Effect of Ultra-Thin Mo and MoSi sub x Layer on Ti Silicide Reaction

The presence of a small amount of Mo was shown to have a significant effect on the C49-TiSi sub 2 to C54-TiSi sub 2 phase transformation in the Ti-Si reaction. The formation of the C54-TiSi sub 2 phase was facilitated when an ultrathin layer of either Mo or alpha-MoSi sub x was inserted at or close to the Ti/Si interface. Mo deposited on the surface of Ti had no beneficial effect on the Ti silicide reaction; neither did Mo implanted into pre-existing C49-TiSi sub 2 films. The optimum thickness of interfacial Mo and alpha-MoSi sub x layers was found to be less than 0.3 nm. Transmission electron microscopy and diffraction investigations demonstrated that Mo did not alter the sequence of the Ti-Si reaction, as proposed in recent studies. Rather, the most obvious effect of molybdenum was a reduction of the grain size of the C49-TiSi sub 2 phase, which could lead to an increase in the nucleation density of the desired C54-TiSi sub 2 phase and account for the observed reduction in formation temperature.