Mitigation of Dopant Deactivation in Heavily Phosphorus-Doped Silicon via Nitrogen Co-Implantation

Abstract

This paper investigates the mitigation of dopant deactivation in heavily phosphorus-doped silicon via phosphorus-nitrogen co-implantation. Dopant-vacancy complexes formed during sequential thermal processes are responsible for a reduction in carrier concentration, thereby narrowing the thermal process window. Nitrogen preferentially binds vacancies relative to phosphorus. Therefore, co-implantation suppresses the formation of phosphorus-vacancy complexes. Hall measurements show reduced deactivation in co-implanted samples. FTIR identifies features consistent with N2V2 formation at higher annealing temperatures. Raman spectroscopy shows reduced intensity of the 520 cm−1 c-Si peak in co-implanted samples, consistent with a degraded crystallinity and reduced mobility. SIMS shows broader phosphorus profiles after the second anneal, with slightly greater broadening in co-implanted samples, and a mid-depth nitrogen signal drop attributable to matrix effects on ion yield. TEM images show additional near-surface dark-contrast features in the co-implanted samples, qualitatively consistent with residual defects or local strain fields. These results indicate that nitrogen co-implantation mitigates deactivation under practical thermal budgets, albeit introducing a trade-off in carrier transport due to impurity/defect scattering.