Nanometer-scale analysis of current limited stresses impact on SiO2 gate oxide reliability using C-AFM

A conductive atomic force microscope (C-AFM) has been used to analyze at a nanometer scale the impact of the current limitation on the breakdown (BD) of thin (<6 nm) SiO₂ gate oxides of metal-oxide-semiconductor (MOS) structures. The high-lateral resolution of the technique (∼10 nm) allows to get more insight in the BD phenomenology and to study, independently, the effect of the current limit on different post-BD oxide properties such as the oxide conductivity at the primary location where the event is triggered (S₀) and the size of the broken-down region (S_BD). The results show that the conductivity at S₀, the total area affected by the BD and the structural damage of the oxide increase when a current limitation is not imposed during the electrical stress, leading to harder BD events. The results demonstrate that the C-AFM is a very suitable tool to perform a complete analysis of the BD phenomenology at such reduced scale.