Transport characteristics of posthard breakdown thin silicon oxide films and consideration of physical models

Abstract

This article describes the constant-voltage-stress-induced breakdown of thin silicon oxide films, as well as the conduction mechanisms of posthard breakdown oxide films which are characterized by means of the differential resistance technique involving posthard breakdown current and spectral analyses of posthard breakdown current fluctuation. A very thin oxide film still shows a high differential resistance just after the first hard breakdown event; additional current stress pushes the film into the final state. On the other hand, a thicker oxide film enters the final state (breakdown) after the first hard breakdown event. It is also shown that there still exists an energy barrier for electrons after the hard breakdown event as already reported. However, it is also shown that the energy barrier places an asymmetric restriction on electron flow in contrast to the past symmetric assumption. Current fluctuation of posthard breakdown oxide films is characterized in detail. Short-time and long-time observations of current fluctuations suggest that there are two different major defects inside posthard breakdown oxide films; in a significant development, Fourier-transformed results are shown to yield a very short time constant and a very long time constant. These results are consistent with past prebreakdown behavior analyses that indicated a significant relationship between the soft breakdown and the hard breakdown.