A method for preparing a tunnel oxide layer, a solar cell and a method for preparing the same

Abstract

The application provides a preparation method of a tunneling oxide layer, a solar cell and a preparation method thereof. The preparation method of the tunneling oxide layer comprises the following steps: in a high-vacuum environment, closing an air exhaust valve of a furnace tube, first introducing small-flow oxygen to perform first-time oxidation treatment on a silicon wafer in the furnace tube, then introducing large-flow oxygen to perform second-time oxidation treatment on the silicon wafer in the furnace tube, stopping the introduction of the large-flow oxygen after reaching a preset pressure, and then keeping the pressure of the furnace tube in a stable state to grow a tunneling oxide layer on the surface of the silicon wafer. The method provided by the application grows a tunneling oxide layer with high quality and uniformity by sequentially using small-flow oxygen and large-flow oxygen to perform oxidation treatment on the silicon wafer, and improves the overall efficiency of the cell sheet, which is conducive to large-scale popularization and application.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, and relates to a tunneling oxide layer, and more particularly to a method for preparing a tunneling oxide layer, a solar cell, and the same method. Background Technology

[0002] A solar cell is a semiconductor device that converts solar energy into electrical energy. Its power generation principle is based on the photovoltaic effect of a semiconductor PN junction. The fabrication process of TOPcon (Tunnel Oxide Passivated Contact) monocrystalline silicon solar cells requires the creation of a tunneling oxide layer and a polycrystalline silicon layer on the back of the cell. These two layers together form a passivated contact structure, which significantly reduces metal-to-metal contact recombination current and improves the cell's conversion efficiency.

[0003] Currently, the industry generally uses LPCVD (low-pressure chemical vapor deposition) with high-flow oxygenation and tube-sealing processes for tunneling oxidation. However, the uneven tunneling oxide layer near the edge of the furnace mouth boat will significantly reduce the overall efficiency of the solar cell and even cause EL black edge defects. There is currently no effective solution to improve this issue.

[0004] CN117936366A discloses an oxide film and its preparation method. The preparation method includes: sequentially subjecting a silicon wafer to a first oxidation treatment and a second oxidation treatment, wherein the oxygen flow rate in the first oxidation treatment is less than the oxygen flow rate in the second oxidation treatment, and the pressure in the first oxidation treatment is less than the pressure in the second oxidation treatment. However, the pressures of the two oxidation treatments are not continuous, and the first oxidation treatment does not start from a vacuum, resulting in significant airflow disturbance, and the uniformity of the obtained oxide film needs further improvement.

[0005] Therefore, how to provide a method to improve the uniformity of the tunneling oxide layer, minimize airflow disturbance during the secondary oxidation process, improve the uniformity of the flow field, thereby improving the uniformity of the tunneling oxide layer and increasing the efficiency of the solar cell, has become an urgent problem that needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a tunneling oxide layer, a solar cell, and a method for preparing the same. The method involves sequentially oxidizing a silicon wafer with a small flow rate of oxygen and a large flow rate of oxygen to grow a high-quality and uniform tunneling oxide layer, thereby improving the overall efficiency of the solar cell and facilitating its large-scale application.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] The first aspect of this application provides a method for preparing a tunneling oxide layer, the method comprising:

[0009] In a high vacuum environment, the exhaust valve of the furnace tube is closed. First, a small flow of oxygen is introduced to perform the first oxidation treatment on the silicon wafer inside the furnace tube. Then, a large flow of oxygen is introduced to perform the second oxidation treatment on the silicon wafer inside the furnace tube. After reaching the preset pressure, the large flow of oxygen is stopped. Then, the pressure inside the furnace tube is kept stable to grow a tunneling oxide layer on the surface of the silicon wafer.

[0010] In one embodiment, during the first oxidation process, the pressure inside the furnace tube increases at a rate of 5.5-28 Torr / min.

[0011] In one embodiment, during the second oxidation process, the pressure inside the furnace tube increases at a rate of 75-155 Torr / min.

[0012] In one embodiment, the flow rate of the low-flow oxygen is 2-10 slm.

[0013] And / or, stop supplying a small flow of oxygen when the pressure inside the furnace tube reaches 180-250 Torr.

[0014] In one embodiment, the flow rate of the high-flow oxygen is 25-50 slm.

[0015] And / or, the preset pressure is 770-780 Torr.

[0016] In one embodiment, the duration of the first oxidation treatment is 360-1800 s.

[0017] And / or, the temperature of the first oxidation treatment is 580-630°C.

[0018] In one embodiment, the second oxidation treatment lasts for 220-450 seconds.

[0019] And / or, the temperature of the second oxidation treatment is 580-630℃.

[0020] In one embodiment, the pressure inside the furnace tube is maintained in a stable state for 60-1800 seconds.

[0021] A second aspect of this application provides a method for fabricating a solar cell, the method comprising forming a tunneling oxide layer on the surface of a silicon wafer using the tunneling oxide layer fabrication method provided in any of the above embodiments, and then forming a polycrystalline silicon layer on the surface of the tunneling oxide layer.

[0022] A third aspect of this application provides a solar cell, which is prepared using the solar cell preparation method provided in any of the above embodiments.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) In this invention, a small flow rate of oxygen is first used to oxidize the silicon wafer. By utilizing the principle that the mean free path of gas molecules increases under low pressure, oxygen is diffused and distributed more quickly and evenly into the reaction chamber, avoiding the uneven local oxygen concentration and thermal field caused by the impact of a large flow rate of air. After the small flow rate of oxygen is used for oxidation, a layer of SiO2 has grown on the surface of the silicon wafer, which can reduce the impact of the uneven gas field caused by the large flow rate of air on the uneven oxidation rate of the subsequent oxidation. Then, a large flow rate of oxygen is used to quickly pressurize and oxidize, which shortens the oxidation time and increases the production capacity. At the same time, the pump valve is closed in a high vacuum environment and no chamber pressure is set, which avoids the air flow disturbance in the reaction chamber caused by the pump, thereby improving the uniformity of the gas field and thermal field and improving the uniformity of the tunnel oxide layer.

[0025] (2) Under high vacuum conditions, the reaction chamber space is under negative pressure relative to the external space. The pressure generated by the pressure difference makes the furnace door more airtight, avoiding the problem of uneven oxide layer tunneling at the edge of the furnace opening boat due to gas leakage during the oxidation process.

[0026] (3) Compared with LPCVD or PECVD deposition of SiO2, the low-pressure thermal oxidation method used in this invention can produce better Si-SiO2 interface states and fewer lattice defects, thereby reducing recombination losses caused by recombination centers, increasing current density, and thus effectively improving the overall efficiency of the cell. Attached Figure Description

[0027] Figure 1 This is a diagram showing the furnace tube pressure change in the method for preparing the tunneling oxide layer provided in Example 1;

[0028] Figure 2 The image shows the photosensitive effect of the tunneling oxide layer prepared using the preparation method of Example 1.

[0029] Figure 3 The image shows the photosensitive effect of the tunneling oxide layer prepared using the preparation method of Example 2.

[0030] Figure 4 The image shows the photosensitive effect of the tunneling oxide layer prepared using the preparation method of Example 3.

[0031] Figure 5 The image shows the photosensitive effect of the tunneling oxide layer prepared using the preparation method of Example 4.

[0032] Figure 6 This is a photosensitive image of the tunneling oxide layer prepared using the preparation method of Example 5;

[0033] Figure 7 This is a photosensitive image of the tunneling oxide layer prepared using the preparation method of Example 6;

[0034] Figure 8 This is a photosensitive image of the tunneling oxide layer prepared using the preparation method of Example 7;

[0035] Figure 9 This is a photosensitive image of the tunneling oxide layer prepared using the preparation method of Example 8;

[0036] Figure 10 This is a photosensitive image of the tunneling oxide layer prepared using the preparation method of Example 9;

[0037] Figure 11 This is a photosensitive image of the tunneling oxide layer prepared using the preparation method of Example 10;

[0038] Figure 12 The image shows the photosensitive effect of the tunneling oxide layer prepared using the preparation method of Example 11.

[0039] Figure 13 The image shows the photosensitive effect of the tunneling oxide layer prepared using the preparation method of Example 12.

[0040] Figure 14 The image shows the photosensitive effect of the tunneling oxide layer prepared using the preparation method of Example 13.

[0041] Figure 15 The image shows the photosensitive effect of the tunneling oxide layer prepared using the preparation method of Example 14.

[0042] Figure 16 This is a photosensitive image of the tunneling oxide layer prepared using the preparation method of Example 15;

[0043] Figure 17 The image shows the photosensitive effect of the tunneling oxide layer prepared using the method of Comparative Example 1.

[0044] Figure 18 This is a photosensitive image of the tunneling oxide layer prepared using the method of Comparative Example 2. Detailed Implementation

[0045] The following describes, with reference to the accompanying drawings, the method for preparing the tunneling oxide layer, the solar cell, and the method for preparing the solar cell according to embodiments of this application.

[0046] In this embodiment, a chemical vapor deposition (CVD) apparatus is used to prepare a tunneling oxide layer. During the preparation process, silicon wafers are placed inside boats. For example, the CVD apparatus may include a furnace tube and boats, with the boats arranged sequentially at intervals along the length of the furnace tube. Each boat carries multiple silicon wafers. The furnace tube also has an inlet for reactive gases, which may be located at the end of the furnace tube along its length.

[0047] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0048] In a first aspect, embodiments of this application provide a method for preparing a tunneling oxide layer, specifically including: in a high vacuum environment, closing the exhaust valve of the furnace tube, first introducing a small flow of oxygen to perform a first oxidation treatment on the silicon wafer inside the furnace tube, then introducing a large flow of oxygen to perform a second oxidation treatment on the silicon wafer inside the furnace tube, stopping the introduction of the large flow of oxygen after reaching a preset pressure, and then maintaining the pressure inside the furnace tube in a stable state to grow a tunneling oxide layer on the surface of the silicon wafer.

[0049] In the above scheme, a small flow rate of oxygen is first used to oxidize the silicon wafer. Utilizing the principle that the mean free path of gas molecules increases under low pressure, oxygen diffuses and distributes more quickly and evenly into the reaction chamber, avoiding the uneven local oxygen concentration and thermal field caused by the impact of a large flow rate. Furthermore, after oxidation with a small flow rate of oxygen, a layer of SiO2 has grown on the silicon wafer surface, which can reduce the impact of uneven gas field caused by a large flow rate on the subsequent uneven oxidation rate. Then, a large flow rate of oxygen is used for rapid pressurization oxidation, shortening the oxidation time and increasing production capacity. At the same time, the evacuation valve is closed in a high vacuum environment, and no chamber pressure is set, avoiding airflow disturbance in the reaction chamber caused by evacuation, thereby improving the uniformity of the gas field and thermal field and improving the uniformity of the tunnel oxide layer.

[0050] Furthermore, during the first oxidation process, the pressure increase rate inside the furnace tube is 5.5-28 Torr / min. Since the temperature of the oxygen during inlet differs from the temperature inside the furnace tube, if the pressure increase rate is too rapid, it will result in significant temperature differences between the inlet and areas far from the inlet, causing uneven thermal distribution within the furnace tube and affecting the uniformity of the tunneling oxide layer on the silicon wafer surface. In practical applications, the pressure increase rate inside the furnace tube can be 5.5 Torr / min, 10 Torr / min, 15 Torr / min, 20 Torr / min, 25 Torr / min, 28 Torr / min, or any value within any two of these ranges.

[0051] Furthermore, during the second oxidation process, the pressure increase rate inside the furnace tube is 75-155 Torr / min. During the second oxidation process, a layer of SiO2 has already grown on the silicon wafer surface, and a large flow of oxygen is introduced to oxidize the silicon wafer. Therefore, the pressure increase rate inside the furnace tube during the second oxidation process is greater than that during the first oxidation process. However, if the pressure increase rate is too high, it will also disrupt the gas and thermal fields inside the furnace tube. Therefore, a pressure increase rate of 75-155 Torr / min is selected. In practical applications, the pressure increase rate inside the furnace tube can be 75 Torr / min, 85 Torr / min, 95 Torr / min, 105 Torr / min, 115 Torr / min, 125 Torr / min, 135 Torr / min, 145 Torr / min, 155 Torr / min, or any value within any two of the above ranges.

[0052] Furthermore, the flow rate of the low-flow oxygen is 2-10 slm. Introducing oxygen at a lower flow rate and under lower pressure allows for a more uniform distribution of oxygen within the furnace tube. Specifically, the flow rate of the low-flow oxygen can be 2 slm, 2.5 slm, 3 slm, 3.5 slm, 4 slm, 4.5 slm, 5 slm, 5.5 slm, 6 slm, 6.5 slm, 7 slm, 7.5 slm, 8 slm, 8.5 slm, 9 slm, 9.5 slm, or 10 slm, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0053] Furthermore, when the pressure inside the furnace tube reaches 180-250 Torr, the small flow rate of oxygen is stopped. For example, this could be 180 Torr, 190 Torr, 200 Torr, 210 Torr, 220 Torr, 230 Torr, 240 Torr, 250 Torr, or any value within any two of these ranges. In this way, even at pressures below atmospheric pressure, the oxygen introduced into the furnace tube can be distributed more evenly within the tube, resulting in a more uniform growth of the tunneled oxide layer on the silicon wafer surface.

[0054] Furthermore, the flow rate of the high-flow-rate oxygen is 25-50 slm, for example, it can be 25 slm, 26 slm, 28 slm, 30 slm, 32 slm, 34 slm, 36 slm, 38 slm, 40 slm, 42 slm, 44 slm, 46 slm, 48 slm, or 50 slm, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Oxygenation with a high flow rate can rapidly increase the pressure for oxidation, thereby shortening the oxidation time.

[0055] Furthermore, the preset pressure is 770-780 Torr, meaning the pressure inside the furnace tube exceeds atmospheric pressure (760 Torr) by 10-20 Torr. The flow of high-flow-rate oxygen is stopped when the pressure inside the furnace tube reaches the preset pressure. For example, this pressure can be 10, 12, 14, 16, 18, or 20 Torr above atmospheric pressure, or any value within any two of these ranges. During the high-flow-rate oxygen charging process, the pressure inside the furnace tube rises from below atmospheric pressure to slightly above atmospheric pressure. This allows for uniform oxygen distribution within the furnace tube at the below-atmospheric pressure level, and also allows for stopping oxygen supply when the pressure exceeds atmospheric pressure by 10-20 Torr, while simultaneously maintaining a stable pressure inside the furnace tube. This pressurized oxidation within the furnace tube achieves rapid oxidation and shortens the oxidation time.

[0056] Furthermore, the duration of the first oxidation treatment is 360-1800s, for example, it can be 360s, 400s, 500s, 600s, 700s, 800s, 900s, 1000s, 1100s, 1200s, 1300s, 1400s, 1500s, 1600s, 1700s or 1800s, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0057] Furthermore, the temperature of the first oxidation treatment is 580-630℃, for example, 580℃, 585℃, 590℃, 595℃, 600℃, 605℃, 610℃, 615℃, 620℃, 625℃, or 630℃, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Maintaining the temperature inside the furnace tube during the oxidation process reduces interference caused by overheating and expansion between adjacent silicon wafers, preventing interference from affecting the growth of the tunnel oxide layer and improving the uniformity of the film formation on each silicon wafer.

[0058] Furthermore, the duration of the second oxidation treatment is 220-450 seconds, for example, 220s, 240s, 260s, 280s, 300s, 320s, 340s, 360s, 380s, 400s, 420s, 440s, or 450s, but is not limited to the listed values; other unlisted values ​​within this range also apply. Because the second oxidation treatment uses a high flow rate of oxygen, the duration of the second oxidation treatment is shorter than that of the first oxidation treatment.

[0059] Furthermore, the temperature of the second oxidation treatment is 580-630℃, for example, it can be 580℃, 585℃, 590℃, 595℃, 600℃, 605℃, 610℃, 615℃, 620℃, 625℃ or 630℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0060] Furthermore, by stopping the oxygen supply and maintaining the temperature inside the furnace tube at 580-630℃, the oxygen introduced in the previous stage is used as a reaction gas, and no more oxygen is introduced. This reduces the drastic fluctuations in the gas atmosphere caused by the turbulence of the reaction gas inside the furnace tube due to the introduction of oxygen. This not only improves the uniformity of the film layer of silicon wafers in the same batch, but also improves the uniformity of the tunnel oxide layer between different batches of silicon wafers.

[0061] Furthermore, maintaining a stable pressure within the furnace tube for 60-1800 s can further improve the uniformity of oxygen distribution within the furnace tube, thereby enhancing the uniformity of the tunneling oxide layer formed on the silicon wafer surface. Based on the growth thickness of the tunneling oxide layer, the pressure maintenance time within the furnace tube can be any value within the range of 60 s, 200 s, 400 s, 600 s, 800 s, 1000 s, 1200 s, 1400 s, 1600 s, 1800 s, or any two of the above values.

[0062] In specific implementation, the method for preparing the tunneling oxide layer in this application embodiment includes:

[0063] Step 1: Entering the Boat

[0064] The silicon wafers are loaded into a small boat and pushed into the furnace tube. After loading, the furnace tube is evacuated to a vacuum level of less than 20 mTorr, or the bottom pressure of the deposition equipment, and then leaks are checked.

[0065] Step 2: Oxygenation

[0066] Heat the furnace tube to 580-630℃. After the temperature stabilizes, first introduce a small flow of oxygen (2-10 slm) for the first oxidation treatment. Stop introducing the small flow of oxygen when the pressure inside the furnace tube reaches 180-250 Torr. Then introduce a large flow of oxygen (25-50 slm). Stop introducing the large flow of oxygen when the pressure inside the furnace tube exceeds atmospheric pressure by 10-20 Torr.

[0067] Step 3: Oxidation by sealing the tube

[0068] Maintain a stable pressure inside the furnace tube for 60-1800 seconds to grow a tunneling oxide layer on the surface of the silicon wafer.

[0069] The following are several specific embodiments illustrating the preparation method of the tunneling oxide layer in this application.

[0070] Example 1

[0071] This embodiment provides a method for preparing a tunneling oxide layer, specifically including the following steps:

[0072] (1) Heat the furnace tube to 580℃. After the temperature stabilizes, first introduce a small flow of oxygen (6 slm) for the first oxidation treatment. The pressure inside the furnace tube increases at a rate of 15 Torr / min. Stop introducing the small flow of oxygen when the pressure inside the furnace tube reaches 220 Torr. The first oxidation treatment lasts for 1000 s. Then, introduce a large flow of oxygen (40 slm) for the second oxidation treatment. The pressure inside the furnace tube increases at a rate of 120 Torr / min. Stop introducing the large flow of oxygen when the pressure inside the furnace tube exceeds atmospheric pressure by 15 Torr. The second oxidation treatment lasts for 350 s. (See the furnace tube pressure versus time curve). Figure 1 );

[0073] (2) Maintain the pressure inside the furnace tube at a stable state for 900s in order to grow a tunnel oxide layer on the surface of the silicon wafer.

[0074] Example 2

[0075] This embodiment provides a method for preparing a tunneling oxide layer. Based on embodiment 1, the temperature of the furnace tube in step (1) is changed to 595°C.

[0076] Example 3

[0077] This embodiment provides a method for preparing a tunneling oxide layer. Based on embodiment 1, the temperature of the furnace tube in step (1) is changed to 615°C.

[0078] Example 4

[0079] This embodiment provides a method for preparing a tunneling oxide layer. Based on embodiment 1, the temperature of the furnace tube in step (1) is changed to 630°C.

[0080] Example 5

[0081] This embodiment provides a method for preparing a tunneling oxide layer, specifically including the following steps:

[0082] (1) Heat the furnace tube to 595℃. After the temperature stabilizes, first introduce a small flow of oxygen of 2slm for the first oxidation treatment. The rate of pressure increase in the furnace tube is 5.5 Torr / min. When the pressure in the furnace tube reaches 180 Torr, stop introducing the small flow of oxygen. The time for the first oxidation treatment is 1800s. Then introduce a large flow of oxygen of 25slm for the second oxidation treatment. The rate of pressure increase in the furnace tube is 75 Torr / min. When the pressure in the furnace tube exceeds atmospheric pressure by 10 Torr, stop introducing the large flow of oxygen. The time for the second oxidation treatment is 450s.

[0083] 2) Maintain the pressure inside the furnace tube at a stable level for 1800s to grow a tunnel oxide layer on the surface of the silicon wafer.

[0084] Example 6

[0085] This embodiment provides a method for preparing a tunneling oxide layer. Based on embodiment 5, the rate of increase of the pressure inside the furnace tube during the first oxidation process in step (1) is changed to 10 Torr / min.

[0086] Example 7

[0087] This embodiment provides a method for preparing a tunneling oxide layer. Based on embodiment 5, the rate of increase of the pressure inside the furnace tube during the first oxidation process in step (1) is changed to 20 Torr / min.

[0088] Example 8

[0089] This embodiment provides a method for preparing a tunneling oxide layer. Based on embodiment 5, the rate of increase of the pressure inside the furnace tube during the first oxidation process in step (1) is changed to 28 Torr / min.

[0090] Example 9

[0091] This embodiment provides a method for preparing a tunneling oxide layer. Based on embodiment 5, the rate of increase of the pressure inside the furnace tube during the second oxidation process in step (1) is changed to 100 Torr / min.

[0092] Example 10

[0093] This embodiment provides a method for preparing a tunneling oxide layer. Based on embodiment 5, the rate of increase of the pressure inside the furnace tube during the second oxidation process in step (1) is changed to 120 Torr / min.

[0094] Example 11

[0095] This embodiment provides a method for preparing a tunneling oxide layer. Based on embodiment 5, the rate of increase of the pressure inside the furnace tube during the second oxidation process in step (1) is changed to 155 Torr / min.

[0096] Example 12

[0097] This embodiment provides a method for preparing a tunneling oxide layer, specifically including the following steps:

[0098] (1) Heat the furnace tube to 615℃. After the temperature stabilizes, first introduce a small flow of oxygen of 10slm for the first oxidation treatment. The pressure inside the furnace tube increases at a rate of 28 Torr / min. When the pressure inside the furnace tube reaches 250 Torr, stop introducing the small flow of oxygen. The time for the first oxidation treatment is 360s. Then introduce a large flow of oxygen of 50slm for the second oxidation treatment. The pressure inside the furnace tube increases at a rate of 155 Torr / min. When the pressure inside the furnace tube exceeds atmospheric pressure by 20 Torr, stop introducing the large flow of oxygen. The time for the second oxidation treatment is 220s.

[0099] (2) Maintain the pressure inside the furnace tube at a stable state for 60 seconds in order to grow a tunnel oxide layer on the surface of the silicon wafer.

[0100] Example 13

[0101] This embodiment provides a method for preparing a tunneling oxide layer. Based on Example 12, the time for maintaining the pressure inside the furnace tube in step (2) is changed to 600s.

[0102] Example 14

[0103] This embodiment provides a method for preparing a tunneling oxide layer. Based on Example 12, the time for maintaining the pressure inside the furnace tube in step (2) is changed to 1200s.

[0104] Example 15

[0105] This embodiment provides a method for preparing a tunneling oxide layer. Based on Example 12, the time for maintaining the pressure inside the furnace tube in step (2) is changed to 1800s.

[0106] Secondly, embodiments of this application also provide a method for preparing a solar cell, the method comprising:

[0107] The method for preparing a tunneling oxide layer according to any of the above embodiments forms a tunneling oxide layer on the surface of a silicon wafer, and then forms a polycrystalline silicon layer on the surface of the tunneling oxide layer, specifically including:

[0108] Step 4: Vacuuming

[0109] After the tunnel oxide layer is prepared, open the evacuation valve on the furnace tube to evacuate the furnace tube and keep the vacuum level inside the furnace tube less than 20 mTorr.

[0110] Step 5: Back pressure

[0111] Nitrogen gas is introduced into the furnace tube for back pressure, and the pressure is kept stable. The nitrogen flow rate is 700 sccm, and the back pressure range is 150 torr-250 torr.

[0112] Step Six: Amorphous Silicon Growth

[0113] After the pressure and temperature inside the furnace tube stabilize, SiH4 is introduced for amorphous silicon growth. The flow rate of SiH4 is 420-1250 sccm, and the duration is 2280-5200 s. After the amorphous silicon growth is completed, the remaining SiH4 in the furnace tube is first evacuated to remove it, and then nitrogen is introduced to purge for 150-200 s to further remove the remaining SiH4 in the furnace tube.

[0114] Step 7: Cooling down before unloading the boat

[0115] Once the temperature inside the furnace tube has dropped to room temperature, the vacuum is broken to remove the small boat from the furnace tube.

[0116] Step 8: Annealing

[0117] Annealing is performed on silicon wafers to convert amorphous silicon into polycrystalline silicon.

[0118] In this application, the specific preparation conditions of the polycrystalline silicon layer do not affect the uniformity of the tunnel oxide layer. As long as the preparation of the polycrystalline silicon layer can be achieved, only the parameter range of each process step is disclosed here, without special explanation of its specific point values.

[0119] Thirdly, embodiments of this application also provide a solar cell, which is fabricated using any of the solar cell fabrication methods described above. It should be noted that the fabrication methods for the solar cell have been described in detail in the foregoing embodiments and will not be repeated here.

[0120] Comparative Example 1

[0121] This comparative example provides a method for preparing a tunneling oxide layer. Except for changing the flow rate of the small flow rate of oxygen in step (1) and the flow rate of the large flow rate of oxygen in step (1) to 25 slm, the other steps and conditions are the same as in Example 1, so they will not be repeated here.

[0122] Comparative Example 2

[0123] This comparative example provides a method for preparing a tunneling oxide layer. Except for changing the flow rate of the small flow rate of oxygen in step (1) and the flow rate of the large flow rate of oxygen in step (1) to 10 slm, the other steps and conditions are the same as in Example 1, so they will not be repeated here.

[0124] Performance testing

[0125] The uniformity of the tunneling oxide layers obtained in Examples 1-15 and Comparative Examples 1-2 was tested. The relevant testing methods were: performing PL detection, detecting the photoluminescence brightness, and obtaining the corresponding photosensitive effect image.

[0126] Figure 2 These are photosensitizing images of a solar cell containing the tunneling oxide layer obtained in Example 1, used in a photoluminescence experiment. The photosensitizing images of the tunneling oxide layers obtained in Examples 1-15 are respectively shown below. Figures 2-16 As shown.

[0127] Figure 17 and Figure 18 These are the photosensitive images of the tunneling oxide layer obtained from Comparative Example 1 and Comparative Example 2, respectively.

[0128] In the photosensitive image, the more uniform the color, the better the uniformity of the tunneling oxide layer.

[0129] visible, Figures 2-16 The color in the middle is relatively uniform, while Figure 17 and Figure 18 Uneven color in the middle, that is Figures 2-16 The uniformity effect is significantly better than Figure 17 and Figure 18 The photosensitive effect diagram shown indicates that the method for preparing the tunneling oxide layer according to the embodiments of this application can improve the film quality of the tunneling oxide layer formed on the silicon wafer, that is, improve the film uniformity of each region on the tunneling oxide layer on the same silicon wafer.

[0130] Therefore, this invention first uses a small flow rate of oxygen to oxidize the silicon wafer. Utilizing the principle that the mean free path of gas molecules increases under low pressure, oxygen diffuses and distributes more quickly and evenly into the reaction chamber, avoiding the uneven local oxygen concentration and thermal field caused by the impact of a large flow rate. Furthermore, after oxidation with a small flow rate of oxygen, a layer of SiO2 has grown on the silicon wafer surface, which can reduce the impact of uneven gas field caused by a large flow rate on the subsequent uneven oxidation rate. Then, a large flow rate of oxygen is used for rapid pressurized oxidation, shortening the oxidation time and increasing production capacity. At the same time, the pump valve is closed in a high vacuum environment, and no chamber pressure is set, avoiding airflow disturbance in the reaction chamber caused by pumping, thereby improving the uniformity of the gas field and thermal field, and improving the uniformity of the tunnel oxide layer.

[0131] In addition, under high vacuum conditions, the reaction chamber is under negative pressure relative to the external space. The pressure generated by the pressure difference makes the furnace door more airtight, avoiding the problem of uneven oxide layer tunneling through the edge of the furnace boat due to air leakage during the oxidation process.

[0132] Furthermore, compared to LPCVD or PECVD deposition of SiO2, the low-pressure thermal oxidation method used in this invention can produce better Si-SiO2 interface states and fewer lattice defects, thereby reducing recombination losses caused by recombination centers, increasing current density, and thus effectively improving the overall efficiency of the solar cell.

[0133] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method of forming a tunnel oxide, comprising: The preparation method includes: in a high vacuum environment, closing the exhaust valve of the furnace tube, first introducing a small flow of oxygen to perform a first oxidation treatment on the silicon wafer in the furnace tube, then introducing a large flow of oxygen to perform a second oxidation treatment on the silicon wafer in the furnace tube, stopping the introduction of a large flow of oxygen after reaching the preset pressure, and then maintaining the pressure in the furnace tube in a stable state to grow a tunneling oxide layer on the surface of the silicon wafer.

2. The production method according to claim 1, characterized by, During the first oxidation process, the pressure inside the furnace tube increases at a rate of 5.5-28 Torr / min.

3. The preparation method according to claim 1, characterized in that, During the second oxidation process, the pressure inside the furnace tube increases at a rate of 75-155 Torr / min.

4. The production method according to claim 1, characterized by, The flow rate of the low-flow oxygen is 2-10 slm; And / or, stop supplying a small flow of oxygen when the pressure inside the furnace tube reaches 180-250 Torr.

5. The preparation method according to claim 1, characterized in that, The flow rate of the high-flow oxygen is 25-50 slm; And / or, the preset pressure is 770-780 Torr.

6. The method of any one of claims 1-5, wherein, The duration of the first oxidation treatment is 360-1800 seconds; And / or, the temperature of the first oxidation treatment is 580-630°C.

7. The method of any one of claims 1-5, wherein, The second oxidation treatment lasts for 220-450 seconds. And / or, the temperature of the second oxidation treatment is 580-630℃.

8. The method of any one of claims 1-5, wherein, The pressure inside the furnace tube remains stable for 60-1800 seconds.

9. A method for producing a solar cell, characterized by, A tunneling oxide layer is formed on the surface of a silicon wafer using the preparation method described in any one of claims 1-8, and then a polycrystalline silicon layer is formed on the surface of the tunneling oxide layer.

10. A solar cell, characterized by, The solar cell is prepared using the method for preparing a solar cell as described in claim 9.

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