We study the growth of amorphous (a‐Si:H,F) and of microcrystalline (&mgr;c‐Si) silicon over trench patterns in crystalline silicon substrates. We vary the conditions of the SiF4‐H2glow discharge from deposition to etching. All deposited films form lips at the trench mouth and are uniformly thick on the trench walls. Therefore, surface diffusion is not important. The results of a Monte Carlo simulation suggest that film growth is governed by a single growth species with a low (∼0.2) sticking coefficient, in combination with a highly reactive etching species.