Patent ID: 7903234

Claim:
A lithographic apparatus comprising: an illumination system configured to condition a radiation beam so as to illuminate a patterning device in a first or a second illumination mode selectively; a support structure constructed to support the patterning device, the patterning device configured to impart the radiation beam with a pattern in its cross-section to form a patterned beam; a substrate table constructed to hold a substrate; a projection system configured to project the patterned beam onto a target portion of the substrate, the projection system comprising a plurality of optical elements and having a pupil plane, at least one of the optical elements being located in or near the pupil plane; and a control system configured to control the illumination system, the support structure and the substrate table to select the first illumination mode when a pattern on the patterning device and a substrate on the substrate table are in the path of the radiation beam to perform a production exposure and to select the second illumination mode during a time that no substrate is in the path of the radiation beam to perform a corrective irradiation process, wherein, in the first illumination mode, an angular distribution of radiation at the patterning device is such that an intensity of the patterned beam is substantially contained within a first part of the cross-sectional area of the at least one optical element and within a second part of the cross-sectional area of the at least one optical element in the second illumination mode, the first and second parts being substantially non-overlapping and the combination of the first and second parts not encompassing the entire cross-sectional area of the at least one optical element, wherein elements of the lithographic apparatus are constructed and arranged such that an intensity distribution of the patterned beam in the second illumination mode results in an optical element heating effect that causes the at least one optical element that is non-uniformly heated in the first illumination mode to be heated substantially uniformly thereby correcting any optical aberrations caused by the non-uniform heating.