X-RAY PHOTOELECTRON SPECTROSCOPIC STUDY OF THE INTERACTIONS OF FLUORINE IONS WITH GALLIUM-ARSENIDE

The surface of gallium arsenide has been bombarded with low energy fluorine ions in order to study their role in modifying the surface during a CHF3 reactive ion etch of oxide overlayers on GaAs. Compositional changes caused by the bombardment of GaAs with ions ranging in energy from 10 to 300 eV have been investigated using x-ray photoelectron spectroscopy. Depth profiling information was obtained using angle-resolved photoemission measurements. Annealing in vacuum of 1 X 10(-6) Pa was investigated as a means of returning the bombarded surface to its original condition. It was found that F+ ion bombardment incorporated fluorine into the surface of GaAs and depleted it of arsenic by forming gallium fluoride and apparently releasing volatile arsenic fluoride. Monitoring the Ga 3d peak revealed that three gallium fluoride phases corresponding to GaF, GaF2, and GaF3 were formed. The extent of fluorine incorporation and arsenic depletion were dependent upon incident F+ ion energy, reaching a maximum at low incident ion energies around 50 eV. At higher ion energies the amounts of GaF2 and GaF3 decreased more than that of GaF. Post-bombardment annealing in vacuum was successful in removing the residual fluoride phases at temperatures below 305-degrees-C. GaF3 was the first component to desorb and GaF the last. The resulting GaAs surface, however, was still gallium rich, likely due to the presence of some residual gallium oxide.