pubs.acs.org/Langmuir © 2009 American Chemical Society
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Formation of Ultrasmooth and Highly Stable Copper Surfaces through Annealing and Self-Assembly of Organic Monolayers Ilia Platzman,† Cecile Saguy,‡ Reuven Brener,‡ Rina Tannenbaum,*,†,§, and Hossam Haick*,†,§ Department of Chemical Engineering and ‡Solid State Institute and §Russell Berrie Nanotechnology Institute, Technion - Israel Institute of Technology, Haifa 32000, Israel, and School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332 )
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Received June 4, 2009. Revised Manuscript Received August 9, 2009 Copper (Cu) has been extensively used as an interconnect material for microelectronic devices because of its high electrical and thermal conductivity and excellent electromigration resistance. However, the formation of relatively rough Cu surfaces (∼5 nm roughness) and Cu-oxide layers upon exposure to air still hinders their reliable application in a wide range of fields. In this article, we show the potential values of highly stable and ultrasmooth polycrystalline bare Cu obtained by simple annealing and chemical modification for a wide range of Cu-based electronic devices. The morphological properties and oxidation behavior of annealed Cu surfaces, before and after coating by self-assembled monolayers of terephthalic acid (TPA), were examined upon exposure to ambient air conditions (∼110 days). Thin films of polycrystalline Cu, deposited on top of an adhesion layer of tantalum nitride (TaN) and annealed for 8 h at 580 °C under 2 10-7 Torr, provided ultrasmooth Cu surfaces (Rrms = 0.15-1.1 nm for fresh samples) and had a stable Cuoxide layer after 65 days (∼3.5 nm). These observations were perceived to be superior to nonannealed polycrystalline Cu samples. Coating fresh (oxide-free) samples of ultrasmooth Cu with TPA molecules created a closely packed monolayer with a standing-up phase configuration and molecular coverage of ∼90%. The TPA-coated Cu surface has not shown any detectable oxidation during the first 2 weeks of exposure. The protection efficiency of this layer was found to be superior to those reported earlier on polycrystalline Cu surfaces. The oxidation mechanisms of both annealed and nonannealed Cu surfaces are presented and discussed.
1. Introduction Copper (Cu) has attracted increasing attention as a candidate to replace aluminum and gold as interconnecting materials in small (
