Electroless Cu deposition on atomic layer deposited Ru as novel seed formation process in through-Si vias

High aspect ratio through Si vias (φ 2 μm, depth 30 μm) 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