The effect of electromigration on unpassivated aluminum thin films has been
studied using the resistometry method. Interim information during current-
stressing can be obtained by this method. Ultimate open-circuit failure has
also been monitored by the presence of a very large increase in resistance
. The relations between the mean-time-to failure (MTTF) with the current de
nsity and with the ambient temperature have been determined. From the resis
tometry measurements, it was found that there are three stages of temporal
evolution for sputtered films. An abrupt resistance change of about 0.02-0.
04% was observed in the films under low or moderate current density. Subseq
uently, a randomly fluctuating period followed, where the fluctuating ampli
tude was about 0.01%. Finally, a fatal stage with an abrupt and tremendous
resistance increase was reached until an open-circuit failure occurred. For
sputtered films under high stressing-current density (J greater than or eq
ual to 2.35 MA cm(-2)), and for all evaporated films, the initial stage of
abrupt resistance change essentially disappeared. From the scanning electro
n microscopy (SEM) micrograph, film thinning, surface coarsening, voids in
irregular shape, and continuous cracks were found near the cathode. "Fan-sh
ape" erosion appeared in the cathode under high current density. In the ano
de, hillocks parallel to the conductor direction were observed. Perpendicul
ar extrusions extending out of the conductor were also present.