A method for detecting selective emitter doping effect of a silicon-based solar cell

Abstract

The application discloses a method for detecting the doping effect of a selective emitter of a silicon-based solar cell, which comprises the following steps: diffusing and doping the whole area on the front surface of a substrate silicon wafer to form a lightly doped area; performing laser doping on a local area on the front surface of the substrate silicon wafer to form a heavily doped area; performing first sheet resistance detection on the lightly doped area and the heavily doped area by using a sheet resistance tester with more than two probes; and the area of the heavily doped area is not less than 1% of the surface area of the substrate silicon wafer. The method forms a locally arranged heavily doped area on the front surface of the substrate silicon wafer, simultaneously completes the first sheet resistance detection on the lightly doped area and the heavily doped area in the same substrate silicon wafer, realizes accurate and rapid sheet resistance detection, reduces the detection times and the detection quantity, and can effectively detect the doping effect of the selective emitter.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solar cells, in particular to a method for detecting the selective emitter doping effect of a silicon-based solar cell. BACKGROUND

[0002] At present, the size of photovoltaic silicon wafers is continuously expanding, and the component technology is continuously innovating. At the same time, high-power components based on large-size silicon wafers have become an innovative trend in the photovoltaic industry. The continuous increase in the size of silicon wafers has also put forward new requirements for the testing and monitoring of various data in the process of large silicon wafers.

[0003] The selective emitter (SE) structure is a kind of high-efficiency solar cell structure. At present, solar cells based on large-size silicon wafers also widely adopt this structure. In the preparation of the selective emitter, the silicon wafer substrate is usually first diffused to form a lightly doped junction, and then a heavily doped junction is formed in the local area of the silicon wafer substrate by laser doping. The selective emitter doping effect has an important influence on the performance of the solar cell. Therefore, it is necessary to provide a method for detecting the selective emitter doping effect. SUMMARY

[0004] The present application provides a method for detecting the selective emitter doping effect of a silicon-based solar cell, which can effectively detect the doping effect of the selective emitter.

[0005] According to some embodiments, the present application provides a method for detecting the selective emitter doping effect of a silicon-based solar cell, comprising: diffusing and doping the entire area of the front surface of a substrate silicon wafer to form a lightly doped region; laser doping a local area of the front surface of the substrate silicon wafer to form a heavily doped region; using a sheet resistance tester with two or more probes to perform a first sheet resistance detection on the lightly doped region and the heavily doped region; and the area of the heavily doped region is not less than 1% of the surface area of the silicon wafer substrate.

[0006] Preferably, the laser doping of the local area of the front surface of the substrate silicon wafer to form a heavily doped region comprises: selecting a pre-designed laser doping pattern; and based on the selected laser doping pattern, laser irradiation is performed on the front surface of the substrate silicon wafer to make the front surface of the substrate silicon wafer become a molten state, and doping atoms enter the molten silicon to form a heavily doped region.

[0007] Preferably, selecting a pre-designed laser doping pattern comprises: the heavily doped region is at least two spaced-apart regions.

[0008] Preferably, the heavily doped region is at least two spaced-apart square regions.

[0009] Preferably, the side length of the square heavily doped region is designed as 12% to 20% of the side length of the substrate silicon wafer.

[0010] Preferably, the laser irradiation on the front surface of the substrate silicon wafer to make the front surface of the substrate silicon wafer into a molten state, and the entry of the doping atoms into the molten silicon to form the heavily doped region comprises: selecting a rectangular spot for the laser, the width of the rectangular spot being between 90 μm and 120 μm, and the height of the rectangular spot being between 90 μm and 120 μm, and the rectangular spots being linearly arranged in a tangential state.

[0011] Preferably, the method further comprises: setting the laser spot process parameters of the laser, the laser power being controlled to be between 65% and 85%, and the frequency being controlled to be between 300 and 400 kHz.

[0012] Preferably, the method further comprises: oxidizing the substrate silicon wafer after the laser doping on the front surface thereof; and performing a second sheet resistance detection on the same position light / heavy doped region after the oxidation.

[0013] Preferably, the method further comprises: performing a third sheet resistance detection on the same position light / heavy doped region after the back surface and alkali cleaning of the substrate silicon wafer after the oxidation.

[0014] Preferably, the substrate silicon wafer is a P-type substrate silicon wafer, and the size of the P-type substrate silicon wafer is G12 or above or M6 or below or M10.

[0015] The embodiments of the present application have at least the following advantages: the detection method of the present application can realize the completion of the sheet resistance value detection of the light / heavy doped region on the same silicon wafer once, without the need for secondary detection, and can sequentially perform the sheet resistance detection on the same position after oxidation and after alkali cleaning, so as to achieve the purposes of diffusion process stability monitoring and SE laser doping effect monitoring, and to help identify the process variation points on site, and to improve the stability of the selective emitter solar cell process.

[0016] The detection method provided by the embodiments of the present application is particularly suitable for the detection of the diffusion doping and laser doping effect in the process of preparing a solar cell with a selective emitter structure by using a large-size silicon wafer. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0018] Figure 1aThe flow chart of the selective emitter doping effect detection method for the silicon-based solar cell in the embodiment one of the present application;

[0019] Figure 1b The flow chart of the same position square resistance test after the laser doping of the substrate silicon wafer, the oxidation and the alkali etching in the embodiment one of the present application;

[0020] Figure 2a The doping layout schematic diagram of the embodiment one of the present application;

[0021] Figure 2b The light / heavy doping area test point schematic diagram of the P-type substrate silicon wafer in the embodiment one of the present application;

[0022] Figure 3a The doping layout schematic diagram of the embodiment two of the present application;

[0023] Figure 3b The light / heavy doping area test point schematic diagram of the P-type substrate silicon wafer in the embodiment two of the present application;

[0024] Figure 4a The schematic diagram of the doped silicon wafer after the film plating in the embodiment one of the present application;

[0025] Figure 4b The schematic diagram of the doped silicon wafer after the film plating in the embodiment two of the present application. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the embodiments of the present application will be described in detail below with reference to the drawings. However, those skilled in the art can understand that in the embodiments of the present application, many technical details are proposed in order to make the readers better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed by the present application can also be implemented. The division of the following embodiments is for the convenience of description, and should not constitute any limitation on the specific implementation of the present application, and the embodiments can be combined with each other and referred to each other without contradiction.

[0027] As a kind of efficient battery structure, selective emitter (SE) structure is widely used in silicon-based solar cell. The selective emitter doping effect has important influence on solar cell performance, therefore, the embodiment of the present application provides a kind of selective emitter doping effect detection method, the selective emitter doping effect is detected, and the optimal selective emitter doping process parameters are determined according to the detection result.

[0028] As shown in Figure 1a The method comprises the following steps:

[0029] Step 1, diffused doping is performed on the entire area of the front surface of the substrate silicon wafer to form a lightly doped region;

[0030] Step 2, laser doping is performed on a partial area of the front surface of the substrate silicon wafer to form a heavily doped region;

[0031] Step 3, a sheet resistance tester with two or more probes is used to detect the sheet resistance of the lightly doped region and the heavily doped region for the first time;

[0032] The area of the heavily doped region is not less than 1% of the surface area of the silicon wafer substrate.

[0033] It can be understood that, in the embodiment of the present application, the area of the heavily doped region is set to be not less than 1% of the surface area of the silicon wafer substrate, so that the probe of the sheet resistance tester can contact the heavily doped region to test the sheet resistance of the heavily doped region, thereby determining the doping effect of the heavily doped region.

[0034] In the process of preparing a solar cell, before forming a selective emitter, steps such as texturing the surface of the substrate silicon wafer can be included, and after forming the selective emitter, steps such as high-temperature oxidation and backside polishing can be included. By using the detection method provided in the embodiment of the present application, not only the doping effect of the initially formed selective emitter can be detected, but also the sheet resistance of the lightly doped region and the heavily doped region after undergoing steps such as high-temperature oxidation and backside polishing can be further detected, thereby further monitoring the doping effect of the selective emitter after undergoing steps such as high-temperature oxidation and backside polishing.

[0035] The following takes a P-type SE+PERC solar cell as an example to further explain and illustrate the present application.

[0036] First, the concept of SE+PERC solar cell is explained, which refers to the combination of selective emitter (SE) and partial contact back passivation technology (PERC). The P-type SE+PERC solar cell refers to a substrate silicon wafer using a P-type silicon wafer.

[0037] Figure 1a is the flowchart of the selective emitter doping effect detection method of the silicon-based solar cell in the first embodiment of the present application; Figure 2a is the doping layout schematic diagram of the first embodiment of the present application.

[0038] The following further details a selective emitter doping effect detection method of a silicon-based solar cell provided in the embodiment, and the specific steps are as follows:

[0039] As shown in Figure 1a Step S101, diffused doping is performed on the entire area of the front surface of the substrate silicon wafer to form a lightly doped region;

[0040] In the present embodiment, it is necessary to note that after diffusion in the process of SE+PERC cell, a P-type substrate silicon wafer with PN junction is formed. Specifically, a certain number of single crystal wafer sources are selected, the selected single crystal wafer sources are subjected to conventional texturing through the same texturing machine, after texturing is completed, the silicon wafer is inserted into a quartz boat to perform optimized diffusion through the same diffusion furnace tube, low-pressure diffusion technology is used to form a PN junction. The entire area of the front surface of the substrate silicon wafer is diffused and doped to form a lightly doped region. Two substrate silicon wafers are selected from the constant temperature zone of the diffusion furnace tube for testing, and the sheet resistance of the selected substrate silicon wafers is 152Ω.

[0041] Step S102, laser doping is performed on the local area of the front surface of the substrate silicon wafer to form a heavily doped region.

[0042] In some embodiments, a laser doping pattern layout is first designed in advance, and then laser irradiation is performed on the front surface of the substrate silicon wafer based on the selected laser doping pattern layout to make the front surface of the substrate silicon wafer become a molten state, and dopant atoms enter the molten silicon to form a heavily doped region, wherein the area of the heavily doped region is not less than 1% of the surface area of the silicon wafer substrate. The pre-designed laser doping pattern layout mainly includes at least two spaced-apart heavily doped regions. In one example, the heavily doped regions are square, and in other embodiments, they can also be other shapes, which are not limited by the present application.

[0043] Since the size of the substrate silicon wafer varies, the size applied in the present embodiment is G12 or below M6 or M10, so the side length of the heavily doped region changes flexibly with the size of the substrate silicon wafer. Preferably, the side length of the square heavily doped region is designed to be 12% to 20% of the side length of the substrate silicon wafer, for example, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc.

[0044] In some embodiments, laser doping is performed on the front surface of the substrate silicon wafer based on the laser doping pattern layout to form locally spaced-apart heavily doped regions. The laser doping technology can be realized by Q-switching and semiconductor-pumped solid-state laser. The parameters of the laser spot process are set, the laser is single laser, and the laser spot is a rectangular spot with a width of 90μm to 120μm and a height of 90μm to 120μm. The rectangular spots are linearly arranged in a tangential state, the laser power is controlled at 65% to 85%, and the frequency is controlled at 300 to 400Khz.

[0045] For the convenience of understanding, the detailed description is made by way of example, it is necessary to point out that the application further forms a heavy doped region on the basis of a light doped region, that is, the region other than the heavy doped region is a light doped region, therefore, in order to test, in the embodiment, the test points are selected in the light doped region, and the test points are set as the same square region as the heavy doped region. For example, in one example, the light doped region and the heavy doped region test points in the same substrate silicon wafer can be sequentially designed according to 2+3 / 3+2 or 4+5 / 5+4 and other quantity matching designs. Referring to Figure 2a , the light doped region and the heavy doped region test points according to the 2+3 quantity matching design represent that there are two light doped regions and three heavy doped regions, and the two light doped regions and the three heavy doped regions are arranged in a cross shape, wherein the two light doped regions are arranged at the periphery and adjacent to each other and are marked as 1 and 2, and the three heavy doped regions are marked as 3, 4 and 5. The light doped region and the heavy doped region test points according to the 3+2 quantity matching design represent that there are three light doped regions and two heavy doped regions, and the same is arranged in a cross shape, and the two heavy doped regions are arranged at the periphery and adjacent to each other.

[0046] Referring to Figure 3a , the light doped region and the heavy doped region test points according to the 4+5 quantity matching design represent that there are four light doped regions and five heavy doped regions, and the four light doped regions and the five heavy doped regions are arranged in three rows and three columns, wherein the four light doped regions are arranged at the four corner positions of the substrate silicon wafer and are sequentially marked as 1, 2, 3 and 4, and the five heavy doped regions are marked as 5, 6, 7, 8 and 9. The light doped region and the heavy doped region test points according to the 5+4 quantity matching design represent that there are five light doped regions and four heavy doped regions, and the same is arranged in three rows and three columns, and the four heavy doped regions are arranged at the four corner positions of the substrate silicon wafer.

[0047] In the embodiment one of the application, the light doped region and the heavy doped region test points are designed according to the 2+3 quantity, for example, as shown in Figure 2a .

[0048] Figure 2b The light / heavy doped region test point schematic diagram of the P-type substrate silicon wafer in the embodiment one of the application.

[0049] Please refer to Figure 2bIn the first embodiment, the width of the laser is 95 μm, the height is 100 μm, the power is 70%, and the frequency is 350 kHz. The front surface of the two substrates of the silicon wafer with the diffused light-doped region is sequentially laser-doped. After diffusion, a P-type substrate silicon wafer forms a phosphorus-rich PSG layer on the surface of the substrate silicon wafer. The selective emitter (SE) laser emitter uses the phosphorus-rich PSG layer as a doping source to emit a laser pulse at a high frequency to melt the surface layer of the substrate silicon wafer, so that the phosphorus atoms in the PSG layer are pushed to the surface layer of the substrate silicon wafer. After the phosphorus atoms are solidified, they quickly replace the positions of silicon atoms to achieve the purpose of diffusion and promotion of doped atoms. A locally heavily doped region is obtained. After doping, the silicon wafer is tested Figure 2b .

[0050] In step S103, a sheet resistance tester with two or more probes is used to detect the sheet resistance of the light-doped region and the heavily doped region for the first time.

[0051] Please continue to refer to Figure 1a In some embodiments, in a conventional PERC (partial contact back passivation technology) high-efficiency solar cell process flow, the front surface sheet resistance of the substrate silicon wafer after diffusion is generally monitored using a four-probe sheet resistance tester. The four-probe sheet resistance tester is composed of four probes with equal distances between the four probes. The four probes are connected to a low-resistance tester. When the four-probe test head is pressed on the conductive thin film material, the low-resistance tester can display the sheet resistance of the material. In this embodiment, the number of test points of the light-doped region and the heavily doped region is taken as an example of 2+3, so a five-probe sheet resistance tester is used to test the sheet resistance values of the light-doped and heavily doped regions in the same wafer. The test data is recorded in Table 1.

[0052] In some related art substrate silicon wafer processes, the sheet resistance monitoring method of the heavily doped region needs to test the sheet resistance values of the substrate silicon wafer before and after the process twice: once after diffusion, which is the front; once after laser doping, which is the back; the difference is the sheet resistance drop. In this way, the surface of the substrate silicon wafer after laser heavy doping is a heavily doped sheet region, and there is no four-probe probe to test the light-doped region on the surface of the substrate silicon wafer. Therefore, the doping sheet resistance change cannot be monitored after the subsequent process of oxidation and alkali etching. Therefore, the substrate silicon wafer processed by the first embodiment can be sequentially tested for the sheet resistance of the light / heavy doped region at the same position after oxidation and alkali etching. The purpose of analyzing the diffusion process stability and the SE laser doping effect monitoring is achieved.

[0053] Figure 1bis a test flow chart of the same position light / heavy doping area sheet resistance after oxidation and alkali polishing of the substrate silicon wafer after laser doping in Embodiment One of the present application; the specific steps include the following:

[0054] As shown in Figure 1b Step S201, the substrate silicon wafer is subjected to high-temperature oxidation to form a front surface oxidation protective layer, and a second sheet resistance test is performed.

[0055] In some embodiments, the substrate silicon wafer is subjected to diffusion and etching processes before oxidation. The substrate silicon wafer will produce a kind of decay after long-term work, which is called PID (Potential Induced Degradation), so that the performance of the substrate silicon wafer is lower than the design standard. In order to achieve the purpose of anti-PID, a layer of silicon dioxide needs to be grown on the surface of the substrate silicon wafer after etching, and a thermal oxidation process is adopted, that is, oxygen is passed through the surface of the furnace tube to form an oxidation layer under high temperature.

[0056] The two pieces of substrate silicon wafer taken are subjected to front surface oxidation process in turn, and after completion, a five-probe sheet resistance tester is used to test and record the sheet resistance values of the same position light doping and heavy doping areas in the substrate silicon wafer. The recorded data is shown in Table 1.

[0057] Step S202, after the oxidation of the substrate silicon wafer, the back surface is cleaned and alkali polished, and a third sheet resistance test is performed.

[0058] In some embodiments, a 6% HF solution by volume is used to remove the phosphosilicate glass (PSG) on the back surface of the substrate silicon wafer, and then the back surface of the substrate silicon wafer is polished with an alkali solution. After back surface polishing and cleaning are completed using a 6.1% potassium hydroxide / additive solution by volume, the same five-probe sheet resistance tester is used to test and record the sheet resistance of the same position light doping and heavy doping areas in the substrate silicon wafer. The recorded data is shown in Table 1.

[0059] After the substrate silicon wafer is tested through the above steps, the test data is sorted and analyzed as follows:

[0060] ① After selective emitter (SE) laser doping, the average sheet resistance of the heavy doping area is 85.7Ω, which is within the normal value of 80-90Ω; the sheet resistance drop is 66.6Ω, which is within the normal range of 60-70Ω;

[0061] ② After oxidation, the sheet resistance of the light doping area changes little compared with that after selective emitter laser doping, which is normal; the sheet resistance of the heavy doping area decreases by 3.6Ω compared with that after selective emitter laser doping, which is within the range of 3-5Ω, which is normal;

[0062] After alkali etching, the sheet resistance of the lightly doped region is increased by 10.3Ω, in the range of 8-11Ω, which is normal; the sheet resistance of the heavily doped region is increased by 2.1Ω, in the range of 2-4Ω, which is normal;

[0063] The above process can be used to test the sheet resistance, and the process monitoring is normal. In order to make the laser doping more obvious, the doped silicon wafer is imaged after PECVD coating, as shown in FIG. 4a, the lightly doped region and the heavily doped region are clearly visible.

[0064] The embodiment of the present application is based on the laser doping pattern of the substrate silicon wafer, and the laser doping is performed on the front surface of the substrate silicon wafer to form a heavily doped region, and the sheet resistance of the lightly / heavily doped region of the same substrate silicon wafer is tested by four probes, which realizes accurate and rapid monitoring of the sheet resistance after selective emitter laser, reduces the number of tests and the number of tests, and can effectively detect the doping effect of the selective emitter. In addition, the detection method provided by the embodiment is particularly suitable for detecting the diffusion doping and laser doping effect in the process of preparing a solar cell with a selective emitter structure by using a large-size silicon wafer. Through the application of the detection method, the sheet resistance change difference can be monitored according to the process, and the sheet resistance change state under the chain oxygen and alkali etching process can be monitored. Through the monitoring of the sheet resistance of the lightly / heavily doped region, the diffusion process stability and the SE laser doping effect monitoring can be analyzed, which helps to identify the process variation point on site, and improves the stability of the process of the selective emitter solar cell.

[0065] Embodiment two

[0066] The parameters of the selective emitter laser are changed to power 80% and frequency 380Khz; at this time, the rectangular spot width of the laser is 105μm, the height is 105μm, and the spots are tangent to each other.

[0067] Figure 3a The doping pattern of the embodiment two of the present application is shown in the figure; Figure 3b The lightly / heavily doped region test point diagram of the P-type substrate silicon wafer of the embodiment two of the present application is shown in the figure.

[0068] Please refer to Figure 3a and Figure 3b In the embodiment two of the present application, the number of test points of the lightly doped region and the heavily doped region is designed as 4+5, as shown in Figure 3a Two P-type substrate silicon wafers after diffusion doping of the entire area of the front surface of the substrate silicon wafer are selected, and the diffusion sheet resistance value is 153Ω. The two diffusion substrate silicon wafers are sequentially laser doped, and the doped silicon wafer is shown in Figure 3b The sheet resistance values of the lightly doped and heavily doped regions of the wafer are tested and recorded by using a nine-probe sheet resistance tester. The recorded data is shown in Table 2.

[0069] The corresponding test data is analyzed and shown in Table 2. After selective emitter laser doping, the sheet resistance of the heavily doped region is abnormal, the average sheet resistance is 112.5Ω, which is much higher than the normal state of 80-90Ω; the sheet resistance drop is 40Ω, which is much smaller than the normal state of 60-70Ω; the sheet resistance test after stopping the subsequent oxidation and alkali etching process is arranged for investigation.

[0070] It is found through on-site analysis that the actual power of the laser is too high, which leads to small laser spot energy. After adjusting the laser, it is confirmed to be normal, which achieves the monitoring purpose. As can be seen, according to the size of the substrate silicon wafer, the square side length of the heavily doped region is selected flexibly, and different numbers of lightly doped regions and heavily doped regions can be matched and designed in the same substrate silicon wafer. The test points can realize accurate and rapid monitoring of the sheet resistance after selective emitter laser and process technology monitoring without abnormality.

[0071] In order to make the laser doping of the present application more obvious, the doped silicon wafer of the embodiment is imaged after PECVD coating, as shown in Figure 4b , the lightly doped region and the heavily doped region are clearly visible.

[0072] It should be understood that the above specific embodiments of the present application are only used for illustrative or explanatory purposes, and do not constitute a limitation on the present application. Therefore, any modification, equivalent replacement, improvement, etc. made without departing from the spirit and scope of the present application shall be included in the protection scope of the present application. In addition, the claims attached to the present application are intended to cover all changes and modifications falling within the scope and boundary of the appended claims, or the equivalent forms of such scope and boundary.

[0073] Table 1.

[0074]

[0075] Table 2.

[0076]

Claims

1. A method for detecting selective emitter doping effect of a silicon-based solar cell, characterized in that, The method comprises the following steps: diffusion doping is performed on the whole area of the front surface of a substrate wafer to form a lightly doped region; laser doping is performed on a local area of the front surface of the substrate wafer to form a heavily doped region; test points are selected in the lightly doped region, and a sheet resistance tester with more than two probes is used to perform first sheet resistance detection on the lightly doped region and the heavily doped region; the area of the heavily doped region is not less than 1% of the surface area of the substrate wafer, the heavily doped region is at least two spaced-apart regions, and the side length of the heavily doped region is designed to be 12% to 20% of the side length of the substrate wafer; the substrate wafer is subjected to high-temperature oxidation to form an oxidation protective layer on the front surface, and second sheet resistance detection is performed on the same position lightly / heavily doped region; after the oxidized substrate wafer is subjected to backside and alkali cleaning, third sheet resistance detection is performed on the same position lightly / heavily doped region; wherein the step of performing laser doping on a local area of the front surface of the substrate wafer to form a heavily doped region comprises: selecting a pre-designed laser doping pattern; on the basis of the selected laser doping pattern, laser irradiation is performed on the front surface of the substrate wafer to make the front surface of the substrate wafer become a molten state, and doping atoms enter the molten silicon to form a heavily doped region; the spot of the laser is selected to be a rectangular spot, the width of the rectangular spot is between 90 μm and 120 μm, the height of the rectangular spot is between 90 μm and 120 μm, and the rectangular spots are linearly arranged in a tangential state; the laser spot process parameters of the laser are set, the laser power is controlled to be between 65% and 85%, and the frequency is controlled to be between 300 kHz and 400 kHz.

2. The detection method according to claim 1, wherein, The heavily doped region is at least two spaced-apart square regions.

3. The detection method according to claim 1 or 2, wherein, The substrate wafer is a P-type substrate wafer, and the size of the P-type substrate wafer is G12 or less than M6 or M10.

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