CoSi2 full silicidation (FUSI) of doped poly-Si metal gates was investigated to further the understanding of the modulation of effective work function from dopants in CoSi2 and NiSi FUSI gated metal oxide semiconductor devices. By using a TiN-capping layer to manipulate the dopant distribution, dopants have been confirmed to be effective in tuning the work function for both CoSi2 and NiSi. However, from the drastic reduction of the As tuning effect in CoSi2, we understand that the amount of effective work function tuning is not only directly dependent on the interfacial dopant concentration, but the mechanism of dopant tuning the work function is strongly dependent of the bulk material type. (C) 2005 The Electrochemical Society.