TDDB characterisation of thin SiO/sub 2/ films with bimodal failure populations

The paper deals with the extensive characterisation of a 20-nm oxide using multiple wafer fabrication lots. The data generated indicate that the intrinsic wearout properties of the oxide are best modelled by the E model with a field-dependent activation energy and a constant field acceleration factor. Of the 3 lots used in the characterisation one exhibited bimodal characteristics with a large extrinsic population. This allowed the investigation of the extrinsic distribution separately which exhibited a 1/E dependence and a field-dependent activation energy. The paper shows that using censored data for bimodal distributions results in the incorrect model (1/E) being used to predict intrinsic wearout. The paper also shows that in order to differentiate between the two models sample sizes must be run to 100% failure to ensure that true intrinsic wearout has been observed. The characterisation matrix used in the evaluation was very comprehensive and indicates E-fields of 7 MV/cm and below must be used to determine the correct field acceleration model.