Etching, smoothing, and deposition with gas-cluster ion beam technology

Gas cluster ion beam (GCIB) processing has recently been introduced as a co mmercial tool for processing 'rough' surfaces, such as polished substrates or thin films. The physical interaction of a gas cluster ion beam with a su rface is strikingly different from that of better-known 'monomer' ion beams . Clusters are formed by the adiabatic expansion of gas through a nozzle, i onization by electron impact, acceleration, and then impingement upon the s urface to be processed. The physics of the surface interaction of the clust er beam strongly depends upon gas composition, cluster size, cluster size d istribution, and beam energy. Typical argon GCIBs are composed of clusters ranging from several hundred to several thousand atoms in size. It has been previously shown that Ar clusters can be used to smooth surfaces at a sub- nanometer level. Argon cluster beam smoothing typically occurs in the energ y range between 15 and similar to 30 keV. As such, the average energy per a tom is of the order of 10 eV/atom upon cluster impact with the surface and subsequent dissociation. Ion cluster beams formed with reactive gases such as oxygen and nitrogen can also be formed, but at somewhat lower current de nsities than those obtainable with argon. Upon impact, reactive gas cluster s undergo strong chemical reactions at the substrate surface. An extension of this chemical interaction is to utilize reactive clusters in an ion beam -assisted, thin-film physical vapor deposition process. This has been demon strated with relatively low energy (E < <similar to> 10 keV) oxygen cluster s in an electron-beam evaporator to form extremely low resistivity indium-t in oxide films on room-temperature substrates. This paper will describe the basics of GCIB formation and application to atomic scale smoothing of tech nologically interesting substrates and thin films, as well as reactive GCIB assisted deposition technology. The results presented demonstrate some of the unique physics and materials science that can be achieved with an emerg ing GCIB technology. (C) 2000 Published by Elsevier Science B.V. All rights reserved.