Evaluation of Direct Cu Electroplating on Ru: Feature Fill, Parametric, and Reliability

Cu films were directly deposited on Ru to check the feasibility of this process for Cu back-end-of-the-line integration beyond 32-nm technology nodes. Feature-fill enhancement was observed from the direct electroplating process as compared to the conventional one with the Cu electroplating performed on a PVD Cu seeding layer. Reasonable parametric yields were demonstrated for the direct electroplating process. The electromigration (EM) resistance of the directly plated Cu lines was degraded relative to that observed on the conventionally plated Cu lines. The observed EM resistance degradation is attributed to a weak interface between Ru/Cu, which can be caused by impurities from the electroplating process.