Critical assessment of soft breakdown stability time and the implementation of new post-breakdown methodology for ultra-thin gate oxides [MOSFET]

The reliability margin seriously shrinks when gate oxide thickness is scaled below 2 nm. In this work we pursue a general picture of the breakdown in ultra-thin oxides by studying the statistics of the residual time, T/sub res/, defined as the time elapsed between the occurrence of the first breakdown (T/sub BD/) and the time of device failure. We have found that a classification of the breakdown events into SBD (soft breakdown) and HBD (hard breakdown) is still meaningful in oxides with thickness down to 1 nm, although both modes finally cause the transistor failure after a certain stress time. The obtained results have allowed us to develop a reliability methodology that includes, in a general framework, the device failure by three different processes: i) progressive HBD; ii) degradation of SBD into HBD and iii) superposition of several successive SBD events.