Structural studies of low-temperature low-pressure chemical deposited polycrystalline silicon

Abstract

Structural studies were performed on Si films formed by chemical-vapor deposition on SiO2 films using silane under pressures below 150 mTorr and temperatures below 640 °C. The mode of growth of these films was found pressure dependent. Films grown at pressures below 10 mTorr were found to have a columnar structure with a (001) preferred orientation ending at a curved surface. The radius of the crystallites increases and the radius of curvature of their free surface decreases as the pressure decreases, while the converse is true for the temperature dependence. Transition from this mode is associated with diminishing of the capillarity effects. For pressures above 10 mTorr the structure is striated with a 〈111〉 twin texture almost perpendicular to the substrate. At pressures above 100 mTorr the structure is similar to the previous one but with a tufty appearance. This structure is associated with compressive and dilatational strain. The size of initial crystallites was found also pressure dependent increasing with pressure.