Influence of Self-Assembled Organic Thin Film Monolayer on Ambient Copper Surfaces Oxidation
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Influence of Self-Assembled Organic Thin Film Monolayer on Ambient Copper Surfaces Oxidation Ilia Platzman1, Hossam Haick1, and Rina Tannenbaum1,2 1 Chemical Engineering, Technion, Technion City, Haifa, 32000, Israel 2 Materials Science and Engineering, Georgia Tech, 771 Ferst Drive, Atlanta, GA, 30332 ABSTRACT Qualitative and quantitative studies of the oxidation of molecularly modified polycrystalline copper (Cu) thin films upon exposure to ambient air conditions for long periods (on the order of several months) are reported in this work. Thin films of Cu, prepared by thermal evaporation, were analyzed by means of x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) to gain an understanding on the growth mechanism of oxide on bare and molecularly modified Cu surfaces. The results from all techniques points for an unstable behavior of bare Cu surfaces characterized in very fast and continuous growth of Cu oxide layers during first 60 days of exposure to overall 6 nm oxide thickness. However, Cu films prepared under the same conditions, but covered with a self-assembled organic thin film layer of 1,4-phenylene diisocyanide (PDI) molecules adsorbed from solution, showed a decrease in the thickness of the copper oxide layer on the Cu surface. Our findings imply that chemisorbed PDI monolayers can serve as protective coatings for Cu. INTRODUCTION The continuous drive for the miniaturizations of electronic devices, as well as the desire to extend current capabilities in order to address future technological needs, are among the factors responsible for the increased interest in Cu as a pattern and interconnecting material in ultra large-scale integration (ULSI) devices. This could be attributed mainly to the high thermal and electrical conductivities and electromigration resistance of Cu, as compared to more traditional interconnection materials, such as gold and aluminum.1-3 However, formation of an oxide layer on Cu (even at room temperature4-7) is thought to induce trap states at the Cu/Cuoxide interface that can ultimately cause a decrease in its thermal and electrical conductivities,8 as well as a significant degradation in its interconnection capabilities.9-11 These effects become more and more critical with the shrinkage of the device dimensions. The mechanism of Cu oxidation at ambient temperatures still remained unresolved due to limitations in precise measurements, as films grown under these conditions had most likely thin oxide layers on their surface. Cabrera and Mott12,13 proposed a theoretical model of Cu oxidation at low temperatures. The oxide film formation is driven by the field-enhanced ionic transport that is accelerated at the initial oxidation stages and attenuated with the increase of the oxide layer thickness. In previous work, we reported on the oxidation mechanism of polycrystalline copper (Cu) thin films upon exposure to ambient air conditions for long time periods.14 The main outcome of this study indicated that the thickness of the native oxide layer
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