Patent ID: 7933016

Claim:
A method for determining overlay between a plurality of first structures in a first layer of a sample and a plurality of second structures in a second layer of the sample, the method comprising: providing a plurality of targets that each include a portion of the first and second structures and each is designed to have an offset between its first and second structure portions; illuminating the targets with electromagnetic radiation to thereby obtain detected output radiation from each target at a −1 st diffraction order and a +1 st diffraction order; and determining any overlay error between the first structures and the second structures using a scatterometry technique based on the detected output radiation by: for each target, determining a first differential intensity between the −1 st diffraction order and the +1 st diffraction order, for a plurality of pairs of targets each having a first target and a second target, determining a second differential intensity between the first differential intensity of the first target and the first differential intensity of the second target, and determining any overlay error between the first structures and the second structures using a scatterometry technique based on the second differential intensities determined from each target pair.