Simulation and measurement of the capacitance benefit of air gap interconnects for advanced technology nodes

•Capacitance benefit of air gap structures is simulated.•Thickness of sidewall liner plays a crucial role.•Geometry of cap layer does not affect the capacitance significantly.•Simulation result matches with the experimental structures.

Air gap (AG) interconnects, with an ideal dielectric constant k of 1, is a promising approach to reduce signal propagation delay. In this paper, a comparative study of AG and dielectric copper damascene interconnect structures is performed through Raphael™ electric field simulation to investigate the capacitance benefit of introducing AG when scaling to small dimensions. The variation in total capacitance as a function of half pitch is simulated for different AG integration schemes proposed in the literature. Ideal and practical cases of these different integration schemes are simulated and compared to assess whether interconnect structures using a low-k (k = 2.3) dielectric are more suitable than AG interconnects at scaled dimensions. The effect of using an additional (SiC-based) stiff liner on the AG capacitance benefit is also investigated. Finally, we verify our simulations using sub-40 nm half pitch AG structures prepared using the conformal and non-conformal processes.

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