Effect of ultrathin Mo and MoSix layer on Ti silicide reaction

The presence of a small amount of Mo was shown to have a significant effect on the C49-TiSi2 to C54-TiSi2 phase transformation in the Ti-Si reaction. The formation of the C54-TiSi2 phase was facilitated when an ultrathin layer of either Mo or alpha-MoSix 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 preexisting C49-TiSi2 films. The optimum thickness of interfacial Mo and alpha-MoSix 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-TiSi2 phase, which could lead to an increase in the nucleation density of the desired C54-TiSi2 phase and account for the observed reduction in formation temperature. (C) 1999 American Institute of Physics. {[}S0021-8979(99)01614-X].