X-ray photoelectron spectroscopic study of the interactions of CF+ ions with gallium arsenide

Abstract

Chemical modifications in the surface of gallium arsenide bombarded with low energy, 3–300 eV CF+ ions have been investigated using x-ray photoelectron spectroscopy (XPS). The effect of temperature on the modified surface was studied by annealing in a vacuum of 1×10−6 Pa prior to further XPS analysis. It was found that CF+ ion bombardment deposited an overlayer containing both carbon and fluorine on the GaAs surface. At 3 eV CF+ ion exposures, the overlayer consists primarily of CF and CC bonds whereas at experimental energies greater than the dissociation energy of the CF bond, there are appreciable amounts of CF2 and CF3 indicated. The GaAs surface itself is modified slightly, to include some gallium and arsenic fluorides, and perhaps some carbides as well. The levels of these components are limited, however, by the presence of the CF overlayer which upon forming encapsulates the GaAs surface, shielding it from subsequent CF+ bombardment. The overlayer also retains gallium and arsenic fluorides in the GaAs surface at temperatures higher than they would appear in the unencapsulated case. Heating in vacuum at 1×10−6 Pa releases some fluorine from the overlayer at and above 350 °C but is ineffective in removing the carbon. Fluorine was still present at low levels after heating to 450 °C but could not be found at higher temperatures.