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Kinetics of deposition and electrical properties of silicon nitride films obtained by 185 nm photolysis of SiH4-NH3 mixtures

The photolysis of NH3 and SiH4 by the 185 nm radiation of a low-pressure Hg lamp is used to deposit silicon nitride films at temperatures ranging from 50 up to 420 degrees C. The deposition kinetics are analysed by considering the gas phase and surface reactions of radicals (H, NH2, SiH3, SiH2) involved in the photochemical process. Radical densities and flux to the walls in the deposition chamber are computed from numerical solutions of one-dimensional spatially resolved balance equations for creation, reaction and diffusion of each species. The film composition is analysed by X-ray photoelectron spectroscopy (XPS) and secondary-ion mass spectrometry (SIMS). The thickness and refractive index are obtained by ellipsometry. Finally the electrical properties are derived from current-voltage I(V) and capacitance-voltage C(V) characteristics. The optimum dielectric properties are obtained for deposition temperatures between 250 and 350 degrees C and for SiH4 concentration in NH3 of about 1%.