Direct observation of trap behaviors during degradation and breakdown evolution in highly stressed SiO/sub 2/ films by conductive atomic force microscopy

Among many models of dielectric degradation and breakdown (BD), electron trap generation is generally considered to be a possible explanation. Although negative charges were reported existing after BD by macroscopic studies, the physical image is still lacking for how the trap is generated and how it relates to a BD event. Although scanning probe microscopy (SPM) has already been used to analyze the degradation process locally, the trap behaviors during BD evolution remain difficult to observe because of the irreversible and transient properties of a BD event. In this study, we report a new method for evaluating the FN-stress-induced trap behaviors in SiO/sub 2/ films pre- and post-BD by conductive atomic force microscopy (CAFM). A transient component of current was detected immediately after BD, showing the negative charge detrapping after BD was from the trap centers to the cathode substrate. Also, a lateral propagation of trap defects was observed before BD with similar size to that of post-BD.