Cluster Ion Beam Process for Nanofabrication
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1020-GG01-02
Cluster Ion Beam Process for Nanofabrication Isao Yamada, and Noriaki Toyoda Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, 671-2280, Japan
Abstract. This paper reviews gas cluster ion beam (GCIB) technology, including the generation of cluster beams, fundamental characteristics of cluster ion to solid surface interactions, emerging industrial applications, and identification of some of the significant events which occurred as the technology has evolved into what it is today. More than 20 years have passed since the author (I.Y) first began to explore feasibility of processing by gas cluster ion beams at the Ion Beam Engineering Experimental Laboratory of Kyoto University. Processes employing ions of gaseous material clusters comprised of a few hundred to many thousand atoms are now being developed into a new field of ion beam technology. Cluster-surface collisions produce important non-linear effects which are being applied to shallow junction formation, to etching and smoothing of semiconductors, metals, and dielectrics, to assisted formation of thin films with nano-scale accuracy, and to other surface modification applications.
HISTORICAL MILESTONES IN GCIB TECHNOLOGY In 1950, Becker et al first studied cluster formation for thermonuclear fuel applications using gaseous materials passed through supersonic nozzles wchichi were cooled by liquid nitrogen and helium shrouds [1]. The supersonic expansion approach was successful in producing cryogenic beams containing large numbers of clusters. This original work opened the way to employ gas clusters for materials processing. During the late 1970's and 1980's, an ionized cluster beam (ICB) technique which employed metal vapor clusters from heated Knudsen cells for thin film formation was studied at Kyoto University and elsewhere. Kyoto University investigations of metal vapor clusters ended when collaborative work with W.L.Brown at Bell Laboratories showed the cluster ion intensities within the metal vapor streams to be too low for most practical purposes [2,3]. Subsequent work at the Kyoto University Ion Beam Engineering Experimental Laboratory then focused upon cluster beam formation employing gas expansion through simple supersonic nozzles. Initial research on gas cluster beam formation showed that supersonic nozzles having converging-diverging shapes operating at room temperature could produce intense beams of gas clusters. This then led to research and development of gas cluster ion beam (GCIB) techniques [4] and to investigations of new ion-solid interactions produced by gas cluster ion impacts. These studies demonstrated that GCIB produces unique ion/solid interactions and offers new atomic and molecular ion beam process opportunities in areas of implantation, sputtering, and ion beam assisted deposition. Most of the original technical results through to the year 2000 have been summarized in a monograph. [5]. Over the first 10 years of GCIB studies, low energy surface interaction effects, lateral sputtering phenomena an
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