Fabrications of high-aspect ratio microstructure on metallic substrate using SU-8 resist

SU-8 is a negative, epoxy type, near-UV photoresist. The resist has been specifically developed for ultrathick, high-aspect-ratio MEMS-type applications. The adhesion of the SU-8 resist with the metallic substrate is very poor, but it is necessary to overcome this shortcoming for providing low-cost LIGA-type process in MEMS applications. In this paper, several metallic films are used as the substrates. The Ti film with oxidation treatment is found to have the strongest adhesion to the resist. SU-8 resist has been proven to be very sensitive to process variations, so the experimental optimizing technique is used in the process. Using processing parameters as control factors, experiments are performed and results are evaluated. As the results being analyzed, a proposed fabrication process is derived from optimizing the control factors. The output structure has straight sidewall profile, fine line and space resolution. The aspect ratio is greater than 20.