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MM: Fachverband Metall- und Materialphysik

MM 18: Electronic properties I

MM 18.2: Vortrag

Dienstag, 27. März 2007, 12:00–12:15, H6

Electromigration in Ag(Cu) lines — •R. Emling, U. Schoepka, M. Becherer, and D. Schmitt-Landsiedel — Technical University Munich, Institute for Technical Electronics

Degradation of conducting lines in integrated circuits due to stress by high current density is referred to as electromigration. Voids and hillocks build up by flow of material and increase resistivity until the line breaks or builds a short with an adjacent line. It is well known that small quantities of impurity in a metal can reduce electromigration significantly while resistivity increases only slightly.

In this work thin films of pure Ag and Ag(Cu) with 1.2 % and 2.0 % of Cu were sputter deposited and patterned by a hybrid etching process to produce NIST electromigration test patterns with 5 µm width, 500 µm length and 300 nm thickness. Deposition of the Ag(Cu) alloy was performed by magnetron sputtering using a process newly developed at the institute: Cu wires were attached in parallel to the surface of a pure silver target which resulted in sputtering both, silver and copper, at the same time. The amount of sputtered copper was controlled by the number and thickness of wires. EDX measurements showed a homogeneous dispersion of copper in the layer.

Electromigration measurements were performed at a constant current density of 22 MA/cm² until the lines failed within up to 16 days. In this process Ag(Cu) lines with 1.2 % Cu turned out to endure three times longer and lines with 2.0 % Cu up to four times longer than pure Ag lines. In conclusion we can assert a significantly higher electromigration resistance of Ag(Cu) lines.