Low Threshold Voltage and High Mobility N-Channel Metal-Oxide-Semiconductor Field-Effect Transistor Using Hf-Si/HfO2 Gate Stack Fabricated by Gate-Last Process

Systematic characterization of Hf-Si/HfO2 gate stacks revealed two mobility degradation modes. One is carrier scattering by fixed charges and/or trapped charges induced by the crystallization in the thick HfO2 case (inversion oxide thickness, T-inv > 1.6 nm). The other is the Hf penetration into the interfacial layer with the Si substrate in the thin HfO2 case (T-inv < 1.6 nm) for the Hf-rich electrode. It was demonstrated that careful optimization of the HfO2 thickness and the Hf-Si composition can suppress both modes. As a result, a high electron mobility equivalent to that of n(+)polycrystalline silicon (poly-Si)/SiO2 (248 cm(2) V-1 s(-1) at E-eff = 1 MV/cm) was obtained at T-inv of 1.47 nm. Moreover, the effective work function of the optimized Hf-Si/HfO2 gate stack is located within 50 mV from the Si band edge (E-c). An extremely high I-on of 1165 mu A/mu m (at I-off 81 nA/mu m) at V-dd 1.0 V was demonstrated for a 45 nm gate n-channel metal-oxide-semiconductor field-effect transistor (n-MOSFET) without strain enhanced technology. (C) 2010 The Japan Society of Applied Physics