DEPENDENCE OF ELECTROMIGRATION DAMAGE ON CURRENT-DENSITY

Detailed analysis of electromigration damage, voids and hillocks, formed in layered conductors of aluminum over tungsten, revealed the following: (i) The number densities (numbers of voids and hillocks formed per unit conductor length) by electromigration are proportional to the current density; (ii) even when the void number density changes, the average growth rate of each void is still proportional to the current density; (iii) the positions of all the voids are uniformly distributed on a line; however, there is a regularity in intervals between one void to the next void and one void to the next hillock. From these results, especially from (i) and (ii), it is suggested that the dependence of void number density on the current density contributes to the higher than expected dependence of electromigration lifetime on the current density.