Statistical analysis of soft and hard breakdown in 1.9-4.8-nm-thick gate oxides

We have systematically analyzed the time-to-hard breakdown (t/sub BD/) and time-to-soft breakdown (t/sub SBD/) distributions for 1.9-4.8-nm-thick oxides. The t/sub BD/ and t/sub SBD/ distributions well fit to the Weibull distribution function. Also, the Weibull slope /spl beta/ of the t/sub SBD/ distributions coincides with that of the t/sub BD/ distributions over the oxide thickness range 1.9-4.8 nm, and /spl beta/ linearly decreases with decrease of oxide thickness. It is also shown that decrease in /spl beta/ of both t/sub SBD/ and t/sub BD/ distributions is well correlated to measured Si-O-Si bond angle reduction induced by compressive stress in the oxide network near the SiO/sub 2/-Si(100) interface. These results suggest that soft breakdown as well as hard breakdown in ultrathin gate oxides are triggered by a common physical mechanism such as defect generation from strained-Si-O-Si bonds under strong electric field.