Atomic diffusion near Al grain boundary. (Molecular dynamics analysis based on effective-medium theory)

Abstract

Atomic diffusion near an aluminum grain boundary is analyzed in order to investigate the basic mechanism of stress-induced migration (SM) in a thin wiring line in LSI. Molecular dynamics based on effective-medium theory (EMT) is applied to a model consisting of a surface and Σ=5[001] symmetrical tilt grain boundary with a bamboo-like structure. EMT is derived without any empirical knowledge and is known to be effective for analysis of an 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 (DCs) which are estimated from the mean square displacement of atoms increase markedly. DC is largest 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 and Wolf [Phys. Rev., B, Vol.41, No. 5 (1990), p. 2712], who used several pair-wise interatomic potentials. It is proven that DC increases exponentially with tensile strain and decreases with compressive strain.