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US 8,138,498 B2Granted
Apparatus and methods for determining overlay of structures having rotational or mirror symmetry
AssigneeKLA-Tencor Technologies Corporation
InventorMark Ghinovker
Life of this patent
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Abstract
Disclosed are overlay targets having flexible symmetry characteristics and metrology techniques for measuring the overlay error between two or more successive layers of such targets. Techniques for imaging targets with flexible symmetry characteristics and analyzing the acquired images to determine overlay or alignment error are disclosed.
Claims11
A semiconductor target for determining a relative shift between two or more successive layers of a substrate, the target comprising:
- a plurality of first structures formed in a first layer, and the first structures having a first center of symmetry (COS), the first structures being aperiodic;
- and
- a plurality of second structures formed in a second layer, and the second structures having a second COS, the second structures being aperiodic,
- wherein the difference between the first COS and the second COS corresponds to an overlay error between the first and second layer and wherein the first and second structures have a 180° rotational symmetry, without having a 90° rotational symmetry, with respect to the first and second COS, respectively.
1 more element
Dependencies are inferred from the claim text.