Materials for Micro and Nano Systems - Effects of Active Atomic Sinks and Reservoirs on the Reliability of Cu/low-k Interconnects

Effects of Active Atomic Sinks and Reservoirs on the Reliability of Cu/low-k Interconnects

F.L. Wei, C.S. Hau-Riege (AMD), A.P. Marathe (AMD), T.J. Park, T. Chookajorn, C.V. Thompson
Sponsorship: Intel, AMD, Texas Instruments, SRC

Electromigration experiments using Cu/low-k interconnect tree structures (as in Figure 1) were carried out in order to study the effects of active atomic sinks and reservoirs on interconnect reliability. In all cases, failures occurred after along period of void growth. Kinetic parameters were extracted from resistance versus time data, giving (Dz*)0,eff = 3.9 x 10-10 m2/s and z* = 0.40 ± 0.12. 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. We made 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. As the Young’s modulus of the inter-level dielectric (ILD) films decreases, B decreases; further, the positive effects of reservoirs are diminished and the negative effects of sinks are amplified [1].

Figure 1: Simple multi-segment interconnect trees were tested with different currents in each segment. In the case shown above, tests were carried out to determine effects of both active (with current) and inactive (without current) segments serving as atomic reservoirs for the short segment. The arrows indicate the direction of electron transport. Both active and inactive reservoirs lead to improved reliability. Interconnect trees were also tested with long segments serving as atomic sinks for short test segments. These atomic sinks led to a degradation in reliability.

Reference
[1] F.L. Wei, C.S. Hau-Riege, A.P. Marathe, and C.V. Thompson, “Effects of active atomic sinks and reservoirs on the reliability of Cu/low interconnects,” Journal of Applied Physics, 2008, to be published.