Scanning electron microscope analog of scatterometry

Abstract

Optical scatterometry has attracted a great deal of interest for linewidth measurement due to its high repeatability and capability of measuring sidewall shape. We have developed an analogous and complementary technique for the scanning electron microscope. The new method, like scatterometry, measures shape parameters (e.g., wall angles) as well as feature widths. Also like scatterometry, it operates by finding a match between the measured signal from an unknown sample and a library of signals calculated for known samples. A physics-based model of the measurement is employed for the calculation of libraries. The method differs from scatterometry in that the signal is an image rather than a scattering pattern, and the probe particles are electrons rather than photons. Because the electron-sample interaction is more highly localized, isolated structures or individual structures within an array can be measured. Results of this technique were compared to an SEM cross section for an isolated polycrystalline silicon line. The agreement was better than 2 nm for the width and 0.2{degrees} for wall angles, differences that can be accounted for by measurement errors arising from line edge roughness.