Low-Pressure Chemical Vapor Deposition SiNx Process Study and Its Impact on Interface Characteristics of AlGaN/GaN MISHEMTs

This study employed low-pressure chemical vapor deposition (LPCVD) SiNx as both the gate dielectric layer and surface passivation layer, systematically investigating the effects of different growth conditions on the dielectric layer quality, two-dimensional electron gas (2DEG) characteristics, interface trap density, and devices’ performance, thereby optimizing the growth parameters of LPCVD SiNx. The experiment investigated the effects of growth parameters such as the growth temperature, chamber pressure, and gas flow ratio on the growth rate of SiNx during the process of growing SiNx using the LPCVD technique. Further studies were performed to analyze the impact of SiNx introduction on the 2DEG performance. The results indicated that both Si-rich and N-rich SiNx compositions could enhance the 2DEG density improvement induced by SiNx passivation. The impact of the gas flow ratio on the interface trap density is studied. Through the quantitative characterization of the interface trap density using the pulse-mode IDS-VGS method and frequency-dependent capacitance–voltage (C-V) measurement, the results show that the interface trap density decreases with an increased Si-to-N ratio.