Three-dimensional (3D) technology is the next step in the development of microelectronic devices. Vertical interconnection is one of the challenging issues. Metal bonding might be one of the possible techniques to address it. In this work, direct Cu/Cu bonding at room temperature, atmospheric pressure. and ambient air was investigated. At room temperature, a 2.8 J/m(2) bonding toughness was achieved. An electron energy loss spectroscopy spectrum pointed out the absence of copper oxide at the interface. Morphological evolutions vs postbonding annealing were presented with transmission electron microscopy and X-ray diffraction analyses. The ohmic behavior of the bonding was highlighted. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3187271] All rights reserved.