Use of nuclear reaction analysis to investigate the thermal growth of SiO2 films on SiC

Full text: Silicon carbide (SiC) is a wide band gap semiconductor that has appropriate properties for high-power, high-frequency, and high-temperature electronic device applications in which Si-based devices cannot be used. However, the presence of residual carbon at the interface between thermally grown SiO2 films and SiC leads to a high density of electronic states and raises several issues in device fabrication. In the present work, nuclear reaction analysis (NRA) and nuclear reaction profiling (NRP) were employed to investigate the formation of silicon oxycarbides at the SiO2/SiC interface as a function of substrate polytype, surface termination, oxidation temperature, and post-oxidation annealing in O2. In addition, the effect of residual silicon oxycarbides on the reactivity of the SiC surface regarding thermal oxidation was investigated. SiO2 films were thermally grown on SiC and Si single-crystalline substrates in dry O2 enriched in the 18O isotope. The use of 18O is crucial, as nuclear reaction analysis allows distinguishing it from oxygen eventually incorporated from other sources - for instance, exposure to the ambient. After oxidation, samples were etched in aqueous hydrofluoric acid (HF) and the amount of residual 18O was determined by NRA using the 18O(p,alpha)15N nuclear reaction at 730 keV. The amount of 18O remaining after etching these samples was two orders of magnitude higher on SiC than on Si. This result was independent of the SiC substrate polytype and oxidation temperature. The depth distribution of 18O in selected samples was determined by NRP using the narrow resonance at 151 keV in the cross section curve of the 18O(p,alpha)15N nuclear reaction. The kinetics of oxide growth on SiC was found to be retarded on substrates previously oxidized and etched in HF. We attribute our observations to the presence of silicon oxycarbides in the SiO2/SiC interface region. Present results demonstrate that nuclear reaction analysis is particularly useful to investigate etching and thermal oxidation processes on SiC. (author)