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 SiH 2 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° C and 0.68 at T s =250° 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 SiH 2 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.