Comparison between AlGaN surfaces etched by carbon tetrafluoride and argon plasmas: Effect of the fluorine impurities incorporated in the surface

Compositional and morphological changes in Al0.24Ga0.76N surfaces etched by CF4 and Ar plasmas were investigated in order to clarify the effect of fluorine impurities incorporated in the surface by the CF4 plasma. The CF4 plasma effectively incorporated the fluorine impurities in the surface even at a short etching time. A small number of the incorporated fluorine impurities only contributed to the formations of Al(OH)xFy and GaFx on the surface even as the etching time increased. Although the CF4 and Ar plasma etchings preferentially remove nitrogen atoms from the surfaces, the preferential removal induced by the CF4 plasma etching was suppressed compared with the case of the Ar plasma etching. The CF4 plasma etching caused a smooth surface regardless of the gas pressure and the etching time, whereas the Ar plasma etching changed the surface morphology depending on the gas pressure and the etching time. The incorporation of the fluorine impurities, which bonded with the cation vacancies such as gallium and aluminum vacancies introduced in the surface by the plasma etching, was considered to concern the suppression of the preferential removal and the formation of the smooth surface.