Ultrahigh NA, high aspect ratio interference lithography with resonant dielectric underlayers

Abstract

High aspect ratio imaging for immersion interference lithography in the ultrahigh numerical aperture regime, where evanescent fields are responsible for the exposure, is demonstrated experimentally using a resonant dielectric underlayer system consisting of HfO stacked upon SiO2. Improvements in producing these high aspect ratio grating structures compared with previous work [P. Mehrotra, C. A. Mack, and R. J. Blaikie, Opt. Express 21, 13710 (2013)] are shown, which has allowed subsequent lift-off pattern transfer for ∼55 nm half-pitch gratings patterned using a 405 nm exposure wavelength, corresponding to better than λ/7 resolution. Resist structures with aspect ratios close to 3:1 (height to half-pitch) demonstrate the limitations of our lithography system and highlight necessary improvements for higher aspect ratio resist structures to be achieved. Model and preliminary experimental results are presented for a scheme to mitigate resist collapse with very high aspect ratio structures.