Patent attributes
A lithographic apparatus comprises an illumination system for providing a projection beam of radiation, a support structure for supporting patterning device, the patterning device serving to transmit or reflect radiation in the projection beam and impart the projection beam with a pattern in its cross-section, a substrate table for holding a substrate, and a projection system for projecting the patterned beam onto a target portion of the substrate. A sensor is provided for measuring the spatial intensity distribution of the projection beam at the substrate. The spatial distribution of transmission or reflectance of the patterning device, together with the distribution of the projection beam incident on the patterning device, may be determined from the measured intensity distribution. By comparing the transmission or reflectance from regions having identical patterns the overall (macroscopic) distribution of the transmission or reflectance of the patterning device can be determined.
