Electrochemical growth of mircon-thick oxide on SiC in acidic fluoride solution

Anodic polarization of SiC at modest potential in dilute fluoride solution of pH 3 surprisingly gives rise to the growth of micrometer-thick surface layers, clearly revealed with scanning electron microscopy. The reaction occurs at p-type SiC in the dark and at n-type SiC under (supra)bandgap illumination. The surface layer was shown by Rutherford backscattering spectrometry (RBS) to consist of silicon dioxide and to contain excess oxygen. Elastic recoil detection (ERD) indicated only a low level of carbon and fluoride in the layer but a considerable content of hydrogen. The growth kinetics was characterized in situ by spectroscopic ellipsometry and electrical impedance spectroscopy. The results suggest the formation of a duplex layer: a thin inner dielectric oxide and a thick hydrated outer oxide. The latter must have a considerable degree of porosity to allow diffusion/migration of reactants and products during oxide growth.