Formation of Metallic Nanowires by Utilizing Electromigration

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A technique for forming metallic nanowires by utilizing electromigration, which is the phenomenon of atomic diffusion due to high current densities, is presented. These diffused atoms can be used for creating metallic nanowires. To specify the position at which a nanowire is formed, some specific conditions need to be established. These conditions are, first, to control the atomic diffusion so the accumulation of atoms produces the desired higher compressive stress; second, to design the structure to control the areas in which diffusion takes place; third, to adjust the thickness of the passivation layer deposited on the metal; and fourth, to form a small slot in the passivation layer through which the compressive stress is released by discharging the diffused atoms. It is shown that when these factors are satisfied, an Al nanowire can be successfully generated in a passivated metal track composed of an Al line buried in a W line.

I. INTRODUCTION

With the scaling of semiconductor devices and the development of micromachines, it has become vital to develop processes that enable materials to be fashioned with extremely small sizes. Minimizing the size of materials makes ultra-large scale integration possible, but at the same time gives the materials physical properties different from those encountered at larger dimensions.1,2 In recent years, it has been demonstrated that as feature sizes are shrunk to less than 100 nm, the top-down approach, such as the conventional deposition, photolithography, and etch, becomes more difficult.3 Thus, a lot of research has been carried out on bottom-up technologies, which are methods for constructing nanomaterials from individual atoms and molecules.4,5 In particular, selforganization, which is a phenomenon in which the structural order of a material is generated by molecular processes, has been used to produce nanomaterials. One of the most frequent causes of failure arising in metal tracks as electronic devices are scaled is electromigration, which is due to high current densities and high Joule heating in thinner and narrower tracks.6 Electromigration is the phenomenon by which metallic atoms are transported by the electron wind caused by the high current density in the metal track. The amount of atom transportation depends on the current density, temperature, and microstructure of the track. At locations in the

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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0340 2712

http://journals.cambridge.org

J. Mater. Res., Vol. 20, No. 10, Oct 2005 Downloaded: 13 Mar 2015

track where depletion of the metal atoms is caused by electromigration, voids are formed. On the other hand, at locations where there is an accumulation of atoms, hillocks are formed. Where these occur depends on the distributions of temperature and current density in the track. In this research, a technique for generating metallic nanowires by utilizing electromigration is proposed as a new and effective method for making fine-structured materials. It is wel

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