Quantitative microscope characterization for optical measurements with sub-nm parametric uncertainties

Recently, a new technique called Fourier normalization has enabled the parametric fitting of optical images with multiple or even a continuum of scattered spatial frequencies. Integral to the performance of this methodology is the characterization of the high magnification imaging microscope used in these experiments. Scatterfield microscopy techniques yield the necessary angular resolution required for determining the effects of the illumination and collection paths upon the electric field within the microscope. A multi-step characterization methodology is presented with experimental examples using a microscope operating at λ = 450 nm. A prior scatterfield characterization technique for specular reflectors is reviewed and shown to be a special case of the newer generalized approach. Possible implications of this methodology for improved critical dimension measurements are assessed.