Multilevel Interconnect With Air-Gap Structure for Next-Generation Interconnections

A misalignment-free multilevel air-gap interconnect with a via-base structure was fabricated by self-aligned gap formation and etch back. Its reliability was investigated by measuring stress-induced voiding, electromigration (EM), and time-dependent dielectric breakdown (TDDB). There was no via degradation after thermal stress (at 200degC for 500 h). The EM lifetime was the same as that of a conventional damascene interconnect, and the TDDB lifetime was about two orders of magnitude longer. Increasing the etch-back thickness of the interlayer dielectric increased the capacitance reduction by about 17%-32%. The frequency of a ring oscillator with an air-gap interconnect was higher by 17% on average than that with a conventional damascene interconnect. The simulation results demonstrate that this air-gap interconnect has the effective dielectric constant required for next-generation interconnects (22-nm node).