Laser Induced Chemical Vapor Deposition of Hydrogenated Amorphous Silicon

ABSTRACTSome results on hydrogenated amorphous silicon growth by CO2 laser photodissociation of silane are reported. A 100 W CW CO2 laser was used as the excitation source. A horizontal configuration was adopted, where the laser beam is sent parallel to the substrate surface inside a flux reactor, and its energy is used to excite and dissociate the silane molecules flowing near the solid surface. The laser has no direct heating effect on the substrate, which is independently heated by an oven.The photoproduced radicals by interacting with the surface grow a film at a rate strongly depending on silane pressure, substrate temperature and laser intensity. This experimental configuration allows depositions on large areas, owing to the large number of reactant molecules involved in the photochemical process. Moreover, material can be produced with a continuously variable hydrogen content, since the substrate temperature required for obtaining depositions can be as low as room temperature and adjusted independently of the other process parameters.The film properties are similar to those of the glow discharge deposited material. The film amorphousness and the hydrogen presence either in monohydride and dihydride groups are evidenced by x-ray patterns and ir spectra. Results on the electrical and optical properties are also reported.