Multi-physics Field Simulation Of RF-PECVD A-Si:H Film Deposition On HJT Solar Cell

Heterojunction(HJT)solar cells are expected to become promising next-generation commercial solar cells.The preparation of the hydrogenated amorphous silicon(a-Si:H)layer is considered to be the key to improving the efficiency of HJT solar cells.RF-PECVD(Radio Frequency Plasma Enhanced Chemical Vapor Deposition)is an effective technology for the deposition of amorphous silicon.The deposition process of a-Si:H is very complex because it involves interactions between multiple physical fields.In this thesis,a two-dimensional simulation model is developed based on COMSOL Multiphysics simulation software.Firstly,the temperature field,flow field,and plasma field are simulated respectively.After clarifying the coupling relationship of multi-physics fields,the multi-field coupling simulation of the amorphous silicon deposition process is carried out.The reliability of the model is verified by comparing the simulation results with the experimental data.Simulation can optimize process parameters and structure parameters,which is of significance to guide amorphous silicon film deposition.The main contents of this thesis are summarized as follows:Firstly,the finite element analysis method is used to establish a two-dimensional flow field and temperature field simulation model according to the structural characteristics of RF-PECVD equipment.The problem of key structural modeling is solved,and the temperature and velocity distribution in the cavity are mainly studied.It is found that the uniformity change of velocity distribution is larger than that of temperature distribution.Then,the mechanism of capacitively coupled plasma discharge was studied,and a two-dimensional plasma discharge electron model was established.Based on this model,the influence of process parameters and structural parameters on plasma discharge was explored.When the RF voltage or chamber pressure is increased,the average electron density will increase but the radial uniformity of electron density will deteriorate.The simulation also found that the influence of process parameters on plasma uniformity was small.When the process parameters were optimized,the electron density uniformity was always less than 90%,indicating that only adjusting the process parameters could not eliminate the edge effect from the root.Compared with the adjustment of process parameters,the change of structural parameters has a greater impact on the uniformity of electron density.When the electrode spacing increases from 20 mm to 35 mm,the average electron density decreases,and the electron density uniformity increases from 36.59% to 82.29%.When the plate length is extended from 450 mm to 480 mm,the average electron density is reduced,and the uniformity of electron density can be improved to 94.41%.Finally,the multi-physics field simulation model of a-Si:H deposition is constructed.And the effects of the electrode spacing and the length of the grounded electrode on the deposition thickness and uniformity of a-Si:H were mainly studied.The simulation results show that the uniformity of a-Si:H layer reaches 98.45% with the increase of plate spacing.But the deposition rate will be reduced,resulting in the deposition of the same thickness of a-Si:H process time becoming longer.Extending the grounded electrode length will also improve the deposition uniformity and reduce the deposition thickness.When the electrode spacing is 30 mm and the grounded electrode length is 470 mm,the deposition effect is the best.