X-RAY PHOTOELECTRON-SPECTROSCOPY STUDY OF LOW-ENERGY CF+ ION INTERACTIONS WITH SILICON

Surface modifications of silicon by exposure to a mass-separated, reactive ion beam of CF+ were studied by x-ray photoelectron spectroscopy. The effects of ion kinetic energy were characterized in terms of the various surface chemical states induced by the bombardment. The results showed that with an ion kinetic energy of 2 eV, which was much lower than the C-F bond energy of about 5 eV, molecular adsorption took place. At a bombardment energy of 10 eV, dissociative chemisorption was observed but the reaction was confined to the top surface with disproportionation of CF as the main route and little fluorination of silicon. With an ion energy of 100 eV, the atomic fragments generated by the CF dissociation possessed enough energy to penetrate below the silicon surface. It was found that silicon carbide and fluorosilyl species comprised the modified surface region and that fluorine atoms were situated closer to the surface than the carbon atoms of the carbide. Fluorocarbon species were minor surface reaction products. This work shows that distinct surface reactions may be chemically switched between the CF + ion and the silicon surface as a function of the ion kinetic energy.