Published online by Cambridge University Press: 01 February 2011
Wafer level monolithic three-dimensional (3D) integration is an emerging technology to realize enhanced performance and functionality with reduced form-factor and manufacturing cost. The cornerstone for this 3D processing technology is full-wafer bonding under back-end-of-the-line (BEOL) compatible process conditions. For the first time to our knowledge, we demonstrate nearly void-free 200 mm wafer-to-wafer bonding with an ultra-thin Ti adhesive coating, annealed at BEOL-compatible temperature (400 °C) in vacuum with external pressure applied. Mechanical integrity test showed that bonded wafer pair survived after a stringent three-step thinning process (grinding/polishing/wet-etching) with complete removal of top Si wafer, while allowing optical inspection of bonding interface. Mechanisms contributing to the strong bonding at Ti/Si interface are briefly discussed.