Electrical characteristics of Al contact to NiSi using thin W layer as a barrier

We show that the thermal instability that is observed in Schottky diodes with an Al film on NiSi contact to can be removed by introducing a very thin (~250 Å) tungsten film between the Al and the NiSi layers. This structure can be formed by sequential evaporation of Ni, W, and Al and subsequent thermal annealing to form NiSi. Schottky barrier measurements show that the contact is thermally stable at 450 °C up to about 1-h annealing with very little change in the electronic barrier height. A model, derived from the electrical measurements, is proposed for the failure mode of the tungsten barrier after excessive annealing.