Interferometric characterization of subwavelength lamellar gratings

We propose a new, to our knowledge, method for determining the two main cri tical parameters of periodic one-dimensional lamellar structures, namely, l inewidths and etched depths. The method is simple and requires-only two mea surements for the phase of the zero-transmitted order under two orthogonal polarizations. It is inspired by the analogy between subwavelength gratings and anisotropic homogeneous thin films. The method is tested with experime ntal data obtained with a Mach-Zehnder interferometer. Etched depths and li newidths derived from the interferograms and electromagnetic theory are com pared with scanning-electron-microscope observations. (C) 1999 Optical Soci ety of America.