Nanoscale Pattern Definition on Nonplanar Surfaces Using Ion Beam Proximity Lithography and Conformal Plasma-Deposited Resist

Ion beam proximity lithography (IBL) is a technique where a broad beam of energetic light ions floods a stencil mask and transmitted beamlets transfer the mask pattern to resist on a substrate. With a depth-of-field up to 20000 times larger than the minimum feature size and the high-throughput potential of a parallel exposure tool, IBL is very attractive for prototyping and manufacturing nanoelectromechanical systems over the steep topography of micromachined silicon wafers. This paper reports a conformal resist coating process that unlocks this potential. This negative-tone resist, plasma-polymerized methyl methacry- late, has a sensitivity of 27 muC/cm² and a contrast of 1.3 for 30-keV He⁺ ion exposures and amyl acetate developer. Sub-100-nm features have been printed down the sidewall and across a membrane at the bottom of a 500-mum-deep anisotropically etched pit in a silicon wafer. Pattern fidelity is near 2 nm for 10-nm features. Lines have also been formed on unpolished substrates, including rolled titanium foils and coarse-ground silicon wafers. Patterns on ground silicon have been etched into the surface using a nickel hard mask and SF₆/O₂ reactive ion etching.