Abstract

A 10× reduction Schwarzschild system is being developed for projection imaging at 13 nm wavelength. The optical design is optimized over a 0.4 mm field of view in the image field using 0.1 µm design rules. An off-set aperture, located on the convex primary, defines an unobscured 0.08 numerical aperture. Multiple primary and secondary elements were fabricated, matched and clocked to minimized the effects of small figure errors on imaging performance. The system is illuminated using soft x-rays emitted from a laser plasma source and collected by an ellipsoidal condenser. A 45° turning mirror is required to direct the collected x-rays onto a near-normal reflecting mask. Precise matching of the Mo/Si multilayer coatings is required on all five reflective surfaces in the system. Incidence angles vary on the Schwarzschild primary as a function of radius from the optical axis, requiring a tapered multilayer coating to maintain peak reflection at the operating wavelength.

© 1993 Optical Society of America