Patent ID: 7532305

Claim:
A lithographic apparatus arranged to transfer a pattern from a patterning device onto a substrate, comprising: a reference set of gratings in the substrate, the reference set consisting of two reference gratings having line elements in a first direction, and one reference grating having line elements in a second direction, the second direction being substantially perpendicular to the first direction; a measurement set of gratings on top of the reference set of gratings, the measurement set consisting of three measurement gratings similar to the reference gratings, in which two of the measurement gratings are oppositely biased in the second direction relative to the respective two reference gratings and one of the measurement gratings is not biased in the first direction relative to the respective one reference grating; and an overlay measurement device, the overlay measurement device being configured 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.