The Research For Microstructure Mask Electroforming Uniformity

With the development of microelectromechanical systems (MEMS)technology, a variety of micro-systems and sensors are emerging and theyplay an important role in many applications. Among them, themicro-fabrication technique is the most important part. LIGA(X-ray deeplithography,electroforming,micro-replication) and quasi-LIGA technologyplay an important role in the field of three-dimensional micro-fabrication.As the intermediate link, micro-electroforming is the core inmicro-systems and devices fabricated by UV-LIGA, and it is crucial forthe quality and performance of micro-devices. In fact, the study on themechanism of microstructure coating uniformity is of great importance inMEMS devices fabrication.Firstly, based on the mass transfer equation and thecurrent-overpotential formula, it proposes the ideas for microstructuremask electroforming uniformity. With the measured polarization curve,the electroforming process is divided into different controlled stage andthe control factors for each stage are different. Based on the theoreticalanalysis, microstructure electroforming coating uniformity is simulated by the finite element analysis software FLUENT. The basic points oftheory and simulation are given, including 1)At the low current, coatinguniformity is controlled by electric field and not related withconvection-diffusion; 2)At the high current, coating uniformity iscontroled by convection-diffusion and not related to electrochemical;3)Higher aspect ratio microstructure is conducive to coating uniform;4)Polarization is conducive to the improvement of coating uniformity;5)Stir is more conducive to improve the coating uniformity; 6)Thevertical flow will improve the coating uniformity than the parallel flow;7)Resist angle has the shielding effect of ion transport.Based on the research above, the experimental bath is designed andfabricated, and both the horizontal and the vertical flow pattern and theadjustable velocity(volume) and the adjustable distance between anodeand cathode are the main features of the bath. Finally, the microstructuresamples which are supported by the metal nickel and glass substrate arefabricated with the use of UV-LIGA process. The coating morphologymeasured through experiment under low current and high current areconsistent with the theoretical simulation, which proves the correctness ofthe above analysis and provide a favorable basis to further improve theprocess parameters.