Experimental characterization of the reliability of multi-terminal dual-damascene copper interconnect trees

The reliability of Cu dual-damascene interconnect trees with 3-terminal (dotted-I), 4-terminal ('T') and 5-terminal ('+') configurations has been investigated. The lifetime of multi-terminal interconnect trees with the same current density through the common middle via was determined to be independent of the number of segments connected at the common junction. Furthermore, our experimental results on dotted-I test structures showed an increase in the reliability of the interconnect tree when the distribution of a same current was not equal in the two connected segments, especially for the cases where one of the segments was acting as a passive reservoir or active source of Cu atoms for the adjoining segment. Due to the low barrier for void nucleation at the Cu/Si₃N₄ interface, the presence of any small atomic source in neighboring segments with enhance the reliability of a connected segment in which Cu atoms are being drained away. As a consequence, failure can occur in a tree segment which is stressed at significantly lower current densities than more highly stressed adjoining segments.