Thick SU-8 photolithography for BioMEMS

SU-8. negative-tone epoxy base, photoresist has a great potential for ultra-thick high aspect ratio structures in low cost micro-fabrication technologies. Commercial formulation of Nano(TM) SU-8 2075 is investigate, process limitations are discuss. Good layer uniformity (few %) for single layer up to 200 mum could be obtained in a covered RC8 (Suss-MicroTec) spin coater, but for ultra-thick microstructures it is also possible to cast on the wafer a volume controlled of resist up to 1.5 mm without barrier. Long baking times are necessary for a well process control. The layout of the photomasks design and process parameters have great impact on residual stress effects and adhesion failures, especially for dense SU-8 patterns on metallic under layer deposited on silicon wafers. A specific treatment applied before the resist coating definitely solved this problem. Bio-fluidic applications of on-wafer direct prototyping (silicon, glass, plastics) are presented. An example will be given on prototyping dielectophorectic micro-cell manipulation component. The SU-8 fluidic structure is made by a self planarized multi-level process (application for 2.5 to 3D microstructures). Biotechnology applications of integrated micro-cells could be considered thanks to the SU-8 good resistance to PCR (Polymerase Chain Reaction). Future developments are focusing on the SU-8 capabilities for Deep Reactive Ion Etching of plastic and 3D shaping of microstructures using a process called : Multidirectional Inclined Exposure Lithography (MIEL).