Smooth, continuous-profile diffractive optical elements and other regular microstructures demand advanced characterization methods. Here the problem of reconstructing the profiles with optical scatterometry is addressed for the first time to our knowledge. We represent the profile of a blazed grating with an analytic Chebyshev series. The coefficients of the series are inferred from the far-field diffraction pattern, when the grating profile is illuminated 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 realistic measurement errors included in the simulations.
© 2001 Optical Society of America
(000.4430) General : Numerical approximation and analysis
(050.1970) Diffraction and gratings : Diffractive optics
(120.4290) Instrumentation, measurement, and metrology : Nondestructive testing
(120.5820) Instrumentation, measurement, and metrology : Scattering measurements
(290.3200) Scattering : Inverse scattering
Anu Huttunen, Ilkka Kallioniemi, and Jyrki Saarinen, "Noninvasive Characterization of Continuous-Profile Blazed Diffraction Gratings," Appl. Opt. 40, 2618-2625 (2001)