Response of aged line/stud structures to stepped current stressing

In this study, we have subjected an aged (stress voided) line/stud test structure to a stepped current at ambient temperature until the structure failed due to Joule-heating-induced thermal runaway. During the current stepping, resistance was also measured at a low current of 1 mA, which was applied periodically to monitor possible structural changes in the line. The resistance vs. monitor-current and the resistance vs. stepped-current measurements demonstrate interesting systematic decreases in resistance on a number of chips. Whether these decreases occur or not appears to be a function of initial damage induced during aging. It is postulated that the stepped-current resistance measurements are influenced by the presence of a flat void or thin crack associated with a stud, while the monitor-current resistance healing is influenced by the redistribution of Al(Cu) into a preexisting void in the line.