Projection exposure apparatus

Abstract

Light from an alignment illumination system having a flash lamp is bent by a beam splitter to be illuminated onto an alignment mark on a wafer through a microscope optical system. An alignment signal treatment system reads output values from wafer stage interfermoters at the same time the flashing light is emitted from the flash lamp of the alignment illumination system. Since an image of the alignment mark focused on an imaging element is generated only when the flashing light is emitted, X, Y coordinate values representing a position of a wafer stage upon emission of the flashing light indicate X, Y coordinate values of the position of the wafer stage at the time when the image of the alignment mark is measured by the imaging element. An imaging element such as a CCD images a wafer alignment mark multiple times in synchronization with emission of pulse light while shifting a wafer stage. A plurality of image data are sampled and stored. A position of the wafer stage upon emission of the pulse light is measured by interferometers and stored. When the plurality of image data are added, a shift amount of the wafer stage is taken into consideration. For example, if the shift amount of the wafer stage within a time period between two successive light emissions corresponds to two pixels, the image data are deviated by two pixels. The signal may also be deviated by interpolation calculation.