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Non-equilibrium molecular dynamics of electromigration in aluminum and its alloys

Şen, Fatih Gürçağ
With constant miniaturization of integrated circuits, the current densities experienced in interconnects in electronic circuits has been multiplied. Aluminum, which is widely used as an interconnect material, has fast diffusion kinetics under low temperatures. Unfortunately, the combination of high current density and fast diffusion at low temperatures causes the circuit to fail by electromigration (EM), which is the mass transport of atoms due to the momentum transfer between conducting electrons and diffusing atoms. In the present study, the effect of alloying elements in aluminum on the diffusion behavior is investigated using a non equilibrium molecular dynamics method (NEMD) under the effect of electromigration wind force. The electromigration force was computed by the use of a pseudopotential method in which the force depends on the imperfections on the lattice. 1.125 at% of various elements, namely Cu, Mg, Mn, Sn and Ti were added into aluminum. The electromigration force was then calculated on the alloying elements and the surrounding aluminum atoms and these forces incorporated into molecular dynamics using the non-equilibrium formalism. The jump frequencies of aluminum in these systems were then computed. Cu, Mn and Sn impurities were found to be very effective in lowering the kinetics of the diffusion under electromigration conditions. Cu was known experimentally to have such an effect on aluminum for several years, but the Mn and Sn elements are shown here for the first time that they can have a similar effect.