INVESTIGATION OF MECHANISMS OF VACANCY GENERATION IN SILICON IN THE PRESENCE OF A TISI2 FILM

We have determined the perturbance in the silicon vacancy concentratio n induced by the presence of TiSi2 films. Antimony in silicon doping s uperlattices was employed as a vacancy detector. Under all conditions studied (deposited titanium thickness 4-312 nn, 800-850 degrees C, 15- 600 min), we always observe a relative vacancy supersaturation on the order of 1.5. Two mechanisms of vacancy injection during titanium sili cidation were studied: (1) stress compensation; by varying the thickne ss of the deposited films and annealing for 60 min at 850 degrees C, a range of stresses was induced in the substrate via the coefficient of thermal expansion mismatch between the film and substrate. The observ ed vacancy supersaturation was independent of film thickness, indicati ng that stress compensation is not a mechanism of vacancy generation f or titanium disilicide; (2) volume contraction; annealing for 15, 60, and 600 min at 800 degrees C after identical 30-nm-thick titanium film s were deposited allowed the time variation of the vacancy supersatura tion to be studied. While the vacancy supersaturation decayed slightly with time, its time dependence is incompatible with a large ''pulse'' of vacancies injected during the silicidation reaction. This indicate s that volume contraction at the growing film interface is not a mecha nism for vacancy generation. The thicker TiSi2 films (>22 nm) and thos e annealed for less than or equal to 60 min were continuous in their c overage of the substrate as observed by transmission electron microsco py, while the thinner films and those annealed for longer times had is landed. However, there was no relationship between film coverage and v acancy behavior in the substrate, or was there any relation between de position method (evaporation versus sputtering) and vacancy behavior. (C) 1997 American Institute of Physics.