Doping characteristics of BF2+ implants in ⟨100⟩ and ⟨111⟩ silicon

Significant differences were noticed between doping characteristics of BF2+ implanted (100) and (111) silicon. High lose BF2+ implants always produced higher sheet resistance (R-s) in (111) silicon, Compared to B+, the BF2+ implants exceeding the amorphization dose always resulted in higher R-s regardless of silicon orientation. Behavior was attributed to fluorine gettered at implant-induced defect sites, Sheet resistance of an F+ + B+ implanted layer was found to increase linearly with F+ dose. Residual fluorine content decreased with temperature, especially for (111) orientation, and coincided with a decrease in R-s. Effects of fluorine and crystal damage were separated experimentally and correlated to R-s of implanted layers. SIMS analysis revealed that fluorine segregated at two peaks in (111) silicon and four peaks in (100) silicon, Experimental results suggest that gettered fluorine and boron-fluorine bonds formed at heavily damaged crystal sites prevent boron from its full electrical activation in BF2+ implanted samples.