Leakage and TDDB Mechanisms in 18 nm Pitch Direct Metal Etch Ru Interconnects with Airgaps

Line-to-line leakage and breakdown mechanisms in 18–26 nm on-pitch Ruthenium and airgap interconnects, fabricated using a direct metal etch process are studied. A correlation between the dominant leakage mechanisms-Fowler-Nordheim at high fields and Poole-Frenkel at low fields-and the time-dependent-dielectric-breakdown acceleration factor, which increases as voltage decreases, is identified. The weak dependence of leakage on metal pitch is attributed to the similar leakage path length through the SiCO cap layer on top of the airgap in between the lines. In contrast, a strong pitch-dependence is consistently observed for TDDB lifetimes, which is attributed to failures in the SiO2 layer at the bottom of the airgap, where the line-to-line spacing is the smallest. When accounting for E-field enhancement at that bottom interface, no dependence of TDDB lifetimes on metal pitch is observed, which is consistent with the small spacing range studied. The high TDDB acceleration factors at lower field (power law slopes ~25) ensure lifetimes of over 10 years at operating voltages and showcase DME Ru+AG as a reliable technology option for pitch scaling below 20 nm.