Statistical analysis of soft breakdown in ultrathin gate oxides

It is found that the Weibull slope /spl beta/ of the time-to-soft breakdown (t/sub SBD/) distributions coincides with that of time-to-hard breakdown (t/sub BD/) distributions over the oxide thickness range 1.9-4.8 nm, and /spl beta/ linearly decreases with decrease of oxide thickness. Such 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 SiO/sub 2/ network. These results suggest that soft breakdown (SBD) as well as hard breakdown (HBD) are triggered by a common physical mechanism such as defect generation from strained Si-O-Si bonds.