Investigation of mechanisms of vacancy generation in silicon in the presence of a TiSi2 film

Abstract

We have determined the perturbance in the silicon vacancy concentration induced by the presence of TiSi2 films. Antimony in silicon doping superlattices was employed as a vacancy detector. Under all conditions studied (deposited titanium thickness 4–312 nm, 800–850 °C, 15–600 min), we always observe a relative vacancy supersaturation on the order of 1.5. Two mechanisms of vacancy injection during titanium silicidation were studied: (1) stress compensation; by varying the thickness of the deposited films and annealing for 60 min at 850 °C, a range of stresses was induced in the substrate via the coefficient of thermal expansion mismatch between the film and substrate. The observed vacancy supersaturation was independent of film thickness, indicating that stress compensation is not a mechanism of vacancy generation for titanium disilicide; (2) volume contraction; annealing for 15, 60, and 600 min at 800 °C after identical 30-nm-thick titanium films were deposited allowed the time variation of the vacancy supersaturation 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 indicates that volume contraction at the growing film interface is not a mechanism for vacancy generation. The thicker TiSi2 films (>22 nm) and those annealed for ⩽60 min were continuous in their coverage of the substrate as observed by transmission electron microscopy, while the thinner films and those annealed for longer times had islanded. However, there was no relationship between film coverage and vacancy behavior in the substrate, or was there any relation between deposition method (evaporation versus sputtering) and vacancy behavior.