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We have systematically analyzed the time-to-hard breakdown (tBD) and time-to-soft breakdown (tSBD) distributions for 1.9-4.8-nm-thick oxides. The tBD and tSBD distributions well fit to the Weibull distribution function. Also, the Weibull slope β of the tSBD distributions coincides with that of the tBD distributions over the oxide thickness range 1.9-4.8 nm, and β linearly decreases with decrease of oxide thickness. It is also shown that decrease in β of both tSBD and tBD distributions is well correlated to measured Si-O-Si bond angle reduction induced by compressive stress in the oxide network near the SiO2-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.
Date of Publication: May 2004