Experimental study of the quasi-breakdwon failure mechanism in 4.5 nm-thick SiO_2 oxides

摘要

In this study, we have investigated the electrical properties of the failure mode referred as quasi-breakdown or soft-breakdwon in MOS capacitors on p-type substrate with an oxide thickness of 4.5nm. 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 20Hz and 100kHz. Quasibreakdown was systematiclly triggered during negateve gae voltage stresses after a threshold between 10 adn 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 pocess, which could result form a local owering of the oxide thickness resulting from a sudden metal/isolant transtion in a localized region of he oxide near the anode due to oxide defects.