High aspect ratio through Si vias (phi 2 mu m, depth 30 mu m) have been filled completely by Cu electroplating using an electroless deposited Cu seed layer. The electroless Cu deposition was carried out on ALD-Ru; the time transient of the mixed potential on Ru showed a catalyst type of behavior. The ELD-Cu, which was deposited inside TSVs along their sidewalls, was defect free and worked as a seed layer for electrodeposition of Cu to fill the structure. With a conventional method, such as PVD-Cu, it is challenging to deposit a seed in such structures. The adhesion strength of this ELD-Cu film on ALD-Ru was measured to be >100 MPa. These coupon-scale results show the feasibility of electroless deposition in TSV processing. (C) 2013 Elsevier Ltd. All rights reserved.