Work function of Ni silicide phases on HfSiON and SiO2: NiSi, Ni2Si, Ni31Si12, and Ni3Si fully silicided gates

A complete determination of the effective work functions (WF) of NiSi, Ni2Si, Ni31Si12 and Ni3Si on HfSiON and on SiO2 is presented. Conditions for formation of fully silicided (FUSI) gates for NiSi2, NiSi, Ni3Si2, Ni2Si, Ni31Si12 and Ni3Si crystalline phases were identified. A double thickness series (HfSiON/SiO2) was used to extract WF on HfSiON accounting for charge effects. A strong effect on WF of Ni content is observed for HfSiON, with higher WF for the Ni-rich silicides suggesting unpinning of the Fermi level. A mild dependence is observed for SiO2. While all Ni-rich silicides have adequate WF for pMOS applications, Nit Si is most attractive due to its low formation temperature, lower volume expansion and ease of integration. Similar threshold voltages (-0.3 V) were obtained on Ni2Si and Ni,, Sit, FUSI HfSiON pMOSFETS.