Visualization of progressive breakdown evolution in gate dielectric by conductive atomic force microscopy

To understand the breakdown (BD) mechanism in gate oxide of MOSFET, BD evolution is investigated by a conductive atomic force microscope. High electric fields of both polarities are applied to induce a pre-BD degradation and a BD transient. Structural hillocks and negative charges are simultaneously observed at both pre- and post-BD stages. The hillocks show stress-polarity dependence, and the height increases with BD evolution. A flat-band shift caused by negative charges does not depend on stress polarity. Lateral size of the hillocks and the electrical degradation remains similar throughout the BD evolution. Progressive structural evolution of dielectric BD is confirmed, where polarity-dependent Si deformation plays an important role.