Oxide thinning percolation statistical model for soft breakdown in ultrathin gate oxides

An existing cell-based percolation model with parameter correlation can fin d its potential applications in assessing soft-breakdown (BD) statistics as long as the oxide thinning due to the localized physical damage near the S iO2/Si interface is accounted for. The resulting model is expressed explici tly with the critical trap number per cell n(BD) and the remaining oxide th ickness t(ox)(') both as parameters. Reproduction of time-to-bimodal (soft- and hard-) breakdown statistical data from 3.3-nm-thick gate-oxide samples yields n(BD) of 3 and 4 for soft and hard breakdown, respectively. The ext racted t(ox)(') of 1.0 nm for soft breakdown, plus the transition layer thi ckness of 0.5 nm in the model, is fairly comparable with literature values from current-voltage fitting. The dimension and area of the localized physi cally damaged region or percolation path (cell) are quantified as well. Bas ed on the work, the origins of soft and hard breakdown are clarified in the following: (i) soft breakdown behaves intrinsically as hard breakdown, tha t is, they share the same defect (neutral trap) generation process and foll ow Poisson random statistics; (ii) both are independent events correspondin g to different t(ox)(') requirements; and (iii) hard breakdown takes place in a certain path located differently from that for the first soft breakdow n. (C) 2000 American Institute of Physics. [S0003-6951(00)02130-6].