Modulation of the workfunction of Ni fully silicided gates by doping: dielectric and silicide phase effects

A systematic study of the modulation of the workfunction (WF) of Ni fully silicided gates by doping is presented, comparing the effects of dopants (Al, B, undoped, P, and As) on the WF for different dielectrics (SiO₂ versus HfSiON) and silicide phases (NiSi, Ni₂Si and Ni₃₁Si₁₂). Dual thickness series (HfSiON/SiO₂) were used to extract accurate WF values accounting for charge effects on HfSiON. While a WF modulation in the range of ∼0.4 V was obtained for NiSi on SiO₂ comparing As, P, and B doped and undoped devices, negligible modulation was obtained for NiSi on HfSiON (≤50 mV) suggesting Fermi-level pinning, and for the Ni-rich silicides on SiO₂ (≤100 mV). Dopant pileup at the dielectric interface, believed to be responsible for the NiSi/SiO₂ WF modulation, was, however, observed for both NiSi and Ni-rich silicides. In contrast the WF of Ni-rich silicides on SiO₂ can be modulated with Al, suggesting a different mechanism of WF tuning for Al compared to B, P, and As.