Plasma-assisted hydrogen passivation technology

Abstract

The invention relates to the technical field of photovoltaic cell manufacturing, and discloses a plasma-assisted hydrogen passivation technology, which is used for solving the problem that defects of a poly-Si / SiOx interface, a SiOx / c-Si interface, a poly-Si body and a c-Si surface layer in an efficient TOPCon cell are difficult to synergistically passivate. According to the technology, a high-frequency power supply is applied to H2 / N2, H2 / D2 / N2, H2O / D2O steam or other hydrogen-containing gas in a reaction cavity to generate high-density plasma, active particles such as hydrogen / deuterium (H, D and ions thereof) are generated, and accurate passivation of multi-interface and in-vivo defects is achieved in combination with tubular furnace thermal annealing treatment. Wherein grain boundary defects and impurities are repaired through thermal annealing, the passivation efficiency of the defects on the interface and in the body is enhanced through active particles in plasma, and the carrier recombination rate can be remarkably reduced. In addition, H / D synergistic passivation can be conveniently achieved, the passivation effect is further optimized, and the conversion efficiency of the TOPCon battery is improved. The method is high in treatment speed (the single process is less than 30 minutes), low in cost, compatible with existing production line equipment and suitable for large-scale production of efficient photovoltaic cells, and an efficient, reliable and economical passivation solution is provided for the photovoltaic industry.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing technology, and particularly to a plasma-assisted hydrogen passivation technology for high-efficiency TOPCon (Tunnel Oxide Passivated Contact) solar cells. Through a synergistic process of plasma and thermal annealing treatments, defect passivation of the polycrystalline silicon / silicon oxide (poly-Si / SiO x ) interface, silicon oxide / crystalline silicon (SiO x / c-Si) interface, polycrystalline silicon bulk, and crystalline silicon surface layer is achieved, and co-passivation of hydrogen isotopes (H / D / T) is supported, significantly improving the carrier lifetime and cell conversion efficiency. Background Art

[0002] During the manufacturing process of high-efficiency TOPCon cells, interface defects and dangling bonds at grain boundaries are the key factors leading to carrier recombination. Traditional hydrogen passivation technologies usually adopt thermal annealing treatment, and passivate defects in silicon materials through the diffusion of hydrogen atoms at high temperatures. However, traditional technologies have the following limitations: 1. Limited passivation effect: Pure thermal annealing relies on the diffusion of hydrogen atoms and is difficult to penetrate the poly-Si / SiO x stacked structure, and it is difficult to achieve precise passivation of different positions (such as the poly-Si / SiO x interface, SiO x / c-Si interface, poly-Si body, and c-Si surface layer) and different types of defects; 2. Long processing time: The thermal annealing method requires a long processing time (usually several hours), with high energy consumption costs, and it is difficult to meet the requirements of high-efficiency production; 3. High cost: Traditional technologies have high requirements for equipment and process conditions, resulting in increased production costs; 4. Unable to achieve co-passivation of hydrogen isotopes: Existing technologies are difficult to conveniently achieve co-injection of hydrogen / deuterium / tritium (H / D / T), while isotope co-passivation can improve the passivation effect.

[0003] In recent years, plasma-assisted passivation technologies have gradually attracted attention. Through the bombardment of high-energy particles and the injection of active hydrogen atoms, they can more effectively repair defects. However, existing plasma technologies still have the following problems: 1. Insufficient plasma density: Some technologies use a relatively low plasma density (<10 11 cm -3 ), making it difficult to generate sufficient active hydrogen particles; 2. Poor process compatibility: Existing technologies are difficult to be compatible with existing TOPCon cell production lines, restricting their large-scale application; 3. Difficulty in achieving co-passivation: It is difficult for existing technologies to flexibly adjust the types and ratios of gases, and it is impossible to conveniently achieve co-passivation of hydrogen isotopes; Therefore, there is an urgent need for a passivation technology that is efficient, low-cost, and easy to scale up production to solve the above problems and further improve the performance of TOPCon cells. Summary of the Invention

[0004] The present invention proposes a plasma-assisted and thermal annealing co-passivation technology, the core of which is: 1. Use RF / VHF frequency bands (1 kHz - 100 MHz) to excite H / D / T isotope gases to generate H + / H - / H 0 mixed active particles; 2. Perform three-stage annealing (low-temperature adsorption → medium-temperature diffusion → high-temperature bonding) in a plasma atmosphere, with the temperature range covering room temperature to 1000 °C; 3. By adjusting the H2 / D2 / T2 mixing ratio (0.1 - 100%), utilize the high mobility of deuterium atoms (1.5 times faster than hydrogen) to preferentially occupy deep-level defects, and hydrogen atoms fill shallow defects. To achieve the above objectives, the technical solutions adopted by the present invention include: 1. Equipment configuration: Use equipment that combines a tube furnace and a dual-frequency ICP processing system, as Figure 1 shown. The equipment includes a vacuum chamber, a multi-channel gas injection module, an ICP plasma generator, a tube furnace, and a sample placement area; 2. Process flow: a) Sample loading: Place the TOPCon cell with a poly-Si / SiOx / c-Si structure on a quartz boat and evacuate to 5×10 -4 Pa; b) Gas introduction: Introduce H2 / N2, H2 / D2 / N2, H2 / D2 / / T2 / N2, H2O / D2O steam, or other hydrogen-containing gases. By adjusting the types and ratios of gases, ordinary hydrogen passivation or co-passivation is achieved; c) Plasma formation: Apply an RF or VHF high-frequency power supply with a frequency range of 1.0 kHz to 100 MHz and a power range of 10 W to 8000 W to form a high-density plasma; d) Gradient treatment: Under the continuous state of the plasma, perform three-stage temperature control continuously: Stage 1: 200 - 400 °C / 1 - 5 min (surface adsorption); Stage 2: 400 - 600 °C / 10 - 30 min (bulk diffusion); Stage 3: 600 - 800 °C / 5 - 15 min (defect bonding); e) Co-passivation characterization: Quasi-steady-state photoconductivity (QSSPC): Measure the minority carrier lifetime (τ eff ).

[0005] Advantages and positive effects of the present invention: 1. High-efficiency passivation: Through high-density hydrogen plasma, it can accurately repair the defects at the poly-Si / SiO x interface, SiO x / c-Si interface, in the poly-Si body and on the c-Si surface layer, significantly reducing the carrier recombination rate; 2. Strong flexibility: The gas type and ratio can be selected according to requirements to achieve ordinary hydrogen passivation or hydrogen / deuterium / tritium co-passivation, meeting different process requirements; 3. Fast processing speed: Combining plasma and thermal annealing treatments can greatly shorten the processing time and improve production efficiency; 4. Low cost: The equipment structure is simple, easy to be compatible with the existing TOPCon cell production line, reducing production costs; 5. Easy to scale up: The process conditions are simple, suitable for large-scale production of high-efficiency TOPCon cells, and have broad application prospects. Description of the Drawings

[0006] Figure 1 : Schematic diagram of the plasma-assisted annealing equipment, showing the gas injection system (101), ICP plasma generation module (102), annealing module (103) and vacuum pumping system (104). Detailed Embodiments

[0007] The technical solutions of the present invention will be further described in detail below in conjunction with the drawings and specific embodiments. Embodiment

[0008] Step 1: Connect the tube furnace to the inductively coupled plasma (ICP) processing system to ensure the normal operation of the gas inlet system and the power supply system. Then place the poly-Si / SiO x / c-Si sample in the sample placement area of the tube furnace to ensure that the sample surface is clean and free of contamination;

[0009] Step 2: Introduce a mixed gas of H2 / D2 / N2, with H2:D2:N2 = 1:1:8 (volume ratio), a total gas pressure of 3 Torr, and the total H / D ratio of 20%;

[0010] Step 3: Apply frequencies of 13.56 MHz (RF) + 60 MHz (VHF) and a power of 5000 W;

[0011] Step 4: Thermal annealing treatment, stage 1: maintain at 300 °C for 3 min; stage 2: maintain at 600 °C for 25 min; stage 3: maintain at 750 °C for 10 min;

[0012] Step 5: Effect verification; The result shows that: Through the minority carrier lifetime test, the carrier lifetime τ eff of the sample reaches 3130.84 μs, and at the same time, the implied open-circuit voltage (iVOC ) is 0.729 V; under standard test conditions (STC, AM1.5G, 100 mW / cm 2 The photoelectric performance of TOPCon cells was characterized at 25°C. The test results showed that the open circuit voltage (V OC ) was increased to 725.9 mV, the fill factor (FF) was 82.82%, and the current density (J SC ) is stable at 39.47 mA / cm 2 , and finally achieved an excellent power conversion efficiency (PCE) of 23.72%.

[0013] Comparative Example 1: (Pure H2 passivation) Under the same process parameters, only pure H2 (20% and the rest N2) is introduced Results: τ eff =2886.34 μs, photoelectric conversion efficiency 22.7%, proving that H / D synergistic passivation can further improve the passivation effect and device efficiency.

[0014] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A plasma-assisted hydrogen passivation technique, characterized in that, It includes the following steps: 1) Place the sample to be processed in a vacuum chamber and introduce a gas containing hydrogen and / or deuterium into the chamber; 2) Apply a high-frequency power supply to the gas to ionize it to form a plasma; 3) Perform thermal annealing treatment on the sample in the plasma atmosphere to achieve hydrogen / deuterium co-passivation of the interface and bulk defects.

2. The plasma-assisted hydrogen passivation technology according to claim 1, wherein The gas containing hydrogen and / or deuterium includes but is not limited to H2, D2, H2O, D2O, H2 / N2 mixture gas, or H2 / D2 / N2 mixture gas, and the hydrogen content ratio in the gas ranges from 0.1% to 100%.

3. The plasma-assisted hydrogen passivation technology according to claim 1, wherein Through the hydrogen isotopes deuterium (D) and tritium (T) in the gas, H passivation, D passivation, and T passivation can be achieved, and H / D co-passivation, H / T co-passivation, D / T co-passivation, and H / D / T co-passivation can also be achieved, etc. The ratio ranges of H, D, and T are 0.1% to 100% respectively.

4. The plasma-assisted hydrogen passivation technology according to claim 1, characterized in that The plasma is formed by radio frequency (RF) or very high frequency (VHF), and the frequency range includes but is not limited to 1.0 kHz to 100 MHz, and the power range is 10 W to 8000 W.

5. The plasma-assisted hydrogen passivation technique according to claim 1, wherein The temperature range of the thermal annealing treatment is from room temperature to 1000 °C, and the treatment time is from 1 minute to 2 hours.

6. The plasma-assisted hydrogen passivation technique according to claim 1, wherein The plasma excitation method can be inductively coupled or capacitively coupled.

7. The plasma-assisted hydrogen passivation technique according to claim 1, wherein In the passivated contact structure adopting the plasma-assisted hydrogen passivation technology, the polycrystalline silicon-based alloy can be one of poly-Si, poly-SiO x , poly-SiC x , poly-SiN x or a combination of more than one of them.

8. The plasma-assisted hydrogen passivation technology according to claim 1, characterized in that, In the passivated contact structure adopting the plasma-assisted hydrogen passivation technology, the tunneling passivation layer can be SiO x 、SiO x N y 、AlO x 、HfO2, etc., or a combination of multiple ones.

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