Study of process-dependent electron-trapping characteristics of thin nitrided oxides

Abstract

A detailed investigation on the process dependent characteristics of electronic traps in thin nitrided oxide films is presented. By monitoring the field shift in the Fowler-Nordheim (FN) plots and the flatband voltage of metal-insulator-semiconductor (MIS) structures, the trap centroid of the nitrided oxide film was found to be process dependent. Turnaround behaviour in the location of the trapped charge centroid ( X 0, measured from the oxide/silicon interface) and trap density were found. The centroid moves to the surface for light nitridation and then moves as close as X 0/ L = 0.48 ( L is the thickness of the dielectric) to the silicon/oxide interface. On the other hand, the current conduction of the nitrided film is found to be enhanced remarkably by shallow traps (∼ 1.0 eV) for electric field strengths less than 8.5 MV/cm. A shallow trap-assisted electronic conduction mechanism in the nitrided oxides is proposed. For electric fields in the range of 8.5–11 MV/cm, a quasi-saturation region due to electron-trapping is observed. In the high electric field region (> 11 MV/cm), the conduction current is governed mainly by the FN mechanism. Detrapping, either by two-step tunnelling or Schottky emission, is also obvious in the high field region.