New insight into the TDDB and breakdown reliability of novel high-к gate dielectric stacks

In order to achieve aggressive scaling of the equivalent oxide thickness (EOT) and simultaneously reduce leakage currents in logic devices, silicon-based oxides (SiON / SiO₂) have been replaced by physically thicker high-κ transition metal oxide thin films by many manufacturers starting from the 45 nm technology node. CMOS process compatibility, integration and reliability are the key issues to address while introducing high-κ at the front end. In this study, we analyze in-depth the reliability aspect of high-κ dielectrics focusing on both the time-dependent-dielectric breakdown (TDDB) and the post breakdown evolution stage. Electrical characterization, physical failure analysis, statistical reliability modeling as well as atomistic simulations have all been used to achieve a comprehensive understanding of the physics of failure in HK and the associated microstructural defects and failure mechanisms. The role played by different gate materials ranging from poly-Si → FUSI → metal gate and different HK materials (HfO₂, HfSiON, HfZrO₄) is also investigated. Based on the results obtained, we emphasize the need and propose a few approaches of design for reliability (DFR) in high-κ gate stacks.