Cluster ion implantation using decaborane (B10H14) has been proposed as a useful technique for shallow junction formation. In order to examine the characteristics and advantages of cluster ion implantation, molecular dynamics simulations of small B cluster and monomer implantation were performed. B1, B4 and B10 are irradiated on Si (001) substrates with acceleration energy of 230 eV/atom so that B4 and B10 are accelerated with 0.92 keV and 2.3 keV, respectively. Those three show the same implant profile and implant efficiency, which agrees with the experimental result of B10H14 implantation. This result suggests that each B atom in a B cluster acts individually in similar way to a monomer ion. B clusters show the same properties in projection range and implant efficiency as the monomer whereas non-linearity is shown in damage formation. The number of displacements by one B atom once increases to the same maximum value for both a B cluster and a B monomer. However, the damage recovery process is different depending on the cluster size. Damage induced by B10 recovers more slowly and 4 times as many displacements remain compared to B1 8 ps after impact. These displacements by B10 clusters concentrate in the near surface region of the impact point, while the ones by B1 reside around the implanted B atom as the end-of-range damage. This characteristic damage formation by B10 cluster is expected to avoid transient-enhanced-diffusion of incident B atoms and achieve the formation of high-quality shallow p-type junction.