Patent ID: 9547244
Date: 2017-01-17
CPC Classifications: G01B,G03F

Claim:
1. A method of simultaneously measuring n overlay errors in a structure, the method comprising: illuminating the structure with obliquely incident radiation, the structure having a plurality of diffraction based overlay pads, each diffraction based overlay pad having a same number m of periodic patterns, where n≧2 and m=n+1, wherein the structure has no more than n+1 diffraction based overlay pads, and wherein there is a programmed shift between each pair of periodic patterns in each diffraction based overlay pad; detecting radiation from the structure after the obliquely incident radiation interacts with the plurality of diffraction based pads; determining n differential signals from the detected radiation from n different pairs of the plurality of diffraction based overlay pads; and using the n differential signals and the programmed shift between each pair of periodic patterns to simultaneously determine the n overlay errors.