Investigation of the Trap States and V _th Instability in Normally-Off GaN MIS-FETs With LPCVD SiN_x/PEALD AlN Gate Dielectric Stack and In Situ H₂/N₂ Plasma Pretreatment

A novel effective reliability improvement technology for gallium nitride (GaN) devices and passivation dielectric stack consisting of a plasma-enhanced atomic layer deposition (PEALD) grown aluminum nitride (AlN, 5 nm) and a low-pressure chemical vapor deposition (LPCVD) grown silicon nitride (SiNx, 30 nm) in normally- OFF GaN metal–insulator–semiconductor field-effect transistors (MIS-FETs) is proposed. This reliability improvement technique features an in situ H2 (15%)/N2 (85%) plasma pretreatment in a PEALD system before the deposition of PEALD AlN. The quality of the AlN/(Al)GaN interface, threshold voltage instability, and dynamic ${R}_{\text {on}}$ in the normally- OFF GaN MIS-FETs with and without the in situ H2 (15%)/N2 (85%) plasma pretreatment was investigated using various methods. The equivalent parallel conductance method, high-frequency capacitance-voltage, time-of-fly (TOF) stress/measures, and quasi-static ${I}_{\text {D}}$ – ${V}_{\text {D}}$ methods were used in the experimental studies. The results showed that the in situ H2 (15%)/N2 (85%) plasma pretreatment technique is effective in improving the quality of the AlN/GaN interface. The devices with the in situ H2 (15%)/N2 (85%) plasma pretreatment had improved ${V}_{\text {th}}$ stability and lower ${R}_{\text {on}, {dynamic}}/{R}_{\text {on}, {static}}$ ratio, which was due to the reduced interface trap densities between the AlN/GaN interface and the improved mobility of 2-D electron gas (2DEG). The time-dependent dielectric breakdown (TDDB) and Weibull performance further verified that the proposed in situ H2 (15%)/N2 (85%) plasma pretreatment techniques were reliable in improving the reliability of GaN power devices.