| 摘要 |
A multi-layer overlay target for use in imaging based metrology is disclosed. The overlay target includes a plurality of target structures including three or more target structures, each target structure including a set of two or more pattern elements, wherein the target structures are configured to share a common center of symmetry upon alignment of the target structures, each target structure being invariant to N degree rotation about the common center of symmetry, wherein N is equal to or greater than 180 degrees, wherein each of the two or more pattern elements has an individual center of symmetry, wherein each of the two or more pattern elements of each target structure is invariant to M degree rotation about the individual center of symmetry, wherein M is equal to or greater than 180 degrees. |
