Results of an intensive study by means of XRD, SEM, AFM and TEM of the microstructure (i.e. the texture and morphology) of LPCVD silicon layers as a function of different process parameters are described. The influence of different deposition parameters, like partial and total pressure, doping, deposition and anneal temperature is shown. In particular the roughness of the silicon surface is investigated. The relation of surface roughness to the electrical properties of dielectrics, grown on these silicon layers, is briefly discussed.