XeF₂ etching of epitaxial Nb₂N for lift-off or micromachining of III-N materials and devices

This paper presents characterization of the effects of XeF₂ vapor phase etching conditions on the lateral etch rate and etch uniformity of a sacrificial, epitaxial Nb₂N layer grown between a III-N high-electron-mobility transistor heterostructure and a 6H-SiC substrate. To achieve uniform and repeatable lateral Nb₂N removal, an etch temperature of 100 °C or higher was required, providing average etch rates ranging from 10 to 40 μm/min. A net compressive stress and positive strain gradient in the released III-N material were inferred from the buckling of clamped-clamped beams and the convex curvature of cantilever structures, respectively. XeF₂ etching of epitaxial Nb₂N sacrificial layers in III-N material structures allows for a highly selective, completely dry release process that is compatible with common micromachining and epitaxial lift-off techniques.