A detailed study of soft- and pre-soft-breakdowns in small geometry MOS structures

A new soft breakdown (SBD) model in weakly stressed thin gate oxides is proposed. Anomalous leakage current prior to soft breakdown is observed under weak current stress, which strongly indicates the cause of erratic retention error in flash memories. Further current stress induces two types of soft breakdown originating from the same precursor, i.e. multi-step tunneling. One of the SBD features current fluctuation accompanying non-switching 1/f noise and the other random telegraph noise. The difference between the two SBD modes reflect the consequence of different amount of Joule heat damage.