Lithography for 0.25 mu m and below using simple high-performance optics

A mostly reflective approach to 0.25- mu m lithography that has great simplicity (only two or three critical optical elements) and outstanding performance is described. A 1/6 scale prototype system has demonstrated 0.25- mu m resolution in a commercially available resist using a conventional mask, and 0.125- mu m resolution using a phase-shifting mask. The approach is particularly amenable to depth of focus enhancement by aperture apodization, and a fundamental trade-off inherent in this technique is described.<>