Phase and surface roughness evolution for as-deposited LPCVD silicon films

In this paper we present a structural and morphological characterisation of the as-deposited low pressure chemically vapor deposited (LPCVD) silicon films prepared from silane. The results are related to the deposition kinetics in the temperature range from 500 to 615°C and the deposition pressure range from 20 to 100 Pa. From XRD measurements we show for the first time the presence of the polycrystalline state (of preferred <211> orientation) in as-deposited films prepared at temperatures as low as 500°C. This result was connected with an increase of the surface roughness of those films with respect to the roughness obtained on the surface of film prepared at 550°C. At 550°C, a minimum surface roughness of 0.5 nm is obtained and this was connected to the amorphous state of the layer revealed for all deposition pressures studied. At temperatures lower than 550°C, the <211> texture presents a decrease of the grain size as a function of pressure increase. At temperatures higher than 550°C, due to a competition in grain growth process, the <220> and <111> crystallites are also evinced in the film structure, while the surface roughness is rapidly increasing to value of 18-20 nm. These last results are explained in terms of three-dimensional nucleation processes at higher deposition temperatures. The atomic force microscopy (AFM) results support this idea by showing the increase of the number of surface asperities as a function of pressure and the strong decrease of that density as a function of deposition temperature.