Determination of optical constants of thin films and multilayer stacks by use of concurrent reflectance, transmittance, and ellipsometric measurements

Using measurements of reflectance, transmittance, and the ellipsometric parameter Δ, we have determined the thickness, refractive index, and the absorption coefficient of various thin films and thin-film stacks. (Δ, the relative phase between the p- and s-polarized components, is measured for both reflected and transmitted light.) These optical measurements are performed with a specially designed system at the fixed wavelength of λ = 633 nm over the 10°—75° range of angles of incidence. The examined samples, prepared by means of sputtering on fused-silica substrates, consist of monolayers and trilayers of various materials of differing thickness and optical constants. These samples, which are representative of the media of rewritable phase-change optical disks, include a dielectric mixture of ZnS and SiO₂, an amorphous film of the Ge₂Sb₂.3Te₅ alloy, and an aluminum chromium alloy film. To avoid complications arising from reflection and transmission losses at the air–substrate interface, the samples are immersed in an index–matching fluid that eliminates the contributions of the substrate to reflected and transmitted light. A computer program estimates the unknown parameters of the film(s) by matching the experimental data to theoretically calculated values. Although our system can be used for measurements over a broad range of wavelengths, we describe only the results obtained at λ; = 633 nm.