INFLUENCE OF SELECTIVE TUNGSTEN DEPOSITION ON SHALLOW JUNCTION LEAKAGE.

We report on the onset of reverse bias diode leakage induced by CVD selective tungsten deposition on (a) shallow n** plus (As)/p diodes made by implantation into silicon and (b) n** plus (As or P)/p or p** plus (BF//2)/n diodes made by implantation into CoSi//2. Tungsten, nominally 1000 Armstrom thick, was selectively deposited in a hot wall tubular reactor using either a one-step or a two-step deposition sequence at 290 degree C. The n** plus (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** plus (As)/p junctions than the one-step process. Arsenic implanted junctions show severe degradation in the leakage distribution of shallow diodes beneath CoSi//2. In contrast to arsenic, shallow junctions made by outdiffusion of phosphorus or boron implanted into CoSi//2 do not show significant changes in leakage population after selective tungsten deposition. Junction leakage measurements, and their temperature dependence, will be correlated with transmission electron micrographs.