Aggressive device scaling calls for gate dielectrics with reduced effective oxide thickness, down to 1 nm and even 0.5 nm, and raises concerns about their reliability. Development of a correct lifetime projection based on the accelerated electrical stress data for such thin oxides requires understanding of the oxide degradation mechanisms. Oxide wear-out represents a multi-step process wherein each step might be limiting under the given conditions, thereby complicating identification of the key degradation factors. The conventional oxide degradation models concentrate on the effects of the injected electron impact on the anode interface. However, holes and/or hydrogen produced by the impact cannot effectively break the bulk Si-O bonds, thus limiting generation of the electron traps only to pre-existing defect sites, for instance oxygen vacancies Si-Si.

A proposed alternative approach to the defect generation phenomenon takes into consideration imperfections in the SiO₂ structure that leads to formation of the localized gap states. Capture of the injected electron by such a localized state can trigger the chain of events leading eventually to the generation of a structural defect. In particular, the increase of the average O-O second nearest neighbors distance induces the oxygen p states to split from the bottom of the conduction band. Electron localization on this anti-bonding state was shown to significantly weaken the corresponding Si-O bond and rendering it unstable with respect to the typically used temperature and applied electric fields. The bond breakage results in the formation of a neutral defect, a three coordinated Si + non-bridging oxygen. The subsequent exothermic reaction between this defect and molecular hydrogen, which can be released into the oxide by the electron impact at the anode interface, stabilizes the broken Si-O bond and leaves behind a neutral E’ center, which was recently identified as a candidate for the stress generated bulk defect.

A suggested mechanism for the defect generation directly in bulk oxide by the injected electrons provides new insights into the processes of the formation of the leakage path, its subsequent degradation, and eventual dielectric hard breakdown. The model successfully describes the charge-to-breakdown dependence on the electron fluence and energy, electric field, temperature and oxide thickness.