EVALUATION OF ANOMALIES DURING NICKEL AND TITANIUM SILICIDE FORMATIONUSING THE EFFECTIVE HEAT OF FORMATION MODEL

The effective heat of formation model allows heats of formation to be calculated as a function of the concentration of the reactants at the growth interface. The effective concentration is taken to be the conce ntration of the liquidus minimum for the relevant binary system. Using this model, the anomalous and contradictory results for initial forma tion of titanium silicide phases are ascribed to the two eutectics at 14 and 84 at.% silicon (both at 1330 degrees C) for the Ti-Si binary s ystem. The native oxide layer usually present on silicon surfaces and the affinity of Ti for oxygen further affect the effective concentrati on, thereby adding to the contradictory experimental results that have been found. In the Ni-Si system our measurements show that a sufficie ntly high concentration of oxygen in amorphous silicon can lead to for mation of NiSi instead of Ni2Si, which is normally the first phase to form. This observation, as well as the formation of NiSi2 as the first phase in the presence of diffusion barriers, is also explained in ter ms of the effective heat of formation model.