Controlling the defects and transition layer in SiO₂ films grown on 4H-SiC via direct plasma-assisted oxidation

The structural stability and electrical performance of SiO₂ grown on SiC via direct plasma-assisted oxidation were investigated. To investigate the changes in the electronic structure and electrical characteristics caused by the interfacial reaction between the SiO₂ film (thickness ~5 nm) and SiC, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), density functional theory (DFT) calculations, and electrical measurements were performed. The SiO₂ films grown via direct plasma-assisted oxidation at room temperature for 300s exhibited significantly decreased concentrations of silicon oxycarbides (SiO_xC_y) in the transition layer compared to that of conventionally grown (i.e., thermally grown) SiO₂ films. Moreover, the plasma-assisted SiO₂ films exhibited enhanced electrical characteristics, such as reduced frequency dispersion, hysteresis, and interface trap density (D_it ≈ 10¹¹ cm^-2 · eV^-1). In particular, stress induced leakage current (SILC) characteristics showed that the generation of defect states can be dramatically suppressed in metal oxide semiconductor (MOS) structures with plasma-assisted oxide layer due to the formation of stable Si-O bonds and the reduced concentrations of SiO_xC_y species defect states in the transition layer. That is, energetically stable interfacial states of high quality SiO₂ on SiC can be obtained by the controlling the formation of SiO_xC_y through the highly reactive direct plasma-assisted oxidation process.