Ultrathin Cu seed layer was deposited by metallorganic chemical vapor deposition (MOCVD) on Ru layer using hexafluoroacetylacetonate copper vinyltrimethylsilane [(hfac)Cu-I(vtms)]. On Ru, the incubation time for Cu MOCVD was nonexistent. As compared with MOCVD Cu on TaN, the nuclei density of Cu was considerably increased on Ru and the wetting angle of Cu on Ru was small (22 degrees). Therefore, the coalescence between Cu islands on Ru layer begins earlier by prohibiting the severe three-dimensional Cu growth that is generally observed on TaN layer. As a result, 10 nm thick continuous Cu film with 1.75 nm root-mean-squared surface roughness was easily prepared on 40 nm thick Ru at 150 degrees C. (c) 2006 The Electrochemical Society.