Copper electroless deposition (ELD) was investigated for applications that create a seed layer for Cu electrodeposition. On Pd catalysts formed on the Ta substrates through Sn sensitization-Pd activation, continuous Cu seed layer of 40 nm was electrolessly deposited in a diluted electrolyte. Dilution of the electrolyte enabled the film to make a thin and conformal layer without oxygen incorporation, by which the ELD Cu seed had properties comparable to the physical vapor deposited seed layer regarding surface roughness and resistivity, even after subsequent Cu electrodeposition, and had superior step coverage. Defect-free bottom-up filling by electrodeposition was achieved on these ELD seed layers. (c) 2006 The Electrochemical Society.