244-nm imaging interferometric lithography

Abstract

Imaging interferometric lithography, combining off-axis illumination, multiple exposures covering different regions of spatial frequency space, and pupil plane filters to ensure uniform frequency-space coverage, is a relatively new imaging concept that provides an approach to accessing the fundamental, linear-systems-resolution limits of optics. With an air medium between the lens and the wafer, the highest spatial frequency available with 244-nm exposure tool with a numerical aperture of 0.9 corresponds to a half-pitch of 68-nm. Allowing for ∼10% subbands above this central frequency, this suggests that ∼75-nm half-pitch patterns should be accessible. A 22× reduction imaging interferometric lithography testbed demonstration of printing a non-periodic (arbitrary) 86-nm half-pitch pattern is reported. This result was achieved with a simple chrome-on-glass mask without the use of any mask-based resolution-enhancement techniques such as phase-shift or optical proximity correction. Scaling this result to a 193 nm wavelength and an immersion numerical aperture of 1.3 directly addresses the 45-nm half-pitch node.