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Modeling for the Diamond-Like Carbon Film Synthesis by Plasma Based Ion Implantation Yoshiko Miyagawa, Flyura Djurabekova and Soji Miyagawa National Institute of Advanced Industrial Science and Technology, 1-1, Hirate-cho, Kita-ku, Nagoya, 462-8510, Japan.

ABSTRACT Dynamic Monte Carlo simulations with the binary collision approximation have been applied to the synthesis of hydrogenated amorphous carbon (a-C:H) films by plasma based ion implantation (PBII). We take as representative carbon carriers energetic CH3+ ions and CH3 radicals. The direct chemical incorporation of the radicals, like CH3 reacting with a diamond surface, is too low for the deposition of DLC films, so that the other reaction mechanisms should be responsible. We assumed (a) complete dissociation of CH3+ ions into one C atom and three H atoms with identical velocities upon bombarding the surface, (b) a unity and only one mono-layer sticking of CH3 radicals on the surface, (c) incorporation (stitching) of H and C atoms under the surface induced by binary collisions with energetic CH3+ ions, (d) release of H atoms by the dissociation of CH3 radicals on the surface, and (e) release of a part of displaced H atom after the subsequent collision cascade. We also assumed only the stitched carbon atoms form sp3 states and all other carbon atoms form sp2 states. The effect of the target voltage on the ion dose was also included. The effects of ion/neutral arrival ratio and ion energy on the growth rate, the mixing layer thickness, the hydrogen content, and the sp3/sp2 ratio in the deposited film are presented.

INTRODUCTION The properties of hydrogenated amorphous carbon (a-C:H) film can be characterized by the hydrogen concentration and by the relative fractions of sp2 and sp3 bonded carbon. Depending on the hydrogen concentration and the microstructure, the a-C:H film changes from diamond-like carbon (DLC) to polymer-like carbon at low ion energy and graphite to DLC at high ion energy. The energy of the impinging ion together with the ion/neutral arrival ratio plays a crucial role for the properties of the film synthesized by PBII. In contrast to the broad range of experimental data, the basic understanding of the mechanisms of DLC film synthesis by ion assisted deposition is still in an immature state. The purpose of this study is to estimate the hydrogen concentration and relative fractions of sp2 and sp3 bonded carbon by making clear the relation between the concentrations and the locally transferred energy in the collision cascades. In the previous works [1, 2] we used the sputtering version of the SASAMAL code in which the collisions with the atom centered out of the surface are omitted [3]. But in this work, these collisions are not omitted since the surface is covered with one mono-layer of CH3 molecules. Further, in the previous works, we assumed 90% of both stitched C atom and implanted C ion form sp3 states and all other knock-on atoms are released into sp2 states in the collision cascade. In this work, we assumed only the stitched atoms form s