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 (Ni 31Si12 and Nirich-Pt-Si). It is shown that the interface layer between gate suicide and dielectric is the key to modulate the workfunction due to Fermi level pining on HfSiO and HfO2. Ge, Yb, Pt, and A1 were fully explored to identify good candidates for N and PFET. A∼400meV workfunction shift was achieved toward the conduction band edge using NiAlSi demonstrating a mobility of 300 cm2Vs at peak, matching NiSi control devices on HfxSiOy, NirichPtSi has shown 4.85eV workfunction and good mobility. Different gate materials were fully explored to understand the mechanism of workfunction modulation depending on the dielectrics. It was found that the workfunction of metal rich suicides are strongly dependent on the pure metal workfunction and it can be changed by controlling the number of metal atoms which are available at the interface. © 2006 IEEE.