Step-and-repeat projection alignment and exposure system

Abstract

An alignment and exposure system is provided with a main stage movable along orthogonal axes to position either a reference mark, aligned with one of those axes, or a semiconductive wafer directly beneath a projection lens. Another stage is disposed above the projection lens to position a reticle, selectively illuminated by a light source unit, with respect to the reference mark. The light source unit includes a lamp for directing illumination and exposure light along an optical path extending through the reticle and projection lens, a pair of filters for selectively controlling whether illumination or exposure light passes along that optical path to the reticle, a pair of shutters for selectively controlling passage of the selected light along that optical path to the reticle, and a plurality of different mask plates for selectively controlling the portions of the reticle illuminated by the selected light when one of the shutters is opened. Images of the illuminated portions of the reticle are projected onto the reference mark or semiconductive wafer by the projection lens. A beam splitter is disposed between the projection lens and reticle to provide a port for viewing aerial images of the portions of the reference mark or semiconductive wafer illuminated by the projected images of the illuminated portions of the reticle. While employing a microscope to view those aerial images, either stage may be controlled to directly align either the semiconductive wafer with respect to the reticle or the reticle with respect to the reference mark.