Process Study Of Metal Micro Devices Fabricated By Copper Or Nickel Electroforming

With the development of MEMS technology, metal micro devices are increasingly demanded in the fields of national defense, semiconductor and bio-engineering. Meanwhile, more and more attention is attached to micro electroforming, which is an important part of UV-LIGA technology. The primary work of this study mainly concentrates on the fabrication processes of micro injection mold, multi-layer micro structure, and electroformed copper coils. The research result provides process reference for relevant technologies in UV-LIGA field.In the UV-LIGA fabrication process of metallic micro mold cavity for injection molding, large internal stress in SU-8layer can result in SU-8mould defects such as micro cracks, distortion or even exfoliation. In order to avoid these defects, the ultrasonic stress relief technology was introduced originally into the fabrication of micro injection mold. The SU-8mould was obtained by coating, soft bake, ultraviolet exposure and post-exposure bake steps, followed by ultrasonic treatment before developing. The backless plate growing method was adopted, and then the nickel micro-electroforming pattern was directly fabricated on a38CrNiMnMo mould steel substrate. With the problems emerged in the process discussed, the SU-8layer defects such as distortion and exfoliation were eliminated, the spin coating on non-circular substrate was achieved, the air bubbles in photoresist layer were prevented, and the adhesion of the plating layer with the substrate was improved. Finally, the micro mold cavity was fabricated with width of80μm and height of35μm. The results show that by using the ultrasonic stress relief technology, the SU-8mould defects caused by large internal stress in SU-8layer are overcome, the capacity of manufacturing micro injection mold via UV-LIGA technology is enhanced, and the success rate of micro injection mold fabrication is greatly improved.A six-layer micro structure was fabricated to meet the demands of multi-layer metal micro devices in fields of aerospace and bio-engineering. First, back mark points were obtained by etching method to ensure high alignment precision and efficiency. Then problems such as low success rate of photoresist pattern fabrication and poor adhesion between electroforming layers were solved, micro structure was realized through processes of SU-8exposure, magnetron sputtering, and micro electroforming of Nickel. At last, vacuum annealing was adopted to remove internal stress, and a six-layer movable device with minimum linewidth of15μm was obtained after inorganic acid boiling.In order to realize the fabrication of copper micro coils, a mature process of copper micro electroforming was achieved by experiment firstly, additives such as honey and dye were tried in the electroforming experiments, technological problems emerged in the process were analyzed, defects such as spot, black coating, burning and dye deposition were eliminated, and a copper electroforming process with dye additive was achieved. Then, a seed layer was obtained by copper sputtering and resist lift-off process, micro pattern was fabricated by SU-8lithography technology. Finally, copper coils with minimum linewidth of10μm and a height of15μm were fabricated by a precise electroforming equipment. The results verify the feasibility of copper electroforming process, which means the process can meet the requirement of micropattern electroforming.