Multispecies focused ion beam lithography system and its applications

Abstract

The authors present a focused ion beam lithography (IBL) instrument and its extension toward using different ion species beyond gallium. The base instrument utilizes a lithography architecture and an ion source and column dedicated to nanofabrication. This includes large area navigation and patterning by a laser interferometer stage, long-term beam to sample positional as well as beam current stability and automation capabilities. Since the ion type can have dramatic consequences on the resulting nanostructures, the authors have extended the gallium IBL tool's ion column and source toward the stable delivery of multiple species for a nanometer scale focused ion beam based on a liquid metal alloy ion source. The IBL system is equipped with an E × B mass filter capable of selecting different single and multiple charged ion species, simultaneously originating from the same source. The authors investigated different AuSi or AuGe based sources and in particular an ion source delivering Au, Si and Be focused ion beams regarding beam current stability, beam diameter and patterning performance. Depending on the ion species and the interaction with the sample material, the authors achieved sub-20 nm results both for beam diameter and minimum line width by direct milling. The alloy ion sources show stability comparable to gallium during measurements over 10–20 h and a lifetime of several months. Initial and potential applications in the field of selective graphene synthesis, membrane and nanopore patterning as well as photonics and plasmonics are discussed.