B activation and F redistribution in low energy BF2+ implanted silicon

In this work the effect of BF2+ energy on dopant activation and fluorine redistribution following thermal processes has been studied in the low energy range (10 to 35 keV). The effect of increased beam current on implant profiles has also been investigated. The crystal quality of the implanted layers and element depth profiles following thermal processes have been studied by HR-XTEM and dynamic SIMS respectively. The dopant activation and carrier mobility as function of depth has been determined by differential Hall and spreading resistance measurements. For the 35 keV implanted wafers, results show sharp segregation of F with formation of precipitates (ppts) around the Rp of the as implanted profile and at the original amorphous/crystalline (a/c) interface. It was also found that molybdenum sputtered in the source are chamber and co-implanted with BF2 segregates together with F. B diffusion is unaffected by the presence of these precipitates. For the 10 keV implanted wafers instead, no segregation of fluorine is found. Hall measurement analysis shows that the fluorine trapped in the layers and the presence of precipitates do not affect the carrier mobility in the high temperature annealed wafers.