Method for detecting and optimizing backside passivation process of solar cell silicon wafer

Abstract

A detection method and optimization method of a back surface passivation process of a solar cell silicon wafer, the back surface of the silicon wafer sequentially deposits a plurality of passivation film layers, the detection method comprises: in the back surface passivation process of the silicon wafer, after each layer of the plurality of passivation film layers is deposited on the back surface of the silicon wafer, a PL test step is entered, and a plurality of test silicon wafers with different numbers of passivation film layers are prepared; the relative change of the dark area of the PL image of the plurality of test silicon wafers is compared to determine the passivation film layer with poor passivation effect of the silicon wafer. The present application can more targetedly detect and optimize the specific steps of the back surface passivation process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of photovoltaic cell manufacturing, and particularly relates to a detection method and an optimization method for a back passivation process of a solar cell silicon wafer. BACKGROUND

[0002] With the rapid development of economy and society, energy shortage has become a resistance to hinder the development of human society, and the development of clean renewable energy has become a highly concerned problem in the world. As an important industry in the utilization technology of renewable energy, the photovoltaic industry is developing rapidly. In addition, the photovoltaic industry is constantly innovating the production process of the battery and developing new high-efficiency solar cells, especially the combination of SE technology and PERC technology in recent years.

[0003] SE-PERC technology refers to that the battery silicon wafer is first processed by selective emitter technology and then a dielectric passivation layer is added. The efficiency of the SE-PERC solar cell made in this way is significantly improved. The processing step of adding the dielectric passivation layer is particularly important in the processing process of the SE-PERC solar cell.

[0004] Generally, adding the dielectric passivation layer includes multiple steps such as boat entering, temperature rising, vacuum pumping, leak detection, vacuum pumping, multi-film layer deposition, vacuum pumping, cleaning, nitrogen filling, and boat returning. Multi-film layer deposition requires adding an aluminum oxide layer, a silicon oxynitride layer, a silicon nitride layer, and a silicon oxide layer on the silicon wafer in sequence. The quality of the four back passivation film layers will affect the efficiency of the battery wafer. Therefore, it is necessary to detect whether the plating process of each film layer is normal during production, and to optimize the plating process with problems. SUMMARY

[0005] The present application aims to provide a detection method and an optimization method for a back passivation process of a solar cell silicon wafer, to solve the technical problem of more targeted detection and optimization of specific steps of the back passivation process.

[0006] To solve the above technical problems, the specific technical solutions of the detection method and the optimization method for the back passivation process of the solar cell silicon wafer of the present application are as follows:

[0007] A detection method for a back passivation process of a solar cell silicon wafer, the back surface of the silicon wafer sequentially deposits a plurality of passivation film layers, the detection method comprising:

[0008] In the back passivation process of the silicon wafer, after each layer of the plurality of passivation film layers is deposited on the back surface of the silicon wafer, a PL test step is entered, and a plurality of test silicon wafers with different numbers of passivation film layers are prepared.

[0009] The relative changes of the dark areas of the PL images of the plurality of test silicon wafers are compared to determine whether the passivation effect of the passivation film layers of the silicon wafers is poor.

[0010] Further, the plurality of passivation film layers deposited on the back surface of the silicon wafer in sequence comprises a first film layer, a second film layer, a third film layer, and a fourth film layer.

[0011] After each of the plurality of passivation film layers is deposited on the back surface of the silicon wafer, a PL test step is performed.

[0012] After the step of depositing the first film layer on the back surface of the silicon wafer is completed, a PL test is performed to obtain a PL image of a test silicon wafer with the first film layer deposited thereon.

[0013] After the step of depositing the first film layer and the second film layer on the back surface of the silicon wafer in sequence is completed, a PL test is performed to obtain a PL image of a test silicon wafer with the first film layer and the second film layer deposited thereon.

[0014] After the step of depositing the first film layer, the second film layer, and the third film layer on the back surface of the silicon wafer in sequence is completed, a PL test is performed to obtain a PL image of a test silicon wafer with the first film layer, the second film layer, and the third film layer deposited thereon.

[0015] After the step of depositing the first film layer, the second film layer, the third film layer, and the fourth film layer on the back surface of the silicon wafer in sequence is completed, a PL test is performed to obtain a PL image of a test silicon wafer with the first film layer, the second film layer, the third film layer, and the fourth film layer deposited thereon.

[0016] Further, the first film layer is an aluminum oxide film layer, the second film layer is a silicon oxynitride film layer, the third film layer is a silicon nitride film layer, and the fourth film layer is a silicon oxide film layer.

[0017] Further, the step of depositing the silicon nitride film layer comprises a pre-deposition treatment, and after each of the plurality of passivation film layers is deposited on the back surface of the silicon wafer, the PL test step further comprises: after the step of depositing the first film layer on the back surface of the silicon wafer and the pre-deposition treatment are completed, a PL test is performed to obtain a PL image of a test silicon wafer with the first film layer and the pre-deposition layer deposited thereon.

[0018] As an implementable manner, the comparison of the relative changes of the dark areas of the PL images of the plurality of test silicon wafers comprises comparing the dark areas of the PL images of the plurality of test silicon wafers to observe whether the dark areas of the PL images become larger in area and / or darker in degree.

[0019] As an implementable manner, the PL test uses a PL tester, which is an online PL machine or an offline PL machine.

[0020] As an implementable manner, the method further comprises a verification step, which comprises: in the back surface passivation process of the silicon wafer, depositing other passivation film layers except the passivation film layer with poor passivation effect on the back surface of the silicon wafer, and testing a PL image for evaluation.

[0021] An optimization method of a back surface passivation process of a solar cell silicon wafer, comprising:

[0022] determining the passivation film layer with poor passivation effect of the silicon wafer based on the detection method of the back surface passivation process of the solar cell silicon wafer;

[0023] optimizing the process parameters of depositing the passivation film layer with poor passivation effect.

[0024] As an implementable manner, the optimization step of the process parameters comprises: after adjusting the process parameters, applying the adjusted process parameters to the passivation process, testing a PL image after the passivation film layers on the back surface of the silicon wafer are deposited in sequence to the passivation film layer with poor passivation effect, comparing the PL images after adjusting different process parameters, and determining the optimal process parameters.

[0025] As an implementable manner, the process parameters comprise temperature, deposition time, flow rate, radio frequency power, pressure and / or pulse ratio.

[0026] In summary, the present application has the following beneficial effects: the present application deposits different numbers of passivation film layers on the silicon wafer, tests the silicon wafer after depositing the passivation film layers, obtains a PL image, compares multiple PL images to obtain the passivation film layer with poor passivation effect, improves the process parameters of the passivation film layer with poor passivation effect, and makes the directionality of process improvement higher. In addition, after adjusting and determining the optimal process parameters, the optimal process parameters are applied to the passivation process again, and the passivation process can be continuously optimized after the optimization method is executed, so as to achieve a virtuous cycle. After the optimization method, the blackening ratio of the PL image of the prepared cell wafer is significantly reduced, and the yield is improved by 0.87%. BRIEF DESCRIPTION OF DRAWINGS

[0027] The present application can be well understood and its advantages are more clearly presented when reading the following detailed description of the embodiments, which are illustrated by non-limiting examples. The description refers to the accompanying drawings, in which:

[0028] Figure 1 is a flowchart of the passivation process provided by the present application;

[0029] Figure 2 is a PL image obtained by example 1 of the present application;

[0030] Figure 3 is a PL image obtained by example 2 of the present application;

[0031] The reference signs are: 1, first PL image; 2, second PL image; 3, third PL image; 4, fourth PL image; 5, fifth PL image; 6, sixth PL image; 2a, image without optimization; 2b, first image after optimization; 2c, second image after optimization; 2d, third image after optimization; 2f, fourth image after optimization. DETAILED DESCRIPTION

[0032] The production process of the P-type SE-PERC solar cell in the application is to sequentially perform front process treatments such as texturing, diffusion, SE laser doping, chain heat oxygen, PSG (phosphor silicon glass) removal, alkali polishing, and tubular heat oxygen on a P-type raw material silicon wafer to obtain a front-processed silicon wafer; and then the front-processed silicon wafer is transferred into a passivation process to obtain a cell wafer.

[0033] The passivation process is composed of a pre-process, a deposition process, and a post-process, wherein the deposition process includes four key processing steps of depositing an aluminum oxide film layer, depositing a silicon oxynitride film layer, depositing a silicon nitride film layer, and depositing a silicon oxide film layer, and the process parameters in the four key processing steps will directly affect the efficiency of the cell wafer obtained.

[0034] As shown in FIG. 1, the passivation process includes the following steps: Figure 1

[0035] S101, a graphite boat is sent into a furnace tube by using a silicon carbide slurry, the furnace tube is heated to 300-330℃, the air and impurities in the furnace tube are evacuated by using a vacuum pump, the vacuum pump is closed, and the air tightness of the furnace tube is checked;

[0036] S102, the vacuum pump is opened to evacuate the furnace tube, TMA (trimethylaluminum) and N2O (laughing gas) are introduced, the back surface of the raw material silicon wafer is deposited, an aluminum oxide passivation film layer with a thickness of about 10 nm is deposited, and a silicon wafer plated with the aluminum oxide passivation film layer is obtained;

[0037] S103, the residual gas in the furnace tube is evacuated, the furnace tube is heated to 430-450℃, NH3 (ammonia) and N2O are introduced to perform pre-deposition on the aluminum oxide passivation film layer to improve the passivation effect of the aluminum oxide passivation film layer, further, NH3, N2O, and SiH4 (silicon tetrahydride) are introduced to deposit a silicon oxynitride film layer on the pre-deposition layer of the raw material silicon wafer to further improve the passivation effect of the aluminum oxide passivation film layer;

[0038] S104, the furnace tube is evacuated, NH3 and SiH4 are introduced to deposit three layers of silicon nitride film layers with different deposition times and different NH3 / SiH4 ratios on the silicon oxynitride film layer, and in some embodiments, the silicon nitride film layer can also be deposited in two layers;

[0039] ​S105, residual gas in the furnace tube is evacuated, and a silicon nitride film layer is deposited on the silicon nitride film layer by using N2O and SiH4 as gas sources;

[0040] S106, residual gas in the furnace tube is evacuated, and nitrogen is introduced to clean the furnace tube, and then the pressure in the furnace tube is adjusted to balance with the external pressure by nitrogen, the furnace door is opened, and the graphite boat after the process is taken out.

[0041] Step S101 is a pre-process, which is used to check the air tightness of the furnace tube and prepare for the subsequent deposition process; step S102 is a step of depositing an aluminum oxide film layer, which can deposit an aluminum oxide film layer on the back of a silicon wafer; step S103 is a step of depositing a silicon oxynitride film layer, which needs to perform a pre-deposition process and a silicon oxynitride deposition process, and the pre-deposition process and the silicon oxynitride deposition process can inject O atoms into the passivation film layer, so that a SiO x layer for valence electron transmission is formed at the interface, the proportion of Al-O tetrahedral structure of AlO x is improved, and the proportion of Si-O bond is increased, thereby playing a role of enhancing passivation effect; S104 is a step of depositing a silicon nitride film layer, which can be used as an outer surface cover layer to further enhance the passivation effect; S105 is a step of depositing a silicon oxide film layer, and the refractive index and extinction coefficient of the silicon oxide film layer are lower than those of the silicon nitride film layer, which can further increase light absorption and improve passivation; S106 is a subsequent process, which first performs cleaning and then balances the pressure by nitrogen, and finally opens the furnace door, so that safe unloading work can be realized, and the pollution of the finished product is reduced.

[0042] The prior art mainly collects a PL image of a battery piece after a passivation process to determine the passivation effect, but in the deposition process of each passivation film layer in steps S102-S105, multiple parameters such as deposition temperature, deposition time, gas flow, radio frequency power, pressure in the furnace tube, and pulse ratio need to be set according to the on-site process, and it is difficult to determine the process step that causes poor passivation effect in the deposition process by only using the PL image measured by the prior art method, so that the direction of process improvement is not strong.

[0043] The PL test of the present application adopts a PL tester, which can be an online PL machine or an offline PL machine.

[0044] In order to solve the above problems, the detection method and optimization method of the back passivation process of the solar cell silicon wafer will be described in further detail below in combination with the drawings.

[0045] Embodiment 1

[0046] The embodiment provides a detection method and optimization method of a back passivation process of a solar cell silicon wafer, which is mainly applied to the preparation process of an SE-PERC solar cell or a PERC solar cell, and the method comprises:

[0047] After each layer of the plurality of passivation film layers is deposited on the back surface of the silicon wafer in the back surface passivation process, the PL test step is entered, and a plurality of test silicon wafers with different numbers of passivation film layers are prepared;

[0048] The dark area of the PL image of the plurality of test silicon wafers is compared to determine the passivation film layer with poor passivation effect of the silicon wafer.

[0049] The back surface of the solar cell silicon wafer provided in the embodiment will sequentially deposit a plurality of passivation film layers in the passivation process. The plurality of passivation film layers deposited on the back surface of the silicon wafer can be two layers, three layers, four layers or more. In the embodiment, the plurality of passivation film layers deposited on the back surface of the silicon wafer is four layers, i.e. a first film layer, a second film layer, a third film layer and a fourth film layer are sequentially deposited on the back surface of the silicon wafer. Preferably, in the embodiment, the plurality of passivation film layers sequentially deposited on the back surface of the solar cell silicon wafer in the passivation process includes an aluminum oxide film layer, a silicon oxynitride film layer, a silicon nitride film layer and a silicon oxide film layer.

[0050] The detection method of the passivation process provided in the embodiment includes:

[0051] After the step A1 of depositing the first film layer on the back surface of the silicon wafer is completed, the PL test is performed to obtain the PL image of the test silicon wafer with the first film layer deposited;

[0052] After the step A2 of sequentially depositing the first film layer and the second silicon film layer on the back surface of the silicon wafer is completed, the PL test is performed to obtain the PL image of the test silicon wafer with the first film layer and the second film layer deposited;

[0053] After the step A3 of sequentially depositing the first film layer, the second film layer and the third film layer on the back surface of the silicon wafer is completed, the PL test is performed to obtain the PL image of the test silicon wafer with the first film layer, the second film layer and the third film layer deposited;

[0054] After the step A4 of sequentially depositing the first film layer, the second film layer, the third film layer and the fourth film layer on the back surface of the silicon wafer is completed, the PL test is performed to obtain the PL image of the test silicon wafer with the first film layer, the second film layer, the third film layer and the fourth film layer deposited.

[0055] Specifically, the step A1 is to force the process to step S106 after the raw silicon wafer is subjected to step S101 and then subjected to step S102 to deposit an aluminum oxide film layer, so as to prepare a first test silicon wafer, and use a PL tester to detect the first test silicon wafer to obtain a first PL image 1;

[0056] Step A2 is to take the raw silicon wafer through step S101, then through step S102 to deposit an aluminum oxide film layer and step S103 to deposit a silicon oxynitride film layer, and then forcibly jump to step S106 to obtain a third test silicon wafer, and use a PL tester to detect the third test silicon wafer to obtain a third PL image 3.

[0057] Step A3 is to take the raw silicon wafer through step S101, then through step S102 to deposit an aluminum oxide film layer, step S103 to deposit a silicon oxynitride film layer, and step S104 to deposit a silicon nitride film layer, and then forcibly jump to step S106 to obtain a fourth test silicon wafer, and use a PL tester to detect the fourth test silicon wafer to obtain a fourth PL image 4.

[0058] Step A4 is to take the raw silicon wafer through steps S101-S106 in sequence to obtain a fifth test silicon wafer, and the back surface of the fifth test silicon wafer is sequentially deposited with an aluminum oxide film layer, a silicon oxynitride film layer, a silicon nitride film layer, and a silicon oxide film layer, and a PL tester is used to detect the fifth test silicon wafer to obtain a fifth PL image 5.

[0059] Preferably, the step of depositing a silicon nitride film layer in the embodiment also includes a pre-deposition treatment, and the pre-deposition layer formed by the pre-deposition treatment can also have a certain influence, so that after each of the plurality of passivation film layers is deposited on the back surface of the silicon wafer in the embodiment, the PL testing step also includes step A5: after the first film layer is deposited on the back surface of the silicon wafer and the pre-deposition treatment is completed, PL testing is performed to obtain a PL image of the test silicon wafer with the first film layer and the pre-deposition layer deposited thereon.

[0060] Specifically, step A5 is to take the raw silicon wafer through step S101, then through the pre-deposition treatment in step S102, and then forcibly jump to step S106 to obtain a second test silicon wafer, and use a PL tester to detect the second test silicon wafer to obtain a second PL image 2.

[0061] Step B1 compares the relative changes in the dark areas of the PL images of the plurality of test silicon wafers to determine the film layer with poor passivation effect of the silicon wafer.

[0062] Specifically, step B1 compares the relative changes in the dark areas of the PL images of the plurality of test silicon wafers to determine the film layer with poor passivation effect of the silicon wafer.

[0063] More specifically, step B1 involves extracting the first PL image 1, the second PL image 2, the third PL image 3, the fourth PL image 4, the fifth PL image 5, and the sixth PL image 6 obtained in steps A1-A5, and observing whether the dark areas in the multiple PL images show changes in area and / or increased darkness. This helps identify passivation films with poor passivation effects in the test silicon wafer. If the dark areas in the PL images increase in size and / or become darker, it indicates an abnormal change. Since this invention uses a method of sequentially increasing the number of coatings, if the passivation effect of the test silicon wafer is determined to be poor, it can be determined that the last passivation film layer deposited on the test silicon wafer has a poor passivation effect, and the process parameters of the passivation film layer need to be improved. If the dark areas in the PL images do not significantly increase in size and / or significantly become darker, it indicates that the changes in the dark areas in the PL images are normal, and the passivation film process does not need optimization.

[0064] Understandably, the luminescence intensity in a photoluminescence (PL) image is proportional to the minority carrier concentration. Bright areas typically indicate a higher minority carrier concentration, while dark areas show a higher defect concentration. If the overall color of the PL image is relatively uniform, it indicates a uniform minority carrier concentration on the cell surface, suggesting that the current coating process is normal, resulting in a relatively uniform film layer and consistent passivation of the silicon wafer surface. Even if the PL image is dark after depositing a certain film layer, as long as the overall brightness is generally consistent, it indicates that the coating process for that film layer is without problems. Conversely, if the PL image is generally bright after depositing a certain film layer, but has localized dark areas, it indicates a problem with the coating process for that film layer, requiring adjustment.

[0065] To further explain the effectiveness of the detection method for the back passivation process of the solar cell silicon wafer of the present invention, such as... Figure 2 As shown, each passivation film layer has three control groups.

[0066] The first PL image 1 is a PL image of a test silicon wafer with an deposited alumina film. It can be seen that the overall surface of the first PL image 1 is dark, indicating that the alumina film alone has little effect on improving the performance of the silicon wafer. However, the darkness of the PL image is relatively uniform, indicating that there are no obvious problems with the process parameters of the passivation film.

[0067] The second PL image 2 is a PL image of the test silicon wafer after the deposition of an alumina film layer and the pre-deposition treatment. It can be seen that irregular dark stripes appear at the beginning of the second PL image 2, but the overall PL image begins to brighten, indicating that the pre-deposition treatment can play a good role in promoting the performance of the silicon wafer, but the process parameters of the passivation film layer need to be adjusted and optimized.

[0068] The third PL image 3 is a PL image of the test wafer on which the aluminum oxide film layer and the silicon oxynitride film layer are deposited. It can be seen that the third PL image 3 is brighter than the second PL image 2, but there are multiple dark stripes, and the darkness is uneven, indicating that the process parameters of the passivation film layer need to be adjusted and optimized.

[0069] The fourth PL image 4 is a PL image of the test wafer on which the aluminum oxide film layer, the silicon oxynitride film layer, and the silicon nitride film layer are deposited. It can be seen that the fourth PL image 4 is exposed, but there are a small number of irregular dark stripes in the PL image. The stripes may be due to the deposition of the silicon oxynitride film layer leaving more dark stripes, which cannot be completely covered after exposure. Therefore, it is judged that the passivation effect of the deposited silicon oxynitride film layer may not be significantly poor

[0070] The fifth PL image 5 is a PL image of the test wafer on which the aluminum oxide film layer, the silicon oxynitride film layer, the silicon nitride film layer, and the silicon oxide film layer are deposited. It can be seen that the fifth PL image is mostly exposed, and there are no irregular dark stripes, but there are still a few dark areas with uneven darkness at the edge of the PL image. This may be due to the uneven area being unable to be completely covered during the deposition of the silicon oxynitride film layer, indicating that the overall passivation process still needs to be improved locally.

[0071] In addition, by comparing multiple PL images, it is found that each passivation film layer has a positive effect on the performance of the silicon wafer, so the passivation film layer with poor passivation effect is not considered for removal.

[0072] In order to improve the accuracy of step B1, in another embodiment, a verification step B2 is also included, which includes: in the back surface passivation process of the silicon wafer, depositing the remaining passivation film layers on the back surface of the silicon wafer except the passivation film layer with poor passivation effect, and testing the PL image for evaluation.

[0073] Specifically, the verification step B2 is based on the result of step B1. Another raw silicon wafer is subjected to steps S101, S102, S104, S105, and S106 to obtain a sixth test wafer. The sixth test wafer has other passivation film layers deposited on it except the silicon oxynitride film layer. A PL tester is used to detect the sixth test wafer to obtain a sixth PL image 6. The obtained sixth PL image 6 and the PL image obtained in step B1 are evaluated to determine whether the passivation film layer with poor passivation effect is the silicon oxynitride film layer.

[0074] For further understanding, as shown in Figure 2 The sixth PL image 6 can be seen that there is no exposure phenomenon in the PL image compared with the fourth PL image 4 and the fifth PL image 5, but the darkness is uniform, indicating that the passivation effect of the silicon oxynitride film layer is poor, and therefore the process parameters of the silicon oxynitride film layer deposited in step S103 need to be optimized.

[0075] Embodiment 2

[0076] In view of the need for step-by-step optimization and comparison during the adjustment of the process, the difference between Embodiment 2 and Embodiment 1 is that a method for optimizing the passivation process based on the results determined by the detection method is added. The optimization method of the back surface passivation process of the solar cell silicon wafer comprises:

[0077] determining a passivation film layer with poor passivation effect based on the detection method of the back surface passivation process of the solar cell silicon wafer; and optimizing the process parameters of depositing the passivation film layer with poor passivation effect.

[0078] Specifically, the passivation film layer with poor passivation effect is determined according to the detection method, and the process parameters of depositing the passivation film layer are optimized, wherein the process parameters that need to be optimized include the temperature, deposition time, gas flow, radio frequency power, pressure and pulse ratio in the furnace tube. Of course, in order to shorten the time required for optimizing the process and reduce the optimization cost, this embodiment does not need to adjust and optimize all the process parameters. If a single process parameter is selected for optimization or a few process parameters are selected for optimization, and the passivation effect is better, it is considered that the optimization of the process parameters is completed. The adjusted process parameters are applied to the passivation film process.

[0079] Preferably, the optimization step of the process parameters comprises: after adjusting the process parameters, applying the adjusted process parameters to the passivation process, and after the passivation film layer on the back surface of the silicon wafer is sequentially deposited to the passivation film layer with poor passivation effect, testing the PL image, comparing the PL images after adjusting different process parameters, and determining the optimal process parameters.

[0080] Specifically, after adjusting the process parameters of depositing the silicon oxynitride film layer in step S103, another raw silicon wafer is taken to perform steps S101, S102 and S103, and the process is forced to jump to step S106 to obtain an optimized silicon wafer, and a PL tester is used to detect the optimized silicon wafer to obtain an image.

[0081] For ease of understanding, the adjustment of the process parameters is taken as an example of pulse ratio, radio frequency power and pressure in the furnace tube

[0082] More specifically, the pulse ratio in the pre-deposition treatment and the deposition of silicon oxynitride is adjusted to 8 / 24, a raw silicon wafer is taken to perform steps S101, S102 and S103, and the process is forced to jump to step S106 to obtain a first optimized silicon wafer, and a PL tester is used to detect the optimized silicon wafer to obtain a first image 2b after optimization.

[0083] The pulse ratio in the pre-deposition process and the deposition of silicon oxynitride film is adjusted to 4 / 12. After the raw silicon wafer is subjected to steps S101, S102 and S103, the process is forced to jump to step S106, and the second optimized silicon wafer is obtained. The PL tester is used to detect the optimized silicon wafer to obtain the second optimized image 2c.

[0084] The power and pressure in the pre-deposition process and the deposition of silicon oxynitride film are adjusted to high power and high pressure. In this embodiment, the high power refers to a radio frequency power ≥5000KW, and the high pressure refers to a high pressure range ≥1800mTorr (millitorr) in the furnace tube. After the raw silicon wafer is subjected to steps S101, S102 and S103, the process is forced to jump to step S106, and the third optimized silicon wafer is obtained. The PL tester is used to detect the optimized silicon wafer to obtain the third optimized image 2d.

[0085] The power and pulse ratio in the pre-deposition process and the deposition of silicon oxynitride film are adjusted to high power and a pulse ratio of 8 / 24. After the raw silicon wafer is subjected to steps S101, S102 and S103, the process is forced to jump to step S106, and the fourth optimized silicon wafer is obtained. The PL tester is used to detect the optimized silicon wafer to obtain the fourth optimized image 2f.

[0086] In addition, in order to have a better comparison, the test silicon wafer under the original passivation process conditions is re-made, and the PL tester is used to detect the PL image of the test silicon wafer to obtain the non-optimized image 2a.

[0087] As shown in Figure 3 As shown in

[0088] As can be seen from the non-optimized image 1a, the PL image obtained by detecting the optimized silicon wafer without process parameter adjustment has a larger dark area and a darker dark color at the edge.

[0089] As can be seen from the first optimized image 2b, when the pulse ratio of the deposited silicon oxynitride film is adjusted to 8 / 24, the first optimized image 2b becomes significantly brighter, the dark color at the edge of the PL image becomes lighter and relatively uniform, indicating that the passivation effect under this process parameter is better.

[0090] As can be seen from the second optimized image 2c, when the pulse ratio of the deposited silicon oxynitride film is adjusted to 4 / 12, the second optimized image 2c becomes brighter, but compared with the first optimized image 2b, the second optimized image 2c has a larger dark area, indicating that the passivation effect of the pulse ratio 4 / 12 is not as good as that of the pulse ratio 8 / 24.

[0091] As can be seen from the third optimized image 2d, when the power and pressure are adjusted to high power and high pressure, the dark area of the PL image of the third optimized image 2d is increased and the dark color of the edge is deepened compared with the first optimized image 2b, which indicates that the passivation effect of the third optimized wafer is not as good as that of the first optimized wafer under the process parameters.

[0092] As can be seen from the fourth optimized image 2f, when the power and pulse ratio are adjusted to high power and pulse ratio of 8 / 24, the dark area of the PL image of the fourth optimized image 2f is increased and the dark color of the edge is deepened compared with the first optimized image 2b, which indicates that the passivation effect of the third optimized wafer is not as good as that of the first optimized wafer under the process parameters.

[0093] After multiple adjustments, it is found that when the pulse ratio in the step S103 of depositing the silicon oxynitride film layer is adjusted to 8 / 24, the dark area of the PL image is small and the dark color is relatively uniform, in addition, this process parameter can solve the problem of irregular dark stripes in the original process, therefore, the pulse ratio of 8 / 24 is applied in the step S103 of depositing the silicon oxynitride film layer.

[0094] It can be understood that the present application is described by some embodiments, and those skilled in the art know that various changes or equivalent replacements can be made to the features and embodiments without departing from the spirit and scope of the present application. In addition, under the guidance of the present application, the features and embodiments can be modified to adapt to specific conditions and materials without departing from the spirit and scope of the present application. Therefore, the present application is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of the present application are within the scope of the present application.

Claims

1. A method for detecting a back surface passivation process of a solar cell silicon wafer, characterized by: The back surface of the silicon wafer is sequentially deposited with multiple passivation film layers, and the detection method comprises: In the passivation process of the back surface of the silicon wafer, after each of the multiple passivation film layers is deposited on the back surface of the silicon wafer, a PL test step is entered to obtain PL images of multiple test silicon wafers with different numbers of passivation film layers deposited thereon; The relative changes of dark areas of the PL images of the multiple test silicon wafers are compared to determine the passivation film layer with poor passivation effect of the silicon wafer; the comparison of the relative changes of the dark areas of the PL images of the multiple test silicon wafers comprises comparing the dark areas of the PL images of the multiple test silicon wafers to observe whether the area of the dark area of the PL image becomes larger and / or the darkening degree becomes deeper; if the area of the dark area of the PL image of one of the test silicon wafers becomes larger and / or the darkening degree becomes deeper, it is determined that the last passivation film layer of the test silicon wafer has poor passivation effect.

2. The method of claim 1, wherein the method is characterized by: The multiple passivation film layers sequentially deposited on the back surface of the silicon wafer comprise a first film layer, a second film layer, a third film layer, and a fourth film layer; After each of the multiple passivation film layers is deposited on the back surface of the silicon wafer, a PL test step is performed, which comprises: After the step of depositing the first film layer on the back surface of the silicon wafer is completed, a PL test is performed to obtain a PL image of a test silicon wafer with the first film layer deposited thereon; After the step of sequentially depositing the first film layer and the second film layer on the back surface of the silicon wafer is completed, a PL test is performed to obtain a PL image of a test silicon wafer with the first film layer and the second film layer deposited thereon; After the step of sequentially depositing the first film layer, the second film layer, and the third film layer on the back surface of the silicon wafer is completed, a PL test is performed to obtain a PL image of a test silicon wafer with the first film layer, the second film layer, and the third film layer deposited thereon; After the step of sequentially depositing the first film layer, the second film layer, the third film layer, and the fourth film layer on the back surface of the silicon wafer is completed, a PL test is performed to obtain a PL image of a test silicon wafer with the first film layer, the second film layer, the third film layer, and the fourth film layer deposited thereon.

3. The method of claim 2, wherein the method is characterized by: The first film layer is an aluminum oxide film layer, the second film layer is a silicon oxynitride film layer, the third film layer is a silicon nitride film layer, and the fourth film layer is a silicon oxide film layer.

4. The method of claim 3, wherein the method is characterized by: The step of depositing the silicon nitride film layer comprises a pre-deposition treatment, and after the step of depositing the aluminum oxide film layer on the back surface of the silicon wafer and the pre-deposition treatment are completed, a PL test is performed to obtain a PL image of a test silicon wafer with the aluminum oxide film layer and the pre-deposition layer deposited thereon.

5. The method of claim 1, wherein the method is characterized by: The PL test uses a PL tester, which can be an online PL machine or an offline PL machine.

6. The method of claim 1-5, wherein the method is characterized by: The method further comprises a verification step, which comprises depositing the remaining passivation film layers except for the passivation film layer with poor passivation effect on the back surface of the silicon wafer in the passivation process of the back surface of the silicon wafer and testing the PL image for evaluation.

7. A method for optimizing a back surface passivation process of a solar cell silicon wafer, characterized in that, comprises: determining the passivation film layer with poor passivation effect of the silicon wafer based on the detection method of the passivation process of the back surface of the solar cell silicon wafer according to any one of claims 1-6; optimizing the process parameters of the deposition of the passivation film layer with poor passivation effect.

8. The method of optimization of the back surface passivation process of a solar cell silicon wafer according to claim 7, characterized in that, The optimization step of the process parameters comprises: after adjusting the process parameters, applying the adjusted process parameters to the passivation process; after the passivation film layer on the back surface of the silicon wafer is sequentially deposited to the passivation film layer with poor passivation effect, testing the PL image, comparing the PL images after adjusting different process parameters, and determining the optimal process parameters.

9. The method of optimizing the back surface passivation process of a solar cell silicon wafer according to claim 7, wherein, The process parameters include temperature, deposition time, flow rate, radio frequency power, pressure, and / or pulse ratio.

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