Soft breakdown in ultrathin gate oxides: Correlation with the percolation theory of nonlinear conductors

The dielectric breakdown under constant current stressing of 4.2 nm SiO2 gate oxides is investigated. After soft breakdown, which corresponds to an anomalous increase of the stress-induced leakage current of metal–oxide–semiconductor capacitors, the current behaves like a power law of the applied gate voltage VG. After soft breakdown, charge is further injected into the SiO2 layer in order to extract the effective resistivity ρeff of the system as a function of the density of oxide traps D generated in the layer. It is found that ρeff behaves like a power law of (D−Dc) where Dc is the critical density of traps generated at soft breakdown. These results are in fair agreement with the predictions of the percolation theory of nonlinear conductor networks. Besides, the value of the critical exponent related to the resistivity is close to the one expected in two dimensions.