Step-and-scan lithography using reduction optics

Scanning 1:1 optical lithography has a long record of success that has been greatly abetted by the relatively straightforward nature of 1:1 ring-field optics and by the fact that mask and wafer can be mounted to a common scanning carriage. However, as lithography requirements progress into the submicron regime, there is strong motivation to employ reduction optics in order to keep the difficulty of the mask-making task within reasonable bounds. A new ‘‘step-and-scan’’ lithography tool achieves this goal and combines the best features of scanners and steppers by sequentially scanning 20×32.5-mm subfields. Key features of this system are a ring-field projection system, with a 4:1 reduction ratio, and a scanning system in which the reticle and wafer are carried by separate stages driven at different but precisely synchronized velocities.