Patent ID: 8426088

Claim:
A lithographic apparatus comprising: a phase modulation element configured to control the phase of at least a portion of radiation constituting each of a plurality of diffracted beams of radiation from a patterning device to form a first phase-wavefront having a first focal plane for the lithographic apparatus, and a second phase-wavefront having a second focal plane for the lithographic apparatus, the first and second focal planes being offset relative to one another along an optical axis of the lithographic apparatus, wherein control of the phase of the radiation constituting at least a portion of the diffracted beams of radiation comprises: control of the phase of a first portion of a first diffracted beam of radiation and a corresponding first portion of a second diffracted beam of radiation so that the first portions of the first and second diffracted beams of radiation are subjected to a first phase change which results in an at least partial formation of the first phase-wavefront, and control of the phase of a second portion of the first diffracted beam of radiation and a corresponding second portion of the second diffracted beam of radiation so that the second portions of the first and second diffracted beams of radiation are subjected to a second phase change which results in an at least partial formation of the second phase-wavefront.