ELECTRONIC CONDUCTION MECHANISMS IN THIN OXYNITRIDE FILMS

We report a new theory for electronic conduction in thin (150 angstrom) oxynitride films. The present experiment reveals that the electronic conduction mechanism in the oxynitride deviates from that in conventionally grown silicon oxide in the electric field ranging from 6 to 14 MV/cm and suggests that the electronic conduction is governed by three different mechanisms according to the strength of electric field. We suggest that the current conduction is trap-assisted at electric fields lower than 8 MV/cm. Specifically, the conduction is due the tunneling of electrons into the shallow traps in the insulator. In the high-field region (> 10 MV/cm), the Fowler-Nordheim (FN) effect becomes dominant and depends on the dielectrics preparation conditions. In the moderate-field region, traps can be filled by both FN current and direct tunneling of electron into the traps which result in a quasi-saturation in the leakage current. The experiment also shows a turnaround behavior in leakage current level, ledge in current-voltage characteristics, and field dependency of the current as the nitridation proceeds. These observations can be readily explained based on the proposed conduction mechanism.