A method for fabricating a tbc back contact solar cell multi-tunnel oxide layer

Abstract

The application discloses a preparation method of a TBC back contact solar cell multi-tunneling oxide layer, utilizes a multi-temperature zone LPCVD device, realizes whole-process precise temperature control from pretreatment to deposition and then to annealing, slow cooling transition and low-temperature interval of the whole deposition process, greatly reduces thermal stress and is suitable for sheeting production; through decomposing the deposition process into three sub-steps and accurately designing pressure environment, gas type, flow and duration of each sub-step, "programmable" growth of the structure, composition and doping concentration of the oxide layer from an interface to a bulk phase and then to a surface layer is realized; this is the core of realizing a high-performance multi-layer tunneling structure, high quality and high uniformity under low temperature; precise cooperation of temperature and gas sequence ensures that even under low temperature, a high-quality oxide layer with density, uniformity and low interface state density can be obtained, and a relatively wide process window and good repeatability are realized.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and in particular to a method for preparing a multi-tunnel oxide layer in a TBC back-contact solar cell. Background Technology

[0002] TOPCon technology has become a research hotspot for high-efficiency crystalline silicon solar cells due to its excellent passivation effect. Among the key aspects, the quality of the tunneling oxide layer located between ultrathin silicon oxide (SiO2) and doped polycrystalline silicon (poly-Si) is crucial, directly affecting carrier transport and surface passivation performance. Traditional high-temperature thermal growth methods struggle to control the uniformity of oxide layer thickness, and the high-temperature process can lead to increased silicon wafer defects and warping, hindering the production of thin-film solar cells. While attempts have been made to prepare tunneling layers using low-temperature deposition methods, these generally suffer from poor process stability and difficulty in simultaneously achieving optimal tunneling and passivation effects. Particularly for the more complex TBC (Tunneling-Based Cell) structure, multi-layer tunneling structures (such as double-tunneling and triple-tunneling) are required to further optimize the band structure and carrier selectivity, placing extremely high demands on process precision and repeatability.

[0003] Therefore, it is necessary to develop a method for preparing the multi-penetrating oxide layer of TBC back-contact solar cells to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to design a method for preparing a multi-penetrating oxide layer for a TBC back-contact solar cell in order to solve the above-mentioned problems.

[0005] The present invention achieves the above objectives through the following technical solutions: A method for preparing a multi-penetrating oxide layer in a TBC back-contact solar cell includes the following steps: S1. The N-type silicon wafer substrate with completed front-side texturing and emitter diffusion is transferred to the reaction chamber of the LPCVD equipment for initial purging and high-temperature stabilization. High-purity inert gas is continuously introduced into the chamber at a flow rate of 5-20 SLM. At the same time, the vacuum pump is turned on to maintain the chamber pressure at 100-500 mTorr for continuous purging. During purging, all 8 temperature zones of the reaction chamber are simultaneously and rapidly raised from room temperature to the first set temperature T1, T1=600°C±5°C, and stabilized at this temperature for 3-10 minutes. S2, Cooling Transition; Precision temperature transition: Under the condition of maintaining an inert gas atmosphere and stable pressure, the temperature of all 8 temperature zones is synchronously and linearly reduced from T1 to the second set temperature T2, T2=560°C±3°C; the cooling rate is controlled at 1-5°C / minute. S3. The entire process of multilayer tunneling oxide layer deposition is completed within the second set temperature T2. By precisely controlling the sequence, flow rate, time, and chamber pressure of different reactive gases, one or more deposition cycles are performed to construct the desired single-layer, double-layer, or triple-layer tunneling oxide layer structure. S4. After deposition, annealing treatment: stop the introduction of all reactive gases and re-introduce inert gas to purge the chamber; under inert gas atmosphere, slowly raise the temperature from 560°C±3°C to an annealing temperature of 580°C±5°C and hold for 5-15 minutes. S5. Cooling and wafer removal: Under the protection of inert gas, the cavity temperature is naturally cooled or controlled to a safe wafer removal temperature, and then the silicon wafer is removed.

[0006] Specifically, in step S3, constructing the three-layer tunneling oxide layer structure includes, Step S3.1, First Sublayer Deposition: Stop the introduction of inert gas and rapidly pump the pressure in the reaction chamber to 100±20 mTorr; first, introduce high-purity oxygen at a flow rate of 50-200 sccm for 30-120 seconds to form an initial adsorbed oxygen layer on the silicon wafer surface; then, while maintaining the oxygen flow rate, introduce undoped silane gas at a flow rate of 10-50 sccm for a reaction time of 60-180 seconds; during this stage, a 0.5-1.0 nm SiO2 layer is grown under low pressure as an interface with the silicon substrate; Step S3.2, Second Sublayer Deposition: Increase the chamber pressure to 300±50 mTorr; keep the oxygen flow rate constant, and simultaneously introduce silane gas and a dopant gas. The dopant gas is diborane or boron trichloride. The flow rate of the dopant gas is gradually increased from 0-300 sccm / min, gradually increasing at a rate of 200 sccm / min. After reaching 300 sccm, the flow rate is stabilized for 10 min, and then reduced to 50 sccm / min for 5 min. During this stage, a 10-20 nm doped polycrystalline silicon layer is generated. Step S3.3, third sublayer deposition: Adjust the chamber pressure to 200±30mTorr; stop the introduction of undoped silane gas, or reduce the flow rate of silane gas by 20%-30%; mainly introduce O2 and dopant gas, deposition time 60-150 seconds; a silicon oxide layer is formed in this stage.

[0007] Preferably, the inert gas is nitrogen.

[0008] Furthermore, the safe temperature for taking the film in step S5 is less than 200°C.

[0009] Preferably, the silane gas is methanesilane.

[0010] The beneficial effects of this invention are: Utilizing a multi-temperature zone LPCVD equipment, precise temperature control was achieved throughout the entire process, from pretreatment to deposition and annealing. In particular, the slow cooling transition in step S2 and the low-temperature range (around 560°C) throughout the deposition process significantly reduced thermal stress, making it suitable for thin-film production. "Pressure-gas sequence" synergistic control: By decomposing the deposition process into three sub-steps (S3.1 to S3.3) and precisely designing the pressure environment, gas type (pure reactants, dopant introduction), flow rate, and duration for each sub-step, "programmable" growth of the oxide layer's structure, composition, and doping concentration from the interface to the bulk phase and then to the surface layer was achieved. This is the core of realizing high-performance multilayer tunneling structures, ensuring high quality and high uniformity at low temperatures. The precise coordination of temperature and gas sequence ensures that even at low temperatures, a dense, uniform, and low-interfacial-state-density high-quality oxide layer can be obtained, with a relatively wide process window and good repeatability. Attached Figure Description

[0011] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0013] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0014] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0015] In the description of this invention, it should be understood that the terms "upper," "lower," "inner," "outer," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0016] Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0017] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, terms such as "set" and "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0018] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0019] like Figure 1 As shown, a method for preparing a multi-penetrating oxide layer in a TBC back-contact solar cell includes the following steps: S1. The N-type silicon wafer substrate that has completed front-side texturing and emitter diffusion is transferred to the LPCVD equipment (the LPCVD equipment in this application has at least 8 independent and precisely temperature-controlled zones, and the reaction chamber has the ability to quickly evacuate and precisely control pressure) for initial purging and high-temperature stabilization. High-purity inert gas is continuously introduced into the chamber at a flow rate of 5-20 SLM (standard liters per minute), and the vacuum pump is turned on to maintain the chamber pressure at 100-500 mTorr for continuous purging. During purging, all 8 temperature zones of the reaction chamber are simultaneously and rapidly raised from room temperature to the first set temperature T1, T1 = 600°C ± 5°C, and stabilized at this temperature for 3-10 minutes. S2. Cooling Transition; Precision temperature transition: Under the condition of maintaining an inert gas atmosphere and stable pressure (e.g., 200 mTorr), the temperature of all 8 temperature zones is synchronously and linearly reduced from T1 to the second set temperature T2, T2 = 560°C ± 3°C; the cooling rate is controlled at 1-5°C / minute; this "slow cooling" process provides a thermal shock-free and highly stable temperature basis for subsequent low-temperature deposition, which is one of the keys to ensuring film quality in this method; S3. The entire process of multi-layer tunneling oxide layer deposition is completed within the second set temperature T2. By precisely controlling the introduction sequence, flow rate, time, and chamber pressure of different reactive gases, one or more deposition cycles are performed to construct the desired single-layer, double-layer, or triple-layer tunneling oxide layer structure. In step S3, the deposition process of the most innovative triple-layer composite tunneling oxide layer is described in detail below. The construction of the triple-layer tunneling oxide layer structure includes... Step S3.1, First Sublayer (Dense Interface Layer) Deposition: Stop the introduction of inert gas and rapidly pump the pressure in the reaction chamber to a low level of 100±20 mTorr; first, introduce high-purity oxygen at a flow rate of 50-200 sccm for 30-120 seconds to form an initial adsorbed oxygen layer on the silicon wafer surface; then, while maintaining the oxygen flow rate, introduce undoped silane gas at a flow rate of 10-50 sccm for a reaction time of 60-180 seconds; during this stage, a 0.5-1.0 nm SiO2 layer is grown under low pressure as the interface with the silicon substrate; Step S3.2, Second Sublayer (Gradient Doped Transition Layer) Deposition: Increase the chamber pressure to 300±50 mTorr; keep the oxygen flow rate constant, and simultaneously introduce silane gas and a dopant gas. The dopant gas is diborane (diborane B2H6 is used to form P-type polycrystalline silicon, diluted in H2 or He) or boron trichloride. The flow rate of the dopant gas is gradually increased from 0-300 sccm / min, gradually increasing at a rate of 200 sccm / min, and after reaching 300 sccm, it is stabilized for 10 min, and then reduced to 50 sccm / min for 5 min. During this stage, a 10-20 nm doped polycrystalline silicon layer is generated. The oxide layer grown in this stage has a certain doping concentration, which plays a role in band gradient and improving carrier transport.

[0020] Step S3.3, Third Sublayer (Doped Surface Layer) Deposition: Adjust the chamber pressure to 200±30 mTorr; stop the introduction of undoped silane gas, or reduce the flow rate of silane gas by 20%-30%; mainly introduce O2 and dopant gas, with a deposition time of 60-150 seconds; this stage forms a silicon oxide layer with a relatively high doping concentration, providing a good nucleation interface for the subsequent deposition of a high-conductivity doped polycrystalline silicon layer.

[0021] S4. Post-deposition annealing: Stop the introduction of all reactive gases (silane, diborane, oxygen), and re-introduce inert gas to purge the chamber; under an inert gas atmosphere, slowly raise the temperature from 560°C±3°C to an annealing temperature of 580°C±5°C, and hold for 5-15 minutes; this gentle annealing process helps to repair microscopic defects in the film, optimize interface quality, and further improve the passivation effect, while the temperature is much lower than that of traditional high-temperature processes.

[0022] S5. Cooling and wafer removal: Under the protection of inert gas, the cavity temperature is naturally cooled or controlled to a safe wafer removal temperature, and then the silicon wafer is removed. The safe wafer removal temperature is less than 200°C.

[0023] In this embodiment, the inert gas is nitrogen.

[0024] In this embodiment, the silane gas is methanesilane.

[0025]

[0026] The control group used conventional production line processes with a sheet resistance of around 50Ω and a film thickness of 200nm; the control group used traditional methods to complete the process in a single step at a temperature greater than 800°C.

[0027] The experimental group adopted a multilayer tunneling oxide layer process with a sheet resistance of 40Ω and a film thickness of 240nm. The experimental group used the innovative method of this application to complete the process in multiple steps at 560°C, which significantly reduced the thermal budget and avoided the disadvantages of high temperature.

[0028] From the experimental electrical performance, the efficiency gain is mainly due to the advantages of voltage opening and filling, which is consistent with the principle of multilayer tunneling oxide layer process.

[0029] The technical effects of this application can be derived from the above comparative analysis: 1. Multi-layer structure design: The multi-layer tunneling oxide layer process of the solar cell optimizes the electron transport path and light utilization by forming a multi-layer structure inside the cell. 2. Optimized electron transport: By constructing efficient electron transport channels inside the battery, the multilayer tunneling oxide layer process greatly improves the sheet resistance of electron transport from the illuminated area to the electrode, thus enhancing the filling advantage of the battery cell. 3. Precise control of doping concentration: The multilayer tunneling oxide process allows for precise control of the doping concentration at different levels, thereby optimizing the electrical and optical performance of the battery; 4. Excellent physical properties: The tunneling oxide layer allows electrons (minority carriers) to tunnel through, but blocks holes; the multilayer tunneling oxide layer process further increases this blocking effect, effectively improving the cell's on-state voltage and filling capacity. This invention innovatively decomposes the deposition process into different pressure stages and differentiated gas introduction sequences (such as purification followed by doping, gradient changes), thereby enabling the active construction of multilayer films with compositional and structural gradients, which is impossible with single-condition deposition. By innovatively designing multi-step precision temperature fields and reactive gas sequences, precise and coordinated control of oxide layer thickness, density, doping distribution, and interface states is achieved at low temperatures. In particular, it can stably prepare multilayer tunneling oxide layer structures with excellent performance, thereby significantly improving the open-circuit voltage (Voc) and fill factor (FF) of the final battery device.

[0030] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a multi-penetrating oxide layer in a TBC back-contact solar cell, characterized in that, Including the following steps: S1. The N-type silicon wafer substrate with completed front-side texturing and emitter diffusion is transferred to the reaction chamber of the LPCVD equipment for initial purging and high-temperature stabilization. High-purity inert gas is continuously introduced into the chamber at a flow rate of 5-20 SLM. At the same time, the vacuum pump is turned on to maintain the chamber pressure at 100-500 mTorr for continuous purging. During purging, all 8 temperature zones of the reaction chamber are simultaneously and rapidly raised from room temperature to the first set temperature T1, T1=600°C±5°C, and stabilized at this temperature for 3-10 minutes. S2, Cooling Transition; Precision temperature transition: Under the condition of maintaining an inert gas atmosphere and stable pressure, the temperature of all 8 temperature zones is synchronously and linearly reduced from T1 to the second set temperature T2, T2=560°C±3°C; the cooling rate is controlled at 1-5°C / minute. S3. The entire process of multilayer tunneling oxide layer deposition is completed within the second set temperature T2. By precisely controlling the sequence, flow rate, time, and chamber pressure of different reactive gases, one or more deposition cycles are performed to construct the desired single-layer, double-layer, or triple-layer tunneling oxide layer structure. S4. After deposition, annealing treatment: stop the introduction of all reactive gases and re-introduce inert gas to purge the chamber; under inert gas atmosphere, slowly raise the temperature from 560°C±3°C to an annealing temperature of 580°C±5°C and hold for 5-15 minutes. S5. Cooling and wafer removal: Under the protection of inert gas, the cavity temperature is naturally cooled or controlled to a safe wafer removal temperature, and then the silicon wafer is removed.

2. The method for preparing a multi-tunneling oxide layer for a TBC back-contact solar cell according to claim 1, characterized in that, In step S3, constructing the three-layer tunneling oxide layer structure includes, Step S3.1, First Sublayer Deposition: Stop the introduction of inert gas and rapidly pump the pressure in the reaction chamber to 100±20 mTorr; first, introduce high-purity oxygen at a flow rate of 50-200 sccm for 30-120 seconds to form an initial adsorbed oxygen layer on the silicon wafer surface; then, while maintaining the oxygen flow rate, introduce undoped silane gas at a flow rate of 10-50 sccm for a reaction time of 60-180 seconds; during this stage, a 0.5-1.0 nm SiO2 layer is grown under low pressure as an interface with the silicon substrate; Step S3.2, Second Sublayer Deposition: Increase the chamber pressure to 300±50 mTorr; keep the oxygen flow rate constant, and simultaneously introduce silane gas and a dopant gas. The dopant gas is diborane or boron trichloride. The flow rate of the dopant gas is gradually increased from 0-300 sccm / min, gradually increasing at a rate of 200 sccm / min. After reaching 300 sccm, the flow rate is stabilized for 10 min, and then reduced to 50 sccm / min for 5 min. During this stage, a 10-20 nm doped polycrystalline silicon layer is generated. Step S3.3, third sublayer deposition: Adjust the chamber pressure to 200±30mTorr; stop the introduction of undoped silane gas, or reduce the flow rate of silane gas by 20%-30%; mainly introduce O2 and dopant gas, deposition time 60-150 seconds; a silicon oxide layer is formed in this stage.

3. The method for preparing a multi-tunneling oxide layer for a TBC back-contact solar cell according to claim 2, characterized in that, The inert gas is nitrogen.

4. The method for preparing a multi-tunneling oxide layer for a TBC back-contact solar cell according to claim 1, characterized in that, In step S5, the safe temperature for taking the film is less than 200°C.

5. The method for preparing a multi-tunneling oxide layer for a TBC back-contact solar cell according to claim 2, characterized in that, The silane gas is methanesilane.

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