Patent ID: 8922749

Claim:
A lithographic apparatus comprising: a support constructed to support a patterning device, the patterning device being capable of imparting a 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; a projection transfer measurement system configured to measure an optical projection transfer information of the projection system during a scanning movement of the substrate table in which the patterned radiation beam is projected onto the target portion of the substrate, the projection transfer measurement system comprising: an optical device configured to direct a measurement beam into the projection system, a detector configured to detect the measurement beam having passed through the projection system, a first optical element to reflect at least part of the measurement beam, after having passed the projection system, back into the projection system during the scanning, and a measurement processor configured to determine the optical projection transfer information from the detected measurement beam, wherein the optical device and the detector are arranged at an upstream end of the projection system, and wherein the projection transfer measurement system is arranged so that, in use during the scanning, the at least part of the measurement beam reflected by the first optical element is detected by the detector without interacting with said optical device.