Anomalous positive-bias temperature instability of high-κ/metal gate nMOSFET devices with Dy2O3 capping

Recently, thin rare-earth oxide dielectric capping layers between the high-k and metal gate have been used to modulate the threshold voltage (Vt) of MOSFETs [Kirsch et al., 2006]. In Dy₂O₃-capped high-k based devices, we observe an anomalous PBTI behavior where the Vt decreases during stress. Results suggest that there are two competing mechanisms - diffusion of preexisting positively-charged species and electron trapping. The charged species is likely located in the mixed high-k dielectric and associated with the interaction between the host dielectric, cap, and metal gate.