Determination of thicknesses and refractive indices of polymer thin films by multiple incident media ellipsometry

Abstract

Single wavelength ellipsometry measurements at Brewster's angle and in multiple incident media provide a powerful technique for characterizing ultrathin (<20–30nm) polymer films. Only one ellipsometric parameter (i.e. amplitude ratio) is obtained at Brewster's angle since phase shift is 90°. By conducting the experiments in different ambient media, simultaneous determinations of a film's thickness and refractive index for ultrathin polymer films are possible at Brewster's angle. Poly(tert-butyl acrylate) (PtBA) Langmuir–Blodgett films serve as a model system for the simultaneous determination of thickness and refractive index (1.45±0.01 at 632nm). Thickness measurements on films of variable thickness agree with X-ray reflectivity results ±0.8nm. The method is also applicable to spincoated films where refractive indices of PtBA, polystyrene and poly(methyl methacrylate) are found to agree with literature values within experimental error.