Optical properties, microstructure and composition of SixN1−x prepared at low temperatures by laser induced CVD

Thin films of silicon nitride were deposited on optical glasses and Si(100) substrates at temperature as low as 170°C, by using laser induced CVD (LCVD). ArF laser was used for dissociation of gas mixture composed of SiH4NH3. The effect of lowering substrate temperature on microstructure, composition and optical properties of the films has been investigated. Amorphous silicon nitride films having uniform composition and thickness, which are transparent in the visible range were obtained. The index of refraction of the film decreases by decreasing substrate temperature from 1.98 at 320°C to 1.75 at 170°C. The decrease is associated with the formation of silicon oxide on the substrate at temperatures lower than 200°C. The deposition of the silicon nitride was found to be limited by the dissociation rate of the ammonia gas and the substrate temperature.