Quantitative tool characterization of 193nm scatterfield microscope

Abstract

Evaluation of uncertainties is a critical element in quantitative nano-scale measurements using optical microscopy techniques. Instrument characterization underlies the quantitative evaluation of measurements of deep sub-wavelength features. The scatterfield microscopy technique, which articulates the illumination at the sample plane, is an efficient method for angle- and polarization-resolved microscope characterization to enable the uncertainty evaluations. The tool characterization results are used for the Fourier space normalization of electromagnetic simulation to permit comparisons with experimental imaging data. For this purpose the NIST 193 nm scatterfield microscope operating with an ArF Excimer laser was characterized. The illumination and collection optics were scanned angularly, utilizing a small aperture at the conjugate back focal plane of the objective lens so that the optics train was characterized with respect to angularly discrete cones of the illumination beam. Each cone beam can be approximated as a plane wave by using Kohler configuration, simplifying the analysis of the scattered light induced by the discrete illumination beam at the sample plane. Under this approximation, the illumination and entire tool function sets were measured at sample and imaging CCD planes, respectively, producing the collection tool function set numerically. We report tool imperfection effects upon these tool functions, specifically, comparing to the optical simulations of the designed optical paths varied with misalignments and aberrations that lead to changes in the tool functions. Through these comparisons, we investigate the relationship between the microscope tool imperfection factors to the deviations in the illumination as well as in the collected scattered light.