Monitoring critical dimensions of bidimensional gratings by spectroscopic ellipsometry and Mueller polarimetry

In this work we characterized two bidimensional gratings consisting each of a square array of square holes etched in a photoresist layer deposited on silicon. Data were taken on both samples with a spectroscopic UV-VIS ellipsometer (SE) operated at 70° incidence and zero azimuth (with the incidence plane parallel to the lines of holes) and VIS Mueller matrix polanimeter (MMP) at various incidence and azimuthal angles. The robustness of the parameters derived from the MMP data was evaluated from the stability of the values provided by regression the spectra taken at different angles. The optimal measurement geometries, featuring high sensitivity and low correlation of the fitting parameters, were determined theoretically, and validated experimentally with the sample featuring wider holes (500 x 500 nm), for which 45° incidence provided better results than the usual 70° value.