A blue film sheet square resistance test method based on WCT120

Abstract

The application provides a WCT120-based blue film sheet square resistance test method, which first determines the original silicon resistivity and thickness of a blue film sheet to be monitored, the blue film sheet comprising a diffusion layer and a silicon substrate layer, the thickness referring to the thickness of the silicon substrate layer; sampling the blue film sheet before screen printing, using WCT120 to obtain the overall resistance R total of the sampled blue film sheet; and then using a calculation model to calculate the diffusion square resistance R emitter of the blue film sheet. In the application, WCT120 is used to test the overall resistance of the blue film sheet first, and then the diffusion square resistance of the blue film sheet is inversely deduced according to the calculation model, so that the semi-finished product after plating, i.e. the blue film sheet, can be obtained before screen printing, the abnormal square resistance of the blue film sheet can be found, the blue film sheet can be directly reworked, the loss caused can be reduced, the cost of rework can be reduced, and the waste of resources and cost of the screen printing process can be avoided. Combined with automation, this step can be integrated into the production line for batch testing, and the blue film sheets with abnormal square resistance can be selected.

Description

Technical Field

[0001] This invention relates to the field of solar cell manufacturing technology, specifically to a method for testing the sheet resistance of a blue film based on WCT120. Background Technology

[0002] Solar cells are the core component of solar cells, and their performance directly affects the cell's conversion efficiency and other performance characteristics. Therefore, monitoring cell performance is crucial during the cell manufacturing process. Currently, electroluminescent (EL) testing is commonly used as an important method to detect and monitor defects in solar cells caused by manufacturing processes or materials. It can reveal electrical problems in the cells. When EL defects occur on the production line, it is necessary to identify the factors or processes that caused the defects.

[0003] Traditional production lines monitor sheet resistance entirely before coating or after screen printing. Pre-coating sheet resistance monitoring typically refers to sheet resistance monitoring after diffusion. Post-screen printing sheet resistance monitoring often refers to Transmission Line Method (TLM) sheet resistance monitoring, which tests the sheet resistance of the finished solar cell to eliminate the influence of the diffusion process.

[0004] The TLM test structure consists of at least three contacts with different spacings. In this method, current is confined to flow from one metal contact to the semiconductor surface, through the semiconductor sheet for a certain distance, and then upwards into the second metal contact. This method can be used to obtain the sheet resistance of the finished solar cell, but it has several drawbacks: 1) It is time-consuming; 2) It requires sample cutting, making it a destructive test, which leads to high testing costs if the number of samples is large; therefore, the number of test samples is generally small; 3) The test results are affected by factors such as sample preparation, sample quantity, probe pressure accuracy, and printing morphology.

[0005] Furthermore, existing testing methods generally monitor the sheet resistance of finished battery cells, which are produced after metal electrodes are formed on a blue film through screen printing. As is well known, the screen printing process accounts for a significant portion of battery production costs. If the sheet resistance of the blue film is abnormal in the initial stage, monitoring it only after the battery cells are manufactured would lead to wasted costs, resulting in substantial economic losses and resource waste. Therefore, identifying sheet resistance abnormalities in semi-finished batteries before screen printing and reworking them as early as possible can greatly reduce rework costs during battery production.

[0006] Therefore, there is an urgent need to provide a sheet resistance testing method that can reduce losses and rework costs and enable monitoring of cell performance. Summary of the Invention

[0007] The technical problem to be solved by the present invention is: in view of the shortcomings of the existing technology in monitoring the performance of battery cells by testing the sheet resistance of finished batteries, the present invention provides a blue film sheet resistance testing method based on WCT120.

[0008] The technical solution adopted by this invention to solve its technical problem is: a blue film sheet resistance testing method based on WCT120, comprising the following steps:

[0009] S1: Determine the base resistivity and thickness Si_thinkness of the blue film to be monitored. The blue film includes a diffusion layer and a silicon substrate layer. The thickness Si_thinkness refers to the thickness of the silicon substrate layer.

[0010] S2: Calculate the substrate resistance R based on the original silicon resistivity (Base_Resistivity) and thickness (Si_thinkness) obtained in step S1. base Then: R base =Base_Resistivity÷Si_thinkness;

[0011] S3: Before screen printing, sample the blue film and use a WCT120 to obtain the overall resistance R of the sampled blue film. total .

[0012] The sheet resistance of finished cells is usually monitored on the production line by sampling, cutting the finished cells to make samples, and testing the sheet resistance of the finished cells according to the TLM method. The method in this invention does not damage the samples and can directly sample and test before screen printing. Since this method is only related to the thickness and resistivity of the sample to be tested, there are no requirements for the number of samples or the size of the samples.

[0013] S4: Given the overall resistance R total , substrate resistance R base Then, R can be derived from the calculation model. emitter The value of the base resistance R is therefore determined. base and overall resistance R total Substituting into the calculation model of diffusion sheet resistance, R is calculated using the calculation model. emitter The numerical value, where the calculation model is:

[0014]

[0015] In the formula, R total R represents the overall resistance of the blue diaphragm. base Indicates substrate resistance; R emitter This represents the emitter resistance, i.e., the sheet resistance of the blue diaphragm. The overall resistance R here... totalIt can be the overall resistance before or after sintering. The diffusion sheet resistance of the blue film before and after sintering can be calculated by using the overall resistance before and after sintering, so that a comparison can be made before and after sintering.

[0016] Furthermore, in step S1, the base resistivity and thickness Si_thinkness of the blue film to be monitored need to be determined before mass production on the production line.

[0017] Furthermore, there are many ways to obtain the resistivity of primary silicon in step S1, including but not limited to using a WCT120, a primary silicon resistivity tester, or a silicon wafer sorting machine.

[0018] Furthermore, in step S3, the WCT120 is used to obtain the overall resistance R of the sampled blue diaphragm. total The steps include: placing the sampled blue film on the test stage of the WCT120, and measuring the substrate resistance R obtained in step S2. base Enter the value into the WCT120, click "Test", and obtain the overall resistance R of the blue diaphragm. total .

[0019] Furthermore, the blue film sampled in step S3 can be directly tested using a WCT120 or tested after sintering. The impact of sintering on square resistance can be compared between these two methods. If only monitoring of the production line level is required, samples can be taken directly before sintering. Sampled products without scratches can continue printing and being produced into finished batteries.

[0020] The beneficial effects of this invention are:

[0021] (1) The blue film is an intermediate product formed after silicon wafer coating. Since the coated SiNx material is an insulator, the sheet resistance of the blue film cannot be directly measured by the conventional four-probe method. Generally, the industry does not monitor the sheet resistance of the blue film. Instead, after screen printing, that is, metallization electrodes are printed on the blue film to form a conductor. After the blue film is made into a finished battery cell, the sheet resistance of the finished battery cell is tested by the TLM method through the electrodes. The test requires cutting the finished battery cell, which is a destructive test. Therefore, considering the cost, the test sample size is generally small and the test time is relatively long. In this invention, the WCT120 is used to test the overall resistance of the blue film first. Then, based on the calculation model, the test method of diffusion sheet resistance of the blue film is derived. It is possible to obtain the semi-finished product after coating - the blue film - before screen printing. If the sheet resistance of the blue film is found to be abnormal, the blue film can be directly reworked, reducing the losses and rework costs, and avoiding the waste of resources and costs in the screen printing process.

[0022] (2) This method avoids slicing tests and does not damage silicon wafers. At the same time, it can effectively monitor the sheet resistance of the blue film on the production line before screen printing, which is convenient for analyzing process abnormalities that occur after diffusion to the finished product. It is of great significance for production line process monitoring.

[0023] (3) Sampling test is ultimately just a small sample monitoring method. In order to monitor the experimental data comprehensively, the invention proposed in this patent can be fully integrated into online production. A belt conveyor device is added before the first printing to achieve full detection of sheet resistance. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Figure 1 This is a schematic diagram of the structure of the blue film of the present invention.

[0026] Figure 2 This is a graph showing the resistivity results of the WCT120 test on primary silicon.

[0027] Figure 3 This is a flowchart of the WCT120 test for primary silicon resistivity. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0029] The present invention provides a blue film sheet resistance testing method based on WCT120, comprising the following steps:

[0030] S1: Before mass production begins, determine the base resistivity and thickness (Si_thinkness) of the blue film to be monitored, such as... Figure 1 As shown, the blue film in this invention includes a diffusion layer and a silicon substrate layer, and the thickness Si_thinkness refers to the thickness of the silicon substrate layer. There are many ways to obtain the resistivity of primary silicon, including but not limited to using a WCT120, a primary silicon resistivity meter, or a silicon wafer sorting machine. This embodiment only exemplifies the results of the WCT120 and the primary silicon resistivity meter to verify the consistency of the test results from the two devices. For example, the resistivity of primary silicon obtained using a resistivity meter is (~0.7 ohm·cm). Figure 2This is a graph showing the resistivity results of silicon measured by WCT120. Squares represent the resistivity of silicon measured before sintering, circles represent the resistivity of silicon measured after sintering, and triangles represent the resistivity of silicon measured by the resistivity meter before and after sintering. The terms "Before Sintering" and "After Sintering" in the graph represent the test results of WCT120, with "Measured_Resistivity" before sintering and "Measured_Resistivity" after sintering. The measured resistivity (Measured_Resistivity) and overall resistance (R) are also shown. total The relationship between the silicon wafer thickness and the measured resistivity is: Measured_Resistivity = R total *Silicon wafer thickness, from which the overall resistance R can be calculated. total The value is denoted by Si_thinkness, where silicon wafer thickness refers to the silicon wafer thickness. Figure 2 The "Base_Resistivity" value is the test result from the original silicon resistivity meter. Figure 2 It can be seen that the "Measured_Resistivity" result of the WCT120 test for wafers that have not undergone diffusion and passivation processes is consistent with the result of the original silicon resistivity tester. Figure 2 This is only to illustrate the accuracy of the WCT120 test for the resistivity of primary silicon. There are many ways to obtain the resistivity of primary silicon, including but not limited to the methods mentioned above.

[0031] S2: Calculate the substrate resistance R based on the original silicon resistivity (Base_Resistivity) and thickness (Si_thinkness) obtained in step S1. base Then: R base =Base_Resistivity÷Si_thinkness;

[0032] For example: Given that the base resistivity of silicon is 0.656 ohm·cm and the silicon wafer thickness (Si_thinkness) is 160 μm, then: R base =(0.656ohm.cm)÷(160μm)=41ohm / sq.

[0033] S3: Before screen printing, sample the blue film, place the sampled blue film on the test platform of WCT120, and use the substrate resistance R obtained in step S2. base Input the value into the WCT120 and click "Test" to obtain the overall resistance R of the sampled blue diaphragm using the WCT120. total .

[0034] In this embodiment, to compare the effect of sintering on the resistivity, the resistivity of the original silicon of the blue film before and after sintering was tested. Then, the overall resistance R of the blue film before and after sintering was measured using a WCT120. total .

[0035] S3: Then, obtain the substrate resistance R before and after sintering in step S2. base and overall resistance R total Substituting these values ​​into the calculation model for diffusion sheet resistance, the emitter resistance R of the blue film before sintering is calculated using the calculation model. emitter The values, and the emitter resistance R of the blue film after sintering. emitter The numerical values ​​are compared to achieve production line monitoring. The calculation model is as follows:

[0036]

[0037] In the formula, R total R represents the overall resistance of the blue diaphragm. base Indicates substrate resistance; R emitter This indicates the emitter resistance.

[0038] In this embodiment, the overall resistance R of the blue film was tested using WCT120. total The result is 34.3 ohms / sq, and the overall resistance R... total The value is 34.3 ohm / sq and the substrate resistance R base Substituting the value 41 ohm / sq into the calculation model, the diffusion sheet resistance R of the blue film is obtained. emitter The value is 209.9 ohm / sq. The diffusion sheet resistance R through the blue diaphragm is... emitter The numerical values ​​can be used for SPC control to determine the current level of the production line and check for any abnormal wafers.

[0039] The testing method of this invention can be used for random sampling of blue films on the production line, or it can be used to modify the equipment before screen printing to achieve automated batch testing on the production line. This enables the monitoring of sheet resistance of blue films on the production line. This method avoids slicing tests, does not damage silicon wafers, and can effectively monitor the sheet resistance before screen printing, which is of great significance for production line process monitoring.

[0040] In later stages of application, this method can be integrated into the production line, and a sheet resistance control range can be set to identify outliers. For example, before the screen printing stage, a WCT120 device can be installed below the battery conveyor to obtain the sheet resistance value of each battery. Once applied to the production line, this method can monitor the sheet resistance, enabling early rework and reducing rework costs, and can also be used for production line data analysis. For instance, analyzing the correlation between batch electrical performance and sheet resistance provides direction for adjusting the diffusion process.

[0041] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the scope of the present invention. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for measuring the sheet resistance of a blue diaphragm based on WCT120, characterized in that: Includes the following steps: S1: Determine the base_resistivity and thickness Si_thinkness of the original silicon resistivity of the blue film to be monitored. The blue film includes a diffusion layer and a silicon substrate layer. The thickness Si_thinkness refers to the thickness of the silicon substrate layer. S2: Calculate the substrate resistance R based on the original silicon resistivity (Base_Resistivity) and thickness (Si_thinkness) obtained in step S1. base Then: R base = Base_Resistivity÷Si_thinkness; S3: Before screen printing, sample the blue film and use a WCT120 to obtain the overall resistance R of the sampled blue film. total ; S4: The base resistor R base and overall resistance R total Substituting into the calculation model of diffusion sheet resistance, R is calculated using the calculation model. emitter The numerical value, where the calculation model is: In the formula, R total R represents the overall resistance of the blue diaphragm. base Indicates substrate resistance; R emitter This represents the emitter resistance, i.e., the sheet resistance of the blue film.

2. The blue diaphragm sheet resistance testing method based on WCT120 as described in claim 1, characterized in that: In step S1, the base resistivity and thickness Si_thinkness of the blue film to be monitored need to be determined before mass production on the production line.

3. The blue diaphragm sheet resistance testing method based on WCT120 as described in claim 1, characterized in that: In step S1, the resistivity of the primary silicon is obtained using a WCT120, a primary silicon resistivity tester, or a silicon wafer sorting machine.

4. The blue diaphragm sheet resistance testing method based on WCT120 as described in claim 1, characterized in that: In step S3, the overall resistance R of the sampled blue film is obtained using a WCT120. total The steps include: placing the sampled blue film on the test stage of the WCT120, and measuring the substrate resistance R obtained in step S2. base Input the value into the WCT120, click "Test", and obtain the overall resistance R of the sampled blue diaphragm. total .

5. The blue diaphragm sheet resistance testing method based on WCT120 as described in claim 1, characterized in that: In step S3, the blue film sampled is tested directly using a WCT120, or the blue film is sintered before being tested using a WCT120.

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