High aperture diffractive x-ray and extreme ultraviolet optical elements for microscopy and lithography applications

Microscopy and Lithography using isotropic plasma x-ray and extreme ultravi olet sources require condenser elements with high numerical aperture. As sh own by coupled-wave theory, zone structures with high aspect ratios can dif fract a sufficiently large proportion of incident radiation into a single h igh order. This enables new diffractive optical elements for these applicat ions with significantly increased numerical aperture. Suitable zone plate m aterials are nickel for water window wavelengths and organic polymers for l ambda=13 nm radiation. Copolymer and nickel zone structures have been produ ced with aspect ratios of 15 and 11, respectively. For optimization of the etched zone profile, the reactive ion etching process with O-2 was periodic ally interrupted. In a first experiment at lambda=3.4 nn a nickel linear zo ne plate with 75 nm outermost zone width and 500 nm height showed a diffrac tion efficiency of 1% in the sixth diffraction order. (C) 1999 American Vac uum Society. [S0734-211X(99)07106-1].