Cross-sectional TEM study of surface modification of nano-structure with gas cluster ion beams
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Cross-sectional TEM study of surface modification of nano-structure with gas cluster ion beams Noriaki Toyoda and Isao Yamada Incubation center, Graduate School of Engineering, University of Hyogo, 2167 Shosha, Himeji, Hyogo, 671-2201, Japan ABSTRACT Surface modification effects on patterned surface with gas cluster ion beam (GCIB) were studied by observation with a cross-sectional transmission electron microscope in order to use it for planarization of patterned media such as discrete track media (DTM) or bit-patterned media (BPM) for future hard disk drives. As a model structure of patterned media, line-and-space or bit patterns were fabricated on Si substrates, and subsequently amorphous carbon films were deposited on them. After Ar-GCIB irradiations on amorphous carbon, it was shown that GCIB preferentially removed bumps or crest on the surface of amorphous carbon at normal incidence. The required thickness for planarization was close to the initial peak-to-valley. At an incident angle of 57o, line-and-space patterns became sharp-pointed shape. On the contrary, line-andspace patterns were planarized without tiny asperity formation at 77o. These results indicate that quite effective planarization of patterned surface is possible using GCIB at normal or glancing angle irradiation. INTRODUCTION Patterned media such as discrete track media (DTM) or bit-patterned media (BPM) have been studied extensively in order to realize high areal recording density for hard disk drives [1]. However, it is necessary to planarize the surfaces of patterned media so as to maintain the flying stability of a slider [2]. Chemical mechanical polishing (CMP) is one of the candidates of planarization for patterned surface. However, it is difficult to employ wet process into the fabrication process of hard disk media. In order to overcome the shortcomings of the planarization technique, we have proposed the gas cluster ion beam (GCIB) processing. GCIB have been considered as a novel ion beam which attains both the dense energy deposition and the ultra low-energy/atom irradiation at the same time. In addition, GCIB induces lateral motion of atoms, which can be used for surface smoothing. These surface modification effects using GCIB have been studied by irradiation experiments [3,4] or molecular dynamics simulations [5,6]. Also, we have reported a demonstration of planarization of DTM with GCIB [7]. However, there has not been experimental study of incident angle dependence on the modification of patterned surface. There is a molecular dynamics simulation study which showed that GCIB preferentially remove a surface bumps at oblique incidence [8]. In this study, lineand-space or dot pattern were fabricated on Si substrate. Subsequently, amorphous carbon films, which can be used for refill materials of pattered media, were deposited on the patterned Si samples. By taking the cross-sectional transmission electron microscope (TEM) images, surface modification effects on the patterned surface with oblique incidence of GCIB were studied.
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