Selective and nonselective plasma etching of (Al0.18Ga0.82)2O3/ Ga2O3 heterostructures

Abstract

The addition of CHF3 to Cl2/Ar inductively coupled plasmas operating at low dc self-biases (<100 V, corresponding to incident ion energies <125 eV) leads to etch selectivity for Ga2O3 over (Al0.18Ga0.82)2O3 of >30, with a maximum value of 55. By sharp contrast, without CHF3, the etching is nonselective over a large range of source and rf chuck powers. We focused on low ion energy conditions that would be required for device fabrication. This result has a direct application to selective removal of Ga2O3 contact layers to expose underlying (Al0.18Ga0.82)2O3 donor layers in high-electron-mobility transistor structures. It is expected that formation of nonvolatile AlF3 species helps produce this selectivity. X-ray photoelectron spectroscopy does detect F residues on the etched surface for the Cl2/Ar/ CHF3 plasma chemistry.