Damage enhancement in BF2+ ion-implanted silicon

The damage introduction rates of BF2+, B+ and F+ ions implanted into (100) bulk silicon have been investigated over the energy range 3 to 13 keV amu-1 at temperatures of 77 K and 300 K. The samples have been analysed using 2 MeV He+ Rutherford backscattering and channelling, and it is found that the damage created by BF2+ molecular ions is significantly greater than that created by an equivalent dose of the atomic species B+ and F+. This damage enhancement by the BF2+ ions can be separated into bulk effects, which are due to displacement spikes, and surface effects, caused by multiple collision sequences involving the constituent particles (B and F) after dissociation of the incident BF2+ ion. Similar surface damage enhancements of 1.8 and 1.9 are found at 77 K and 300 K respectively, for particle energies of 3 keV amu-1. The energy dependence of the surface enhancement factor shows a strong dependence upon ion energy reaching a maximum of 3.5 at 8 keV amu-1 but approaches unity at higher energies. (Author)