The effects of deposition parameters on the optical performance of thin dielectric films

Abstract

For certain applications of multilayer optical systems the need for minimum scattering losses is paramount. From the polycrystalline nature of most optical films, some scattering is unavoidable. Its extent depends on the conditions of deposition, especially the rate of deposition and substrate temperature. There is however considerable disagreement in the literature on the effects of these parameters and it is suspected that observed effects of these parameters have been masked by unrecognized extraneous effects. In this paper results are given for scattering losses in MgF 2 and ZnS films measured by three methods, namely (a) lateral waves, (b) waveguide modes and (c) integrating sphere. In addition, ellipsometric studies have been made of ZnS films. Variations of scattering loss with the deposition parameters mentioned have been studied, leading to the establishment of conditions of preparation which produce minimal scattering. The results, together with electron microscope studies of the films, provide some insight into the scattering process.