Self-aligned multi-level air gap integration

Dual damascene self-aligned air gap structures have been fabricated through selective removal of interline plasma-damaged SiOC material using dilute HF solutions after metal CMP. The extent of the gaps was shown to be tuneable. The creation of interline air gaps through removal of damaged dielectric yielded significant capacitance reduction plus in addition dielectric reliability improvement. The via-reliability of 2 metal-build air gap structures was tested by thermal cycling and constant thermal stress. No significant difference in via reliability was observed between SiOC interconnects with and without air gaps. However, failure analysis showed weak spots near the bottom of the barrier, which could be detrimental for dual damascene reliability. These weak spots at the barrier bottom could lead to catastrophic failures in both via and lines during electromigration stressing. Moreover, process-related issues such as bottom liner undercut and copper corrosion need to be controlled more stringent before this air gap approach can be successfully implemented.