Refractive Index Modification During Deposition of Silicon Oxynitride Films Prepared by Reactive Laser Ablation

Inhomogeneous low-k thin films of SiOxNy have been deposited by laser ablation of a Si3N4 sintered target in presence of oxygen gas. The high oxidation rate of silicon nitride has been used to control the stoichiometry of the films by modifying the oxygen partial pressure. The refractive index of the deposited material was able to be tailored at any value between 1.47 (SiO2) to 2.03 (Si3N4) by this approach. In situ optical characterization of the growing films was possible using kinetic and spectro ellipsometry. The refractive index was determined by applying the Effective Medium Approximation (EMA) and considering a mixture of SiO2, Si3N4, and voids. The volumetric composition obtained by ellipsometry was compared to the results determined by AES and XPS characterization. The purpose of this application is to show that reactive PLD can be used to produce high quality optical filters.