Time-frequency analysis assisted determination of ruthenium optical constants in the sub-EUV spectral range 8 nm-23.75 nm

The optical constants of ruthenium in the spectral range 8 nm - 23.75 nm are determined with their corresponding uncertainties from the reflectance of a sputtered ruthenium thin film, measured using monochromatized synchrotron radiation. This work emphasizes the correlation between structure modelling and the determined optical parameters in a robust inverse-problem solving strategy. Complementary X-ray Reflectivity (XRR) measurements are coupled with Markov chain Monte Carlo (MCMC) based Bayesian inferences and a quasi-model-independent method to create a model factoring the sample's oxidation, contamination, and interfacial imperfections. The robustness of the modelling scheme against contamination and oxidation is tested and verified by measurements after hydrogen-radical cleaning of the sample's surface. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement