Thick Resist Pattern Replication Using Low Numerical-Aperture Projection Lithography and It's Application to Fabrication of Micro Components

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Combination of optical lithography patterning in a thickly coated resist and electroplating into the resist replica is investigated for developing a new easy, low-cost and high-performance micro-fabrication method. In order to form patterns with a high aspect ratio and vertical side walls, low numerical aperture (NA) projection exposure is applied, and acrylic resist SU-8 with high transparency for the exposure light of near UV is used. When a lens with a low NA of 0.063 is applied, large DOF of more than 200 μm is obtained for 50-μm wide and 100-μm thick resist. If the focal position is adjusted suitably, 275-μm thick patterns with vertical side walls and a high aspect ratio of more than 10 are obtained. These resist patterns are printed on copper clad plastic boards instead of silicon wafers. The copper clad boards are directly available for electroplating without evaporating a base metal layers on them. Thus, fabrication of micro nickel gears is demonstrated successfully. Since the new method uses low cost optical lithography, it is applicable even for small production, and will be useful for fabricating various micro parts.
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