<i>In situ</i> XPS investigation of β-Ga2O3 surface chemistry for the development of SF6/Ar based plasma atomic layer etching processes

Atomic layer etching (ALE) is promising approach for low-damage etching of β-Ga2O3, a key ultrawide bandgap semiconductor for next-generation electronic and optoelectronic devices. ALE offers nanometer-scale control over the etching process, enabling the fabrication of smooth surfaces and precise management of surface defect density. In this work, an SF6/Ar-based ALE process is investigated with a focus on plasma–surface interactions and surface chemical evolution. In situ x-ray photoelectron spectroscopy is used to monitor chemical changes after the modification and activation steps, while atomic force microscopy is used to evaluate surface morphology. The modification step is dominated by fluorine-based surface reactions, leading to the formation of stable Ga–F species and exhibiting an intrinsically self-limiting behavior. Material removal occurs during the activation step under Ar+ ion bombardment, where physical sputtering competes with fluorine redeposition. Insufficient activation results in fluorine accumulation and surface degradation, whereas optimized ion energy and activation time establish a stable surface composition and yield smooth, defect-free surfaces. These results highlight the critical role of plasma conditions in controlling ALE mechanisms and demonstrate the potential of fluorine-based ALE for controlled etching and surface smoothing of β-Ga2O3.