Improvement of P–N Junction Leakage and Reduction in Interface State Density in Transistors by Cryo Implantation Technology

Abstract

Cryo implantation by a rapid thermal annealing process was applied to achieve defect-free shallow junctions. Boron ions were implanted in (100) Si substrates cooled using liquid nitrogen, with temperature controlled at -160 °C or lower during ion implantation. It was found that an amorphous layer was formed by boron implantation and that the amorphous layer completely recovered to single crystals after annealing at 900 °C for 30 s. No dislocation was observed in the implanted layer. It was also found that the thermal diffusion of boron was suppressed by cryo implantation. Furthermore, cryo implantation was found to be very effective in reducing the density of defects, and P–N junction leakage was reduced by one order of magnitude compared with that in the case of room temperature implantation. These results suggest that the transient enhanced diffusion of boron can be reduced by suppressing vacancy migration toward the surface during implantation. Moreover, the substrate-cooling effect is very effective for improving surface roughness, and it is a very effective technology not only for reducing Si/SiO2 interface state density but also for improving the reliability of gate oxide.