Molecular Dynamics (MD) and Metropolis Monte-Carlo (MMC) models of monomer B and decaborane implantation into Si and following rapid thermal annealing (RTA) processes have been developed in this paper. The implanted B dopant diffusion coefficients were obtained for different substrate temperatures. The simulation of decaborane ion implantation has revealed the formation of an amorphized area in a subsurface region, much larger than that of a single B+ implantation, with the same energy per ion. The B diffusion coefficient shows an unusual temperature dependence with two different activation energies. Low activation energy, less than 0.2, was obtained for a low-temperature region, and a higher activation energy, ˜ 3 ev, for a higher-temperature region which is typical for the RTA processing. The higher activation energy is comparable with the equilibrium activation energy, 3.4 ev, for B diffusion in Si.