Tunable Workfunction for Fully Silicied Gates (FUSI) and Proposed Mechanisms

We present fully silicided gate (FUSI) work function modulation and mechanisms using different NiSi alloys as well as different phases (Ni₃₁Si₁₂ and Ni_rich-Pt-Si). It is shown that the interface layer between gate silicide and dielectric is the key to modulate the work function due to Fermi level pining on HfSiO and HfO₂. Ge, Yb, Pt, and Al were fully explored to identify good candidates for N and PFET. A ~400meV work function shift was achieved toward the conduction band edge using NiAlSi demonstrating a mobility of 300 cm₂/Vs at peak, matching NiSi control devices on Hf_xSiO_y. Ni_richPtSi has shown 4.85eV work function and good mobility. Different gate materials were fully explored to understand the mechanism of work function modulation depending on the dielectrics. It was found that the work function of metal rich silicides are strongly dependent on the pure metal work function and it can be changed by controlling the number of metal atoms which are available at the interface