Gas flow and plasma simulation for parallel plate PACVD reactors

Parallel plate reactors for plasma activated chemical vapor deposition (PACVD) of a-Si:H/µc-Si:H are an established technology for the fabrication of thin film solar cells based on a-Si:H as well as a-Si:H/µc-Si:H tandem solar cells. In solar cell fabrication lines, a high deposition rate and a rate homogeneity better than 5% are required on the one hand, while on the other hand only a certain window of energy impact onto the substrate during film growth is tolerable with respect to the resulting solar cell performance. Consequently, in PACVD production lines an optimal tradeoff between throughput, solar cell performance an technical tolerance limits is an important goal. In order to promote this goal, we have developed a self-consistent particle-in-cell simulation model of a H2 plasma as well as a transport simulation of H2/SiH4 gas mixtures within a parallel plate RF-PACDVreactor. With this model, we analyze the a-Si:H/µc-Si:H deposition homogeneity with respect to gas nozzele seperation and technical tolerance. Furthermore, the dependency of the deposition rate and the energy impact is analyzed as a function of process parameters such as gap width, RF frequency, temperature and total pressure. Our plasma simulatio model yield an improved understanding of the relation between process parameters and growth conditions at the substrate even for modified or novel deposition technologies. This enables a higher efficiency in prototyping new a-Si:H/µc-Si:H deposition technologies with both optimized throughput and optimized solar cell performance.