Method for growing tunneling oxide layer of XBC battery

Abstract

The invention discloses a method for growing a tunneling oxide layer of an XBC battery, and relates to the technical field of XBC battery manufacturing, and the method comprises the steps: enabling a silicon wafer to enter a furnace tube after cleaning, and setting the standby temperature of the furnace tube to be 450 DEG C; vacuumizing, raising the temperature of the furnace tube to 500-530 DEG C, controlling the pressure of the furnace tube to be low pressure, and respectively introducing nitrogen and oxygen carrying water vapor to grow a first tunneling oxide layer; after the growth is finished, the furnace tube starts to be heated and vacuumized, and the furnace tube is purged by nitrogen and vacuumized; raising the temperature of the furnace tube to 600-630 DEG C, introducing oxygen at the same time, closing the vacuum pump to stop vacuumizing operation, and enabling the pressure of the furnace tube to return to normal pressure to grow a second tunneling oxide layer; and after the growth is finished, purging and vacuumizing. The low-temperature growth stage can avoid thermal damage to the silicon wafer caused by high temperature in the traditional process, the yield of the silicon wafer is improved, hydrogen ions in wet oxygen can achieve hydrogen passivation, and the passivation performance of the tunneling oxide layer is improved by matching with the dense oxide layer grown in dry oxygen, so that the photoelectric conversion efficiency of the XBC battery is improved.

Description

Technical Field

[0001] This invention relates to the field of XBC battery manufacturing technology, specifically a method for growing a tunnel oxide layer in XBC batteries. Background Technology

[0002] LPCVD is one of the key processes in the production of XBC solar cells. The key technologies of XBC cells lie in the excellent passivation and good contact of high-quality ultrathin silicon oxide and doped polycrystalline silicon layers (p+poly and n+poly layers). The ultrathin silicon oxide directly contacts the silicon surface to avoid contact between the semiconductor silicon and the metal electrodes, thereby reducing recombination and carrier collection losses at the back surface of the cell and achieving excellent surface passivation. Currently, XBC cell factories mainly grow tunneling oxide layers using the LPCVD process at high temperatures with oxygen. Although this method produces tunneling oxide layers with good density, the growth rate is slow because the oxygen used throughout the process is dry oxygen, resulting in a long process time, which is not conducive to increasing factory capacity. Furthermore, it requires high temperatures, which can cause thermal damage to the silicon wafer.

[0003] Based on this, a method for growing a tunnel oxide layer in XBC batteries is now provided, which can eliminate the drawbacks of existing technical solutions. Summary of the Invention

[0004] The purpose of this invention is to provide a method for growing a tunnel oxide layer in XBC cells, so as to solve the problems of long oxidation time, high temperature and easy thermal damage to silicon wafers in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for growing a tunnel oxide layer in an XBC solar cell specifically includes the following steps: Step S1: The cleaned silicon wafers are placed into the LPCVD furnace tube, and the standby temperature of the furnace tube is set to 450℃. Step S2: Perform a vacuuming operation while raising the furnace tube temperature to 500-530°C. Step S3: Control the furnace tube pressure at a low pressure of 300-500 mtorr, and introduce nitrogen and oxygen carrying water vapor to grow the first tunnel oxide layer. The growth time is set to 60-120 seconds. Step S4: After the first tunnel oxide layer has grown, the LPCVD furnace tube is heated and a vacuuming operation is performed. The inside of the LPCVD furnace tube is purged with nitrogen and a vacuuming operation is performed again to remove residual water vapor and oxygen inside the furnace tube. Step S5: Raise the furnace tube temperature to 600-630°C, introduce oxygen at the same time, turn off the vacuum pump to stop the vacuuming operation, and return the furnace tube pressure to atmospheric pressure to grow the second tunnel oxide layer. Set the growth time to 600-800 seconds. Step S6: After the growth oxidation operation is completed, perform a purging and vacuuming operation to remove residual oxygen in the furnace tube.

[0006] Furthermore, in step S3, the flow rate of nitrogen carrying water vapor is 500-800 sccm, and the flow rate of oxygen is 1000-1500 sccm.

[0007] Furthermore, the oxygen flow rate introduced in step S5 is 15,000 to 30,000 sccm.

[0008] Furthermore, in step S3, the growth thickness of the first tunneling oxide layer is 0.8–1 nm.

[0009] Furthermore, in step S3, the nitrogen carrying water vapor is prepared by bubbling nitrogen gas through deionized water.

[0010] Furthermore, in step S5, the growth thickness of the second tunneling oxide layer is 0.7–0.8 nm.

[0011] Furthermore, the total thickness of the first tunneling oxide layer and the second tunneling oxide layer is controlled to be 1.5 to 1.8 nm.

[0012] Furthermore, in step S5, the purity of the oxygen is ≥99.99%.

[0013] Furthermore, in step S5, the atmospheric pressure is 760,000 mtorr.

[0014] Furthermore, the silicon wafer in step S1 is a P-type monocrystalline silicon wafer or an N-type monocrystalline silicon wafer.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a method for growing a tunneling oxide layer in XBC cells. Since the oxidation rate of wet oxygen is 5 to 10 times that of dry oxygen, this method can significantly reduce the growth time of the first tunneling oxide layer. Combined with eliminating the tube-battery oxidation step, the overall oxidation time is reduced by 50% to 60%, effectively increasing factory capacity. Furthermore, the furnace tube standby temperature and the growth temperature of the first tunneling oxide layer are both reduced by 100°C, and the dry oxygen flow rate is reduced by 20% to 50%, further reducing gas consumable costs. In addition, the low-temperature growth stage of this invention can avoid the thermal damage to silicon wafers caused by the high temperatures of traditional processes, improving the silicon wafer yield. Hydrogen ions in wet oxygen can achieve hydrogen passivation, which, combined with the dense oxide layer grown by dry oxygen, significantly improves the passivation performance of the tunneling oxide layer, thereby improving the photoelectric conversion efficiency of XBC cells. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the method steps of the present invention.

[0017] Figure 2 This is a schematic diagram of the method steps in Comparative Example 1. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0019] Currently, the growth of tunneling oxide layers in XBC battery factories mainly relies on LPCVD thermo-oxidative growth, as shown in Comparative Example 1. Addressing the issues of long processing times and high-temperature thermal damage, this invention proposes a method for growing tunneling oxide layers using a combination of wet and dry oxygen at low and high temperatures. By introducing a mixed gas of wet and dry oxygen, the tunneling oxide growth rate is increased, and the hydrogen ions in the water from the wet oxygen process enhance hydrogen passivation (hydrogen passivation refers to the process by which hydrogen ions...). + A surface treatment method that combines dangling bonds on the silicon surface to reduce the interface state density and thus reduce the carrier recombination rate is beneficial to improving the passivation effect of the tunneling oxide layer. The quality of tunneling oxygen growth is improved by introducing dry oxygen. The specific steps of the above method are shown in Example 1.

[0020] Example 1 In this embodiment, as Figure 1 As shown, a method for growing a tunneling oxide layer in an XBC cell specifically includes the following steps: Step S1: The cleaned silicon wafer enters the LPCVD furnace tube. The standby temperature of the furnace tube is set to 450℃. LPCVD, or Low Pressure Chemical Vapor Deposition, is a process that deposits thin films on the surface of a substrate through chemical reactions under low pressure. It is commonly used in the fabrication of semiconductors and photovoltaic devices. Specifically, the silicon wafer is a P-type monocrystalline silicon wafer or an N-type monocrystalline silicon wafer, and the furnace tube standby temperature is reduced from 550°C in the existing technology to 450°C in the improved version, which is a reduction of 100°C. Step S2: Perform a vacuuming operation while raising the furnace tube temperature to 500-530°C. Specifically, the furnace tube temperature is preferably 500–530℃. With the gas flow rate and growth time remaining constant, several control groups with different growth temperatures are set up, including 400–450℃, 450–500℃, 500–530℃, 530–560℃, and 560–600℃. When the furnace tube temperature is set to 400–450℃, the thickness of the first tunneling oxide layer is 0.4–0.5 nm; when the furnace tube temperature is set to 450–500℃, the thickness of the first tunneling oxide layer is 0.5–0.6 nm; and when the furnace tube temperature is set to 500–530℃… The thickness of the first tunneling oxide layer is 0.8–1.0 nm. When the furnace tube temperature is set to 530–560°C, the thickness of the first tunneling oxide layer is 1.4–1.8 nm. When the furnace tube temperature is set to 560–600°C, the thickness of the first tunneling oxide layer is 2.2–2.5 nm. It can be seen that if the furnace tube temperature is too low, the tunneling oxide growth rate will be very slow, and if the furnace tube temperature is too high, the tunneling oxide growth rate will be too fast, neither of which can achieve the required tunneling oxide thickness. Therefore, the preferred furnace tube temperature of this invention is 500–530°C, at which the tunneling oxide thickness can reach the required value. Step S3: Control the furnace tube pressure at a low pressure of 300-500 mtorr, and introduce nitrogen and oxygen carrying water vapor to grow the first tunnel oxide layer. The growth time is set to 60-120 seconds. Specifically, the tunneling oxide layer is an ultrathin insulating oxide layer located between the silicon substrate and the doped polycrystalline silicon layer. It is used to reduce carrier recombination and improve surface passivation performance. The growth thickness of the first tunneling oxide layer is 0.8-1 nm. The flow rate of nitrogen carrying water vapor is 500-800 sccm, and the flow rate of oxygen is 1000-1500 sccm. The nitrogen carrying water vapor is prepared by bubbling nitrogen into deionized water. By controlling the bubbler temperature (20-30℃) and the nitrogen flow rate, a stable output of water vapor content can be achieved. The water vapor content can be monitored in real time by a dew point meter to ensure a stable supply of water vapor during the oxidation reaction. The preferred growth time for this step is 60–120 seconds. With constant gas flow rate and furnace tube temperature, several control groups with different growth times are set up, including 30–60 seconds, 60–120 seconds, 120–180 seconds, and 180–240 seconds. When the growth time is set to 30–60 seconds, the thickness of the first tunneling oxide layer is 0.5–0.6 nm; when the growth time is set to 60–120 seconds, the thickness of the first tunneling oxide layer is 0.8–1.0 nm. When the growth time is set to 120-180 seconds, the thickness of the first tunneling oxide layer is 1.3-1.6 nm. When the growth time is set to 180-240 seconds, the thickness of the first tunneling oxide layer is 1.8-2.2 nm. It can be seen that too short a growth time will result in a tunneling oxide layer that is too thin, and too long a growth time will result in a tunneling oxide layer that is too thick. Neither of these can achieve the required tunneling oxide thickness. Therefore, the preferred growth time of this invention is 60-120 seconds, at which the tunneling oxide thickness can reach the required value. The preferred flow rate of nitrogen carrying water vapor in this step is 500–800 sccm, and the preferred flow rate of oxygen is 1000–1500 sccm. With the growth time and furnace tube temperature constant, several control groups with different gas flow rates are set up: when the nitrogen flow rate carrying water vapor is set to 200–400 sccm and the oxygen flow rate is set to 400–800 sccm, the thickness of the first tunneling oxide layer is 0.5–0.7 nm. When the nitrogen flow rate carrying water vapor is set to 500–800 sccm and the oxygen flow rate is set to 1000–1500 sccm... When the flow rate is sccm, the thickness of the first tunneling oxide layer is 0.8–1.0 nm. When the flow rate of nitrogen carrying water vapor is set to 900–1200 sccm and the flow rate of oxygen is set to 1600–2000 sccm, the thickness of the first tunneling oxide layer is 1.4–1.6 nm. It can be seen that if the flow rate of the gas is too low or too high, the required tunneling oxide thickness cannot be achieved. Therefore, the present invention preferably uses a flow rate of 500–800 sccm for nitrogen carrying water vapor and a flow rate of 1000–1500 sccm for oxygen. At this gas flow rate, the tunneling oxide thickness can reach the required value. Step S4: After the first tunnel oxide layer growth is completed, the LPCVD furnace tube is heated and a vacuuming operation is performed. The inside of the LPCVD furnace tube is purged with nitrogen and a vacuuming operation is performed again to remove residual water vapor and oxygen in the furnace tube, so as to avoid affecting the subsequent dry oxygen oxidation effect. Dry oxygen refers to high-purity oxygen without water vapor, with a purity ≥99.99% (volume fraction), which is usually used for high-temperature oxidation to form a dense oxide layer. Step S5: Raise the furnace tube temperature to 600-630°C, introduce oxygen at the same time, turn off the vacuum pump to stop the vacuuming operation, and return the furnace tube pressure to atmospheric pressure to grow the second tunnel oxide layer. The growth time is set to 600-800 seconds to meet the passivation requirements of XBC cells. Specifically, the oxygen flow rate is 15,000–30,000 sccm, the oxygen purity is ≥99.99%, the atmospheric pressure is 760,000 mtorr, the growth thickness of the second tunneling oxide layer is 0.7–0.8 nm, and the total thickness of the first and second tunneling oxide layers is controlled at 1.5–1.8 nm. The furnace tube temperature and growth time for the dry oxygen high-temperature growth of the second tunneling oxide layer are the same as those for existing tunneling oxygen growth. When the oxygen flow rate is also the same as the existing 30,000–35,000 sccm, the thickness of the second tunneling oxide layer is 1.0–1.2 nm, which exceeds the required thickness. Therefore, this invention adjusts it to 15,000–30,000 sccm. This parameter makes the thickness of the second tunneling oxide layer 0.7–0.8 nm, while reducing the oxygen flow rate by 20%–50%. Step S6: After the growth oxidation operation is completed, perform a purging and vacuuming operation to remove residual oxygen in the furnace tube; In this embodiment, considering that dry oxygen oxidation is slow at low temperatures, resulting in a thinner tunneling oxide layer and poorer passivation, thus failing to achieve the desired improvement effect, and that dry oxygen can only grow a tunneling oxide layer to the required thickness at high temperatures for a long time, this would prolong the process time, and the energy consumption of the oxide layer growth equipment would also be relatively high if the entire process is carried out at high temperatures, while the oxidation rate of wet oxygen is 5 to 10 times that of dry oxygen, and the hydrogen ions in the water of wet oxygen can increase hydrogen passivation, which is beneficial to improving the passivation effect of the tunneling oxide layer. Therefore, this method uses dry oxygen combined with low-temperature and high-temperature mixed oxidation to grow the tunneling oxide layer in the early stage. While ensuring the acquisition of a high-quality tunneling oxide layer, it shortens the growth time of the tunneling oxide layer, thereby reducing the overall LPCVD process time. The energy consumption of growing the tunneling oxide layer at low temperatures is lower than that at high temperatures, thus reducing the overall production cost.

[0021] Comparative Example 1 The difference from Example 1 is that, as in Example 1, Figure 2 As shown, the existing process flow for traditional LPCVD thermo-oxidative growth of tunnel oxide layers specifically includes the following steps: Step 1: The cleaned silicon wafers are placed into the LPCVD furnace tube. The standby temperature of the furnace tube is set to 550°C. The silicon wafers are either P-type or N-type monocrystalline silicon wafers. The silicon wafer selection parameters, as well as the parameters and equipment in the silicon wafer pretreatment, are the same as in Example 1. The only difference between this step and step S1 in Example 1 is the furnace tube standby temperature. Step 2: Perform a vacuuming operation and simultaneously raise the furnace tube temperature to 600-630°C. The vacuuming operation, LPCVD furnace tube parameters, and equipment are the same as in Example 1. The only difference between this step and step S2 in Example 1 is the furnace tube temperature. Step 3: Introduce oxygen, turn off the vacuum pump to stop the vacuuming operation, and return the furnace tube pressure to atmospheric pressure to grow the tunnel oxide layer. The growth time is set to 400-800 seconds, the oxygen flow rate is 30000-35000 sccm, the oxygen purity is ≥99.99%, and the atmospheric pressure is 760000 mtorr. This step differs from step S5 in Example 1 in terms of gas flow rate and growth time. Step 4: After stopping the oxygen supply, oxidize the furnace tubes under normal pressure with oxygen filling for 800-1000 seconds at a temperature of 600-630℃, and control the thickness of the tunneling oxide layer to 1.5-1.8 nm. Step 5: After the tube annealing oxidation operation is completed, perform a purging and vacuuming operation to remove residual oxygen inside the furnace tubes; The improvements made by comparing Example 1 with the present comparative example are in the furnace tube standby temperature, growth time, gas flow rate and furnace tube temperature. The parameters of the comparative example and the example are compared as shown in Table 1 below. Table 1 - Parameter Comparison Table between Example 1 and Comparative Example 1 ; According to the table above, the LPCVD furnace tube standby temperature was reduced from 550℃ to the improved 450℃, a decrease of 100℃, resulting in a reduction of energy consumption of approximately 16%. Compared with the dry oxygen growth tunneling oxide layer in Comparative Example 1, the wet oxygen growth tunneling oxide layer in Example 1 reduced the oxidation growth temperature by 100℃ (from 600-630℃ to 500-530℃), resulting in a reduction of energy consumption of approximately 16%. The wet oxygen growth tunneling oxide layer is faster and shorter, reducing the total oxidation time by approximately 50%-60% compared to the dry oxygen growth tunneling oxide layer, from the original 1200-1800s to 460-920s. The existing process uses dry oxygen with a flow rate of 30000-35000 sccm, while the dry oxygen flow rate in Example 1 is 15000-30000 sccm, a reduction of 20%-50%.

[0022] In summary, this invention introduces water vapor during the wet oxygen stage to increase the oxidation rate and achieve hydrogen passivation. It also combines high-temperature densification during the dry oxygen stage to form a tunnel oxide layer with a complete structure and excellent passivation performance, thereby shortening the growth time and furnace tube temperature, and has good industrial application value.

[0023] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for growing a tunneling oxide layer in an XBC battery, characterized in that, Specifically, the following steps are included: Step S1: The cleaned silicon wafers are placed into the LPCVD furnace tube, and the standby temperature of the furnace tube is set to 450℃. Step S2: Perform a vacuuming operation while raising the furnace tube temperature to 500-530°C. Step S3: Control the furnace tube pressure at a low pressure of 300-500 mtorr, and introduce nitrogen and oxygen carrying water vapor to grow the first tunnel oxide layer. The growth time is set to 60-120 seconds. Step S4: After the first tunnel oxide layer has grown, the LPCVD furnace tube is heated and a vacuuming operation is performed. The inside of the LPCVD furnace tube is purged with nitrogen and a vacuuming operation is performed again to remove residual water vapor and oxygen inside the furnace tube. Step S5: Raise the furnace tube temperature to 600-630°C, introduce oxygen at the same time, turn off the vacuum pump to stop the vacuuming operation, and return the furnace tube pressure to atmospheric pressure to grow the second tunnel oxide layer. Set the growth time to 600-800 seconds. Step S6: After the growth oxidation operation is completed, perform a purging and vacuuming operation to remove residual oxygen in the furnace tube.

2. The method for growing a tunneling oxide layer in an XBC battery according to claim 1, characterized in that, In step S3, the flow rate of nitrogen carrying water vapor is 500-800 sccm, and the flow rate of oxygen is 1000-1500 sccm.

3. The method for growing a tunneling oxide layer in an XBC battery according to claim 1, characterized in that, The oxygen flow rate introduced in step S5 is 15,000 to 30,000 sccm.

4. The method for growing a tunneling oxide layer in an XBC battery according to claim 1, characterized in that, In step S3, the growth thickness of the first tunneling oxide layer is 0.8 to 1 nm.

5. The method for growing a tunneling oxide layer in an XBC battery according to claim 1, characterized in that, In step S3, the nitrogen carrying water vapor is prepared by bubbling nitrogen gas through deionized water.

6. The method for growing a tunneling oxide layer in an XBC battery according to claim 1, characterized in that, In step S5, the growth thickness of the second tunneling oxide layer is 0.7 to 0.8 nm.

7. The method for growing a tunneling oxide layer in an XBC battery according to claim 1, characterized in that, The total thickness of the first tunneling oxide layer and the second tunneling oxide layer is controlled to be 1.5 to 1.8 nm.

8. The method for growing a tunneling oxide layer in an XBC battery according to claim 1, characterized in that, In step S5, the purity of the oxygen is ≥99.99%.

9. The method for growing a tunneling oxide layer in an XBC battery according to claim 1, characterized in that, In step S5, the atmospheric pressure is 760,000 mtorr.

10. The method for growing a tunneling oxide layer in an XBC battery according to claim 1, characterized in that, The silicon wafer used in step S1 is a P-type monocrystalline silicon wafer or an N-type monocrystalline silicon wafer.

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