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 par ameter Delta, we have determined the thickness, refractive index, and the a bsorption coefficient of various thin films and thin-film stacks. (Delta, t he relative phase between the p- and s-polarized components, is measured fo r both reflected and transmitted light.) These optical measurements are per formed with a specially designed system at the fixed wavelength of lambda = 633 nm over the 10 degrees -75 degrees range of angles of incidence, The e xamined samples, prepared by means of sputtering on fused-silica substrates , consist of monolayers and trilayers of various materials of differing thi ckness and optical constants. These samples, which are representative of th e media of rewritable phase-change optical disks, include a dielectric mixt ure of ZnS and SiO2, an amorphous film of the Ge2Sb2.3Te5 alloy, and an alu minum chromium alloy film. To avoid complications arising from reflection a nd transmission losses at the air-substrate interface, the samples are imme rsed in an index-matching fluid that eliminates the contributions of the su bstrate to reflected and transmitted light. A computer program estimates th e unknown parameters of the film(s) by matching the experimental data to th eoretically calculated values. Although our system can be used for measurem ents over a broad range of wavelengths, we describe only the results obtain ed at lambda = 633 nm. (C) 2001 Optical Society of America.