| 摘要 |
Disclosed are overlay targets having flexible and symmetric characteristics and metrology techniques for measuring the overlay error between two or more successive layers of such targets. In one embodiment, the semiconductor target comprises a plurality of first structures having a first center of symmetry or a first line of symmetry being arranged to determine the relative shift in an x direction by analyzing an image of the first structure. The target further comprises a plurality of second structures having a second center of symmetry or a second line of symmetry being arranged to determine the relative shift in an x direction by analyzing an image of the second structures, wherein the first center of symmetry or first line of symmetry has a different location than the second center of symmetry or second line of symmetry. |
