CHARACTERIZATION OF THE EARLY STAGES OF ELECTROMIGRATION AT GRAIN-BOUNDARY TRIPLE JUNCTIONS

The formation and growth of holes and hillocks at grain boundary triple junctions in thin-film conductors of gold on gallium arsenide and thin-film conductors of aluminum-1 wt. % silicon on (oxidized) silicon during the early stages of electromigration have been investigated through measurement of fractional change of electrical resistance DELTA-R/R and microstructural characterization by scanning and transmission electron microscopy. Each grain boundary triple junction is characterized by a unique structure factor DELTA-Y, which defines the degree of cumulative flux divergence and, consequently, the degree of susceptibility to formation and growth of holes or hillocks. Resultant holes are characterized by a shape factor f, which defines the degree of noncircularity and, consequently, relates fractional change of hole area to DELTA-R/R. Estimates of the upper limit for DELTA-Y and the average value of f are in good agreement with measured values of DELTA-R/R and consistent with observed microstructure.