Exploring the Limits of Cobalt Liner Thickness in Advanced Copper Interconnects

摘要

We investigate the performance and reliability characteristics of Cu interconnects with Ta-based barrier layers and Co wetting layers at 7nm node dimensions with a focus on the impacts of reducing the Co thickness from 30 & x00C5; down to 10 & x00C5;. We demonstrate that while reducing Co liner thickness significantly reduces RC delay, there is a significant reduction in electromigration reliability below a thickness of 20 & x00C5; if used in conjunction with a PVD (physical vapor deposition) TaN barrier. However, if the PVD treatment is followed by deposition of a thin ALD (atomic layer deposition) TaN, the Co layer thickness can be scaled down to 10 & x00C5; without any penalty in either electromigration or time dependent dielectric breakdown (TDDB.) The combined PVD/ALD process with 10 & x00C5; Co enables a 14 & x0025; reduction in RC delay relative to our control split.