Nonselective and smooth etching of GaN/AlGaN heterostructures by Cl2/Ar/BCl3 inductively coupled plasmas

Abstract

A systematic study of the nonselective and smooth etching of GaN/AlGaN heterostructures was performed using Cl2/Ar/BCl3 inductively coupled plasmas (ICPs). Nonselective etching can be realized by adjusting the BCl3 ratio in the Cl2/Ar/BCl3 mixture (20%–60%), increasing the ICP power, and decreasing the chamber pressure. Surface morphology of the etched heterostructures strongly depends on the gas chemistry and the chamber pressure, whereas selectivity and surface morphology show a slight dependence on the dc bias and total flow rate. Specifically, with the addition of 20% BCl3 to Cl2/Ar (4:1) gas mixture, nonselective etching of GaN/Al0.28Ga0.72N heterostructures at a high etch rate is maintained and the surface root-mean-square roughness is reduced from 10.6 nm to 0.5 nm, which is smoother than the as-grown sample. Auger electron spectroscopy analysis shows that the effective removal of residual oxygen from the surface of AlGaN during the etching process is crucial to the nonselective and smooth etching of GaN/AlGaN herterostructures at high etch rate.