Creep and contact opening electromigration failures in miniaturized interconnects

Transition from transport-controlled to interface reaction-controlled regime is a characteristic feature of diffusion mass transfer in small dimensions. Applied to contact opening electromigration (EM) failures in microelectric thin metal film conductor lines (interconnects), this concept predicts transition from electrotransport – to the creep-controlled regime (CCEM), with diffusional creep assumed as the kinetic mechanism of EM stress relaxation. In CCEM, the contact opening rate is totally controlled by stress relaxation into hillocks, a strictly local mechanical process, which acts at the anode end of the line in series with electrotransport along the line. Instead of the diffusivity along the line, the creep viscosity evolves to be the major material property, which determines the failure rate in short interconnects. This provides conceptually new explanation of the short stripe effect in EM, which has become a core element in the analysis of EM. Complemented by the idea that the conventionally measured EM threshold is apparent, and not a true value, this approach provides a self-consistent, quantitative description of the available EM kinetics and threshold observations and suggests a paradigm shift in the analysis of EM in miniaturized interconnects. Finally, implications of the results for the EM time-to-failure prediction are discussed.