Surface processes on Si(1 1 1)7×7 and SiO 2 mediated by low-energy ion irradiation in CF 4

Abstract

The surface reactions of the 7×7 and oxidized surfaces of Si(1 1 1) mediated by ion irradiation in CF 4 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F x ( 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 CF x ( x=1–3) surface species. The TDS results also show that SiF 4 is the major desorption product and CF x desorption products are not observed. These results therefore suggest that SiC and SiF x ( x=1–3) make up the reaction layer when Si(1 1 1)7×7 is ion-irradiated with a high exposure of CF 4 at low impact energy. When oxidized Si(1 1 1) is irradiated by the same dose of fluorocarbon ions, evidence for deposition of more SiF x 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 CO 2, 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.