Abstract

Fresnel zone plate lenses are used in a wide variety of x-ray optical instruments for imaging, forming small x-ray probes, etc. A zone plate consists of a concentric ring of alternating transmissive material with opaque (and/or phase shifting) material. For diffraction-limited lens performance, the placement of the zones is critical. The maximum placement error should be less than a small fraction (i.e., 1/4) of the smallest zonewidth. For the highest resolution zone plate, with smallest zonewidths of 30-40 nm, achieving the required placement accuracy is a challenge. New techniques have been developed to measure placement errors in electron beam systems, and measurements on IBM’s VS-6 high resolution electron beam lithography tool show small but nonzero errors. Small amounts of drift from thermal and other sources can cause serious placement errors during the zone plate's exposure time.

© 1991 Optical Society of America