High-rate Etching of Organic Materials using Gas Cluster Beam
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High-rate Etching of Organic Materials using Gas Cluster Beam Takanori Suda, Noriaki Toyoda and Isao Yamada Incubation center, Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280, Japan ABSTRACT Organic materials or polymers, which are widely used in electronic devices, are easily damaged by energetic ion or electron bombardment. Therefore, it is difficult to use conventional ion or electron beam processes for etching organic materials. In this study, a gas cluster beam possessing kinetic energy of the order of several hundred eV was used as a novel means to realize high-rate, low-damage etching. Polyethylene (PE) and polyvinyl chloride (PVC) were used as the target organic materials. Using a SF6 cluster beam, the etching depth suddenly increased when the nozzle gas pressure exceeded 0.6 MPa, as in the case of cluster beam formation. When the SF6 gas pressure in the nozzle was 1.2 MPa, the etching rates of PVC and PE were 2.88 μm/s and 1.62 μm/s, respectively. The dependence of the etching effect on cluster size was studied by varying the gas temperature. The etching depth of PVC increased with increasing average cluster size and intensity of the beam. The flow rate of the gas was constant; hence, etching of the organic materials did not occur because of the individual impact of the molecular beam. In fact, it occurred because of the neutral cluster, which had a large total kinetic energy. The energy per molecule of the gas cluster beam is of the order of several tens of meV; hence, high-rate, low-damage etching of organic materials can be potentially achieved. INTRODUCTION Although organic materials or polymers have recently attracted considerable attention as candidate materials for various electronic devices such as organic semiconductors and organic electroluminescent diodes [1], they are easily damaged by energetic ion or electron bombardment [2]. Therefore, it is difficult to employ the existing etching process that is used for inorganic materials. We have reported a low-damage process using gas cluster ion beams (GCIBs) [3]. A GCIB is an aggregation of several thousand atoms or molecules. The kinetic energy of each atom is the total acceleration energy of the cluster divided by the number of atoms in the cluster; hence, the energy per atom of a GCIB may be extremely low (~ several eV/atom). A gas cluster beam is formed by the supersonic expansion of a high-pressure gas through a nozzle. Owing to the cooling process during adiabatic expansion, a gas cluster comprising several thousand atoms or molecules is produced. During supersonic expansion, the atoms collide with one another and exchange energy. Thus, all the particles attain the same translational velocity. The kinetic energy of a neutral cluster beam is proportional to the cluster size [4]. The kinetic energy of the molecules is of the order of several tens of meV each, in the same direction; hence, the total kinetic energy of a neutral cluster, which comprises several thousand atoms or molecules, is of the order of s
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