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W17.13.1

Threshold Energy for Generating Damage with Cluster Ion Irradiation Toshio Seki1,2, Takaaki Aoki1,2, Atsuko Nakai1, Jiro Matsuo1 and Gikan H. Takaoka1 1 Ion Beam Engineering Experimental Laboratory, Kyoto University, Kyoto, 606-8501, JAPAN 2 Collaborative Research Center for Cluster Ion Beam Process Technology ABSTRACT In order to understand the damage formation by cluster ion irradiation, Si substrates were irradiated with Ar cluster ions at the acceleration energy of 1-20keV. The mean size of cluster was about 3000 atoms. The amount of damage after Ar cluster ion irradiation was measured with Rutherford backscattering spectrometry (RBS). The amount of damage was decreased with decrease of the energy and no damage formed at less than 2keV. This energy of 2keV represents the threshold energy to generate damage with the cluster size of 3000. According to Molecular dynamics (MD) simulation, the damage formation with cluster ion irradiation also depends on cluster size. The size dependence of amount of damage has been investigated experimentally. The cluster size distribution could be changed with the ionization condition and could be measured using Time-of-Flight (TOF) method. The threshold energy was increased with cluster size. These results indicate that undamaged films can be created by using large size of cluster ion with low acceleration energy. INTRODUCTION A cluster is an aggregate of a few to several thousand atoms. Because many atoms constituting a cluster ion bombard a local area, high-density energy deposition and multiple-collision are realized. Because of the interactions, cluster ion beam processes can produce unusual new surface modification effects, such as surface smoothing, high rate sputtering and very shallow implantation [1-4]. Various outstanding applications of the cluster ion beam have included so far: High quality tin doped indium oxide (ITO) films obtained by O2 cluster ion assisted deposition at room temperature [5], smoothing of diamond films by Ar cluster beam [6,7], formation of ultra shallow junction by using B10H14 ion implantation [8]. Cluster ion assisted deposition can be used for ultra high quality films [9]. It is necessary to understand the damage formation by cluster ion irradiation during film formation for the further developments of this technology. Energy dependence of damage created by cluster ion impact was already studied with Scanning Tunneling Microscope (STM) [10]. It was reported that the depth of the damaged region in the target became shallower with decreasing impact

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energy and no damage was formed at the impact energy of 1keV. In this paper, both computer simulations and experiments were performed in order to examine the cluster size effect on the damage formation and discuss the efficiency of the development of size control technique for cluster ion beams. THEORY Molecular dynamics (MD) simulation is one of the powerful methods to understand the collisional process of cluster on solid surfaces. Cluster size dependence on damage formation was