Surface processes on Si(111)7x7 and SiO2 mediated by low-energy ion irradiation in CF4

The surface reactions of the 7x7 and oxidized surfaces of S(1 1 1) mediated by ion irradiation in CF4 at 50 eV impact energy have been investigated by using electron energy loss spectroscopy (EELS), thermal desorption spectro metry (TDS) and low energy electron diffraction (LEED). The reaction layer for the fluorocarbon-ion-irradiated Si(1 1 1)7x7 sample is characterized by the presence of Si-C stretching, Si-F-x (x = 1-3) stretching and bending m odes in the EELS spectra. The lack of any observable C-F stretching feature in the EELS spectra further indicates the absence of any appreciable amoun t of as-formed CF, (x = 1-3) surface species. The TDS results also show tha t SiF4 is the major desorption product and CF, desorption products are not observed. These results therefore suggest that SiC and SiFx(x = 1-3) make u p the reaction layer when Si(1 1 1)7x7 is ion-irradiated with a high exposu re of CF4 at low impact energy. When oxidized Si(1 1 1) is irradiated by th e same dose of fluorocarbon ions, evidence for deposition of more SiFx but less SiC species (relative to the 7x7 surface) is found, which indicates th at the surface O may combine with surface C to form gaseous CO or CO2, leav ing behind more F to react or bind with the Si substrate atoms. The corresp onding TDS data suggests that the OCF radical may be one of the minor desor ption products. (C) 2001 Elsevier Science B.V. All rights reserved.