Electromigration in Metals

An applied electrical potential gradient can induce diffusion (electromigration) in metals due to a cross effect between the diffusing species and the flux of conduction electrons that will be present. When an electric field is applied to a dilute solution of interstitial atoms in a metal, there are two fluxes in the system a flux of conduction electrons, Jq, and a flux of the interstitials, J. For a system maintained at constant temperature with Fq = -V f = E, Eq. 2.21 gives 

Consider now the interstitial flux in a material subjected to both an electrostatic driving force and a concentration gradient. Using Eqs. 3.36, 3.43, 3.51, and 3.54, for a dilute species obeying Henry s law, 

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The progress achieved in the field of isotope electromigration in metals, salts, and aqueous solutions since the meeting on isotope separation in Paris in 1963 is reported. It is shown that the temperature dependence of the isotope effect in liquid metals leads to the conclusion that it is a result of classical atom—atom interactions. Isotope effects in molten salts are smaller than in classical ionic gases. A three stage model is proposed for an explanation of the temperature dependences of the isotope effects in molten salts. The available data of the relative difference in mobilities of isotopes in aqueous solutions are summarized. 

Huntington, H.B., 1975b, Electromigration in Metals, in Nowick, A.S. and JJ. Burton, eds.. Diffusion in Solids-Recent Developments (Academic Press, New York) ch. 6. 

Many studies have been focused on electromigration in metal interconnects [59-65]. However, these studies were based on electrically isotropic materials, such as aluminum or copper. The vacancy flux in such materials causes the inverse gradient of mechanical stress (a so-called back stress) mainly in the direction parallel to the current flow but not in the direction normal to it, hence there is no grain rotation. 

Hau-Riege, S. P. and Thompson, C. V. (2000), The effects of mechanical properties of the confinement material on electromigration in metallic interconnects. Journal of Materials Research 15, 1797-1802. 

Lattice defects in the film can affect the electrical conductivity and electromigration in metallic films, and carrier mobility and lifetime in semiconductor materials. Generally high defect concentrations result in poor electromigration properties. Lattice defects have been shown to be important to the properties of the high transition temperature superconductor films. 

Tachibana A (2002) First- Principle Theoretical Study on the Dynamical Electronic Characteristics of Electromigration in the Bulk, Surface and Grain Boundary. In Baker SP (ed) Stress Induced Phenomena in Metallization. American Institute of Physics, New York, pp 105-116... 

Step coverage. Due to the poor step coverage properties of the PVD technique, the reliability of the aluminum metallization suffers from opens due to enhanced electromigration in the contacts and vias during current passage (see chapter II). 

Next, we will apply the general equations to the problem of electromigration in a metal. In this case, the components of the mixture will be conduction electrons and metallic ions. The motion of the metallic ions in the interconnect constitutes a failure mechanism, which has received renewed interest as production circuit dimensions approach one micron (5). In this work, the ions are considered to constitute a linearly "elastic material 2). The results will be compared to previous work by approximations, and a set of equations with initial and boundary conditions, which could be solved numerically, will be presented for the first time. 

Figure 1. Electromigration in a metal block between two blocks of n+ silicon.

Graphitic polymers would be linked by strong bonds between the atoms. Unlike in metals, where metal-metal bonding is weak, these covalent structures should not be susceptible to electromigration or other processes that could change the shape of a nanometer scale fabricated structure under the influence of an electrical or magnetic field. 

Kuzmenko, P.P. (1983) Electromigration Thermomigration and Diffitsion in Metals, High School, Kyiv (in Russian). 

Stresses induced by electromigration, in conjunction with those produced by thermal fluctuations, collectively lead to diffusion of vacancies and inelastic deformation processes which cause stress-voiding and slit cracking in metal interconnects (Sanchez et al. (1992) and Joo and Thompson (1997)). Such failure processes are also strongly influenced by the crystallo-... 

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