High-κ/metal-gate stack and its MOSFET characteristics

We show experimental evidence of surface phonon scattering in the high-kappa dielectric being the primary cause of channel electron mobility degradation. Next, we show that midgap TiN metal-gate electrode is effective in screening phonon scattering in the high-kappa dielectric from coupling to the channel under inversion conditions, resulting in improved channel electron mobility. We then show that other metal-gate electrodes, such as the ones with n+ and p+ work functions, are also effective in improving channel mobilities to close to those of the conventional SiO2/poly-Si stack. Finally, we demonstrate this mobility degradation recovery translates directly into high drive performance on high-kappa/metal-gate CMOS transistors with desirable threshold voltages.