Development of low-damage plasma etching processes for preserving AlGaN/GaN heterostructure integrity in MIS HEMT

Two low-damage plasma etching processes have been investigated to evaluate their impact on the integrity of the AlGaN layer during the SiN gate opening process of Metal Insulator Semiconductor High Electron Mobility Transistors (MIS-HEMT). We show that the low ion energy fluorocarbon plasma presents an infinite SiN/AlGaN etch selectivity despite significant surface modifications. In contrast, the smart etch process, that alternates H2 plasma-based surface modification with chemical removal of the modified surface, preserves the surface of AlGaN. However it can lead to AlGaN recess due to over-implantation during the H2 plasma step. Finally, we show that a KOH post etchi treatment removes plasma-induced damages. Therefore, combining the smart etch process with a KOH post etch treatment offers an interesting solution for SiN patterning over AlGaN with minimized surface modification and restored AlGaN surface quality.