STRESS-INDUCED PRECIPITATION OF DOPANTS DIFFUSED INTO SI FROM TISI2 AND COSI2 IMPLANTED LAYERS

As, P and B ions were implanted into TiSi2 and CoSi2 thin layers and s ubsequently diffused into the underlying silicon substrate either by a rapid thermal process or by a long annealing in a furnace. For all th e species, shallow junctions (20-400 nm depth) were obtained with a hi gh dopant concentration (10(19)-10(20) cm-3) at the silicide/silicon i nterface. In the case of As, the comparison between the amount of diff used substitutional arsenic and the carrier profile indicates the pres ence of inactive substitutional atoms at the silicide/silicon interfac e. These As atoms form coherent precipitates at the silicide/silicon i nterface as evidenced by transmission electron microscopy cross sectio ns. Precipitates were also found for P and B dopants, but for this lat ter species they were located inside the silicon substrate at 30 nm fr om the interface. The precipitate formation has been associated with t he high tensile stress induced by the silicide layer on the surface si licon region and to its influence on the solid solubility of the dopan t. The precipitate density decreases if the silicide thickness is redu ced, i.e. if the tensile stress produced by silicide layer becomes low er. These precipitates are easily dissolved during high-temperature an nealing after removal of the silicide layer.