Fluorination of the silicon dioxide surface during reactive ion and plasma etching in halocarbon plasmas

Abstract

Surface sensitive spectroscopies were employed to investigate the surface modifications which occur on SiO2 during actual reactive ion and plasma etching in CF4 and CF4/O2 plasmas. Photoemission and electron energy loss spectroscopies were used to characterize the composition and bonding in the modified layer. Core level photoemission measurements indicated a reaction layer 10-15 Å thick with a mean composition of SiOF2. Photoemission and EELS studies of the valence bands identified several features due to SiF bonding. Comparisons with the SiO2 valence bands and implications for bonding are discussed. Electron energy loss spectra were also used to determine if ion induced "defect" species formed during reactive etching persist in the reaction layer. A comparison of reactive ion etching samples with those exposed to plasma etching conditions (negligible ion bombardment) indicated that the ion bombarded surfaces exhibit a reduced level of fluorination during steady state etching. Low energy ion scattering was used to determine the composition of the outermost atomic layer. These measurements indicated a fluorine terminated surface with virtually no remaining surface oxygen. © 1989.