Patent ID: 7518703

Claim:
A lithographic apparatus comprising: an illumination system configured to condition a radiation beam; a support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and an interferometric measurement system configured to measure at least one property of the apparatus, wherein the measurement system comprises: a radiation steering device configured to steer radiation received from the illumination system through the projection system; a source module at the level of the substrate table configured to receive steered radiation from the radiation steering device and to provide an effective angularly dispersed source of radiation; and a sensor unit, at the level of the support, configured to receive radiation from the source module through the projection system to perform the measurement.