The effects of process variables on the surface roughness, surface morphology, film quality and film stress of a-Si:C:H films deposited in a 13.56-MHz parallel plate plasma reactor were investigated. A two-level factorial design is employed to quantify these effects and interactions between the process variables. The energy of the bombarding ions had a significant influence on the intrinsic stress of the films. The ratio of precursor gases and the flow-rate of the diluent gas interacted in their effect on the film stress. Different surface morphologies and film qualities were observed using atomic force microscopy. The best quality films were obtained when a high ratio of tetramethylsilane/acetylene was used in the precursor gas mixture. Analysis of roughness measurements made from atomic force microscope images showed that the precursor gas ratio, the argon flow-rate and the ion energy all had significant effects on the surface roughness. Interactions between the precursor gas ratio and the ion energy as well as between the argon flow-rate and the ion energy were detected.