Patent ID: 7330259

Claim:
A method for use in measuring/inspecting a patterned article, the method comprising applying optical measurements to a measurement site on the article by illuminating the measurement site with a plurality of wavelengths at substantially normal incidence of the illuminating light, detecting light returned from the illuminated site, and generating measured data indicative thereof, wherein the measurements are applied to the measurement site through a polarizer rotatable between its different orientations selected from a number of pre-calibrated orientations; wherein the measurements applied to the measurement site are carried out with the at least three different orientations of the polarizer selected from the at least four pre-calibrated orientations; wherein said at least three selected polarization orientations include two mutually perpendicular polarizations corresponding to the angular orientations β and (90+β), and at least one intermediate polarization orientation corresponding to the polarization vector orientation in between said mutually perpendicular polarization states.