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(≤4 wt % Cu) thin films as a function of annealing. The growth of Θ-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-μm-wide lines was found to be strongly influenced by the details of the annealing sequence; however, 1-μm-wide lines were less affected. The difference in the electromigration behavior of 0.5-μm-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 Θ-phase precipitates were found to be a strong function of both the annealing conditions and the linewidth in 0.5-1-μm-thick Al(Cu) films.