Abstract: A rectangular or bar-shaped, on-axis illumination mask with radiation polarized parallel to the length of the bar provides improved DOF and exposure latitude with less lens heating as compared to a circular monopole with equivalent ?.

Abstract: An optical element for effecting a desired change in incident radiation at a plane of an illumination system of a lithographic apparatus comprises an array of cells manufactured as a single unit, each cell being arranged to redirect the incident radiation in a predetermined direction. An array of polarizing regions is also provided, each polarizing region being associated with a corresponding cell. Each cell arranged to redirect radiation in a first direction has associated with it a polarizing region ensuring that the redirected radiation has a first polarization, so that all of the radiation redirected in the first direction has the same polarization.