137 INHOMOGENEITY AND MICROSTRUCTURE IN e-BEAM EVAPORATED ZrO2 FILMS aa a ~ N a M. BELLYba , C. CREMONESI, F. PARMIGIANIa, M. SCAGLIOTTI and S. BERETTAb. a. CISE-Tecnologie Innovative, P.O.Box 12081, 1-20134 Milan, Italy b. ALENIA, 1-20014 Nerviano, Italy ABSTRACT Thin films of zirconium dioxide are deposited by e-beam evaporation on optically polished borosilicate crown glass. Two different oxygen partial pressures in the chamber are used. The optical properties of the films are characterized by ellipsometry. The influence of oxygen stoichiometry on the composition and microstructure of the material is investigated by polycrystalline X-ray diffraction for different film thicknesses. The films are found to be inhomogeneous, and a composition gradient (i.e. amorphous s tetragonal o monoclinic) is observed from the substrate to the surface. The oxygen partial pressure influences the growth of the films. INTRODUCTION Optical applications of thin films, such as high reflection coatings, polarizers, beam splitters and spectral filters are quite common. In the design of these devices thin film inhomogeneity is a major problem, because many algorithms assume that the refractive index is independent of film thickness. On the contrary a density gradient along the growth direction, typical of columnar microstucture, is a frequent source of refractive index variation [I]. Electron-beam evaporated ZrO2 is a suitable material for visible and infrared optical coatings due to its high refractive index, low loss and low scatter. It has a large band gap, a high laser damage threshold, it is hard and chemically stable. Pure ZrO2 films, however, exhibit structural inhomogeneities related to the presence of different polymorphs in the film thickness. Previous investigations [21 suggested that zirconia nucleates in the cubic polymorph and only when a critical thickness is reached the surface conditions become favorable for the growth of the monoclinic phase, which is the stable form at room temperature. On the other hand it is well known [3,4] that it is possible to stabilize high temperature ZrO2 polymorphs at lower temperatures by the application of stress, high defect concentration and small crystallite size. Aim of the present work is to provide a detailed analysis of the origin of the structural inhomogeneities in e-beam evaporated ZrO2 thin films and on the role of microstructure in determining the film properties. The influence of oxygen partial pressure in the evaporation chamber, is investigated for different film thicknesses. Mat. Res. Soc. Symp. Proc. Vol. 208. @1991 Materials Research Society