Formation kinetics and work function tuning of Pd2Si fully silicided metal gate

The formation kinetics of Pd2Si for fully silicided (FUSI) gate formation and the work function tuning of a Pd2Si FUSI gate by impurity predoping were investigated. It has been found that the morphology and phase of a formed FUSI layer depend not only on the silicidation annealing temperature but also on the heating ramp-up rate and the presence of impurities. Fast ramp-up annealing was necessary to avoid defect formation, such as voids in the silicide film at the oxide interface, and to obtain a homogeneous silicide film containing only Pd2Si phase. The most severe effect on the silicidation reaction, that is the increase in defect formation, was brought about by As predoping. The work function of the Pd2Si FUSI gate was modulated by impurity pileup at the Pd2Si/SiO2 interface, as in the case of the NiSi FUSI gate. However, the work function shifted in the opposite direction to that of the NiSi FUSI gate for As, P, Sb, and BF2. A wide range of work function shift, comparable to that of the NiSi FUSI gate, has been obtained for a Pd2Si FUSI gate.