Abnormal threshold voltage shift under hot carrier stress in Ti_(1-x)N_x/HfO_2 p-channel metal-oxide-semiconductor field-effect transistors

摘要

This work investigates the channel hot carrier (CHC) effect in HfO_2/Ti_(1-x)N_x p-channel metal oxide semiconductor field effect transistors (p-MOSFETs). Generally, the subthreshold swing (S.S.) should increase during CHC stress (CHCS), since interface states will be generated near the drain side under high electric field due to drain voltage (V_d). However, our experimental data indicate that S.S. has no evident change under CHCS, but threshold voltage (V_(th)) shifts positively. This result can be attributed to hot carrier injected into high-k dielectric near the drain side. Meanwhile, it is surprising that such V_(th) degradation is not observed in the saturation region during stress. Therefore, drain-induced-barrier-lowering (DIBL) as a result of CHC-induced electron trapping is proposed to explain the different V_(th) behaviors in the linear and saturation regions. Additionally, the influence of different nitrogen concentrations in HfO_2/Ti_(1-x)N_x p-MOSFETs on CHCS is also investigated in this work. Since nitrogen diffuses to SiO_2/Si interface induced pre-N_(it) occurring to degrades channel mobility during the annealing process, a device with more nitrogen shows slightly less impact ionization, leading to insignificant charge trapping-induced DIBL behavior.