Electron cyclotron resonance plasma etching of AlGaN in Cl-2/Ar and BCl3/Ar plasmas

A comparison of etch rates for AlxGa1-xN alloys was performed in Cl-2/Ar and BCl3/Ar electron cyclotron resonance plasmas. The etch rates were generally found to decrease with increasing AlN concentration, due to the increasing average bond strengths at higher Al compositions. The fastest rates were found in the Cl-2/Ar chemistry, with rates of similar to 3500 Angstrom/min for GaN, 1700 Angstrom/min for AlN, 2500 Angstrom/min for Al0.31Ga0.69N, and 3300 Angstrom/min for Al0.2Ga0.8N. The etched surfaces were also smoother with the Cl-2/Ar plasma chemistry than the BCl3/Ar plasma chemistry. The etch selectivities for GaN over Al0.2Ga0.8N, Al(0.3)1Ga(0.69)N, and AlN were quite low, less than or equal to 5 for all conditions, and this is due to the ion-driven nature of the removal mechanism.