The use of bis͑3-sulfopropyl͒ disulfide ͑SPS͒ in Cu electroless deposition resulted in Cu bottom-up filling. However, the high accelerating effect of SPS led to a poor electrical property of the film and generated many voids in the film by increasing the surface roughness and causing unstable deposition behavior. The addition of 2,2Ј-dipyridyl together with SPS substantially improved the film quality of the gap-filled Cu maintaining the bottom-up filling behavior. It lowered the film

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... by approximately 23% and enhanced the crystallinity. No voids were detected in the as-deposited Cu even after annealing.