Invited: X-Ray Lithography

Abstract

X-ray lithography has been used in the fabrication of surface-acoustic-wave, bubble-domain, and silicon MOS devices and is well suited for replicating sub-micrometer linewidth patterns. In order to be applied in the commercial exposure of silicon IC devices, however, high power sources, sensitive resists, distortion free masks, multiple mask alignment, and repeatability of local mask-to-wafer gap will be required. These items are discussed from the point-of-view of developing design criteria for an X-ray lithography system optimized for 1/2 µm linewidths, 1/10 µm superposition, and exposure times under 200. For linewidths below 1/2 µm, copper (λ=13.3 Å) or carbon (λ=44.7 Å) sources are preferred. Recent progress in using the copper radiation to replicate grating patterns with linewidths of the order of 1000 Å with sharp vertical sidewall profiles are described.