AlGaN surfaces etched by CF4 plasma with and without the assistance of near-ultraviolet irradiation

Al0.24Ga0.76N thin film surfaces were etched with CF4 plasma, with and without the assistance of near-ultraviolet (UV) irradiation. The near-UV source was a black light lamp, which emitted wavelengths of 300-400 nm. The chemical compositions and morphologies of surfaces etched under the two plasma conditions were compared, to clarify the effect of near-UV irradiation on the properties of the AlGaN surface. Near-UV irradiation during CF4 plasma etching reduced the amounts of F atoms, AlFx fluorides, and GaFx fluorides incorporated into the surface, and enhanced the amount of CFx fluorocarbons. Near-UV irradiation did not influence the depth distribution of incorporated fluorine-related impurities, or the degree of nitrogen deficiency caused in the surface. These compositional changes in the surface occurred irrespective of the gas pressure. Near-UV irradiation caused a significant change in the morphology of surfaces etched at high gas pressure (13 Pa), as the etching time was increased to 60 and 100 min. Near-UV irradiation did not change the morphologies of surfaces etched at lower gas pressures (1.3 and 6.7 Pa), irrespective of etching time.