Cu Wiring Fabrication by Supercritical Fluid Deposition for MEMS Devices

Process technologies that use supercritical CO 2 fluids to fabricate high-aspect-ratio three-dimensional nano- and micro-components are described. Supercritical CO 2 is a state of CO 2 above the critical point. Supercritical CO 2 fluids are used as alternatives to common media (gases and liquids) in MEMS device fabrication to both overcome the drawbacks of these materials and to realize a superior three-dimensional process opportunity. Supercritical fluids behave as both gases and liquids, offer many of the advantages of both, and have zero surface tension. Supercritical fluids are an ideal medium for fabricating very high-aspect-ratio features owing to their superior capability of diffusion transport. As MEMSs have complex and high-aspect-ratio structures, using a supercritical fluid as a process medium in MEMS fabrication provides ideal performance in film coating, plug filling of concave features, and the etching/cleaning of residues. In this chapter, the physicochemical properties of supercritical fluids are first described in terms of MEMS processing, but from a different point of view than that of the common literature on supercritical chemical processing. Next, various applications to thin film processing are described with a focus on interconnect/wiring fabrication of MEMS devices.