Impact of bilayer character on High K gate stack dielectrics breakdown obtained by conductive atomic force microscopy

The time to breakdown distribution of bilayer gate stack dielectrics is measured at nanometric scale using an atomic force microscope in conduction mode under ultra-high vacuum. The bilayer consists of a SiON interfacial layer and a HfSiON High-K layer. Thanks to the small tip/sample contact area the time to breakdown distribution of the single interfacial layer is measured separately. It is found that the Weibull parameters of the Interfacial layer distribution are the same as those of the high percentile part of the bilayer bimodal distribution. This experimentally confirms the validity of former dielectric breakdown model assumptions. Considering the fields in each layer an accurate evaluation of acceleration factors and voltage scaling of the bimodal distribution are given.