Packaging of devices for topside cooling by replacing air-bridges with Su-8 polymer bridges [MESFET example]

This paper takes an in-depth look at the qualifications of Su-8 photoresist as a low-k dielectric in the fabrication of integrated circuits (ICs). This paper discusses replacing air bridges on MESFET devices with polymer bridges fabricated from Su-8. This polymer bridge structure has several impacts for on-wafer processing as well as topside cooling packaging techniques for microwave devices. For on-wafer processing, replacing airbridges with polymer bridges eliminates the need for wafer thinning, through-wafer vias, and provides a dielectric interface material for Cu interconnects. Eliminating processing steps as well as the fragile topside air-bridge structures improves both the yield and the reliability. From a packaging perspective, fabricating polymer bridges allows further topside processing to take place in order to build packaging structures that can both remove the FET generated heat from the topside of the device as well as have access to the electrical I/Os.