Development of 3d microstructures by using grayscale photolithographic technique
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Date
2016-03-01
Authors
Lee Tze Pin
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Abstract
Recently, the rapid development of technology, such as biochips, microfluidic device, micro-optical devices, and micro-electromechanical-systems (MEMS), demands the capability to create complex designs of three-dimensional (3D) microstructures. Nevertheless, in order to create 3D microstructures, the traditional photolithography process often requires multiple photomasks to generate a 3D pattern from several stacked photoresist layers. This fabrication method is extremely time consuming, has low throughput, and is complicated for high volume manufacturing scale. On the other hand, the next generation lithography, such as electron beam lithography (EBL), focused ion beam lithography (FIB), and extreme ultraviolet lithography (EUV) is however too costly and requires experts to setup the machines. Therefore, the purpose of this study had been to develop a microfabrication method in producing 3D curvature microstructures by employing the single-step grayscale emulsion mask photolithography technique. In the first part of this study, suitable procedure and parameters were determined to produce optimum microfabrication results. In the experiment, the concentration of grayscale was determined by the percentages of halftone dots filling in a particular area. Therefore, the lower the concentration of halftone dots on the emulsion mask, the thicker the developed microstructure will be. First, the designed patterns were printed out on a transparent sheet. Then, the patterns were transferred onto an emulsion glass mask (High Precision Photo Plate) from Konica Minolta, Inc. After that, SU-8 2010 negative photoresist (MicroChem) was deposited on a glass substrate, while the
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patterns from the emulsion glass were transferred onto a photoresist coated glass substrate. From this microfabrication method, a microstructure with maximum and minimum thickness of 750 μm and 17 μm respectively had been obtained in a single-step lithography exposure. On the other hand, as for the second part of this study, this grayscale fabrication method was demonstrated on the fabrication of microfluidic channel. The microfluidic channel was then evaluated under InfiniteFocus measurement systems from ALICONA and also under scanning electron microscope (SEM). By using this microfabrication method, microfluidic channel with 35 μm pores was successfully fabricated. Therefore, it is concluded that different thickness of developed photoresist can be obtained by manipulating the percentage of grayscale concentration during the mask designing stage.