By using an acid-copper electrolyte without levelers and brighteners, we achieved defect-free filling of 0.13 mum vias with aspect ratio 8:1. This novel electrolyte consisted of copper sulfate (CuSO4.5H(2)O), sulfuric acid (H2SO4), chloride ions (Cl-), and two different average molecular weights of polyethylene glycols (PEG). The smaller-molecular-weight PEG200, with higher diffusion ability, was identified to enhance cupric ions transporting into deep features and was treated as a bottom-up filling promoter. The larger-molecular-weight PEG2000, with higher polarization resistance, provided enough inhibition effect on cupric ion reduction to obtain denser and small-grained deposits in a lower-current-density region, which benefits the filling capability in submicron features. In addition, adding PEG2000 could reduce the interfacial energy between the electrolyte and the opening of trenches/vias to enhance the filling capability.