Proceedings Article | 14 May 2004
KEYWORDS: Polymers, Microfluidics, Microelectromechanical systems, Optical lithography, Crystals, Fabrication, Promethium, Glasses, Semiconducting wafers, Lithography
In the rapidly growing field of microfluidics, there is a tremendous need for alternative fabrication processes and for simple methods to integrate higher levels of functionality into microfluidic systems (i.e., fully-integrated, multi-level fluidic systems with functional valves, pumping systems, and other MEMS components). A fabrication technique recently developed at Georgia Tech involving thermally sacrificial polymeric materials allows for these innovations. In this method, which is completely compatible with traditional IC fabrication processes, thermally sacrificial polymers are coated onto a substrate and patterned into the shape of the desired channels and devices. These polymeric structures are then overcoated with a permanent structural material such as an inorganic glass or polymer. These steps can be repeated to produce complex, three-dimensional systems. Finally, the completed device structure is heated to the decomposition temperature of the sacrificial polymer which volatilizes to leave behind the desired open-channeled structures. These same materials and techniques can also be applied to the fabrication of a variety of microelectromechanical system components, including suspended membrane structures and cantilevers, that are integrated directly with IC devices on a common substrate. This process was first developed using functionalized polynorbornenes that decompose at temperatures near 425°C. In order to make this approach compatible with a wider range of substrates and structural materials, polymers with lower decomposition temperatures were desired, and polycarbonates were identified as a class of polymers with decomposition temperatures in the desired range (200-300°C). In addition, utilizing a polymer that can be patterned directly by conventional lithography greatly simplifies the fabrication process. By exploiting the acid-catalyzed thermolysis of polycarbonates, low decomposition temperature, photosensitive sacrificial polymers can be developed using mixtures of photoacid generators [PAG] and polycarbonates. Preliminary studies of several different polycarbonates, both photosensitive and non-photosensitive, have shown promising results, but optimization of these materials will be required to realize their full potential as sacrificial materials for use in microsystems manufacturing. The imaging characteristics of these polycarbonates vary greatly with the differing polymer thermal properties and polymer crystallinity, which are directly related to the polymer structure. A comparison of several new secondary and tertiary co-polycarbonates and their ability to maintain feature integrity during photolithography are presented.
