Growth mechanisms of SiO2 thin films prepared by plasma enhanced chemical vapour deposition

The growth mechanism of SiO2 thin films prepared by PECVD in a downstream configuration and using tetramethylsilane (TMS) as precursor has been studied within the frame of the dynamic scaling theory (DST). Atomic force microscopy images of the samples have been taken as a function of deposition time and analysed within the DST. From this analysis growth and roughness exponents with values α = 0.71 and β = 0.19 have been obtained. These exponents define a self-affine class of films where the growth is controlled by a diffusion process with a non-linear component. It has been also found that the growth rate of the films increases with the pressure and that the intensity of the emission lines of the plasma due to oxygen and hydrogen species decreases with this experimental parameter. Based on these facts and the determined DST exponents a growth mechanism has been proposed where the diffusion of fragments of the precursor (TMS) on the surface is the controlling step of growth of SiO2 films.