TISI2 PHASE-TRANSFORMATION CHARACTERISTICS ON NARROW DEVICES

Accurate prediction of TiSi2 transformation requires test structures w ith small silicided surface areas. To evaluate the area dependence of the C49 to C54 transformation, a new monitor was developed with minima l silicide surface area. Small area structures were found to exhibit a bimodal resistance distribution that was nearly insensitive to proces s transformation conditions. Starvation for C54 nucleation sites resul ted in a high frequency of non-transformation even at high annealing t emperatures. Transmission electron microscopy analysis showed that the Ti silicide in these structures is either C49 or C54 phase, with litt le or no mixed phases present. A cooperative C54 nucleation mechanism is proposed to explain this phenomena. The presence of small quantitie s of a molybdenum impurity such as molybdenum during silicide formatio n has been found to increase the availability of C54 forming nuclei by two orders of magnitude. The molybdenum acts as a catalyst and does n ot require interface mixing or the creation of an amorphous Si layer t o enhance nucleation The addition of molybdenum has been demonstrated to eliminate the bimodal resistance distribution.