Molecular Dynamics Study of Suface Structure and Sputtering Process by Sequencial Fluorine Cluster Impacts
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MOLECULAR DYNAMICS STUDY OF SUFACE STRUCTURE AND SPUTTERING PROCESS BY SEQUENCIAL FLUORINE CLUSTER IMPACTS Takaaki Aoki1,2 and Jiro Matsuo1 1 Quantum Science and Engineering Center, Kyoto University, Gokasho, Uji, 611-0011, JAPAN 2 Osaka Science and Technology Center, Utsubo-Honmachi, Nishi-ku, Osaka, 550-0004, JAPAN ABSTRACT In order to study the surface reaction process under cluster ion impact, molecular dynamics simulations of sequential cluster impacts of fluorine and neon clusters were performed. (F2)300 and Ne600 clusters were accelerated with totally 6keV and irradiated on bare Si(100) target. By iterating impact simulation sequentially, change of surface morphology and composition of desorbed materials were studied. In the case of fluorine cluster impact, the rough surface structure was made compared with neon cluster impact because fluorine atoms adsorb on the target, which work to keep pillar structure on the surface, whereas Ne atoms evaporate immediately leaving spherical mound structure on the surface. From the study of desorption process, it was observed that large number of Si atoms are desorbed in the form of silicon fluorides. The major sputtered material was SiF2, but various types of silicon-fluorides, including the molecules consists of several tens to hundreds silicon and fluorine atoms, were observed. The distribution of clusters in desorbed materials obeyed the classical model of cluster emission from quasi-liquid phase excited with ion bombardment. From these results, the irradiation effects of reactive cluster ions were discussed. INTRODUCTION The impact processes of gas clusters on solid surfaces are of great interest for the new surface modification techniques [1,2]. Cluster is an aggregated material, which consists of several tens to thousands atoms. When a cluster is accelerated and impacts on a solid target, high-density atomic collision occurs and the kinetic energy of the cluster is deposited on very shallow area of the target. This collisional process is different from that of monomer ions, and is expected to develop new surface modification technologies. The study of gas cluster ion impact has been started with argon gas cluster mainly, which is inert material and is suitable to understand the physical effect of multiple collision effect of clusters. Recently, it has been reported that, gas cluster ion beam can be generated with various gas-phase materials such as SF6, CF4, etc [3,4]. Expansion of source materials implies that gas cluster ion beam will be available for various surface modification process by combining the non-linear effects inherits in cluster impact and chemical properties of source gas materials. Fot the example in the field of sputtering, it has been demonstrated that, when a (SF6)2000 cluster is irradiated on Si and W substrate, the sputtering yield is 10 times higher than that of Ar2000 cluster, which in turn is 10 times higher than monomer ions with the same total acceleration energy of 20keV [4,5]. The high etching ratio of reactive cluster ions is n
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