Line edge roughness characterization of sub-50nm structures using CD-SAXS: round-robin benchmark results

Abstract

The need to characterize line edge and line width roughness in patterns with sub-50 nm critical dimension challenges existing platforms based on electron microscopy and optical scatterometry. The development of x-ray based metrology platforms provides a potential route to characterize a variety of parameters related to line edge roughness by analyzing the diffracted intensity from a periodic array of test patterns. In this study, data from a series of photoresist line/space patterns featuring programmed line width roughness measured by critical dimension small angle x-ray scattering (CDSAXS) is presented. For samples with periodic roughness, CD-SAXS provides the wavelength and amplitude of the periodic roughness through satellite diffraction peaks. In addition, the rate of decay of intensity, termed an effective "Debye-Waller" factor, as a function of scattering vector provides a measure of the fluctuation in line volume. CDSAXS data are compared to analogous values obtained from critical dimension scanning electron microscopy (CDSEM). Correlations between the techniques exist, however significant differences are observed for the current samples. Calibrated atomic force microscopy (C-AFM) data reveal large fluctuations in both line height and line width, providing a potential explanation for the observed disparity between CD-SEM and CD-SAXS.