Patent ID: 7317531

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 targets A, B, C and D that each include a portion of the first and second structures, wherein the target A is designed to have an offset Xa between its first and second structures' portions, wherein the target B is designed to have an offset Xb between its first and second structures' portions, wherein the target C is designed to have an offset Xc between its first and second structures' portions, wherein the target D is designed to have an offset Xd between its first and second structures' portions, wherein each of the offsets Xa, Xb, Xc and Xd is different from zero, Xa is an opposite sign and differs from Xb, and Xc is an opposite sign and differs from Xd; illuminating the targets A, B, C and D with electromagnetic radiation to obtain spectra S A , S B , S C , and S D from targets A, B, C, and D, respectively; and determining and storing any overlay error between the first structures and the second structures using a scatterometry technique based on the obtained spectra S A , S B , S C , and S D , wherein obtaining the spectra S A , S B , S C , and S D comprises acquiring radiation from the targets A, B, C, and D using an optical apparatus comprising (i) a spectroscopic normal incidence polarized differential reflectometer and an oblique incidence spectroscopic ellipsometer or (ii) a spectroscopic near-normal incidence polarized differential reflectometer and an oblique incidence spectroscopic ellipsometer.