5.1 Electromigration Failure in Open TSVs

Open TSV structures are composed of different materials and their design comprises various corners and material interfaces. These regions of the interconnect structure represent potential technology weaknesses which break the homogeneity of the current flow and promote electromigration failure. The electromigration wear-out failure mechanism is normally examined by considering an initial nucleation of the void and its subsequent growth, which triggers an open circuit type of failure. Voids nucleate in the interconnect due to the development of tensile stress, particularly at those locations, where the adhesion between the metal layer and the surrounding material is weak [63]. Once the void has nucleated, the void evolution mechanism leads to a rapid increase in the interconnect resistance eventually resulting in an open circuit failure. After the maximum tolerable resistance level is exceeded, the interconnect is deemed to fail. The time-to-failure (TTF) of the interconnect is defined as the time required to reach the threshold resistance.

It is convenient to analyze the electromigration problem in the open TSV structure by treating the two phases of failure, namely the early phase of void nucleation and the late phase of void evolution, separately, as discussed in previous chapters.