Study of preferential localized degradation and breakdown of HfO_2/SiO_x dielectric stacks at grain boundary sites of polycrystalline HfO_2 dielectrics

摘要

Grain boundaries (GBs) in polycrystalline high-K (HK) dielectric films affect the performance and reliability metrics of HK based advanced metal-oxide-semiconductor (MOS) devices. A full understanding of device reliability can only be had with the knowledge of the detrimental role of GB in degradation and breakdown (BD) of polycrystalline HK/interfacial layer (IL) dielectric stacks. In this work, we present a nanoscale resolution study on how the polycrystalline microstructure affects the degradation and BD at GB sites of polycrystalline HfO_2 in HfO_2/SiO_x (x ≤ 2) dielectric stacks using conductive-atomic force microscopy (C-AFM), supported by a statistical failure distribution model and device level simulations. Results clearly show an enhanced trap generation and faster degradation of polycrystalline HfO_2 gate dielectrics at GB sites as compared to the bulk (grain) regions implying shorter time-dependent dielectric breakdown (TDDB) lifetime at the GB sites. The SiO_x IL below the degraded GB experiences a BD event when an enhanced electric field across the SiO_x IL reaches the critical BD field, eventually triggering the overall BD of the HfO_2/SiO_x dielectric stack.