Process technologies that use supercritical CO2 fluids to fabricate high-aspect-ratio three-dimensional nano- and micro-components are described. Supercritical CO2 is a state of CO2 above the critical point. Supercritical CO2 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.
Part of the book: Novel Metal Electrodeposition and the Recent Application
Reliable and high-precision Cu/glass stacks are particularly desirable for microelectromechanical systems and packaging technologies. One solution for improving the adhesion strength of Cu/glass stacks is to form adhesion layers between the Cu films and the glass substrate. Many studies have shown that a strong adhesion layer is formed at the interface by high-temperature annealing when a Cu alloy is used instead of pure Cu. It is important to reduce the temperature and process time in order to reduce the thermal budget and fabrication cost. Therefore, the room-temperature process for fabrication of Cu/glass stack is desirable. In this chapter, typical advanced low-temperature processes including room-temperature process are introduced.
Part of the book: Lead Free Solders