A new methodology to quantify the sensitivity and resolution of infrared variable angle spectroscopic ellipsometry (IRSE) measurements was developed for probing the depth profile of composition in thin polymer films. A multilayer system comprised of sub-100 nm films of poly(4-hydroxystyrene) upon poly(methyladamantyl methacrylate) was used as a model test structure to develop the IRSE technique for characterization of bilayer film thickness, composition profile, and layout. Based upon sensitivity and contrast guidelines we demonstrate that the substrate type, incident angle and specific spectral band regions influence the sensitivity of IRSE. A judicious choice of measurement variables and infrared spectral regions substantially improves the measurement precision. The results of the IRSE are validated by comparison to high-resolution neutron reflectivity. Most strikingly, the Brewster angle incidence does not lend to the maximum sensitivity. Discussions as to the origin of these new results and metrics are provided.
IRSE, ellipsometry, interface, diffusion, thin film, photoresist, sensitivity