CONTRIBUTIONS OF SILICON-HYDRIDE RADICALS TO HYDROGENATED AMORPHOUS-SILICON FILM FORMATION IN WINDOWLESS PHOTOCHEMICAL VAPOR-DEPOSITION SYSTEM

Hydrogenated amorphous silicon (a-Si:H) films are prepared using a windowless photochemical vapor deposition system. Vacuum ultraviolet light of 121.6 nm from hydrogen-helium mixture plasma is thought to decompose silane molecules into mainly SiH and SiH2 radicals. Contributions of these radicals to film growth result in growth rate dependence upon substrate temperature (T(s)). The apparent sticking probability of both radicals is determined to be 0.84 at T(s)=100-degrees-C and 0.68 at T(s)=250-degrees-C, from the variation of step coverage as a function of T(s). Adjusting the substrate position close to the light source brings about an increase of incident SiH and SiH2 radicals through primary photolysis by 121.6 nm light, as well as decrease of gas-phase reactions, which allows us to control the Si-H-2 bond density in the film. The effect of the Si-H-2 bond in the film is also shown.