Effects of active atomic sinks and reservoirs on the reliability of Cu ∕ low - k interconnects

Electromigration experiments using Cu ∕ low - k interconnect tree structures were carried out in order to study the effects of active atomic sinks and reservoirs on interconnect reliability. In all cases, failures occurred after a long period of void growth. Kinetic parameters were extracted from resistance versus time data, giving ( D z * ) 0 , eff = 3.9 × 10 − 10 m 2 ∕ s and z * = 0.40 ± 0.12 . By using these values, the evolution of stress in each of the interconnect tree segments could be calculated and correlated with the rate of void growth and failure times for all test configurations. It is demonstrated that segments that serve as atomic sinks and reservoirs for the failing segments affect the lifetime by modifying the conditions for stress induced migration. Reservoirs can lead to increased lifetimes, while sinks can lead to reduced lifetimes. Quantitative predictions of the times required for failure for Cu ∕ low - k interconnect trees as a function of the effective bulk elastic modulus of the interconnect system, B , are made. As Young's modulus of the interlevel dielectric films decreases, B decreases, and the positive effects of reservoirs are diminished and the negative effects of sinks are amplified.