Fabrication of $100{\mu}m$ High Metallic Structure Using Negative Thick Photoresist and Electroplating

Negative Thick Photoresist를 이용한 $100{\mu}m$ 높이의 금속 구조물의 제작에 관한 연구

This paper describes the fabrication process to fabricate metallic structure of high aspect ratio using LlGA-like process. SU-8 is used as an electroplating mold. SU-8 is an epoxy-based photoresist, designed for ultrathick PR structure with single layer coating [1,2]. We can get more than $100{\mu}m$ thick layer by single coating with conventional spin coater, and applying multiple coating can make thicker layers. In the experiments, we used different kinds of SU-8, having different viscosity. To optimize the conditions for mold fabrication process, experiments are performed varying spinning time and speed, soft-bake, develop and PEB (Post Expose Bake) condition. With the optimized condition, minimum line and space of $3{\mu}m$ pattern with a thickness of $40{\mu}m$ and $4{\mu}m$ pattern with a thickness of $130{\mu}m$ were obtained. Using the patterned PR as a plating mold, metallic structure was fabricated by electroplating. We have fabricated a electroplated nickel comb actuator using SU-8 as plating mold. The thickness of PR mold is $45{\mu}m$ and that of plated nickel is$40{\mu}m$. Minimum line of the mold is $5{\mu}m$. Patterned metallic layer or polymer layer, which has selectivity with the structural plated metallic layer, can be used as sacrificial layer for fabrication of free-standing structure.