Activation improvement of ion implanted boron in silicon through fluorine co-implantation

In this study, boron diffusion and activation characteristics of samples implanted with F co-implantation were studied to meet the challenge of lower sheet resistance. Samples were implanted with F co-implantation in a dose range of 0 (no F) to 5×1015 cm−2, at a fixed energy of 25 keV, followed by 950 °C/10 s rapid thermal annealing. It was found that although the fluorine has a negligible affect on the boron diffusion at the specified conditions, a higher F dose reduced the boron sheet resistance. Using reverse modeling, the boron solid solubility at 950 °C was extracted as function of the F co-implant concentration. For low fluorine doses (0–1×1014 cm−2), the boron solid solubility is similar to that reported in the literature (9×1019 cm−3). At higher doses, boron solid solubility increased by 25% and even 50% for F co-implantation doses of 1×1015 and 5×1015, respectively. We suggest that the F co-implantation terminates some of the defects created by the implantation, inactivating the defects and improving boron activation.