Step-and-repeat alignment and exposure system

Abstract

An improved step and repeat alignment and exposure system for printing an image of a reticle onto a semiconductive wafer. A unit magnification catadioptric lens projects the reticle image onto the semiconductive wafer, and includes prisms to separate the image plane of the lens from the object plane. The semiconductive wafer is supported on stage means, which stage means provide motion in the X,Y directions. Viewing port means supplement the unit magnification catadioptric lens to provide a direct view of a portion of the semiconductive wafer which portion has been illuminated by the projected rectile image. A beam splitter is formed on a face of one of the prisms of the unit magnification catadioptric lens and is supplemented by an additional prism which provides optical path compatibility. A novel microscope structure is employed with large aperture focusing lenses to permit the infinity corrected objectives to translate about the field of view of the viewing port means without the requirement that any utilization device also translate in unison. Means are also provided for calibrating the position of the stage with respect to the reticle. Included are stage reference means which image a stage reference mark into the image plane of the unit magnification catadioptric lens when said stage reference means are illuminated by the projected reticle image. Means are provided for determining offset values between the projected reticle image and the stage reference mark and for utilizing said offsets in controlling the position of the stage. Further, means are provided for focusing and leveling the surface of the semiconductive wafer, wherein said means maintain, in a servo-controlled manner, said surface in a known position with respect to the stage. A six-degree of freedom support system is controlled by said focusing and leveling means to provide vertical position, pitch and roll movement of the semiconductive wafer.