Noninvasive characterization ef continuous-profile blazed diffraction gratings

Smooth, continuous-profile diffractive optical elements and other regular m icrostructures demand advanced characterization methods. Here the problem o f reconstructing the profiles with optical scatterometry is addressed for t he first time to our knowledge. We represent the profile of a blazed gratin g with an analytic Chebyshev series. The coefficients of the series are inf erred from the far-field diffraction pattern, when the grating profile is i lluminated with coherent light. An advanced neural-network model is used as a nonlinear statistical estimator. The reconstruction error is found to be less than 4% as normalized to the depth of the profile, even with realisti c measurement errors included in the simulations. (C) 2001 Optical Society of America.