Modulation of the effective work function of fully-silicided (FUSI) gate stacks

A systematic analysis of the different methods of work function (WF) tuning for gate stacks using fully silicided (FUSI) gate electrodes is presented. We show that FUSI gates have the potential to meet the WF requirements for future nodes, including high performance applications, achieving band edge WF, with total WF range of up to ∼900 meV. The introduction of dopants (such as Sb, As, P, B) by ion implantation is shown to be effective to tune the WF of NiSi or Ni3Si2 on SiO2 or SiON by ∼550 meV, but is ineffective on HfSiON or for Ni-richer silicides. Different silicide phases can be used for Ni FUSI gates on HfSiON dielectrics, taking advantage of the higher WF of metal-rich silicides, achieving a WF range of ∼400 meV. This method is not effective, however, on SiON dielectrics. The introduction of Lanthanides by several techniques (such as dielectric cap deposition, ion implantation into poly-Si, or at metal deposition) that result in the modification of the dielectric, is found, for Ni FUSI gates, to achieve low WF (∼4.0 eV) suitable for NMOS. Similarly, incorporation of Al can be used to achieve PMOS type WF, as well as the use of metal-rich Ni and/or Pt based FUSI gates (with WF as high as 5.0 eV).