A linear stability analysis was performed for a partially conductive circular void in an otherwise infinite conductive medium. A relationship was established between the inner conductivity (that of the medium in the void) and the critical remote electric field intensity for linear stability of the void. It was proved that, when the inner conductivity became zero, the critical remote electric field intensity became infinite. The inner conductivity of a vacuum void could be considered to be zero. This explained why the vacuum circular void was linearly stable. It was also shown that, when the inner conductivity was very small, the stability of a void was sensitive to its magnitude. If the inner conductivity was equal to 0.1% of that outside the void, the critical remote electric field intensity was only 20 times that for the dislocation loop case.

Linear Analysis of Electromigration-Induced Void Instability in Al-Based Interconnects T.H.Hao, Q.M.Li: Journal of Applied Physics, 1998, 83[2], 754-9