Evidence of grain-boundary versus interface diffusion in electromigration experiments in copper damascene interconnects

Abstract

In this work, evidence of copper diffusion paths is shown with fine scanning electron microscopy failure analysis after electromigration failures in single damascene interconnect structures. For the polycrystalline grain structures, it is established that grain-boundary diffusion occurred, although experimental electromigration activation energy values are ranging from 0.65 to 0.80 eV. Narrow lines with quasibamboo microstructures showed interface diffusion located at upper surface of Cu damascene e.g., SiN capping layer interface, with activation energy values ranging from 0.80 to 1.06 eV. Due to the compression stress state in copper under electromigration and oxide cracking, respectively, SiN cap debonding occurred at the upper corners of the damascene trench and resulted in copper extrusions. For both microstructures, this failure mode provided decreased extrapolated lifetimes. Electromigration experiments on two-level damascene test structures provided an upper limit of Blech length threshold product jLth<4000 A/cm. Our data are finally compared to available literature results and to studies on AlCu.

Statistical Analysis of Electromigration Lifetimes and Void Evolution for Cu Interconnects

“…As a result, the EM driving force is relatively small in most grain boundaries. It needs to be pointed out that in wide lines with polycrystalline grain structure, the influence of grain boundaries on mass flux can be significant [Arnaud 2003]. While a major contribution of grain boundaries towards the EM mass flux is not expected in submicron lines, an influence on the determination of the initial flux divergence sites is likely.…”

Physically based models of electromigration: From Black’s equation to modern TCAD models

“…The void evolution phase can encompass several processes: a void can migrate along the interconnect [52,55], interact with the local microstructure [55,69,70] and grow, or even heal [55,71], undergo morphologic changes, assuming wedge-like shape or slit-like shape [58], before it definitely triggers interconnect failure. Furthermore, multiple voids can form in a line, so that their migration and agglomeration at a specific critical site can be the mechanism responsible for the interconnect failure [52][53][54].…”

Electrical Failure Analysis of Au Nanowires

“…5(e). The global temperature gradient across the wire is usually small except near the electrodes or the contact pads [15]. In general, voids and hillocks (or extrusions) are formed close to the cathode and anode.…”