Experimental study of the quasi-breakdown failure mechanism in 4.5 nm-thick SiO2 oxides

Abstract In this study, we have investigated the electrical properties of the failure mode referred as quasi-breakdown or soft-breakdown in MOS capacitors on p -type substrate with an oxide thickness of 4.5 nm. Quasi-breakdown appears during high field stresses as a sudden increase between two and four orders of magnitude in the gate current over the whole gate voltage range, but remains undetected in C ( V ) characteristics between 20 Hz and 100 kHz. Quasi-breakdown was systematically triggered during negative gate voltage stresses after a threshold between 10 and 15 C/cm 2 was reached in the injected charge, this threshold being independent of the stressing oxide field. A very weak temperature dependence and a low frequency noise in the gate current were also observed. The I ( V ) characteristics are found to follow a first-order exponential law versus the gate voltage, indicative of a direct tunneling process, which could result from a local lowering of the oxide thickness resulting from a sudden metal/isolant transition in a localized region of the oxide near the anode due to oxide defects.