A New Insight into the Breakdown Mechanism in Ultrathin Gate Oxides by Conductive Atomic Force Microscopy

The structural and electrical evolution process of gate dielectric breakdown (BD) is investigated by conductive atomic force microscopy (CAFM) with ultrathin SiO₂ films. The degradation mode is found to be quite different from that in the case of thick films. Both the structural deformation at the pre-BD stage and the lateral expansion from degradation are found to be less pronounced with decreasing thickness and stress voltage. Stress induced leakage current (SILC) is found to be dominant rather than a trap effect and occurs prior to structural deformation. A BD transient is observed at higher electric field and current density than in 5 nm-thick SiO₂ films. It is suggested that the pre-BD Si deformation is induced by the inelastic tunneling of energetic carriers