Surface processes on Si(1 1 1)7×7 and SiO2 mediated by low-energy ion irradiation in CF4

The surface reactions of the 7×7 and oxidized surfaces of Si(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 spectrometry (TDS) and low energy electron diffraction (LEED). The reaction layer for the fluorocarbon-ion-irradiated Si(1 1 1)7×7 sample is characterized by the presence of SiC stretching, SiFx (x=1–3) stretching and bending modes in the EELS spectra. The lack of any observable CF stretching feature in the EELS spectra further indicates the absence of any appreciable amount of as-formed CFx (x=1–3) surface species. The TDS results also show that SiF4 is the major desorption product and CFx desorption products are not observed. These results therefore suggest that SiC and SiFx (x=1–3) make up the reaction layer when Si(1 1 1)7×7 is ion-irradiated with a high exposure of CF4 at low impact energy. When oxidized Si(1 1 1) is irradiated by the same dose of fluorocarbon ions, evidence for deposition of more SiFx but less SiC species (relative to the 7×7 surface) is found, which indicates that the surface O may combine with surface C to form gaseous CO or CO2, leaving behind more F to react or bind with the Si substrate atoms. The corresponding TDS data suggests that the OCF radical may be one of the minor desorption products.