Formation of Slanted Gates for GaN-Based HEMTs by Combined Plasma and Wet Chemical Etching of Silicon Nitride

Published in:
Int. Conf. on Compound Semiconductor Manufacturing Technology (CS ManTech 2013), New Orleans, USA, May 13-16, paper 112 (2013).
Copyright 2013 CSManTech All Rights Reserved. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from CSManTech.

Abstract:
We propose a new method for the formation of slanted gates for GaN-based HEMTS that consists of the combination of an anisotropic plasma and an isotropic wet chemical etch step. By combining these two steps, a slanted trench is formed in silicon nitride, followed by the gate metallization sequence. During the plasma etch step, the silicon nitride is only partially etched; the slanted profile is created during the wet etch process step. The ratio of plasma etch to wet etch determines the angle of the slant. This process was successfully applied to a HEMT structure consisting of an epitaxial layer of a 17 nm thick Al_0.25Ga_0.75N barrier and a 5 nm thick GaN cap on a 4 inch n-type SiC substrate. The process yielded 280 nm long slanted gates. Electrical tests showed that 2×50 µm devices reached a typical maximum output current of 0.75 A/mm with a high fabrication yield.

Keywords:
Slanted gates, SiNx etch, phosphoric acid, plasma etch, wet etching, submicron trench