Doping characteristics of BF/sub 2//sup +/ implants in <100> and <111> silicon

Significant differences were noticed between doping characteristics of BF/sub 2//sup +/ implanted [100] and [111] silicon. High dose BF/sub 2//sup +/ implants always produced higher sheet resistance (R/sub s/) in [111] silicon. Compared to B/sup +/, the BF/sub 2//sup +/ implants exceeding the amorphization dose always resulted in higher R/sub s/ regardless of silicon orientation, Behavior was attributed to fluorine gettered at implant-induced defect sites. Sheet resistance of an F/sup +/+B/sup +/ implanted layer was found to increase linearly with F/sup +/ dose. Residual fluorine content decreased with temperature, especially for [111] orientation, and coincided with a decrease in R/sub s/. Effects of fluorine and crystal damage were separated experimentally and correlated to R/sub 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 BF/sub 2//sup +/ implanted samples.