Method for determination of the parameters of transparent ultrathin films deposited on transparent substrates under conditions of low optical contrast

In the present work we suggest an original ellipsometric technique for independently determining strongly correlated refractive index and thickness of transparent ultrathin films. We demonstrate significant accuracy improvement for the single-wavelength null-ellipsometry measurements when using multiple incidence angles for the system "transparent film on a transparent substrate" studied in the thickness range of 1.0-20.0 nm and the low-contrast region for the film-substrate surface. A straightforward relationship is obtained between the refractive index n(1) of the transparent film and the incidence angle φ. It follows from invariability ensured for the amplitude ellipsometric parameter Ψ with respect to the film thickness changes.