Improved Re-Crystallization of p+ Poly-Si Gates with Molecular Ion Implantation

Implantation of B18H22 molecules at 80 keV and doses up to 4X1016 cm-2 were evaluated for the application of p-type counterdoping of in situ n-type doped polysilicon gates. Compared to conventional B implants, molecular implantation provides greatly improved throughput without the risk of energy contamination. Implants at these high doses resulted in poor re-crystallization of the polysilicon layer due to the formation of excessive cluster-type defects. Subjecting the polysilicon to either UV-curing or low temperature soak annealing prior to dopant activation was not effective in improving the re-crystallization process. However, breaking the dose into two portions at two different energies was shown to significantly improve re-crystallization of the polysilicon layer. Improved dopant activation was confirmed by a > 90% reduction in ring oscillator delay time on a 60 nm PMOSFET.