Spatial distribution of Cu sputter ejected by very low energy ion bombardment

Filling of submicron width trenches with Cu from a highly ionized plasma is sensitive to both the directionality of the depositing flux and reflection and resputtering at the film surface. The spatial distributions of Cu atoms sputtered by He+, Ar+, and Xe+ ions incident at 30 degrees, 45 degrees and 60 degrees and over an ion energy range of similar to 55-600 eV have been investigated. In all cases, the distribution is forward directed and cannot be described by a cosine distribution about the surface normal. Decreasing energy, increasing angles of incidence, and increasing ion mass yield more forward directed distributions. For similar to 55 eV Ar+ incident at 60 degrees, similar to 85% of the resputtered flux is in the forward direction. From these distributions, in a 50% ionized physical vapor deposition system the depositing flux due to forward directed resputtering is estimated to be of the same order of magnitude as the neutral flux. (C) 1997 American Institute of Physics.