EFFECTS OF INTERFACE ROUGHNESS AND CONDUCTING FILAMENTS IN METAL-OXIDE-SEMICONDUCTOR TUNNEL STRUCTURES

The current-voltage characteristics of nf poly-Si/SiO2/p-Si tunnel str uctures containing nonuniform ultrathin oxide layers are studied using three-dimensional quantum mechanical scattering calculations. We find that, in general, roughness at the Si/SiO2 interface renders the oxid e layer more permeable. In the direct-tunneling regime, interface roug hness induces lateral localization of wave functions, which leads to p referential current paths. But in the Fowler-Nordheim tunneling regime it affects transport primarily through scattering. These two distinct mechanisms lead to opposite current density dependencies on island si ze. We have also examined oxide-embedded conducting filaments, and fou nd that they act as highly efficient localized conduction paths and le ad to dramatic increases in current densities. Depending on the filame nt length, our model can mimic experimental current voltage for ultrat hin oxides having undergone either quasibreakdown or breakdown. We als o found that the lower bias current densities in the structure with lo ng filaments are greatly enhanced by resonant tunneling through states identified as quantum dots, and that this current enhancement is high ly temperature dependent. We also report on the dependence of current- voltage characteristics on filament diameter size and filament density . (C) 1998 American Vacuum Society.