Patent ID: 7990549
Filing Date: 2011-08-02
Classification: G01B,G01N

Abstract:
1. A method of characterizing a diffraction grating structure, comprising collecting a first set of reflected data from the grating structure by providing incident light at a first angle of azimuthal incidence with respect to the grating structure; collecting a second set of reflected data from the grating structure by providing incident light at a second angle of azimuthal incidence with respect to the grating structure, the first and second angles being effectively orthogonal and the second angle of azimuthal incidence being different from zero; analyzing a combination of at least the first and second set of reflected data; and utilizing symmetrical characteristics of a diffraction analysis of the second angle of azimuthal incidence reflected data so as to reduce the computation complexity of the analysis of the second set of reflected data during the determination of at least one geometrical characteristic of the grating structure, where one or more of the sets of data are used to normalize other set(s) of data so that optical metrology data comprises ratios of reflected data collected for different incident conditions, avoiding the need to determine incident intensity via an absolute calibration process.