Nanofabrication at a 10 nm length scale: Limits of lift-off and electroplating transfer processes

Abstract

Transfer processes like lift-off and electroplating are investigated at dimensions close to 10 nm after very high resolution electron beam lithography. Specific material problems for gold deposition at this critical dimension range are highlighted. We report the reproducible fabrication of sub-10 nm lines by conventional 200 kV electron-beam lithography and lift-off of a granular gold film on polymethylmethacrylate resist. We show that when the linewidth is smaller than 7 nm only one metallic grain can be formed in the width of the lines opened in the resist. The fabrication of very regular features at a sub-10 nm dimension range by a lift-off technique, sheds some light on the limitations usually encountered in the fabrication of continuous sub-10 nm metallic lines by lift-off. For high aspect ratio, gold electroplating is demonstrated to be an alternative efficient method to the lift off technique at a 20 nm scale: 15 nm narrow electroplated wires are routinely fabricated with an aspect ratio of 10. Two growth modes are identified as a function of the linewidth. For over 20 nm linewidths, thickness variations are in agreement with classical plating models at the pattern scale. In the sub 20 nm width range, corresponding to a mass transfer limited regime, growth in the resist nanotrench is shown to be mainly governed by the texture of the plating base associated to an anisotropy of the growth rate in the direction.