More than ten years have passed since cluster ion implantation was proposed by Kyoto University. Cluster ion implanters equipped with a specially designed ion source are announced for device manufacturing. This technique is now a candidate for ultra shallow junction formation in the ITRS Road Map [1]. It is essential to understand the atomistic mechanism of cluster implantation, because the behavior of damaged atoms during annealing is a very important topic for high-quality shallow junction formation. The damage induced with cluster ions is presented. ©2007 IEEE.