Research on the process of fabricating a multi-layer metal micro-structure based on UV-LIGA overlay technology

Abstract

In this paper, we report the study of the process of fabricating a multi-layer metal micro-structure using UV-LIGA overlay technology, including mask fabrication, substrate treatment, and UV-LIGA overlay processes. To solve the process problems in the masking procedure, the swelling problem of the first layer of SU-8 thick photoresist was studied experimentally. The 5 μm line-width compensation and closed 20 μm and 30 μm isolation strips were designed and fabricated around the micro-structure pattern. The pore problem in the Ni micro-electroforming layer was analyzed and the electroforming parameters were improved. The pH value of the electroforming solution should be controlled between 3.8 and 4.4 and the current density should be below 3 A/dm². To solve the problems of high inner stress and incomplete development of the micro-cylinder hole array with a diameter of 30 μm, the lithography process was optimized. The pre-baking temperature was increased via gradient heating and rose every 5 °C from 65 °C to 85 °C and then remained at 85 °C for 50 min – 1 h. In addition, the full contact exposure was used. Finally, a multi-layer metal micro-structure with high precision and good quality of micro-electroforming layer was fabricated using UV-LIGA overlay technology.