A novel method for nanoprecision alignment in wafer bonding applications

Wafer bonding has been identified as a promising technique to enable fabrication of many advanced semiconductor devices such as three-dimensional integrated circuits (3D IC) and micro /nano systems. However, with the device dimensions already in the nanometre range, the lack of approaches to achieve high precision bonding alignment has restricted many applications. With this increasing demand for wafer bonding applications, a novel mechanical passive alignment technique is described in this work aiming at nanoprecision alignment based on kinematic and elastic averaging effects. A number of cantilever-supported pyramid and V-pit microstructures have been incorporated into the outer circumference area of the to-be-bonded Si chips, respectively. The engagement between the convex pyramids and concave V-pits and the compliance of the support cantilever flexures result in micromechanical passive alignment which is followed by direct bonding between the Si chips. The subsequent infrared (IR) and scanning electron microscopy (SEM) inspections repeatedly confirmed the achievement of alignment accuracy of better than 200 nm at the bonding interface with good bonding quality. The impact and potential applications of the developed alignment technique are also discussed