Taguchi optimization for SU-8 photoresist and its applications in microfluidic systems

In this paper, the optimization and application results of SU-8 are reported. SU-8 is an ultra-thick, negative, epoxy- type, near UV photoresist based on EPON SU-8 resins from Microchem Corp. SU-8 is a highly photosensitive resist and its properties are greatly affected by the process parameters. The parameters, which have influence on the properties, were optimized by three level, L9 Orthogonal Array of Taguchi Method. Two kinds of photoresists, SU-8 and SU-8 50, and four parameters such as the prebake time, postbake time, exposure time and developing time were chosen to optimize. We found that there exist some minor differences between out result and the published data. This different could be due to either the EPON SU-8 content or the fabrication conditions. According to the optimized data, for SU-8 and SU-8 50, many microstructures with thickness more than 100, 500 micrometers and aspect ratio more than 20, 50 were obtained, respectively. All these were achieve without the introduction of GPL, a stronger developing solution. The positive photoresists AZ9260 with thickness more than 20 micron were patterned as the sacrificial layer. Using SU-8 as the structural layer, we fabricated some micro-components such as micro-cantilevers, microchannels and micro- heatpipes. The primary experiments demonstrated that SU-8 could be used as the structural material for micro- components and even for some MicroElectroMechanical Systems.