valve is closed for a waiting time of 5 seconds; repeat the above process 5 times.

[0064] 5. Preparation of a loose deposition layer: The chamber temperature was set to 190℃. Al(CH3)3 and O3 were used as growth sources, and alternating pulses were introduced into the chamber. The temperature of the Al(CH3)3 storage tank was set to 65℃, the temperature of the Al(CH3)3 pipeline was set to 75℃, and the pressure of the Al(CH3)3 pipeline was controlled at 35 Torr. The Al(CH3)3 vent valve was opened for a 2-second venting pulse, and closed for a 4-second waiting period. Then, nitrogen purging was performed with a nitrogen flow rate of 1200 Nm³ / h. 0ccm, open the nitrogen purge valve for 6s, close the nitrogen purge valve and wait for 5s; set the O3 concentration to 300g / m3, the O3 flow rate to 9000sccm, open the O3 vent valve for 2s pulse duration, close the O3 vent valve and wait for 4s, then perform nitrogen purge, set the nitrogen flow rate to 12000sccm, open the nitrogen purge valve for 5s purge duration, close the nitrogen purge valve and wait for 6s, repeat the above process 6 times to obtain a loose deposit layer.

[0065] 6. Dense deposition layer preparation: The chamber temperature was set to 190℃. Al(CH3)3 and O3 were used as growth sources, and alternating pulses were introduced into the chamber. The Al(CH3)3 storage tank temperature was set to 65℃, the Al(CH3)3 pipeline temperature was set to 75℃, and the Al(CH3)3 pipeline pressure was controlled at 35 Torr. The Al(CH3)3 vent valve was opened for a 4-second venting pulse, and closed for a 6-second waiting period. Then, nitrogen purging was performed with a nitrogen flow rate of 1200 Nm³ / h. The nitrogen purging valve is opened at 0 sccm for 6 seconds, and then closed for 6 seconds. The O3 concentration is set to 300 g / m3, the O3 flow rate is set to 5000 sccm, the O3 vent valve is opened for 8 seconds, and then closed for 6 seconds. Then, nitrogen purging is performed with a nitrogen flow rate of 12000 sccm. The nitrogen purging valve is opened for 5 seconds, and then closed for 6 seconds. The above process is repeated 8 times to obtain a dense deposition layer.

[0066] 7. Preparation of the hydrogen-rich deposition layer: The chamber temperature was set to 190℃. Al(CH3)3 and H2O were used as the growth source, and alternating pulses were introduced into the chamber. The temperature of the Al(CH3)3 storage tank was set to 65℃, the temperature of the Al(CH3)3 pipeline was set to 70℃, and the pressure of the Al(CH3)3 pipeline was controlled at 35 Torr. The Al(CH3)3 vent valve was opened for a 5-second venting pulse, and closed for a 6-second waiting period. Then, nitrogen purging was performed with a nitrogen flow rate of 12000 sccm. The purging valve is purged for 5 seconds, and the nitrogen purging valve is closed for 6 seconds. The H2O storage tank temperature is set to 50℃, the H2O pipeline temperature is set to 60℃, and the H2O pipeline pressure is controlled at 50 Torr. The H2O vent valve is opened for a 5-second venting pulse, and then closed for 6 seconds. Nitrogen purging is then performed with a flow rate of 12000 sccm. The nitrogen purging valve is opened for 5 seconds, and then closed for 6 seconds. The above process is repeated 10 times to obtain a hydrogen-rich deposition layer.

[0067] 8: The loose deposited layer, dense deposited layer and hydrogen-rich deposited layer obtained by sequential deposition together form an ALD multilayer film. After the process, nitrogen is purged at a flow rate of 12000 sccm for 120 s.

[0068] 9: Evacuate the cavity to remove all gas and ensure no reaction residue remains.

[0069] 10: Fill the chamber with nitrogen until the pressure reaches atmospheric pressure, in preparation for opening the furnace door.

[0070] 11: Open the furnace door, unload the aluminum boat. The boat handling mechanism transports the finished aluminum boat out of the furnace. Close the furnace door, and the aluminum boat enters the wafer unloading mechanism to unload the finished silicon wafers into the carrying basket and transfer them to the next process.

[0071] Example 2:

[0072] All other parameters are the same as in Example 1, except that:

[0073] The cavity temperature was set to 210℃ during the preparation of loose, dense, and hydrogen-rich deposition layers.

[0074] Example 3:

[0075] All other parameters are the same as in Example 1, except that:

[0076] The cavity temperature was set to 230°C during the preparation of loose, dense, and hydrogen-rich deposition layers.

[0077] Example 4:

[0078] All other parameters are the same as in Example 1, except that:

[0079] The cavity temperature was set to 250°C during the preparation of loose, dense, and hydrogen-rich deposition layers.

[0080] Comparative Example 1:

[0081] 1. The silicon wafers that have completed the previous process are placed into the aluminum boat of the ALD process through the wafer insertion machine. The furnace door of the ALD machine is opened, and the aluminum boat filled with silicon wafers to be processed is transported into the process chamber by the boat transfer mechanism. The furnace door is then closed.

[0082] 2. Evacuate the process chamber to a low pressure of 0.015 Torr; then heat the process chamber to a temperature range of 210℃; finally, check for leaks in the process chamber, with the leak rate controlled within 0.1 Torr / min.

[0083] 3: Purge the process chamber with nitrogen gas before the process begins. The nitrogen purging flow rate is 12000 sccm and the purging time is 120s.

[0084] 4. Dense deposition layer preparation: The chamber temperature was set to 210℃. Al(CH3)3 and O3 were used as growth sources, and alternating pulses were introduced into the chamber. The Al(CH3)3 storage tank temperature was set to 65℃, the Al(CH3)3 pipeline temperature was set to 75℃, and the Al(CH3)3 pipeline pressure was controlled at 35 Torr. The Al(CH3)3 vent valve was opened for a 5s venting pulse duration, and closed for a 4s waiting period. Then, nitrogen purging was performed with a nitrogen flow rate of 1200. 0ccm, open the nitrogen purge valve for 6s, close the nitrogen purge valve and wait for 5s; set the O3 concentration to 300g / m3, the O3 flow rate to 8000sccm, open the O3 vent valve for 6s pulse duration, close the O3 vent valve and wait for 5s, then perform nitrogen purge, set the nitrogen flow rate to 12000sccm, open the nitrogen purge valve for 5s purge duration, close the nitrogen purge valve and wait for 6s, repeat the above process, cycle 15 times, to obtain a dense deposition layer.

[0085] 5. Preparation of the hydrogen-rich deposition layer: The chamber temperature was set to 210℃. Al(CH3)3 and H2O were used as the growth source, and alternating pulses were introduced into the chamber. The temperature of the Al(CH3)3 storage tank was set to 65℃, the temperature of the Al(CH3)3 pipeline was set to 70℃, and the pressure of the Al(CH3)3 pipeline was controlled at 35 Torr. The Al(CH3)3 vent valve was opened for a 5-second venting pulse, and closed for a 6-second waiting period. Then, nitrogen purging was performed with a nitrogen flow rate of 12000 sccm. The purging valve is purged for 5 seconds, and the nitrogen purging valve is closed for 6 seconds. The H2O storage tank temperature is set to 50℃, the H2O pipeline temperature is set to 60℃, and the H2O pipeline pressure is controlled at 50 Torr. The H2O vent valve is opened for a 5-second venting pulse, and then closed for 6 seconds. Nitrogen purging is then performed with a flow rate of 12000 sccm. The nitrogen purging valve is opened for 5 seconds, and then closed for 6 seconds. The above process is repeated 10 times to obtain a hydrogen-rich deposition layer.

[0086] 6: Nitrogen purging after the process, with a nitrogen purging flow rate of 12000 sccm and a purging time of 120s.

[0087] 7: Evacuate the cavity to remove all gas and ensure no reaction residue remains.

[0088] 8: Fill the chamber with nitrogen until the pressure reaches atmospheric pressure, in preparation for opening the furnace door.

[0089] 9: Open the furnace door, unload the aluminum boat, and the boat-moving mechanism will transport the finished aluminum boat out of the furnace. Close the furnace door, and the aluminum boat will enter the wafer unloading mechanism to unload the finished silicon wafers into the carrying basket and transfer them to the next process.

[0090] Comparative Example 2:

[0091] 1. The silicon wafers that have completed the previous process are placed into the aluminum boat of the ALD process through the wafer insertion machine. The furnace door of the ALD machine is opened, and the aluminum boat filled with silicon wafers to be processed is transported into the process chamber by the boat transfer mechanism. The furnace door is then closed.

[0092] 2. Evacuate the process chamber to a low pressure of 0.015 Torr; then heat the process chamber to a temperature range of 210℃; finally, check for leaks in the process chamber, with the leak rate controlled within 0.1 Torr / min.

[0093] 3: Purge the process chamber with nitrogen gas before the process begins. The nitrogen purging flow rate is 12000 sccm and the purging time is 120s.

[0094] 4. Silicon wafer pretreatment: The chamber temperature is set to 210℃, the O3 flow rate is set to 8000 sccm, the O3 vent valve is opened for a pulse duration of 3 seconds, and the O3 vent valve is closed for a waiting time of 5 seconds; then nitrogen purging is performed, the nitrogen flow rate is set to 12000 sccm, the nitrogen purging valve is opened for a purging duration of 8 seconds, and the nitrogen purging valve is closed for a waiting time of 5 seconds; repeat the above process 5 times.

[0095] 5. Dense deposition layer preparation: The chamber temperature was set to 210℃. Al(CH3)3 and O3 were used as growth sources, alternately pulsed into the chamber. The Al(CH3)3 storage tank temperature was set to 65℃, the Al(CH3)3 pipeline temperature was set to 75℃, and the Al(CH3)3 pipeline pressure was controlled at 35 Torr. The Al(CH3)3 vent valve was opened for a 4s venting pulse duration, and closed for a 6s waiting period. Nitrogen purging was then performed with a flow rate of 12000ccm. The nitrogen purging valve was opened for a 6s purging duration, and closed for a 6s waiting period. The O3 concentration was set to 300g / m³. 3 The O3 flow rate is set to 8000 sccm, the O3 vent valve is opened for a pulse duration of 8 seconds, the O3 vent valve is closed for a waiting time of 6 seconds, and then nitrogen purging is performed. The nitrogen flow rate is set to 12000 sccm, the nitrogen purging valve is opened for a purging time of 5 seconds, the nitrogen purging valve is closed for a waiting time of 6 seconds, and the above process is repeated for 25 cycles to obtain a dense deposition layer.

[0096] 6: Nitrogen purging after the process, with a nitrogen purging flow rate of 12000 sccm and a purging time of 120s.

[0097] 7: Evacuate the cavity to remove all gas and ensure no reaction residue remains.

[0098] 8: Fill the chamber with nitrogen until the pressure reaches atmospheric pressure, in preparation for opening the furnace door.

[0099] 9: Open the furnace door, unload the aluminum boat, and the boat-moving mechanism will transport the finished aluminum boat out of the furnace. Close the furnace door, and the aluminum boat will enter the wafer unloading mechanism to unload the finished silicon wafers into the carrying basket and transfer them to the next process.

[0100] Comparative Example 3: Using ALD single-layer membrane technology

[0101] 1. The silicon wafers that have completed the previous process are placed into the aluminum boat of the ALD process through the wafer insertion machine. The furnace door of the ALD machine is opened, and the aluminum boat filled with silicon wafers to be processed is transported into the process chamber by the boat transfer mechanism. The furnace door is then closed.

[0102] 2. Evacuate the process chamber to a low pressure of 0.015 Torr; then heat the process chamber to a temperature range of 210℃; finally, check for leaks in the process chamber, with the leak rate controlled within 0.1 Torr / min.

[0103] 3: Purge the process chamber with nitrogen gas before the process begins. The nitrogen purging flow rate is 12000 sccm and the purging time is 120s.

[0104] 4. Dense deposition layer preparation: The chamber temperature was set to 210℃. Al(CH3)3 and O3 were used as growth sources, and alternating pulses were introduced into the chamber. The Al(CH3)3 storage tank temperature was set to 65℃, the Al(CH3)3 pipeline temperature was set to 75℃, and the Al(CH3)3 pipeline pressure was controlled at 35 Torr. The Al(CH3)3 vent valve was opened for a 4-second venting pulse, and closed for a 4-second waiting period before nitrogen purging was performed at a flow rate of 1200 Nm³ / h. 0ccm, open the nitrogen purge valve for 6s, close the nitrogen purge valve and wait for 5s; set the O3 concentration to 300g / m3, the O3 flow rate to 7000sccm, open the O3 vent valve for 5s pulse duration, close the O3 vent valve and wait for 4s, then perform nitrogen purge, set the nitrogen flow rate to 12000sccm, open the nitrogen purge valve for 5s purge duration, close the nitrogen purge valve and wait for 6s, repeat the above process, cycle 25 times, to obtain a dense deposition layer.

[0105] 5: Nitrogen purging after the process, with a nitrogen purging flow rate of 12000 sccm and a purging time of 120s.

[0106] 6: Evacuate the cavity to remove all gas and ensure no reaction residue remains.

[0107] 7: Fill the chamber with nitrogen until the pressure reaches atmospheric pressure, in preparation for opening the furnace door.

[0108] 8: Open the furnace door, unload the aluminum boat, and the boat-moving mechanism will transport the finished aluminum boat out of the furnace. Close the furnace door, and the aluminum boat will enter the wafer unloading mechanism to unload the finished silicon wafers into the carrying basket and transfer them to the next process.

[0109] After the previous process is completed, the 7,000 silicon wafers are slitting and divided into seven groups of 1,000 wafers each. Each group is processed using an embodiment or comparative example of ALD (Alternating Deposition) process. After the ALD process is completed, the four groups of 1,000 wafers are sent down the same path. After screen printing, the electrical performance data of the solar cells are statistically analyzed, as shown in the table below. The comparison results show that the process of this invention can make the solar cells achieve higher photoelectric conversion efficiency and stronger surface passivation effect.

[0110]

[0111] As can be seen from the table above, the photoelectric conversion effect of Examples 1-4 of the present invention is higher than that of the comparative examples. Furthermore, the combination of ozone pretreatment, loose deposition layer, dense deposition layer and hydrogen-rich deposition layer in the present invention has a more significant improvement over the prior art and has unique effects.

[0112] In embodiments of the present invention, the loose deposition layer uses a shorter Al(CH3)3 and O3 introduction time, resulting in a more open structure of the grown alumina layer, which enhances its ability to fix negative charges. The dense deposition layer uses a longer Al(CH3)3 and O3 introduction time, resulting in a denser film layer that ensures complete coverage of the silicon wafer surface and has a better step coverage rate. The increase in open-circuit voltage indicates an enhanced passivation effect of the prepared multilayer alumina structure. The hydrogen-rich deposition layer is rich in hydrogen, which can form a chemical passivation effect. Furthermore, the ALD multilayer film composed of the loose deposition layer, the dense deposition layer, and the hydrogen-rich deposition layer has more unexpected effects.

[0113] The loose deposition layer contains more hydroxyl groups, which helps to adsorb more negative charges on the silicon wafer surface. This forms an electric field shielding effect with the minority electrons in the silicon wafer, reducing minority carrier recombination and improving minority carrier lifetime. The dense deposition layer has a fully conformal structure, which can reduce the escape of hydroxyl groups and hydrogen bonds, ensuring the passivation effect of the film. Both the loose and dense deposition layers use ozone as an oxygen source, which has a strong ability to capture defects and can reduce defect states in the film and on the surface. The hydrogen-rich deposition layer uses water as an oxygen source and has a high hydrogen content. It can combine with silicon nitride in the coating process to improve the hydrogen passivation effect of the silicon wafer.

[0114] Because the surface defects of the silicon wafer are reduced, it is beneficial to the collection of current in the solar cell, which increases the short-circuit current by more than 30mA in the electrical performance parameters of the present invention, and the photoelectric conversion efficiency of the solar cell can be increased by more than 0.08%. Compared with simple alumina deposition, the photoelectric conversion efficiency of the solar cell can be increased by more than 0.16%. Therefore, the use of this embodiment has the effect of significantly enhancing the photoelectric conversion efficiency of crystalline silicon solar cells, and has good economic and social benefits.

[0115] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various modifications can be made to the technical solutions of the present invention without departing from the spirit of the present invention or the scope of disclosure.

Claims

1. A method for depositing ALD multilayer films to improve photoelectric conversion efficiency, using trimethylaluminum (Al(CH3)3) as the aluminum source and O3 and H2O as oxygen source precursors, characterized in that, The specific deposition method includes the following steps: Step 1): Silicon wafer pretreatment; Step 2): Al(CH3)3 and O3 are alternately introduced onto the pretreated surface of the silicon wafer. The Al(CH3)3 introduction time is 1-3s and the O3 introduction time is 2-4s. Inert gas is used to purge between the alternations to generate an aluminum oxide layer. This process is repeated 3-6 times to obtain a loose deposition layer. Step 3): Al(CH3)3 and O3 are alternately introduced onto the loose deposited layer surface. The Al(CH3)3 introduction time is 4-8s and the O3 introduction time is 5-10s. Inert gas is used to purge between the alternations to generate an alumina layer. This alternation is repeated 7-10 times to obtain a dense deposited layer. Step 4): Al(CH3)3 and H2O are alternately introduced onto the surface of the dense deposition layer. The Al(CH3)3 introduction time is 3-8s and the H2O introduction time is 5-10s. Inert gas is used to purge between the alternations to generate an alumina layer. This process is repeated 10-20 times to obtain a hydrogen-rich deposition layer. Step 5): The loose deposited layer, dense deposited layer and hydrogen-rich deposited layer obtained in Steps 2), 3), and 4) together form an ALD multilayer film.

2. The ALD multilayer film deposition method for improving photoelectric conversion efficiency according to claim 1, characterized in that, The silicon wafer pretreatment process in step 1) is based on the alternating introduction of O3 and N2 onto the cleaned silicon wafer surface. The O3 introduction time is 3-10s, and the N2 introduction time is 5-15s. The temperature inside the atomic layer deposition coating equipment is 230℃-250℃, and the alternation is repeated 3-10 times.

3. The ALD multilayer film deposition method for improving photoelectric conversion efficiency according to claim 1, characterized in that, The temperature inside the atomic layer deposition coating equipment in steps 2)-4) is 190-250℃.

4. The ALD multilayer film deposition method for improving photoelectric conversion efficiency according to claim 3, characterized in that, The temperature inside the cavity of the atomic layer deposition coating equipment in steps 2)-4) is 210-230℃.

5. The ALD multilayer film deposition method for improving photoelectric conversion efficiency according to claim 1, characterized in that, The inert gas used in steps 2) to 4) is nitrogen.

6. The ALD multilayer film deposition method for improving photoelectric conversion efficiency according to claim 2, characterized in that, The O3 concentration in steps 1)-3) is 300 g / m³. 3 In steps 2)-4), the temperature of the Al(CH3)3 storage tank is 40℃-70℃, the temperature of the Al(CH3)3 pipeline is 50℃-80℃, the pressure of the Al(CH3)3 pipeline is 20-40 Torr, and the purging flow rate in steps 1)-4) is 10000-15000 sccm.

7. The ALD multilayer film deposition method for improving photoelectric conversion efficiency according to claim 1, characterized in that, In step 4), the temperature of the H2O storage tank is 40℃-60℃, the temperature of the H2O pipeline is 50℃-70℃, and the pressure of the H2O pipeline is 40-70 Torr.

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