Cluster ion implantation using small boron cluster, decaborane (B10H14), has been proposed as the solution for shallow junction formation. Investigation of damage formation process by low-energy ion impact is important issue because diffusion and activation mechanism of dopant depend on the structure of defects in the substrate. In order to study difference of damage characteristics between monomer and cluster implantation, the molecular dynamics simulation of low-energy boron monomer and cluster (such like B4, B8 and B10) implantation into silicon substrate were performed. Additionally damage induced by boron monomer and cluster ion beam implantation is examined using RBS channeling method. From both simulation and experimental results, the amount and structure of defects caused by boron monomer/cluster implantation were discussed.