Two-dimensional distribution of leakage current in ultrathin oxide on stepped Si surface

Two-dimensional distribution of leakage current in ultrathin SiO₂ film formed on stepped Si surface was investigated by using atomic force microscopy with conductive cantilever. Regions with the initially higher leakage current of 1.0nm thick SiO₂ were observed in line along the bunched atomic steps. The higher leakage current regions change from line to spot along steps and finally disappear with increasing oxide thickness. Even if the leakage current is not observed at the initial stage, the local leakage current began to be observed after high voltage stress application. It is found that the degraded regions under high electric stress are also spotty along the atomic steps. It is found that for the ultrathin oxide, their initial leakage and the reliability depend on the micro-structure on the Si surface such an atomic step and so on.