Fabrication of All-GaN Integrated MIS-HEMTs with High Threshold Voltage Stability Using Supercritical Technology.

Meihua Liu,Lei Li,Changkuan Chang,Yang Yang,Yufeng Jin

doi:10.3390/mi12050572

Abstract

In this paper, a novel method to achieve all-GaN integrated MIS-HEMTs in a Si-CMOS platform by self-terminated and self-alignment process is reported. Furthermore, a process of repairing interface defects by supercritical technology is proposed to suppress the threshold voltage shift of all GaN integrated MIS-HEMTs. The threshold voltage characteristics of all-GaN integrated MIS-HEMTs are simulated and analyzed. We found that supercritical NH fluid has the characteristics of both liquid NH and gaseous NH simultaneously, i.e., high penetration and high solubility, which penetrate the packaging of MIS-HEMTs. In addition, NH produced via the auto coupling ionization of NH has strong nucleophilic ability, and is able to fill nitrogen vacancies near the GaN surface created by high temperature process. The fabricated device delivers a threshold voltage of 2.67 V. After supercritical fluid treatment, the threshold voltage shift is reduced from 0.67 V to 0.13 V. Our demonstration of the supercritical technology to repair defects of wide-bandgap family of semiconductors may bring about great changes in the field of device fabrication.

Highlights

Micromachines 2021, 12, 572. https://GaN-based high electron mobility transistors (HEMTs) are good candidates for high frequency and high efficiency power switching applications owing to their attractive superiorities of high breakdown electric field and high saturation electron velocity [1].Normally-off property is strongly required for GaN devices used in the power electronics systems
For the all-GaN MIS-HEMTs without supercritical nitridation treatment (SNT), significant hysteresis was observed during the sweep, suggesting severe trap-induced integrated MIS-HEMTs
Due to the dry etch process and high growth temperature in low-pressure chemical vapor deposition (LPCVD), the very surface of the AlGaN layer and the interface between Si3 N4 and AlGaN layer may be relatively defective, which could lead to the trap-induced Vth shift phenomena in GaN MIS-HEMTs [20]

Summary

Introduction

GaN-based high electron mobility transistors (HEMTs) are good candidates for high frequency and high efficiency power switching applications owing to their attractive superiorities of high breakdown electric field and high saturation electron velocity [1]. High temperature deposited gate insulator, such as low-pressure chemical vapor deposition (LPCVD) grown SiNx has been proven to be a robust gate dielectric for both normally-on GaN MIS-HEMTs and normally-off gate recessed hybrid MIS-HEMTs with low bulk trap density. We propose the application of supercritical nitridation treatment (SNT) to passivate the defects and mitigate the shift of Vth in the all-GaN MISHEMTs. After SNT, the interface trap density in LPCVD Si3 N4 /AlGaN layer interface is effectively reduced and near 0.13 V shift of Vth in the transfer curve of a GaN power device is observed with a bidirectional gate bias sweep up to 15 V

Device Fabrications

Transport Measurements

Threshold Voltage Stability

Conclusions