Study of preferential localized degradation and breakdown of HfO2/SiOx dielectric stacks at grain boundary sites of polycrystalline HfO2 dielectrics

Abstract

• The real-time observation of faster degradation at GB sites of HfO 2 dielectric . • C-AFM results show enhanced defect generation rate at the GB sites. • Preferential breakdown of SiO x IL occurs below the degraded GB region. • A breakdown sequence in polycrystalline HfO 2 /SiO x dielectric stacks was proposed. Grain boundaries (GBs) in polycrystalline high-κ (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.