Patent ID: 9739702
Date: 2017-08-22
CPC Classifications: G01B,G01N,G02B,G03F

Claim:
1. A method of estimating an overlay error between at least two layers, the method comprising: illuminating a metrology target that comprises at least two periodic structures which are at different layers, are along a direction parallel to the target and have a same pitch, such that at least two of the at least two periodic structures are arranged such that they at least partly share a same border or line with each other when observed from a perspective perpendicular to the target and do not overlap in a direction perpendicular to the target, wherein the metrology target is symmetric with respect to a 180° rotation about an axis that is perpendicular to the target, and wherein the illumination is carried out simultaneously with respect to the at least two periodic structures in order to effect a result selected from the group of: measuring interference of at least one diffraction order from the at least two periodic structures; and extracting the overlay error from the measured interference.