High-speed Processing with Cluster Ion Beams
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R9.29.1
High-speed Processing with Cluster Ion Beams Toshio Seki1,2,3 and Jiro Matsuo1 Quantum Science and Engineering Center, Kyoto Univ., Yoshida-honmachi Sakyo-ku, Kyoto 606-8501, Japan 2 Collaborative Research Center for Advanced Quantum Beam Process Technology, Japan 3 Collaborative Research Center for Cluster Ion Beam Process Technology, Japan 1
ABSTRACT Cluster ion beam processes can produce high rate sputtering with low damage in comparison with monomer ion beam processes. Especially, it is expected that extreme high rate sputtering can be obtained using reactive cluster ion beams. High current SF6 cluster ion beams were recently obtained with new modifications in the basic cluster ion beam technique. The cluster size distribution was measured with Time-of-Flight (TOF) method and the mean size of cluster was about 500 molecules. Si substrates were irradiated with SF6 cluster ions at the acceleration energy of 5-45 keV. Sputtering yield with SF6 cluster ions was increased with acceleration energy and was about 2300 atoms/ion at 45 keV. The sputtering yield was about 1000 times higher than that of Ar monomer ions and was also higher than that of Ar cluster ions. It was found that reactive sputtering occurred with SF6 cluster ion irradiation. These results indicate that high-speed fabrication can be realized with reactive cluster ion irradiation at high energy. INTRODUCTION A cluster is an aggregate of a few to several thousands atoms. When many atoms constituting a cluster ion bombard a local area, high-density energy deposition and multiple-collision processes are realized. Because of the unique interaction between cluster ions and surface atoms, new surface modification processes, such as surface smoothing [1-3], shallow implantation [4,5] and high rate sputtering [6], have been demonstrated using gas cluster ions. High ion dose is required for nano-level smoothing and etching of hard materials, and large current cluster ion beam is in demand. High sputtering yield is also needed to realize high-speed fabrications. It is expected that the extreme high rate sputtering can be realized with reactive cluster ion beams. If un-reactive materials were used as mask, high selectivity can be realized, and patterns of high aspect ratio can be fabricated. Figure 1 shows a schematic diagram of the cluster ion beam irradiation system. Adiabatic expansion of a high-pressure gas through a nozzle is utilized for the formation of gas cluster beams. When a supersonic flow ejects from the nozzle, shockwaves are generated [7]. These shockwaves disturb the generation of neutral cluster beams. To avoid formation of such shockwaves, a skimmer was utilized to pass the core of the supersonic flow into high vacuum. The neutral clusters are ionized by the electron bombardment method. The ionizer consists of filaments and anode. Electrons ejected from hot filaments are accelerated towards the neutral cluster beam and ionize clusters. The ionized clusters are extracted and accelerated towards targets. In order to generate large current
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