SPUTTERING YIELD OF OPTICAL-MATERIALS - SIGMUND MODEL AND EXPERIMENTAL RESULTS

The main drawback of the ion beam assistance during optical thin film deposition is the stoichiometry alteration due to the different sputte ring yield of elements which compose the film itself. In optical mater ials such effect causes both an increase of absorption coefficient and undesirable variation of refractive index. In order to maintain the a dvantages of the ion beam assistance (i.e., enhancement of adhesion, c ompactness, good control of optical properties) the sputtering phenome na should be modeled to recognize the parameters of the ion beam (ener gy, angle of incidence, and ion mass) that minimize the stoichiometry alteration. The Sigmund's model is an analytical approach widely used to treat the modelling of the sputtering phenomenon. In this work the Sigmund's model was applied to fit the experimentally measured sputter ing yield of several materials typically employed to fabricate optical coatings: silicon dioxide (SiO2), Yttrium oxide (Y2O3) and zinc selen ide (ZnSe). The yield measurements were performed both at different an gle of incidence of the beam (0-degrees, 45-degrees) and with differen t bombarding ion mass and energy. The experimental results appear well fitted by the relation of the sputtering yield (Sigmund's model) at a ll considered angles and ion masses. Sputtering yields of the material components as for instance silicon (Y(ion)Si) and oxygen (Y(ion)O) fo r Sio2 material, were modeled as well as their behavior with either io n energy or ion mass.