Local electrical characteristics of ultra-thin SiO2 films formed on Si(0 0 1) surfaces

We have investigated the dielectric degradation of 0.6-nm-thick silicon oxide films formed on Si(0 0 1) substrates by measuring local current–voltage (I–V) characteristics, using current sensing atomic force microscopy (AFM). It is found that the step edges are more conductive than the terraces on the oxide surface. In the local I–V characteristics, the mechanism of carrier transportation changes from electron direct tunneling to electron Fowler–Nordheim tunneling at a sample voltage of −4.2 V. This result suggests that the 0.6-nm-thick oxide film explicitly has the same band structure in the conduction band as that of bulk SiO2. Furthermore, experimental results reveal that neutral traps contributing to electron tunneling and positive charges are created in the oxide film under a high electric field stress given by a Pt-coated AFM cantilever. It is considered that the region where only the neutral trap exists corresponds to metastable states of leakage current path. On the other hand, the region where both the neutral and positive traps are present contains stable leakage sites.