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 Si O2 gate oxides is investigated. After soft breakdown, which correspond s to an anomalous increase of the stress-induced leakage current of me tal-oxide-semiconductor capacitors, the current behaves like a power l aw of the applied gate voltage V-G. After soft breakdown, charge is fu rther injected into the SiO2 layer in order to extract the effective r esistivity rho(eff) of the system as a function of the density of oxid e traps D generated in the layer. It is found that rho(eff) behaves li ke a power law of (D-D-c) where D-c is the critical density of traps g enerated at soft breakdown. These results are in fair agreement with t he predictions of the percolation theory of nonlinear conductor networ ks, Besides, the value of the critical exponent related to the resisti vity is close Co the one expected in two dimensions. (C) 1998 American Institute of Physics.