A Tri-Layer PECVD SiN Passivation Process for Improved AlGaN/GaN HEMT Performance

Abstract

A tri-layer plasma enhanced CVD (PECVD) process for SiN deposition was developed to effectively passivate AlGaN/GaN high electron mobility transistors (HEMTs). A combination of thin, pre-gate SiN film deposited at high frequency (13.56 MHz) to minimize N-ion surface bombardment caused by low frequency ions, and a thick, post-gate bilayer SiN film designed to suppress on-state conductance degradation were demonstrated. By combining an annealed, 10.5 nm thick pre-gate SiN film with a bilayer post-gate SiN film, a trilayer PECVD SiN film with a total thickness of 122 nm was developed which maintained mobility, reduced on-resistance, improved drain-source current density, minimized degradation in dynamic on-state conductance upon off-state drain voltage stress, and minimized additional tensile stress.