XPS study of a selective GaN etching process using self-limiting cyclic approach for power devices application

Abstract

Full recess architecture for GaN based High Electron Mobility Transistor (HEMT) enables high mobility and high density of electrons to be conserved without compromising on voltage threshold. To obtain such architecture, standard RIE plasma etching processes are not suitable due to electrical degradation effects and to the lack of well controlled etch depth. To address these limitations, several Atomic Layer Etching (ALE) processes have been developed in the past. In this work, we study an atomic layer etching (ALE) of GaN based on cyclic steps composed of O2 plasma followed by BCl3 plasma. XPS analysis of the GaN's top surface after each step of the O2-BCl3 process enabled to propose an etching mechanism and to track nitrogen depletion. The cyclic process conserves the surface stoichiometry. Finally, this cyclic process has been validated on patterns, showing a good morphology, a good etch depth control and a slightly lower electrical degradation compared to standard RIE process.