Dynamics of low temperature PECVD growth of microcristalline silicon thin films: impact of substrate surface treatments

Microcrystalline silicon (mu c-Si) films have been deposited on polyimide, Corning glass and c-Si(001) by rf plasma-enhanced chemical vapour deposition (PECVD) using both SiF4-H-2 and SiH4-H-2 plasmas. The effect of substrate pre-treatment using SiF4-He and H-2 plasmas on the nucleation of crystallites is investigated. Real-time laser reflectance interferometry monitoring (LRI) revealed the existence of a 'crystalline seeding time' that strongly impacts on the crystallite nucleation, on the structural quality of the substrate/mu c-Si interface and on film microstructure. It is found that SiF4-He pre-treatment of substrates is effective in suppressing porous and amorphous interface layer at the early nucleation stage of crystallites, resulting in direct deposition of mu c-Si films also on polyimide at the temperature of 120 degrees C.