A comprehensive model for breakdown mechanism in HfO2 high-k gate stacks

Based on physical analysis results, a model describing the breakdown (BD) mechanism of HfO₂/polysilicon gate stack is proposed. Due to the high mechanical strength and the polycrystalline nature of annealed HfO₂ dielectrics, and a very complicated BD induced thermo-chemical reaction and self-healing process, the BD mechanism and transient evolution in HfO₂ gate stacks are different from that of ultrathin SiO_xN_y. The formation of a percolation path is probably assisted by grain boundaries and/or enhanced electric field strength near the poly-Si edge. Besides polarity-dependent dielectric-BD-induced epitaxy (DBIE), due to the BD induced thermo-chemical reactions among HfO₂, SiO_x (i.e. IL oxide), Hf-compounds and Si, the formation of a dielectric-based "clog" which is HfSi_x O_y-rich, termed as dielectric-BD-induced self-healing insulating cap (SHIC), is proposed. The microstructures of DBIE and SHIC are responsible for the leakage current evolution during a BD event in HfO₂ gate stacks.