The process scheme that forms NiSi-silicided shallow p ϩ n junctions by BF 2 ϩ implantation into thin amorphous-Si (a-Si) or Ni/a-Si films on Si substrates and subsequent Ni silicidation has been studied. As for the scheme using a-Si as an implantation barrier, an NiSi-silicided junction with a leakage of about 0.7 nA/cm 2 at Ϫ5 V is obtained by the sample Ni silicided at 700°C for 30 min. The implantation energy and the crystallinity of the deposited Si films after annealing would greatly

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... t the junctions formed at various temperatures, attributable to different implantation effects and boron depth profile. However, the junctions formed by rapid thermal processing or high implant energy are considerably degraded at 800°C, attributable to anomalous Ni penetration into the Si substrate with the further silicidation of NiSi into NiSi 2 . On the other hand, the specimens with Ni/a-Si as an implantation barrier sustain few defects, thus significantly suppressing the junction degradation at 800°C. However, the formed junctions are worse than those by the former scheme, mainly due to lower dopant drive-in efficiency.