FABRICATION AND CHARACTERIZATION OF GALLIUM NITRIDE HIGH ELECTRON MOBILITY TRANSISTOR (HEMT)

Abstract

GaN is promising material for high voltage - high power amplifier application with its extraordinary wide band-gap property. Currently GaN high electron mobility transistor (HEMT) technology is under extensive research in both industry and institutes. Tinggi Technologies started to development its own HEMT process from 2005. This paper evaluates the development of GaN HEMT in past 15 years and the entire fabrication process of Tinggi top GaN HEMT. Two different HEMT samples are purchased from vendors Powdec, Japan and SVT, U.S. Before fabrication, compositions and structure of samples are characterized through X-ray diffraction (XRD) and Secondary Ion Mass Spectroscopy (SIMS). Five steps are involved during process flow, namely, 1. Mesa etch; 2. Open window; 3. Surface etch treatment; 4. Ohmic contact formation; 5. Schottky gate formation. Image reversal is proposed and successfully adopted during open-window. Physics behind Ohmic and Schottky contact formation is explained in details. Choice of contact metal is also extensively discussed. Using previous data from Tinggi Technologies, Schottky contact curves and I-V family curves are presented and analyzed. Finally air bridge and gate oxide are figured out to further improve process flow in future. It is advised to start high temperature reliability test after fabrication to expedite the launch of Tinggi GaN HEMT products in market.