SU-8: promising resist for advanced direct LIGA applications for high aspect ratio mechanical microparts

A case study of use of negative type SU-8 X-ray sensitive resist for fabrication of advanced, highly precise, ultra tall direct LIGA mechanical microparts is presented in this paper. Using direct LIGA technique, ～1 mm tall highly precise metallic gear wheels are being fabricated, previously using PMMA based process. Starting from a non-optimized non-satisfying SU-8 process, significant process parameters for process optimization were identified using statistical design of experiment. By varying the significant process parameters, SU-8 process was further optimized with respect to critical aspect of sidewall bow and tilt of metallic structures. After the optimization, metallic parts fabricated using SU-8 process showed comparable quality as those fabricated using PMMA based process.