Adhesion Strength and Microstructure of Cu/Ni/OsO x /glass Structure for Highly-Reliable Cu Interconnection
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Adhesion Strength and Microstructure of Cu/Ni/OsOx/glass Structure for Highly-Reliable Cu Interconnection Mitsuhiro Watanabe and Eiichi Kondoh Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, 4-3-11 Takeda, Kofu, Yamanashi, 4008511, Japan ABSTRACT This study demonstrates that thin metallic oxide layers, such as OsOx and ZnO, function as a strong adhesion layer between Cu film and glass substrate. The adhesion strength was studied with a micro-scratch tester and the films and interfaces were characterized by energydispersive X-ray spectrometry. The presence of an extremely thin intermixing layer was confirmed at the metal/glass interfaces. The formation of such an interfacial layer increased the adhesion strength significantly. INTRODUCTION To fabricate a highly-reliable Cu/glass structure has been required in microelectromechanical system (MEMS) and packaging technologies. A crucial issue is that Cu/glass structures have generally low adhesion strength. Conventional techniques, such as brazing and mechanical interlocking, can not be applied to those applications, because these conventional techniques need to form an intermixing layer (anchor layer) with a scale of micrometers, or larger, so as to ensure the mechanical strength. Therefore, atomically scaled interface bonding is demanded for fabricating a highly reliable Cu/glass structure. One solution for strengthening the interface bonding is to form a chemically strong adhesion layer between a Cu film and a glass substrate. Past researches have indicated that effective adhesion layers contain reactive elements that are miscible in Cu [1,2]. Those reactive elements segregated at surfaces and interfaces, and formed an oxide layer after carefullycontrolled annealing. In this study, based on results of these studies, we examined two different oxides as an adhesion layer, namely OsOx and ZnO, where those oxide layers were directly formed on glass substrates. OsOx films are popular antistatic films for observing insulator materials with secondary electron microscopes because of their superior electrical conductivity and secondary electron emission efficiency [3]. Originally we planned to use OsOx layers directly as an adhesionpromoting layer. After screening tests, we immediately understood that direct Cu metallization to the OsOx/glass is not very effective. We therefore inserted Ni between Cu and OsOx, because Ni is miscible in Cu at all compositions and in Os up to 64.2 at% Ni. (Os is hardly miscible in Cu at all composition ratios.) In addition, Ni can be deposited by common deposition techniques. ZnO has gained considerable attention in microelectronics as an alternative transparent conductor [4], because Zn is a recyclable, abundant, and affordable element. Zn is miscible in Cu up to 38.27 at% Zn, and ZnO generally shows good adhesion to glasses or oxides [5], indicating that ZnO is a potential adhesion layer in Cu/glass structures. Indeed, past research studies demonstrated that a ZnO layer works as an effective adhesion lay
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