Study on fabrication of high aspect ratio microparts using the LIGA process

In order to fabricate high-aspect ratio microparts for micro electro mechanical systems (MEMS), we have investigated the LIGA process. Exposure for deep X-ray lithography has been carried out using the world´s smallest synchrotron radiation (SR) source, AURORA. An X-ray mask, which was composed of 5 μm thick Au as an absorber and 2 μm thick SiC as a membrane, was produced. As a resist, commercially available polymethyl-methacrylate (PMMA) sheets of a thickness above 200 μm were directly glued by PMMA resin on Si wafers. Consequently, we could fabricate PMMA microstructures of 200 μm height and 4 μm width, an aspect ratio of about 50. Using these PMMA microstructures as molds, we electroformed 200 μm high Ni microstructures with the maximum aspect ratio of 40. These results show there is a good prospect of fabricating high aspect ratio microparts for MEMS