SPECTROSCOPIC ELLIPSOMETRY WITH COMPENSATOR AND X-RAY SPECULAR REFLECTIVITY FOR CHARACTERIZATION OF THIN OPTICAL-LAYERS ON TRANSPARENT SUBSTRATES

It is demonstrated that the use of X-ray specular reflectivity (XRSR) to measure the geometrical thickness of thin layers allows one to over come the thickness-optical property correlation in ellipsometry. In ad dition, a quasi-achromatic compensator is fitted to a rotating polariz er ellipsometer allowing the measurement of cos Delta with an accuracy better than 10(-4) for values close to one, over the entire 0.25-1.7- mu m spectral range. This set up is applied to the study of transparen t materials such as Ion Beam Sputtering (IBS) of thin SiO2 layers depo sited on silica glass substrates. Thus, a transition layer at the top surface of the substrate has been detected through the cos Delta measu rements. Ellipsometric results are in very good agreement with those o btained by photogoniometry. The knowledge of the optical properties of IBS SiO2 leads to a complete understanding of the ellipsometric respo nse of a TiO2/SiO2 mirror. (C) 1995 Elsevier Science S.A.