Fabrication of high aspect ratio 35 μm pitch through-wafer copper interconnects by electroplating for 3-D wafer stacking

We report the fabrication of high aspect ratio (similar to 15) ultradense (similar to 80000/cm(2)) through-wafer copper interconnects by a special aspect ratio dependent electroplating technique. In this approach, electroplating process parameters were continuously varied along with varying unfilled via depth, to maintain the uniform current distribution and thus uniform metal deposition. Copper interconnects, with diameters as small as 12 mu m and a pitch of 35 mu m, were electroplated without any voids. Due to ultrafine pitch and extremely high number of I/Os per cm(2), these interconnects were found to have significant potential in three-dimensional (3-D) wafer stacking and other high-density electronic packaging applications. (c) 2006 The Electrochemical Society.