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 dose 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