Atomic Diffusion near Al-Grain Boundary : A Molecular Dynamics Analysis Based on Effective-Medium Theory

Atomic diffusion near an aluminum grain boundary is analyzed in order to investigate a basic mechanism of stress-induced migration (SM) in a thin wiring line in LSI. Molecular dynamics which is based on the effective-medium theory (EMT) is applied to a model containing a surface and Σ=5[001] symmetrical tilt grain boundary with bamboo-like structure. EMT is constructed using no empirical knowledge and is known to be effective for analysis of inhomogeneous atomic structure. Above the transition temperature from low-to high-temperature modes of SM, jump motion of atoms near the grain boundary occurs and the diffusion coefficients (DC) which are estimated from the mean square displacement of atoms increase remarkably. DC has the largest value in the region where the grain boundary intersects the surface. The magnitude of DC in the grain boundary region and its temperature dependence agree well with the results obtained by Plimpton et al., who have used several pair-wise interatomic potentials. It is proven that DC increases with an exponential function of the tensile strain.