Amorphization process associated with cluster implants has been studied by cross-sectional transmission electron microscopy for P-4 cluster implants (5 keV equivalent monomer energy) as a function of dose and compared to that of monomer P implant at the same equivalent energy. Amorphous pockets are formed by the cluster implant at doses of as low as 6 x 10(13)/cm(2), and a continuous amorphous layer is formed at dose of 2 x 10(14)/cm(2). The reduction by about 2.5 times in amorphization threshold by clusters with respect to the monomer implant is a consequence of the simultaneous deposition of energy carried by the atoms in the clusters, which enhances the damage yield in the overlapped collision cascades. 2009 American Vacuum Society. [DOI: 10.1116/1.3089372]