High NA and low residual aberration projection lens for DUV scanner

This paper describes several kinds of new technologies, which are introduced into newly developed 0.78 NA ArF projection lens for Nikon's latest DUV scanner, the NSR-S306C. A new lens configuration for an ArF projection system is obtained as a result of a minute survey of the space of the aspheric optical design. The new configuration uses fewer elements and less volume of calcium fluoride (CaF2) than a conventional type. Lens mounting performance and its stability is another key issue to realizing a high performance imaging system, because lens element deformation due to lens mounting degrades imaging performance severely. Reduction of the number of the elements of a new optical design can increase room for the opto-mechanical system. Even complicated mechanisms, such as kinematic lens mounting, can fit in the space. A pure kinematic lens mounting is developed for the new ArF projection lens system to minimize lens deformation due to lens mounting, The same mechanism is applied to the positioning scheme of a lens element for high precision lens adjustment. Simultaneous use of the new lens positioning system and a lens controller can perform high precision and rather complex lens fine-tuning. Intrinsic birefringence of calcium fluoride (CaF2) is a new item, which is a hot issue in F2 optics. Even for ArF projection lens system, the intrinsic birefringence is one of the most critical issues in terms of impact upon lens performance. Special treatment is required to avoid the degradation of imaging performance due to the intrinsic birefringence effects. Resist image comparison between an ArF lens with the treatment and that without is reviewed. Finally, actual lens performance is shown.