Electromigration Activation Energies in Alternative Metal Interconnects

The electromigration (EM) activation energy (E-A) of alternativemetals, such as Ru and Co, was obtained using low-frequency noise (LFN) measurements. High activation energies were expected, but values of 1 eV are found, most likely related to diffusion along with the metaldielectric interface. Wafer-level accelerated EM tests were carried out to compare the LFN E-A to the EM E-A in the Ru wires. The calculation of the EM E-A is found to be strongly dependent on the assumed temperature profile in the wire due to Joule heating (JH). The temperature profile was calculated analytically, assuming the contacts are at ambient temperature. For a void forming in direct proximity of the contact, the EM E-A then matches the LFN E-A. For a void at average wire temperature (ambient + JH), E-A 2 eV. In addition to demonstrating the application of LFN to study EM in alternative metals, this article also cautions for the impact of JH on the calculation of E-A in interconnects.