Electro-stress migration induced instability at heterogenous interfaces

Voiding by electromigration and stress migration is accepted as the main cause of failure in today's integrated circuits. A linear stability analysis is employed to assess the likelihood of voiding at the interface between a thin metal layer and two conductive half-planes. By perturbing the interface chemical potential an atomic mass flux is generated, which in turn alters the interface morphology and consequently the chemical potential. A critical electric current density j_cr is derived as a function of the perturbation periodicity λ and dimensionless electromechanical parameters of the system above which the interface is unstable: voids are likely to nucleate. It is shown that (i) as the thickness of the layer reduces or the periodicity of the perturbation increases, and (ii) as the dimensionless interface mobility, effective charge and elastic modulus increase the critical current reduces and so does the risk of voiding.