Evolution of surface topography of as-grown Si films near amorphous-to-polycrystalline transition

The evolution of the surface topography and microstructure of silicon films deposited near the amorpbous-to-polycrystalline transition was investigated, and was found to be accompanied by the appearance of crystalline aggregates whose density and size distribution strongly depend on deposition parameters. The films were deposited by low-pressure chemical vapor deposition, and the parameters varied were temperature, pressure, film thickness, and substrate material. Both temperature and pressure have a dramatic effect on the density and size of surface aggregates. A transition from amorphous to polycrystalline silicon at the critical temperature, T_c ∼ 580°C, is evident from the abrupt change in surface roughness. This effect was far more pronounced for thin (55 nm) silicon films than for their thicker (ISO nm) counterparts and was generally larger for films grown directly on c-Si rather than on SiOx substrates. Evidence for nanocrystalline silicon particles embedded into the amorphous matrix below T_c was found. In this study, it is suggested that the amorphous-polycrystalline silicon transition and consequently the surface topography evolution of the films is fluctuation assisted. The transition manifests itself in an enhanced population of Si nucleation centers, which are mostly formed at the upper surface of the deposited film.