Defects produced in Si p + n diodes by B+ implantation at liquid nitrogen temperature or −60 °C

Defects induced by B+ implantation (35 keV) at liquid-nitrogen (LN) temperature and −60 °C are examined using transmission electron microscopy (TEM), secondary-ion-mass spectroscopy, and electrical characterization of p+n diodes. B+ implantation at LN temperature produces a 120-nm-thick amorphous layer with a residual surface crystalline region. B+ implantation at −60 °C does not produce an amorphous layer, but damage can be observed as a dark band at the depth of B+ projected range Rp. For RT implantation, cross-sectional transmission electron microscopy reveals no visible damage in contrast to implantation at −60 °C. Frenkel-pair diffusion and annihilation is suppressed during implantation at the low temperature. The damage accumulates to form an amorphous layer for LN temperature. At −60 °C, the defects are confined near Rp. After annealing at 1000 °C for 10 min, near-surface and depth-encountering solid-phase-epitaxy dislocation-loop defects are observed in the sample implanted at LN temperature. The density of these is about several 108 cm−2, which is 10 or 100 times smaller than samples implanted at higher temperature. The annealed samples implanted at −60 °C and RT are mainly 〈111〉-plane directed defects and dislocation loops, respectively. Corresponding to the degree of as-implanted damage, the defects distribute at a shallower depth in the sample implanted at −60 °C than at RT, and have about 10 times higher density. The leakage current characteristics of p+n diodes indicate that the LN temperature and −60 °C implanted samples have lower leakage than RT samples at all annealing conditions. Notably, at 1000 °C for 10 min the leakage current is reduced to 56%. This is consistent with the result of TEM analysis; thus, the defect confinement to shallow layer by cooling contributes to lower the leakage current. Implantation at −60 °C is suitable for modern high-current implanters, due to practical coolant and less mechanical stress by thermoplasticity.