Submicron, Soft-X-Ray Fluorescence Imaging

Submicron fluorescence imaging of soft x-ray aerial images, using a high resolution fluorescent crystal is reported. Features as small as 0.1 μm were observed using a commercially available single-crystal phosphor, STI-F10G (Star Tech Instruments Inc. P. O. Box 2536, Danbury, CT 06813-2536), excited with 139 Å light. Its quantum efficiency was estimated to be 5–10 times that of sodium salicylate and to be constant over a broad spectral range from 30 to 400 Å. A comparison with a terbium-activated yttrium orthosilicate fluorescent crystal is also presented. Several applications, such as the characterization of the aerial images produced by deep ultraviolet or extreme ultraviolet lithographic exposure tools, are envisaged.