Patent ID: 8848186

Claim:
A method for determining an overlay offset comprising: obtaining a first anti-symmetric differential signal (ΔS 1 ) associated with a first scatterometry cell; obtaining a second anti-symmetric differential signal (ΔS 2 ) associated with a second scatterometry cell; and computing an overlay offset from the first anti-symmetric differential (ΔS 1 ) signal associated with the first scatterometry cell and the second anti-symmetric differential signal (ΔS 2 ) associated with the second scatterometry cell according to the equation: overlay ⁢ ⁢ offset = f 0 · Δ ⁢ ⁢ S 1 + Δ ⁢ ⁢ S 2 Δ ⁢ ⁢ S 1 - Δ ⁢ ⁢ S 2 wherein f 0 is a magnitude of a programmed offset for the first scatterometry cell and the second scatterometry cell.