Long nanoscale gaps on III–V substrates by electron beam lithography

Abstract

Deep submicron gaps between metal pads of around 100 μm in size are difficult to fabricate on III-V substrates using electron beam lithography, polymethyl methacrylate (PMMA) resist, and metal lift-off. In device fabrication, gold is commonly used to form metal contacts. However, gold etch methods are not well suited to high resolution patterning and lift-off methods are frequently employed. In this paper, the authors investigate a number of different methods for realizing long 100 nm scale gaps for structures fabricated on III–V substrates. Initially, they explain why the fabrication of long narrow gaps between metal pads using PMMA resist and metal lift-off is difficult. The authors show that 15 nm gaps can be fabricated using a double patterning method and discuss the limitations of this technique. They show that good undercut profiles for metal lift-off can be realized by the controlled etching of a sacrificial polymer layer placed beneath the resist. The authors demonstrate that reliable 100 nm scale gaps can be fabricated between 100 μm square metal pads using these methods.