Novel room-temperature first-level packaging process for microscale devices

Elastomer-supported cold-welding is a novel wafer-bonding process that can be performed at room-temperature, with low applied load and without applied voltage or vacuum [W.-Y. Zhang, G.S. Ferguson, S. Tatic-Lucic, Elastomer-supported cold welding for room temperature wafer-level bonding, Technical Digest of 17th IEEE International Conference on Micro Electro Mechanical Systems (MEMS 2004), Maastricht, The Netherlands, January 25–29, 2004, pp. 741–744]. It has multiple possible applications, both for temporary and permanent encapsulation of devices. In this paper, we report on the refinement and characterization of this bonding technology. First, we demonstrate improvements when new photo-patternable spin-on silicones are used instead of polydimethylsiloxane (PDMS) as the supporting material. These new materials not only simplify the patterning processing, but also reduce roughening of the bonding surfaces and enhance bond strength. We also found that self-assembled monolayers (SAMs) could be used to reduce surface roughness of the bonding surface. The Young's moduli of the new silicone materials were measured; this property was crucial in determining the load necessary for successful bonding. In addition, the surface reconstruction of the surface of the photo-patternable elastomers after modification with an oxygen plasma was characterized. This process was important in determining the maximum allowed idle time between performing key steps in the bonding process.