We describe reverse bias diode leakage and physical analysis (secondary ion mass spectroscopy, Rutherford backscattering and transmission electron microscopy) data from shallowp+/njunctions made by implanting various doses of BF2into polycrystalline Si and out‐diffusing at various temperature/time conditions, into the underlying (100) Si substrate. The polycrystalline Si is cobalt disilicided to provide the first level of metallization. Subsequent metallization consists of electroless plated Co followed by sputtered Al. The minimum process specifications giving good junction quality (reverse bias diode leakage current density ≤10 nA/cm2at 10 V) are 5×1015cm−2BF2outdiffused at 900 °C, 30 min with a junction depth 1200 A˚ below the polycrystalline Si. At these conditions, most of the BF2(>90%) uniformly redistributes in the polycrystalline Si. There is a slight increase in B concentration towards the polycrystalline Si/Si interface which is characterized by a porous, <50‐A˚ thin silicon oxide interface. The polycrystalline Si/Si interface is also characterized by a peaked fluorine concentration. The lower boron dose diffusing into the Si substrate may be used to explain the observation that thesep+/ndiodes are ∼10 times leakier than similarn+/pdiodes made by outdiffusing As or P implanted from the polycrystalline Si diffusion source.