Detection and fitting of the soft breakdown failure mode in MOS structures

Despite the numerous publications dealing with the soft breakdown (SBD) failure mode in ultrathin gate oxides, there is still a large disagreement on the actual functional form of the associated current-voltage (I-V) characteristic. Here, we show that a power law, for applied voltages less than approximately 3.5 V, and an exponential law for higher voltages form suitable fitting models. The discrepancy has its origin in the fact that the SBD experimental detection window is variable, since it is determined not only by the geometrical parameters of the device under test, which set the fresh I-V characteristic of the sample, but also by the strength of the breakdown event. In addition, we analyze the scatter of the SBD I-V curves as a function of the stress current.