Relative importance of hydrogen atom flux and ion bombardment to the growth of μc-Si:H thin films

An investigation of the relative importance of H atoms and ions to the transition from amorphous to microcrystalline silicon growth was performed by applying in situ plasma diagnostics and a 2D simulator of SiH4/H2 discharges. The growth transition was achieved by reducing the % SiH4 in the SiH4/H2 discharges while keeping all the other plasma parameters constant. The distribution of the main species in the discharge space, as well as the flux of H atoms and ions per monolayer and the energy transferred by each to the growing film surface, was estimated from the simulation results. H atoms flux was found to be much higher compared to ions but the total amount of energy transferred from both H atoms and ions was found to be much lower than the activation energy required for crystallization of stable a-Si:H films with low H-content. These results support the theory that in the present conditions the formation of microcrystals proceeds via the initial growth of an unstable a-Si:H with high H content, which reduces significantly the energy barrier for crystallization.