Electromigration Behavior in Layered Ti/AlCu/Ti Films and its Dependence on Intermetallic Structure

Abstract

ABSTRACTA sputtered aluminum-low copper (Cu concentration < 2wt.%Cu), multilayered, submicron, device interconnect metallurgy consisting of two TiAl3 layers (∼,0.1μm thick) under and over an Al-Cu alloy conductor (0.95μm thick) with either an Al-Cu or TiN cap layer (0.05μm thick) has been developed. These films were patterned by reactive ion etching, and showed both a low susceptibility to corrosion and a low resistivity. Electromigration lifetime data on Al, Al-Cu, and both dc magnetron sputtered and electron gun evaporated multilayered fine lines, fabricated and tested in the same laboratory, are included for a direct comparison. Outstanding electromigration behavior was measured for sputtered, multilayered, submicron films with copper concentrations between 0.12 – 2wt.%Cu. In contrast, electromigration lifetimes of evaporated, multilayered films were found to degrade rapidly at < 2wt.%Cu. This anomalous electromigration behavior was attributed to structural differences in the Ti-Al intermetallics formed. It is proposed that defects present in the Ti-Al superlattice phase cause decreased electromigration performance compared to films in which TiAl3 exclusively forms. Multilevel structures, consisting of CVD W interlevel vias, were also investigated and found to have significantly degraded electromigration performance compared to planar samples. This was attributed to geometric and material flux divergences at the via/conductor interfaces.