BCB Wafer Bonding Compatible With Bulk Micro Machining

Adhesive wafer bonding is a good substitute in wafer-to-wafer bonding applications requiring low processing temperatures and electrical potentials, though at the expense of difficulty with chemical, mechanical, and thermal stability over time. In the case of wafer bonding for Micro-Electro-Mechanical System (MEMS) applications, the problem is compounded not just by consideration of bond strength, but also by limitations in the way adhesives are delivered to the interface, since traditional spin-coating methods cannot be directly employed. A typical approach is the formation of micro-fluidic channels via wafer bonding, where the adhesive layer should only be present on the mesa structures. The introduction of BCB (benzocyclobutene), dry-etchable polymers, makes it possible to pattern the adhesive layer in a similar fashion with the rest of the bulk material. In this paper we present a BCB-based wafer bonding process, which is compatible with bulk micro machining. Depending on applications, BCB can replace the silicon oxide or silicon nitride as a hard mask in bulk micro machining. A process using BCB as both bonding adhesive and bulk-etch mask is a good option for stacking microstructures such as building micro-fluidic circuitry.