Electrically isolated nanostructures fabricated using self-assembled multilayers and a novel negative-tone bi-layer resist stack

Abstract

We create metal nanoelectrode structures with precise proximal placement by blending traditional top-down and bottom-up lithography. Multiple levels of conventional lithography are used in combination with self-assembled multilayer resists (molecular rulers) to generate metallic electrode structures with nanoscale spacings. These multilayers are deposited on initial lithographic gold electrode structures forming a type of lift-off resist used to fabricate proximally placed secondary metal structures with nanometer-scale resolution. By controlling the thicknesses of these multilayers, selective self-assembly is exploited to generate molecular ruler resists, enabling the creation of tailored nanogaps in the 10–50 nm regime. The ability to fabricate electrically isolated nanoelectrodes would enable reliable measurement of the conducting properties of single molecules, nanoparticles and other low-dimensional materials. This paper outlines a new process using a lift-off resist (LOR)/SU-8 negative-tone bi-layer stack to improve the yield of nanoelectrodes. SU-8 finds application in a variety of fabrication techniques, but is difficult to release from the substrate. The LOR/SU-8 process that we have developed possesses the following additional advantages: easy chemical removal of the resist stack with the LOR acting as a release layer, creation of metal lift-off patterns with near-vertical sidewalls, and the ability to withstand chemical processing.