Effect of Fluoride-based Plasma Treatment on the Performance of AlGaN/GaN MISFET

Abstract

This paper demonstrates the effect of fluoride-based plasma treatment on the performance of Al 2 O 3 /AlGaN/ GaN metal-insulator-semiconductor heterostructure field effect transistors (MISHFETs) with a T-shaped gate length of 0.20 μm. For the fabrication of the MISHFET, an Al 2 O 3 layer as a gate dielectric was deposited using atomic layer deposition, which greatly decreases the gate leakage current, followed by the deposition of the silicon nitride layer. The silicon nitride layer on the gate foot region was then selectively removed through a reactive ion etching technique using CF 4 plasma. The etching process was continued for a longer period of time even after the complete removal of the silicon nitride layer to expose the Al 2 O 3 gate dielectric layer to the plasma environment. The thickness of the Al 2 O 3 gate dielectric layer was slowly reduced during the plasma exposure. Through this plasma treatment, the device exhibited a threshold voltage shift of 3.1 V in the positive direction, an increase of 50 mS/mm in trans conductance, a degraded off-state performance and a larger gate leakage current compared with that of the reference device without a plasma treatment.

Subthreshold Characteristics of AlGaN/GaN MIS-FinFETs with Controlling Threshold Voltages

“…This positive shift of the V TH is due to lateral depletion of the 2DEG channel from the sidewall. The SS values for all devices are smaller than 72 mV/dec, which are relatively low compared to those of conventional AlGaN/GaN-based HEMTs [21][22][23]. For the wide FinFETs with W fin of 150 and 80 nm, the V TH of the 2DEG channel is much lower than that of the MOS channel at sidewall surface and hence the 2DEG channel current dominates the subthreshold current of the device.…”

Hydrazine (N2H4)-Based Surface Treatment for Interface Quality Improvement in Al2O3/AlGaN/GaN MIS-HEMT

“…Efforts have been made to address these issues, by using a metal-insulatorsemiconductor (MIS) structure, 2,3 but the existence of the native oxide at insulator/III-nitride interface causes the interface trap, leading to threshold voltage (V th ) instability in MIS-HEMTs. [4][5][6] While various surface treatments using HF, HCl, NH 4 OH, and (NH 4 ) 2 S have been reported to reduce the native oxide to improve the interface quality and device performance, [7][8][9][10][11] there has not been any established standard surface treatment process for III-nitride based device fabrication. Thus, the development of a standard surface treatment process is strongly needed to fulfill the industry demands.…”