Charge trapping induced frequency-dependence degradation in n-MOSFETs with high-k/metal gate stacks

This letter investigates the reliability issues of HfO2/Ti1 − xNx metal-oxide-semiconductor field effect transistor in terms of static and dynamic stress. The results indicate threshold voltage (Vth) instability under dynamic stress is more serious than that under static stress, owning to transient charge trapping within high-k dielectric. Capacitance–voltage techniques verified that electron trapping under dynamic stress was located in high-k dielectric near the source/drain (S/D) overlap region, rather than the overall dielectric. Furthermore, the Vth shift clearly increases with an increase in dynamic stress operation frequency. This phenomenon can be attributed to the fact that electrons injecting to the S/D overlap region have insufficient time to de-trap from high-k dielectric. We further investigated the impact of different Ti1 − xNx composition of metal-gate electrode on charge trapping characteristics, and observed that Vth shift decreases significantly with an increase in the ratio of nitride. This is because the nitride atoms diffusing from the metal gate fill up oxygen vacancies and reduce the concentration of traps in high-k dielectric.