Patent ID: 8072611
Filing Date: 2011-12-06
Classification: G01B

Abstract:
1. A method, comprising: directing test light reflected from an object to form an image of the object on a detector, where the object includes a diffractive structure, the test light at the detector comprises both specularly and non-specularly reflected light from the diffractive structure, and the diffractive structure is under-resolved in the image; directing reference light to interfere with the test light at the detector, the reference and test light being derived from a common source; varying an optical path length difference between the test and reference light; acquiring an interference signal from the detector while varying the optical path length difference so that a contribution to the interference signal from the non-specularly reflected light is reduced to be negligible relative to a contribution to the interference signal from the specularly reflected light, wherein acquiring the interference signal includes detecting an intensity image with the detector and laterally integrating intensity values of the intensity image over an averaging area of the detector; and determining information about the diffractive structure based on the interference signal and on predetermined information derived from a mathematical model of light reflection from a model diffractive structure.