Precision Passive Alignment of Wafers

Several macro-scale bench level experiments were carried out to evaluate the alignment repeatability that can be obtained through the elastic averaging principle. Based on these results, a precision passive alignment technique for wafer bonding application was devel-oped. Wafer integral features that allow two stacked wafers to self-align were designed, fabricated and tested for wafer alignment repeatability and accuracy. Testing has demon-strated sub-micrometer repeatability and accuracy can be held using the proposed tech-nique on 4 inch wafers. Passive alignment of the wafers is achieved when convex pyramids, supported on flexural cantlievers, and concave v-grooves patterned on the edges of the wafer engage and are preloaded. A silicon cantilever beam flexure between one of the wafers and the pyramid provides compliance to the coupling to avoid strain on the wafers and allows the surfaces of the wafers to mate. Both the concave coupling features and the convex coupling features are bulk microma-chined through wet anisotropic etch (KOH). The convex features are then release etche