Effects of Cobalt Silicidation on the Electrical Characteristics of Shallow p*n Junctions Formed by Implantation into Thin Polycrystalline Si Films

Excellent shallow p+n junctions have been formed by implanting BF~ ions into thin polycrystalline Si films and subsequent annealing. The samples implanted at 50 keV to a dose 5 x i0 I~ cm -2 show a leakage of i nA/cm 2 and a junction depth of about 0.05 ~m after a 800~ annealing. To reduce the series resistances of the junctions, silicidation with different cobalt thickness was used to drive the as-implanted dopants in the polysilicon films into the resultant junctions of the silicon substrates. For the low energy implantation at 50 keV at all dosages, silicidation can result in poor electrical characteristics due to the confinement of the dopants by the silieidation process. On the other hand, the electrical characteristics can be retained when a higher implantation energy of i00 keV with a dosage higher than 5 x I0 I~ cm -2 was used. In addition, the samples implanted at 125 keV show poor electrical characteristics for the nonsilicided junctions but good characteristics after the silieidation. It is attributed to the enhanced defect annihilation by the formed silicide. Furthermore, silicided implanted through poly-Si junctions with excellent characteristics can be fabricated after a low temperature (600~ annealing if the samples are implanted at i00 keV with a dosage higher than 5 x i015 cm -2.