Growth mechanism of sputtered amorphous silicon thin films

A comprehensive study of the growth mechanism of sputtered amorphous silicon thin films (a-Si:H) is presented. Different films were prepared with various substrate temperatures and RF powers. These two parameters were varied in order to control the energy, the flux of the incoming adatoms and their reactivity on the growing surface. Independently of the deposition RF power, the influence of substrate temperature can be divided into two ranges: (i) a low temperature range where the deposition rate is controlled by the flux of incoming adatoms from the plasma, and the growth mechanism is governed by the incorporation of SiHx   (x=0–1x=0–1) species incorporation. In this range, the deposition rate increases with substrate temperature. (ii) A high temperature range where the growth mechanism is surface reaction dominated. The deposition rate here decreases with substrate temperature increase. The optimal substrate temperature, defined as the temperature leading to the growth of less disordered film, is 300 and 400 °C for deposition RF power equal to 70 and 100 W, respectively. The optimum growth temperature increase with RF power is explained in terms of hydrogen diffusion and widening of the subsurface growth region layer.