AbstractSurface processing of microelectronic materials by bombardment with nanoparticles of condensed gases (i.e., clusters) in the form of an ion beam, makes possible etching and smoothing of those surfaces to very high figures of merit. As this is not possible with any conventional ion method, gas-cluster ion-beam systems have great potential in manufacturing. The formation of gas clusters and their collision with surfaces provides an interesting arena for novel physics and surface science. This paper outlines a physical model for the clusters and surface interactions, and provides examples of surface processing. In particular, the reduction of surface roughness while etching by cluster-ion bombardment is illustrated for various materials utilized in microelectronics.