A Novel Atomic-Level Post-Etch-Surface-Reinforcement Process for High-Performance p-GaN Gate HEMTs Fabrication

Abstract

A novel atomic-level post-etch-surface-reinforcement (PESR) process is developed to recover the p-GaN etching induced damage region for high performance p-GaN gate HEMTs fabrication. This process is composed of a self-limited surface modification step with O2 plasma, following by an oxide removal step with BCl3 plasma. With PESR process, the AlGaN surface morphology after p-GaN etching was comparable to the as-epitaxial level by AFM characterization, and the AlGaN lattice crystallization was also recovered which was measured in a confocal Raman system. The electrical measurement further confirmed the significant improvement of AlGaN surface quality, with one-order of magnitude lower surface leakage in a metal-semiconductor (MS) Schottky-diode and 6 times lower interface density of states (Dit) in a MIS C-V characterization. The XPS analysis of Al2O3/AlGaN showed that the p-GaN etching induced F-byproduct and Ga-oxide was well removed and suppressed by PESR process. Finally, the developed PESR process was successfully integrated in p-GaN gate HEMTs fabrication, and the device performance was significantly enhanced with ~20% lower of on-resistance and ~25% less of current collapse at Vds,Q bias of 40 V, showing great potential of leverage p-GaN gate HEMTs reliability.

Fluorine-Based Low-Damage Selective Etching Process for E-Mode p-GaN/AlGaN/GaN HFET Fabrication

“…During the etching process, when the AlGaN surface is exposed to a fluorine-based plasma environment, the interaction between aluminum (Al) and fluorine (F) leads to the formation of an etch-resistant aluminum fluoride (AlF x ) layer, acting as an etching barrier [21]. However, fluorine can also react with gallium (Ga) in the p-GaN, resulting in the formation of involatile gallium fluoride (GaF x ) [22].…”

“…Given the thinness of the AlGaN barrier layer, even slight over-etching of the AlGaN layer or plasmainduced damage at the etched surface can substantially reduce the 2DEG channel density, increasing the on-resistance. Thus, research efforts have been dedicated to selectively etching the p-GaN layer, utilizing either oxygen-based processes [13][14][15][16][17] or fluorine-based plasma etching [18][19][20][21][22]. In the context of the selective etching process, the inclusion of an over-etching step is essential to guarantee the complete removal of the p-GaN layer.…”