Evaluation of Scatterometry Tools for Critical Dimension Metrology

With decreasing critical dimensions (CD) on lithography masks, increasing demands on CD metrology techniques come along. Already today the results of the three standard methods for CD measurements currently used, atomic force microscopy, scanning electron microscopy, and optical microscopy, typically do not yield the same results. This is because of, e.g. incomplete knowledge of the material parameters, insufficient modelling or insufficient resolution. With decreasing CD’s these systematic differences increase. The need on new cross-calibration strategies arises. Scatterometry as a non-imaging metrology method offers access to the geometrical parameters and provides independently achieved additional information that can be used for cross-calibration. A comparison of simulations, achieved with rigorous coupled-wave analysis methods and a finite element method, respectively with the experimental results measured with two scatterometers (VIS @ 633 nm, EUV @ 13.5 nm) on a periodically structured chrome on glass mask will be presented. Special attention is given to the sensitivity of surface parameters with respect to the inspection wavelength.