DEPENDENCE OF ELECTROMIGRATION DAMAGE ON CURRENT-DENSITY

Detailed analysis of electromigration damage, voids and hillocks, form ed in layered conductors of aluminum over tungsten, revealed the follo wing: (i) The number densities (numbers of voids and hillocks formed p er unit conductor length) by electromigration are proportional to the current density; (ii) even when the void number density changes, the a verage growth rate of each void is still proportional to the current d ensity; (iii) the positions of all the voids are uniformly distributed on a line; however, there is a regularity in intervals between one vo id to the next void and one void to the next hillock. From these resul ts, especially from (i) and (ii), it is suggested that the dependence of void number density on the current density contributes to the highe r than expected dependence of electromigration lifetime on the current density.