The surface roughness of polycrystalline and amorphous silicon films deposited by low-pressure chemical vapour deposition (LPCVD) was investigated using light scattering in the visible range, as well as scanning electron microscopy. Several processing steps, including in situ POCl3 doping, oxidation and diffusion, were performed to simulate the thermal effects typical of a two-level polysilicon technology. Angle-resolved light scattering was used to characterize the lateral structure of the surface corrugations. Angle-integrated light scattering was used to estimate the root mean square (RMS) surface roughness. The films deposited in the polycrystalline state at 620-degrees-C show a short-range corrugation of about 3 nM RMS with a typical lateral size of the surface irregularities of about 100 nm. This short-range corrugation is not observed on initially amorphous films deposited at 560-degrees-C, either after the deposition process or after the subsequent sintering steps. Upon sintering at 900-degrees-C, both polycrystalline and initially amorphous films recrystallize, which results in a long-range corrugation of the surface. In both cases, the Rms roughness is about 14 nm. The presence of dopants enhances crystallite growth. After the oxidation step at 1070-degrees-C, doped samples show significantly larger surface structures, reflecting larger crystallite size. The advantage of depositing amorphous silicon is thus to prevent the formation of a short-range roughness which is much more detrimental to the silicon/oxide interface quality than the long-range waviness.