Formation of thick SU-8 mold for the fabrication of UV-LIGA based nickel micro-gyroscope structures

SU-8 is a high contrast, epoxy based negative tone photoresist designed for MEMS and other microelectronic applications, where a thick, chemically and thermally stable image is desired. However, in practice, SU-8 is found to be very sensitive to process parameters variation. This paper reports an optimized process for creating thick SU-8 mold and its application in the fabrication of UV-LIGA based nickel micro-gyroscope structures. Initial experiments are carried out on 4 inch silicon wafers with two different micro-gyroscope structures, a 2-DOF linear micro-gyroscope having minimum feature size of 5 mu m and a 4-DOF linear micro-gyroscope having minimum feature size of 3 mu m. The patterned SU-8 is examined using scanning electron microscopy (SEM) and is found to be completely resolved having near vertical side walls. Finally, the micro-gyroscope structures are successfully fabricated using SU-8 based UV-LIGA process having 10 mu m thick nickel as the key structural layer.