The effect of process parameters on the plasma deposition of μc-Si:H solar cells is reviewed in this article. Several in situ diagnostics are presented, which can be used to study the process stability as an additional parameter in the deposition process. The diagnostics were used to investigate the stability of the substrate temperature during deposition at elevated power and the gas composition during deposition at decreased hydrogen dilution. Based on these investigations, an updated view on the role of the process parameters of plasma power, heater temperature, total gas flow rate, and hydrogen dilution is presented. © 2007 Materials Research Society.