Precision passive mechanical alignment of wafers

A passive mechanical wafer alignment technique, capable of micron and better alignment accuracy, was developed, fabricated and tested. This technique is based on the principle of elastic averaging: It uses mating pyramid (convex) and groove (concave) elements, which have been previously patterned on the wafers, to passively align wafers to each other as they are stacked. The concave and convex elements were micro machined on 4-in (100) silicon wafers using wet anisotropic (KOH) etching and deep reactive ion etching. Submicron repeatability and accuracy on the order of one micron were shown through testing. Repeatability and accuracy were also measured as a function of the number of engaged elements. Submicrometer repeatability was achieved with as little as eight mating elements. Potential applications of this technique are precision alignment for bonding of multiwafer MEMS devices and three-dimensional (3-D) interconnect integrated circuits (ICs), as well as one-step alignment for simultaneous bonding of multiple wafer stacks. Future work will focus on minimizing the size of the elements.