Mass Separation of Water Cluster Ion Beam Using Two Rotating Electric Fields and Sputtering of a Polymer Thin Film

Abstract

Selection of the cluster size of an ion beam is a key factor for controlling sputtering speeds or the damaged layer of polymer materials. We developed a two rotating electric fields (REFs) type of mass spectrum (MS) filter or analyzer using a novel principle. The REF-MS can continuously separate typical sizes of cluster ions by optimizing the frequencies of the REFs. In this study, we developed an electrospray ionization (ESI) gun column to optimize the cluster sizes of a water ion beam by REF-MS. Annular ring patterns of size-selected clusters were observed using optimized focusing frequencies on typical water molecule clusters. The patterns were compared with the results of the finite difference simulation method. We sputtered a spin-coated polymer film using a size-filtered water cluster ion beam. A sputtering crater was observed on the polystyrene film sputtered by the size-optimized water cluster ion beam. Here, we discuss the cluster size dependence of sputtering speeds for an ion beam for typical numbers of water clusters.