Effect of copper on the microstructure and electromigration lifetime of Ti-AlCu-Ti fine lines in the presence of tungsten diffusion barriers

Abstract

A systematic study was performed of the microstructural and electromigration characteristics of Ti-Al(Cu)-Ti laminate structures fabricated from two metal wiring levels 1 μm in width. The total Cu content in the Al(Cu) core layers was varied from 0.5 to 2.0 wt %. A high degree of 〈111〉 texture was found for all Cu concentrations except for the 0.5 wt % film. Grain size statistics were found to be independent of the Cu concentration. The Al grains were supersaturated with Cu which led to shifts in resistance during low temperature baking and electromigration testing. The electromigration lifetime of stripes connected to large reservoirs of Cu and Al was found to be linearly dependent on the total Cu content, whereas there was a "roll off" in the lifetime of two-level W stud structures as the Cu content was increased. The activation energy for electromigration induced failure was found to be 0.78-0.93 eV. Resistance shifts during electromigration and temperature only stressing and the microstructural characteristics of failed structures were explained terms of the distribution of Cu in the Al matrix and the geometry of the structures using a blocking boundary model. © 1996 American Institute of Physics.