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) SiN_x 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 SiN_x. The experiment investigated the effects of growth parameters such as the growth temperature, chamber pressure, and gas flow ratio on the growth rate of SiN_x during the process of growing SiN_x using the LPCVD technique. Further studies were performed to analyze the impact of SiN_x introduction on the 2DEG performance. The results indicated that both Si-rich and N-rich SiN_x compositions could enhance the 2DEG density improvement induced by SiN_x 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 I_DS-V_GS 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.