Void-Free Copper Pillar Hybrid Wafer Bonding Using a BCB Based Polymer Adhesive and Chemical Mechanical Polishing

To maintain the industry goal of increasing performance with every new generation of technology it is necessary to further shrink the package size in the zdimension through the use of 3D-TSV and copper pillar structures. This approach will allow electronics manufacturers to reduce the die-to-die distance while maintaining reliability of the device. In this paper, we demonstrate the feasibility of an alternative TSV buildup approach through planarizing both copper pillars with a height of less than 10 microns and partially cured polymer adhesive using chemical mechanical polishing, followed by bonding of the singulated die. Previously, researchers at RPI [1-2] demonstrated the ability to bond copper-polymer structures using a copper dual damascene integration scheme. In this approach, copper slurries removed the copper overburden and, although bonding of the copper areas was achieved, gaps between the polymeric adhesive layers were visible after bonding. To overcome this issue, we have developed two approaches to planarize both the copper pillar as well as the polymeric adhesive. The first approach relies on non-selective CMP of the two materials; the second approach relies on sequential steps of polymer and copper removal.