Patent ID: 7379153

Claim:
A lithographic projection apparatus, comprising: a radiation system constructed and arranged to provide a beam of radiation; a support constructed and arranged to support a patterning device, the patterning device constructed and arranged to pattern the beam according to a desired pattern; a substrate table constructed and arranged to hold a substrate; a projection system constructed and arranged to project the patterned beam onto a target portion of the substrate; and an alignment sensor comprising: an electron beam source constructed and arranged to provide an electron beam for impinging on an alignment marker on a substrate on the substrate table, the electron beam in the alignment sensor being spatially controllable such that the electron beam impinges on the alignment marker with a predetermined spatial intensity distribution; and a back-scattered electron detector constructed and arranged to detect electrons back-scattered from the alignment marker, wherein the alignment sensor is independent of the radiation system of the lithographic projection apparatus but is provided within the lithographic projection apparatus to enable alignment to be performed in situ within the lithographic projection apparatus.