SPECTROSCOPIC ELLIPSOMETRY CHARACTERIZATION OF THIN-FILM SILICON-NITRIDE

We have measured and analyzed the optical characteristics of a series of silicon nitride thin films prepared by plasma-enhanced chemical vap or deposition on silicon substrates for photovoltaic applications. Spe ctroscopic ellipsometry measurements were made by using a two-channel spectroscopic polarization modulator ellipsometer that measures N, S, and C data simultaneously. The data were fit to a model consisting of air/roughness/SiN/crystalline silicon. The roughness was modeled using the Bruggeman effective medium approximation, assuming 50% SiN, 50% v oids. The optical functions of the SiN film were parameterized using a model by Jellison and Modine (Appl. Phys. Lett. 69 (1996) 371; 69 (19 96) 2137). All the chi(2) are near 1, demonstrating that this model wo rks extremely well for all SIN films. The measured dielectric function s were used to make optimized SIN anti-reflection coatings for crystal line silicon solar cells. (C) 1998 Elsevier Science S.A.