Patent ID: 7075696

Claim:
A lithographic apparatus comprising: a radiation system configured to condition a beam of radiation; a patterning device configured to pattern the beam of radiation to form a patterned beam of radiation; and a projection system configured to project the patterned beam of radiation onto a surface of a substrate, the projection system including a plurality of cubic crystalline optical elements that each impart retardance to the patterned beam of radiation, said plurality of cubic crystalline optical elements being aligned along an optical axis of the projection system and including two adjacent crystalline optical elements having a common crystalline lattice direction oriented along said optical axis, each of said two adjacent crystalline optical elements having a substantially rotationally symmetric surface about said optical axis and having increased intrinsic birefringence magnitude at a set of lobes at a set of locations arranged in an azimuthal direction about said optical axis, and a first of said two adjacent crystalline optical elements being rotated about said optical axis with respect to a second of the adjacent crystalline optical elements with a predetermined rotation angle such that the set of lobes of the first of said two adjacent crystalline optical elements is positioned at locations azimuthally offset from the set of locations of the set of lobes of the second of the adjacent crystalline optical elements, said plurality of crystalline optical elements being selected and positioned along said optical axis and said rotation angle being selected such that, for each of two substantially perpendicular polarization states of said beam of radiation having a radiation wavelength of about 193 nm, said patterned beam of radiation has less than about 0.012 waves RMS of wavefront aberration across an exit pupil of the projection system.