A comparative study of different thick photoresists for MEMS applications

This work reports on recent advances in microfabrication process technology for medium to high-aspect ratio structures realised by UV photolithography using different kinds of photoresists. The resulting structures were used as moulds and will be translated into metallic structures by electroplating. We used four types of photoresists: SPR 220-7 novalak based (positive), SU8 epoxy based (negative), Ordyl P-50100 acrylate based (negative) dry film photoresist, and Diaplate 132 acrylate based wet photoresist (negative). The motivation for this work was to find an alternative to SU-8 photoresist, which is difficult to process and remove after electroplating. Depending on the application, we found that Ordyl P-50100 dry film photoresist is the best alternative to SU8 for realization of approximately 100 μm deep moulds for electroplating in acidic electroplating solution. SPR 220-7 is a good alternative to SU8 for fabrication of 50 μm deep moulds and electroplating in alkaline solutions.The results presented in this paper will open up new possibilities for low-cost processes using electroplating for MEMS applications