Abstract
In this study, a fabrication method of tapered microstructures with high aspect ratio was proposed by deep X-ray lithography. Tapered microstructures with several hundred micrometers and high aspect ratio are demanded owing to the high applicability in the fields of various microelectromechanical systems (MEMS) such as optical components and microfluidic channels. However, as the pattern and gap size were downsized to smaller micro-scale with higher aspect ratio over 5, microstructures were easily deformed or clustered together due to capillary force during the drying process. Here, we describe a novel manufacturing process of tapered microstructures with high aspect ratio. To selectively block the deep X-ray irradiation, an X-ray mask was prepared via conventional ultraviolet (UV) lithography. A double X-ray exposure process with and without X-ray mask was applied to impose a two-step dose distribution on a photoresist. For the clear removal of the exposed region, the product was developed in the downward direction, which encourages a gravity-induced pulling force as well as a convective transport of the developer. After a drying process with the surface additive, tapered microstructures were successfully fabricated with a pattern size of 130 μm, gap size of 40 μm, and aspect ratio over 7.
Highlights
Synchrotron X-ray lithography has emerged as a novel micromachining technology to fabricate nano/micropillars with high aspect ratio and precise optics
Deep X-ray lithography experiments were performed at the 9D X-ray nano/micromachining beamline of the Pohang Accelerator Laboratory (PAL)
aa photoresist substrate. Gold (Au) electroplating between micropatterning process on the seed layer by UV lithography; (c) Au electroplating between thethe mask patterns; and (d) detached from the mask and (d)
Summary
Synchrotron X-ray lithography has emerged as a novel micromachining technology to fabricate nano/micropillars with high aspect ratio and precise optics. The X-ray beam, which has high collimation and intensity, passes through a thick polymer and other materials and allows the materials to be shaped into a nearly vertical structure with good sidewall roughness and high pattern accuracy. The nano/micropillars could be metal-electroformed as a mold insert and used for injection molding [5,6] and an embossing process [7] This sequential process, called LIGA (German abbreviation: Lithographie, Galvanoformung, and Abformung) is beneficial for mass-production of micro-scale polymers and metal/ceramic structures with high aspect ratios. Matsuzuka et al [10] adopted a double X-ray exposure technique to attain a tapered microstructure, and tens of micro-scale tapered structures with aspect ratio under 3 were manufactured. This study proposed and developed a novel technique using X-ray lithography to fabricate tapered micropillars with high aspect ratio. Based on the optimized process, tapered micropillars with aspect ratio over 7 were successfully obtained without any visible defects
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