Nitrogen rich PECVD silicon nitride for passivation of Si and AlGaN/GaN HEMT devices

Abstract

In this work, we have investigated the material properties of PECVD (Plasma Enhanced Chemical Vapor Deposition) amorphous Silicon nitride (SiN) films and the influence of deposition conditions on gate-leakage increase of AlGaN/GaN HEMT’s (High Electron Mobility Transistor) after passivation. We have studied the effect of gas flow ratio (SiH4/NH3) on the structural and compositional properties of SiNx deposited on crystalline Silicon (Si). Based on the inference, electrical properties of the SiNx films were examined by depositing on AlGaN/GaN HEMT as a passivation layer. The optimized SiNx which is N-rich with a refractive index of 1.83, tensile stress of 681 MPa and NH3/SiH4 ratio of 18 shows only a 1.2x variation in gate leakage, 1.4x increase in gm, minimum left shift of 0.03 V in Vth and 1.26x increase Ion/Ioff ratio after passivation. We believe that the 3x reduction in Si-H bonds resulting in reduced interface traps at SiN/AlGaN interface is the reason for the minimal increase in gate leakage after passivation.