Soft breakdown in ultrathin SiO <inf>2</inf> layers: The conduction problem from a new point of view

In this work, the soft breakdown failure mode in ultralhin (<5 nm) SiO 2 layers is experimentally examined by means of current-voltage measurements performed on samples with different gate areas, oxide thicknesses and substrate types. The observed astounding matching which exhibits some of these characteristics, as well as the common features with the final breakdown, leads us to suggest that the current flow in the analysed regime might be largely controlled by the extremely constrictive dimensions of the oxide leakage spots. We present an alternative explanation to the soft breakdown phenomenon which can be naturally extended to the final breakdown conduction stage. In order to illustrate our ideas, a qualitative comparison with the theoretical behaviour of a classical point contact system is also discussed. ©1999 Publication Board, Japanese Journal of Applied Physics.