Performance enhancement of 157 nm Newtonian catadioptric objectives

Newtonian design forms have been developed to explore high numerical aperture imaging systems at the wavelength of 157 nm with elements made of CaF 2 crystal. First-generation systems working at 0.60 numerical aperature (NA) are currently printing features smaller than 130 nm for resist-process development. Second-generation design forms, working with variable numerical apertures above 0.75 NA, will push feature sizes significantly below 100 nm. Several aspects of second-generation designs have been improved to accommodate the need for characterizing and enhancing imaging performance. Closed-loop methods of optimization to reduce aberrations have been developed to characterize and control the effects of crystal-related birefringence on imagery. In addition these systems are learning vehicles to enhance knowledge of aberration-image performance dependence at high numerical apertures.