Patent ID: 7324209

Claim:
A method of detecting non-uniform ellipsometric properties of a substrate surface wherein the non-uniform ellipsometric properties are characterized by a characteristic dimension, said method comprising: generating an input beam for illuminating a spot at a selected location on or in the substrate, said spot having a size L that is substantially larger than said characteristic dimension; deriving a measurement beam and a reference beam from the input beam; directing the measurement beam onto the substrate as an incident measurement beam that illuminates said spot at that selected location on or in the substrate to produce a scattered measurement beam; for each orientation of a plurality of different orientations of the reference beam relative to the scattered measurement beam, interfering the scattered measurement beam with the reference beam to produce a corresponding interference beam, wherein each of said different orientations of the reference beam is selected to produce a peak sensitivity for a portion of the scattered measurement beam that emanates from the substrate at a corresponding different diffraction angle of a plurality of diffraction angles; for each orientation of the plurality of different orientations of the reference beam relative to the scattered measurement beam, converting the interference beam into an interference signal; and using the interference signals for each orientation of the plurality of different orientations to determine whether any non-uniform ellipsometric properties that are characterized by said characteristic dimension are present anywhere within a region on or in the substrate defined by the spot at that selected location.