Analysis of electron mobility in HfO2/TiN gate metal-oxide-semiconductor field effect transistors: The influence of HfO2 thickness, temperature, and oxide charge

Abstract

We report a new analysis of electron mobility in HfO2/TiN gate metal-oxide-semiconductor field effect transistors (MOSFETs) by investigating the influence of HfO2 thickness (1.6–3 nm), temperature (50–350 K), and oxide charge (∼1×1011–8×1012 cm−2) in the high inversion charge region. The fixed oxide charge and interface state densities are deliberately increased using negative-bias-temperature stress, allowing the determination of the Coulomb scattering term as a function of temperature for various oxide charge levels. The temperature dependence of the Coulomb scattering term is consistent with the case of a strongly screened Coulomb potential. Using the experimentally determined temperature dependence of Coulomb scattering term, a model is developed for the electron mobility, including the effects oxide charge (μC), high-k phonon (μPh-Hk), silicon phonon (μPh-Si), and surface roughness scattering (μSR). The model provides an accurate description of the experimental data for variations in HfO2 thickness, temperature, and oxide charge. Using the model the relative contributions of each mobility component are presented for varying oxide charge and high-k thickness. Scaling of the HfO2 physical thickness provided a reduction in the oxide charge and high-k phonon scattering mechanisms, leading to an increase in electron mobility in HfO2/TiN gate MOSFETs.