Molecular dynamics study of nano-scale Ag surface electromigration and effect of Pd coating layer

Ag is the most conductive metal but is vulnerable to electromigration (EM), which can limit its application in e.g. microelectronics. Molecular dynamics (MD) is used to simulate the migrating behavior of an Ag surface by adding an extra directional force on each atom. The migration of Ag atoms is found to be limited to the topmost 4 (002) lattice planes in the first 40 ns while atoms in the crystal bulk remain oscillating around their equilibrium positions. A Pd coating layer is shown to be a protection from EM for an Ag surface. After adding a layer of 9 Pd (002) lattice planes, the same procedure is repeated with different forces. No migration happens until the extra directional force become so large that all atoms of the model end up moving freely. The MD model presented in this paper can lead to an understanding of EM at the atomic scale and a guideline for potential reliability improvement of microelectronics by coating technology.