Incident angle dependence of the sputtering effect of Ar-cluster-ion bombardment

Gas cluster ions impact onto a solid surface with low energy and with high density. At the moment of ion impact, multiple-collisions cause several unique effects, such as lateral sputtering, high-rate sputtering and surface cleaning and smoothing at normal incidence. We have irradiated Cu and Ag thin films with a 20 keV Ar cluster ion beam (mean cluster size is 3000) at several different incident angles. The sputtering yield of the cluster ion bombardment decreased with increase of the incident angle in proportion to cos theta, while that by monomer ion bombardment increased, The roughness of the Cu surface, bombarded with cluster ion, monotonically increased with increase of the incident angle. These characteristics of energetic cluster impact show quite a different dependence on the incident angle than those of monomer ion. The sputtering effect of the impact of energetic clusters is strongly dependent on the incident angle.