ABSTRACT
Far shorter in wavelength of electromagnetic waves is the x-ray. It has passed almost a quarter century since x-ray lithography was described in 1972 by Spears and Smith [1]. A lot of research institutes have been concerned with x-ray lithography. However, the application of x-ray lithography to real production environments has not yet materialized. The main reason for this delay is that optical lithography has been doing much better than expected a decade ago. When x-ray lithography was proposed, the resolution limit of optical lithography was considered to be 2-3 |im. Today one does not have much difficulty in fabricating half-submicron patterns with a current i-line reduction projection aligner. Attempts to develop the exposure machines with large NA lens and for short-wavelength irradiation have been continued to obtain better resolution. Developments in resist processes and resist materials for high resolution have extended the use of optical lithography.
