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Low-damage Processing of Organic Materials with Size-controlled Gas Cluster Ion Beams. Motohiro Nakagiri, Noriaki Toyoda, and Isao Yamada Incubation Center, Graduate School of Engineering, University of Hyogo 2167 Shosha, Himeji, Hyogo, 671-2280, Japan ABSTRACT Organic materials have been widely used in various fields of electronic applications. However, they are difficult to process without damage by using a conventional ion beam which use energetic ions. In this study, gas cluster ion beam (GCIB), which shows low-damage process, was used for organic materials, and irradiation effect of size selected GCIB was studied with Xray photoelectron spectroscopy (XPS). In the case of irradiation of 500 eV Ar ion (monomer ion) on polyimide, the intensities of both N-C=O and C-O bond decreased after irradiation. On the other hand, there was small change in the XPS spectra after 15 keV Ar-GCIB irradiation with the same ion dose. The etching rate of polyimide per one ion with 15 keV Ar-GCIB was almost 1.8×104 times higher than that with 500 eV Ar monomer ions. The damages in polyimide decreased with increasing the Ar cluster size owing to the reduction of energy per atom at acceleration voltage of 15 kV. After irradiation of size selected 5 kV Ar cluster ion, damage was almost negligible. Although, the surface became rough after irradiation of Ar-GCIB, surface roughness and the change of chemical bond were very small with N2-GCIB irradiation. Ar-GCIB irradiation on dye-sensitized solar cells (N719) showed that very low-damage process is possible with GCIB, and it indicated that GCIB is suitable for surface processing of organic materials used in electronic devices. INTRODUCTION Recently, organic materials have been widely used in various fields of electronic applications, such as solar cells [1], organic light-emitting diode [2] and so on. However, they are easily damaged by irradiation of energetic ions [3]. Therefore, it is still difficult to use conventional ion beam process as a precise etching technique for organic materials. Furthermore, alternative ion beam in surface analysis equipment is required for surface cleaning or depth profiling of organic materials because Ar monomer ion beam easily induces damages in organic materials. We have studied gas cluster ion beam (GCIB) process to realize very low-energy irradiation. Gas cluster is an aggregate of thousand atoms or molecules. For example, if a gas cluster ion with 1000 atoms is accelerated at 10 keV, the energy per atoms is 10 eV. Therefore, low damage processing is possible with GCIB. It has been demonstrated for various materials such as Si [4], magnetic materials [5]. Recently, low-damage irradiation on organic materials with GCIB was characterized with XPS [6]. However, the number of atoms or molecules (cluster sizes) dependence was not evaluated in the previous study. Since the energy per atom of cluster is defined by cluster size, it is important to study the cluster size effect on damage formation in organic materials. In this study, size-controlled GCIB irradi