Bottom-up copper electroplating using transfer wafers for fabrication of high aspect-ratio through-silicon-vias
Three-dimensional (3D) integration is emerging as an attractive technology to continue Moores law through the integration of multi-stacked chips interconnected with through-silicon-vias (TSVs). To address the challenge in filling high aspect-ratio TSVs with copper, this paper reports an improved bottom-up copper electroplating (BCE) technique by introducing a glass transfer wafer, which is temporarily bonded with the device wafer to provide a copper seed layer. As the copper seed layer on the transfer wafer covers the through-holes, copper is electroplated from the bottom seed layer to the top opening of the through-holes without forming any voids or seams. This avoids the time consuming sealing process in conventional BCE, which normally takes 35h. Thanks to the mechanical support of the transfer wafer, the device wafer can be thinned to several tens of micrometers. Using this technique, TSVs with diameter of 5?m and aspect-ratio of 13:1 have been achieved. Based on the improved BCE technique, a through-via type 3D integration strategy is developed.
transfer wafer through-silicon-vias (tsvs) bottom-up copper electroplating (bce) 3d integration