Quantitative Analysis of Oxide Voltage and Field Dependence of Time-Dependent Dielectric Soft Breakdown and Hard Breakdown in Ultrathin Gate Oxides

Soft breakdown (SBD) and hard breakdown (HBD) mechanisms have been studied for 2.2-4.9-nm-thick gate oxides. The charge-to-soft breakdown ( Q SBD ) is correlated to the incremental change in the stress-induced current at the time-to-soft breakdown ( t SBD ) under constant voltage stress, while the charge-to-hard breakdown ( Q BD ) exhibits no correlation with change in the stress-induced current because of the temporal fluctuation of the SBD current. By noting that strained Si–O–Si bonds existing in SiO 2 within 1.5 nm of the SiO 2 /Si(100) interface could be defect precursors which cause the SBD, time-dependent dielectric soft breakdown in ultrathin gate oxides is consistently explained by the thermochemical electric field model. It is shown that SBD and HBD are caused by a common physical mechanism.