Process optimization for high electron mobility in nMOSFETs with aggressively scaled HfO₂/metal stacks

The performance of aggressively scaled (4 nm < Tinv < 2.1 nm) self-aligned HfO2-based nMOSFETs with various metal gate electrodes (W, TaN, TiN, and TaSiN) is optimized. It is shown that high mobility values, competitive with oxynitride controls (SiON/poly-Si, Tinv ∼ 1.8 - 2.1 nm), can be achieved. Detailed studies of the role of interface states, remote charges in the HfO2 layer, interfacial layer regrowth, and nitrogen-induced charge lead to the conclusion that high-temperature-induced structural modifications near the SiO2/HfO2 interface substantially improve the electron mobility. © 2006 IEEE.