Anomalous positive-bias temperature instability of high-κ/metal gate devices with Dy_2O_3 capping

摘要

Substantial V_t modulation of 150-220 mV in n-type metal-oxide-semiconductor devices without mobility degradation is possible by inserting a 1 nm Dy_2O_3 cap between the HfSiON and TaN metal gate. However, in the Dy_2O_3-capped devices we observe an anomalous positive-bias temperature instability behavior where the threshold voltage (V_t) decreases substantially during the electrical stress and eventually saturates. The stress polarity effect, the strong temperature dependence, full recovery, and the response to hot carriers suggest that two competing physical mechanisms are responsible for the V_t behavior-diffusion of preexisting positively charged species dominating at high temperature and electron trapping dominating at low temperature. The charged species are likely located in the mixed high-κ dielectric and associated with the interaction between the host dielectric, cap, and metal gate.