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

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 p H 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 30μm, 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 microelectroforming layer was fabricated using UV-LIGA overlay technology.