ION-ASSISTED REACTIVE DEPOSITION PROCESSES FOR OPTICAL COATINGS

Thin films generally have properties which are different from those of the bulk starting material. Regarding optical properties, the observed values of the refractive indices and absorption coefficients are often lower or higher than the optical constants of the same bulk material. The resulting film properties are influenced by the production methods, such as ion-assisted deposition, activated reactive evaporation, ion beam sputtering, reactive ion plating and ion cluster beam deposition, and by the coating conditions, such as substrate temperature, deposition rate, pressure of the reactive gas, ion energy and ion current density. Reactive evaporation and sputtering with partial ionization of the reactive gas enhance chemical reactions and change the microstructure of the layers. Stoichiometry, very low absorption values and small scatter losses have been obtained when films have been prepared by activated reactive processes. In order to prevent the decomposition of chemical compounds and to produce stoichiometric films, ions with low energy have to be used. The purpose of this paper is to review low energy reactive and plasma processes for the production of low loss optical coatings.