Vibrational electron energy loss studies of surface processes on Si(1 1 1)7×7 and vitreous SiO 2 ion-mediated in CF 4 and CH 2F 2

Abstract

The surface species produced on Si(1 1 1)7×7 and vitreous SiO 2 surfaces by ion irradiation in CF 4 and in CH 2F 2 at 50 eV impact energy have been investigated by electron energy loss spectroscopy (EELS), thermal desorption spectrometry (TDS) and low energy electron diffraction (LEED). In particular, the reaction layer for Si(1 1 1)7×7 ion-irradiated in CF 4 is characterized by the presence of Si–C stretching, Si–F x ( x=1–3) stretching and bending modes, while ion irradiation in CH 2F 2 introduces additional C–H stretching mode. For both cases, the absence of C–F stretching feature in the corresponding EELS spectra indicates that CF x ( x=1–3) surface species do not present in any appreciable amount. These EELS results are consistent with the TDS data, which shows that SiF 4 is the major desorption product and desorption products such as CF x ( x=1–3) are not observed. Ion irradiation of Si(1 1 1)7×7 in CF 4 or CH 2F 2 at low impact energy therefore produces SiC and SiF x ( x=1–3) as the primary surface products, while additional CH species is found in the latter case of ion-irradiation in CH 2F 2. When the oxidized surface instead of the 7×7 surface of Si(1 1 1) is used as the substrate, ion irradiation by the same dose of fluorocarbon ions appears to enhance the deposition of SiF x but reduce the amount of SiC species, which provides evidence for recombination reaction of surface O with surface C to form gaseous CO or CO 2, leaving behind more F to interact with the Si substrate atoms. The corresponding TDS data suggests that the OCF radical may also be one of the minor desorption products.