Patent ID: 7119886

Claim:
A lithographic projection apparatus, comprising: a radiation system configured to provide a beam of radiation; a support configured to support a patterning device, the patterning device configured to pattern the beam according to a desired pattern; a substrate table configured to hold a substrate; a projection system configured to project the patterned beam onto a target portion of the substrate; a reference frame; a first measuring system configured to measure at least one of positions and displacements of the substrate table relative to the reference frame, the measuring system including a plurality of first sensors mounted on the reference frame and having respective measurement axes; and a second measuring system configured to measure at least one of positions and displacements of the projection system relative to the reference frame, the measuring system including a plurality of second sensors mounted on the reference frame and having respective measurement axes, wherein at least one sensor of the second measuring system has a measurement axis passing through an invariant point of the projection system and the second measuring system comprises three linear sensors configured to measure along measurement axes passing through the invariant point.