Hydrogenated silicon–carbon thin films were deposited by Radio Frequency Plasma Enhanced Chemical Vapor Deposition using silane–methane gas mixtures highly diluted in hydrogen. The effects of the presence of a microcrystalline silicon seed layer and of the methane flow rate during deposition were investigated in order to find the optimal conditions for microcrystalline growth. The presence of a seed layer promotes the amorphous to microcrystalline transition at the interface with the substrate, reducing the incubation layer to a 5–10 nm thickness. At the same time, an excessive increase in the CH 4 flow rate suppresses crystalline growth, leading to extremely flat amorphous samples (root-mean-square surface roughness ρ RMS~ 0.5 nm), even with a seed layer. The total carbon content was measured by Radio Frequency Glow Discharge Optical Emission …