Effective and efficient removing method of micromolds in UV-LIGA using CO2 laser ablation followed by O2/CF4 plasma finishing for high-aspect-ratio metallic microstructures

Abstract

UV-LIGA process has manifested its potential in the fabrication of high-aspect-ratio metallic microstructures. However, how to attain the complete, fast, and non-swelling removability of the crosslinked SU-8 micromolds remains a grand challenge. To address this challenge, we propose an effective and efficient removing method utilizing CO2 laser ablation followed by O2/CF4 plasma finishing for the fabrication of metallic microstructures in UV-LIGA. As the focused CO2 laser beam with a specific wavelength ablates the non-metal polymers but does not react with the electroformed nickel, it is used as the primary step to remove most of crosslinked SU-8 without swelling in a very short time. As the finishing step, the O2/CF4 plasma is then implemented to remove the residues and keep the metallic structures clean. We quantitatively investigate the effects of laser power, laser scanning speed, and laser pass numbers on the SU-8 ablation thickness to obtain the proper removal conditions. Utilizing the UV-LIGA fabricated micromolds and the proposed removal method, we successfully fabricate the metallic microstructures with aspect ratio up to five. Also, we evaluate the performance of the proposed method by changing various shapes, grating widths, and space intervals for the grating structure. These results prove that our method is effective and efficient in removing the SU-8 micromolds in UV-LIGA for the fabrication of metallic microstructures.