Electromigration Activation Energies in Alternative Metal Interconnects

Abstract

The electromigration (EM) activation energy (E A ) of alternative metals, 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.

Electromigration Reliability of Barrierless Ruthenium and Molybdenum for Sub-10 nm Interconnection

“…The MTTF was obtained from EM devices via the accelerated EM test. Beyne et al suggested that the EM-induced-void formation temperature could be the sum of the ambient temperature and the Joule heating temperature ( T amb + T JH ) . In our devices, we confirmed that voids were formed at the moment of EM failure (Figures S2 and S3).…”

“…Traditionally, the ambient temperature has been directly used for calculating E A,EM from the Arrhenius plot of Black’s equation. However, recent studies suggest that considering the additional temperature increase by Joule heating caused by a current flow can lead to a more accurate derivation of E A,EM . ,, Therefore, we determined the final temperature of EM samples during CCS measurements by employing TCR measurements. We directly measured the thermal properties of the film samples, while we calculated the parameters for wire samples, considering their geometrical differences relative to the film samples.…”

“…27 Furthermore, Beyne et al calculated the E A,EM of Ru with passivation to be about 2 eV, considering Joule heating using low-frequency noise (LFN) measurements. 28 Although a high EM performance is expected for Ru, comprehensive confirmation is required based on electrical, electrochemical, and geometrical analysis without the barrier.…”

Low-Frequency Noise Measurements for Electromigration Characterization in BEOL Interconnects

“…The type of process (metal etch or damascene) does not impact the Ru activation energy and neither does the difference in grain structure and surface roughness (associated with the different process conditions). In Ru, the 1 eV E A is attributed to surface diffusion [37][38][39]. Sample Ru 3, does have a slightly lower E A (-0.05 eV), which is attributed to its lack of adhesion layer, resulting in a weaker SiO 2 -Ru interface.…”

Recent Progress in Physics-Based Modeling of Electromigration in Integrated Circuit Interconnects

“…the current density that induces failure at 10 y. Under such a scenario, interconnects based on Ru and Co are potential replacements with better reliability than Cu because of their lower resistivity and higher EM activation energies [55][56][57][58][59][60]. The barrierless Ru interconnect together with an integration scheme have been identified to be more EM reliable than Cu [61].…”