In situ infrared characterisation of the interfacial oxide during the anodic dissolution of a silicon electrode in fluoride electrolytes

The interfacial oxides formed under steady-state anodic polarisation of p-silicon in fluoride electrolytes have been studied using in situ infrared spectroscopy in the difference mode. The oxide is characterized in the 900 to 1250 cm(-1) range by the vSiO TO and LO bands, and by other absorption bands related to oxide defects such as non-bridging oxygens. The shape and magnitude of all these bands strongly depend on formation potential as well as on electrolyte composition. Oxide thickness can be estimated from the intensity of the TO absorption band. It is shown to increase with potential and to be little dependent on electrolyte composition. On the other hand, obtaining reliable structural information requires to quantitatively account for both LO and TO bands. Specifically, the frequency splitting between LO and TO modes as well as a properly defined average frequency appear as the relevant parameters. In the present case, the oxides grown at low current (i.e., for low fluoride concentration and at potentials corresponding to the second electropolishing plateau) are those exhibiting a high SiO vibrator density and a low defect concentration.