ROLE OF IMPLANTATION-INDUCED DEFECTS IN SURFACE-ORIENTED DIFFUSION OFFLUORINE IN SILICON

Open-volume defects introduced in Si(100) crystals during fluorine imp lantation were investigated by variable-energy positron beam depth pro filing. The behavior of the implantation-induced lattice defects upon high temperature annealing and their role in the surface-oriented diff usion of F impurities were examined. The defects become mobile and und ergo recovery at temperatures below 550 degrees C, i.e., well before t he onset of fluorine diffusion as seen by secondary ion mass spectrosc opy (SIMS) profiling. This behavior suggests that after irradiation an d annealing the fluorine occupies substitutional sites to which positr ons are insensitive. The anomalous F diffusion seen in SIMS has been e xplained through a two-step diffusion mechanism, in which the diffusio n kinetics is determined by dissociation of the substitutional F into an interstitial F and a vacancy, followed by a rapid diffusion of the interstitial F and the vacancy through the crystal to the surface.