Irradiation Effects of Methanol Cluster Ion Beams on Solid Surfaces
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1020-GG07-07
Irradiation Effects of Methanol Cluster Ion Beams on Solid Surfaces Gikan Takaoka, Masakazu Kawashita, and Takeshi Okada Ion Beam Engineering Experimental Laboratory, Kyoto University, Nishikyo-ku, Kyoto, 6158510, Japan
ABSTRACT In order to investigate the interactions of methanol cluster ion beams with solid surfaces, Si substrates and SiO2 films were irradiated at different acceleration voltages. The sputtered depth increased with increase of the acceleration voltage. When the acceleration voltage was 9 kV, the sputtered depths of Si and SiO2 at a dose of 1×1016 ions/cm2 were 1497.1 nm and 147.8 nm, respectively. The selectivity between Si and SiO2 surfaces arose from the volatility of the reaction products. Furthermore, the sputtering yield for the Si surface was approximately seven hundreds times larger than that by Ar monomer ion beams. This suggested that chemical sputtering was predominant for the methanol cluster ion irradiation. In addition, the etching and cleaning process by the methanol cluster ion irradiation was performed on the Si surfaces contaminated with a small amount of metal particles such as Au and Al. Thus, methanol cluster ion beams have unique characteristics such as surface etching and cleaning with high sputtering yield and smooth surface. INTRODUCTION The demand for material processing technologies for LSI devices has recently been increasing, and the development of new surface processes has been required [1-3]. For example, surface cleaning and etching processes are of much importance in semiconductor device fabrication. It is well known that the wet process using organic liquid materials has been applied to the surface treatment for solid surfaces. However, etching by organic liquid materials, such as ethanol and methanol, is not achieved even at elevated temperatures. When advanced devices in the next generation are fabricated, conventional processes for surface cleaning and etching meet the difficulties such as removable of contamination, damage-free formation, atomically flatsurface formation. Cluster ion beams are useful tools for the investigation of the fundamentals of solid state physics, chemistry and related materials science [4-6]. High-energy-density deposition and the collective motions of the cluster atoms during impact play important roles in the surface process kinetics such as deposition, etching, cleaning or implantation. In order to overcome the limitations associated with current wet processes for surface cleaning, we have developed a new type of liquid cluster ion source, and investigated the impact processes of the liquid cluster ions on solid surfaces [7,8]. In a previous study, using ethanol cluster ions, Si surfaces were etched with high sputtering yield, and they had a lower damage and an atomically flat surface [9,10]. These features have not been obtained by the conventional wet process using alcohol. On the other hand, methanol has a lower boiling temperature and a higher specific heat ratio than ethanol, thereby giving the possibility of large
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