High aspect ratio nanostructuring by high energy electrons and electroplating

Abstract

Due to the ability of 100keV electrons to penetrate deep into resist with little scattering, we were able to directly write various dense and high aspect ratio nanostructures in up to 1.65μm thick layers of poly(methyl methacrylate) (PMMA) resist. The PMMA molds produced by electron beam lithography were developed using a high contrast developer. The molds were used to transfer the pattern into metallic nanostructures by filling the developed trenches with Au by electroplating. By exposing lines narrower than the target width, we observed improved process latitude and line width control. The obtained aspect ratios of the dense structures are nearly 17 in 1.1μm PMMA layers and >13 for structures electroplated into these PMMA molds. The fabrication method was successfully applied to produce Au diffractive X-ray Fresnel zone plates of exceptionally good quality with 70nm outermost zones using 1.1μm thick PMMA mold. In addition, we also produced regular arrays of high aspect ratio and dense Au nanorods and high aspect ratio split ring resonators with line widths down to 65nm and with heights up to 1.5μm.