THE ROLE OF CU DISTRIBUTION AND AL2CU PRECIPITATION ON THE ELECTROMIGRATION RELIABILITY OF SUBMICROMETER AL(CU) LINES

The microstructure and Cu distribution were determined for blanket and patterned Al(less-than-or-equal-to 4 wt % Cu) thin films as function of annealing. The growth of THETA-phase (Al2Cu) precipitates in blanket and patterned submicrometer-wide lines was quantified along with the Cu concentrations within the Al grains. The reliability of 0.5-mum-wide lines was found to be strongly influenced by the details of the annealing sequence; however, 1-mum-wide lines were less affected. The difference in the electromigration behavior of 0.5-mum-wide lines is shown to be due to the different film microstructures formed in the patterned lines as a function of annealing history. Specifically, the amount of Cu in the grains and the size and distribution of the THETA-phase precipitates were found to be a strong function of both the annealing conditions and the linewidth in 0.5-1-mum-thick Al(Cu) films.