Deposition mechanism of a-Si: H films fabricated by coaxial-line-type microwave plasma chemical vapour deposition

Hydrogenated amorphous silicon (a-Si:H) films are fabricated outside of hydrogen or argon plasma by using a double-tubed, coaxial-line-type, microwave plasma chemical vapor deposition (CVD) system. Thermal stability of the films is investigated by annealing. A deposition mechanism and a hydrogen evolution mechanism are proposed. By using hydrogen discharge, good quality, thermally stable films are obtained even at room temperature. In this case, silane radicals have large surface mobility due to the covering effect of hydrogen atoms and the soft-landing of silane radicals on the film's surface. The large surface mobility allows the silane radicals to move and to from bands with dangling bonds having a low potential energy and hence contributes to atructural stabilization.