ASML Holding N.V.
Lithographic method and apparatus

Abstract:

Method of determining a photodetector contribution to a measurement of apodization of a projection system of an immersion lithography apparatus, the method comprising providing a beam of radiation, illuminating an object with the beam of radiation, using the projection system to project an image of the object through a liquid layer and onto a photodetector, performing a first set of measurements of radiation intensity across a pupil plane of the projection system at a first liquid layer thickness, performing a second set of measurements of radiation intensity across the pupil plane of the projection system at a different liquid layer thickness, determining a set of intensity differences from the first set of measurements and the second set of measurements, comparing the determined set of intensity differences to an expected set of intensity difference, and using the results of the comparison to determine the photodetector contribution to a measurement of apodization.