This paper presents novel low-temperature processes that combine high-aspect-ratio polymer structures with electroless copper plating to create laterally compliant MEMS structures. This low-cost processing was developed for two applications: 1. Low-voltage comb-drive actuators for tunable capacitors to reduce the tuning voltage in MEMS structures to less than 5V and simultaneously increase the capacitance in between the electrode fingers, 2. Compliant IC-package interconnects for reliable, low-cost and high-performance nano wafer-level packaging. High-aspect-ratio polymer structures were fabricated from a photo-definable process using SU8 photoresist. The plasma/permanganate etching and electroless plating conditions were optimized to give the required adhesion and plating thickness for the SU8 structures. While SU8 can result in easy fabrication of high-aspect ratio structures, other polymers were also investigated for their superior mechanical properties. High-aspect-ratio polyimide structures with much lower stress, higher toughness and strength were fabricated using plasma etching. The dry etching results in a wall angle above 80 degrees and can lead to an aspect ratio higher than 4. The etching process also leads to roughened side walls for selective electroless plating on the side walls of the polymer structures. Simulations of these fabricated structures show tremendous reduction in the stresses at the interfaces and superior reliability and improved electrical performance for both tunable capacitors and nano interconnects. Metal-coated polymer structures from MEMS fabrication techniques can provide low-cost high-performance solutions for RF-components and wafer-level-packaging.
