| 摘要 |
A lithographic apparatus arranged to transfer a pattern from a patterning device onto a substrate includes a reference set of gratings provided in the substrate, the reference set including two reference gratings having line elements in a first direction and one reference grating having line elements in a second, perpendicular, direction. A measurement set of gratings is provided on top of the reference set of gratings, the measurement set comprising three measurement gratings similar to the reference gratings. Two of the measurement gratings are oppositely biased in the second direction relative to the respective reference gratings. An overlay measurement device is provided to measure asymmetry of the three gratings in the reference set and the measurement set, and to derive from the measured asymmetry the overlay in both the first and second direction.
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