Postvoiding Stress Evolution in Confined Metal Lines

PROJECT TITLE :

Postvoiding Stress Evolution in Confined Metal Lines

ABSTRACT:

Electromigration (EM)-induced voiding is a vital reliability concern in modern integrated circuits. Resistance degradation in interconnect metal lines caused by voiding was studied in this paper theoretically by solving the continuity equation describing the stress evolution caused by growing void. A rigid confinement surrounding a metal line makes inapplicable an approximation of the road edge drift for modeling the void volume evolution unless a line is during a stress-free equilibrium state caused by the presence of a saturated void. Derived analytical answer to the continuity equation with a voidless initial condition provides drastically different stress evolution kinetics compared with the case of the road edge drift model. It demonstrates that a massive stress gradient, that was developed between the surface of a void precursor (flaw) and a metal, becomes a serious driving force for the atom migration from the void surface to the metal. In this case, the initial evolution of the void volume will not depend on the electric current density contrary to the case of the road edge drift approximation characterised by the linear dependence of the void growth rate on this density. At while limit, the derived resolution provides the identical kinetics and therefore the steady state with the stress linearly distributed along the line as within the case of preexisted void. The proposed model results a lot of faster kinetics of the void growth and the road resistance degradation than the road edge drift approximation. Void nucleation time can be used as a affordable approximation of the EM-induced time to failure within the confined metal line.

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