REFLECTIVE OPTICAL IMAGING SYSTEMS WITH BALANCED DISTORTION

摘要

Optical systems compatible with extreme ultraviolet radiation (501) comprising four reflective elements (505, 509, 513, 517) for projecting a mask image onto a substrate are described. The four optical elements comprise, in order from object (503) to image (521), convex, concave, convex and concave mirrors. The optical systems are particularly suited for step and scan lithography methods. The invention enables the use of larger slit dimensions associated with ring field scanning optics, improves wafer throughput, and allows higher semiconductor device density. The inventive optical systems are characterized be reduced dynamic distortion because the static distortion is balanced across the slit width.