Critical dimensions of biperiodic gratings determined by spectral ellipsometry and Mueller matrix polarimetry

We characterized two samples consisting of photoresist layers on silicon with square arrays of square holes by spectroscopic ellipsometry (SE) and Mueller matrix polarimetry (MMP). Hole lateral dimensions and depths were determined by fitting either SE data taken in conventional planar geometry or MMP data in general conical diffraction configurations. A method for objective determination of the optimal measurement conditions based on sensitivity and parameter correlations is presented.When applied to MMP, this approach showed that for one of the samples the optimal incidence angle was 45◦, much below the widely used 70 degrees value. The robustness of the dimensional characterisation based on MMP is demonstrated by the high stability of the results provided by separated fits of the data taken at different azimuthal angles.