Comparison of spectroscopic Mueller polarimetry, standard scatterometry, and real space imaging techniques (SEM and 3D-AFM) for dimensional characterization of periodic structures

Abstract

Spectroscopic Mueller polarimetry may provide a useful alternative to standard spectroscopic ellipsometry (SE) for the dimensional characterization of periodic structures, as it provides 16 quantities instead of 2 for SE. We present a detailed experimental comparison of the results provided by conventional scatterometry (0.7 - 5 eV) spectral range), Mueller polarimetry in the visible (450 - 825 nm), electron microscopy (top CD-SEM and cross section) and state-of-the-art CDAFM (Veeco X3D). This last instrument was considered as the best reference currently available. The samples were 1D gratings etched in bulk Si, with 150 and 250 nm nominal CDs and several pitches for each CD. SE spectra were taken at zero azimuthal angles (i.e. with the grooves perpendicular to the incidence plane), as it is usually done with standard scatterometers, while Mueller spectra were measured at all azimuths in steps of 5°, allowing significant consistency tests by comparing the results of the corresponding fits. Both techniques provided CD values in agreement with AFM and CD-SEM data to within 5 nm, comparable to the AFM precision. Grating thickness and sidewall angle (SWA) were best determined by Mueller polarimetry at 90° azimuth, while in the usual zero azimuth configuration, SWA was typically underestimated by several degrees.