A new soft breakdown model for thin thermal SiO2 films under constant current stress

Soft breakdown properties of thin gate oxide films are investigated using a constant current stress measurement. The soft breakdown can be classified into two different modes from the current conduction characteristics of post breakdown oxides: one of the modes shows a telegraph switching pattern and the other random noise. The generation probabilities of two soft breakdown modes and hard breakdown strongly depend on the stress current. Time-to-breakdown is well characterized by a universal function of stress conditions regardless of the breakdown modes. These experimental findings imply that all types of breakdown originate from the same precursor and the magnitude of the following local heating due to the transient current in a conductive micro spot determines the charge conduction properties after a breakdown event.