Nanofabrication of air-spaced field-plate gates with ultra-short footprint

Abstract

This paper reports our recent work on nanofabrication of air-spaced field-plate (ASFP) gates with ultra-short foot-print using one step electron beam lithography (EBL) combined with reactive ion etch (RIE) for which are suitable for GaN based high electron mobility transistors (HEMTs). Electron beam lithography on a tri-layer stack with PMMA350K/PMMA100K/Al/UVIII is carried out to form the required profile in resist. A low damage RIE dry-etch process is developed to create two different kinds of shapes in the 100nm SiNx layer which serves as a footprint definition and mechanical support to the field-plate. The process enables us to fabricate air spaced field-plates with 60nm foot-print and 50nm air gap. Its advantages over traditional field-plates as well as T shape gate are discussed.