Accurate investigation of the high-k soft phonon scattering mechanism in metal gate MOSFETs

We report an experimental study of the mobility in TiN/HfO₂ gate stacks focused on the accurate determination of the HfO₂ remote soft phonon scattering mechanism. The high-K intrinsic mechanism is clearly dissociated from Coulomb scattering which generally dominates the mobility degradation in high-K/metal gate stacks. The temperature dependence of this additional phonon scattering mechanism is nearly linear. This scattering mechanism is shown to be negligible with a metal gate for a SiO_x interfacial layer (IL) thicker than 9-10Å. For a IL thickness of 7˚A, this mechanism degrades the electron mobility at high effective fields by ∼16% at 300K and ∼13%at 400K.