The influence of selective tungsten deposition on shallow junction leakage

The authors report on the onset of reverse bias diode leakage induced by CVD selective tungsten deposition on (a) shallow n/sup +/(As)/p diodes made by implantation into silicon and (b) n/sup +/(As or P)/p or p/sup +/(BF/sub 2/)/n diodes made by implantation into CoSi/sub 2/. Tungsten, nominally 1000A thick, was selectively deposited in a hot wall tubular reactor using either a one-step or a two-step deposition sequence at 2900C. The n/sup +/(As)/p junctions show an increase in leakage population after tungsten deposition, as the junction depth decreases. The two-step process was found to produce greater leakage in shallow n/sup +/(As)/p junctions than the one-step process. Arsenic implanted junctions show severe degradation in the leakage distribution of shallow diodes beneath CoSi/sub 2/. In contrast to arsenic, shallow junctions made by outdiffusion of phosphorus or boron implanted into CoSi/sub 2/ do not show significant changes in leakage population after selective tungsten deposition. Junction leakage measurements, and their temperature dependence, is correlated with transmission electron micrographs