Work function of Ni silicide phases on HfSiON and SiO/sub 2/: NiSi, Ni/sub 2/Si, Ni/sub 31/Si/sub 12/, and Ni/sub 3/Si fully silicided gates

Abstract

A complete determination of the effective work functions (WF) of NiSi, Ni/sub 2/Si, Ni/sub 31/Si/sub 12/ and Ni/sub 3/Si on HfSiON and on SiO/sub 2/ is presented. Conditions for formation of fully silicided (FUSI) gates for NiSi/sub 2/, NiSi, Ni/sub 3/Si/sub 2/, Ni/sub 2/Si, Ni/sub 31/Si/sub 12/ and Ni/sub 3/Si crystalline phases were identified. A double thickness series (HfSiON/SiO/sub 2/) 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 SiO/sub 2/. While all Ni-rich silicides have adequate WF for pMOS applications, Ni/sub 2/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 Ni/sub 2/Si and Ni/sub 31/Si/sub 12/ FUSI HfSiON pMOSFETS.