Lithographic projection apparatus, a grating module, a sensor module, a method of measuring wave front aberrations

A lithographic projection apparatus comprising:

• a radiation system to provide a projection beam of radiation;
• a support structure to support patterning structure, the patterning structure serving to pattern the projection beam, according to a desired pattern, in an object plane traversed by the projection beam;
• a substrate table to hold a substrate;
• a projection system downstream of said object plane, to project the patterned beam onto a target portion of the substrate;
• an interferometric measurement system to measure wave front aberrations of the projection system, the interferometric measurement system including:
• a grating, including a grating pattern in a grating plane, said grating being movable into and out of the projection beam, such that the grating plane is substantially coincident with said object plane;
• a pinhole, including a pinhole pattern in a pinhole plane and arranged in a pinhole plate, said pinhole being movable into and out of the projection beam, such that the pinhole plane is substantially coincident with a plane downstream of the projection system and optically conjugate to said object plane, and
• a detector having a detector surface substantially coincident with a detection plane, said detection plane located downstream of the pinhole at a location where a spatial distribution of the electric field amplitude of the projection beam is substantially a Fourier transformation of a spatial distribution of the electric field amplitude of the projection beam in the pinhole plane.