Abstract
Abstract UV-LIGA is a lithography process used for low-cost mass production of microstructures. However, the attenuation in intensity of UV light (wavelength 365 nm) easily generates microstructures with larger heads and smaller bottoms (the so-called “big head effect”) in conventional proximity lithography. In order to overcome the big head effect, we have developed a backside exposure lithography fabrication process. Backside exposure lithography is a fabrication process that generates high-aspect-ratio microstructures with larger taper angles. In this dissertation, we built a complete three-dimensional (3D) Fresnel–Kirchhoff diffraction model and used a binary approach to simulate the curing threshold of SU-8 photoresist. We controlled the aperture diameter and gap (distance between the photomask and photoresist) to generate various microstructure profiles. From the numerical and experimental results, we found that the far-field diffraction pattern resulted in an increase in the height, needle-like structure, and taper angle of the microstructures. In contrast, the near-field diffraction pattern resulted in an increase in the width of the microstructure, generating cone-like microstructures and a taper angle that was not influenced by an increase in aperture size. In addition, we used backside exposure lithography to eliminate the diffraction phenomenon and generate ultra-high-aspect-ratio microstructures with vertical sidewalls (micro 3D Taiwan pillars and interesting microstructures). The microstructures fabricated using backside exposure lithography provided various microstructure profiles and a large surface area. Therefore, we applied the advantages of backside exposure lithography to bioengineering. We created a 3D tissue culture environment to provide a physiologically relevant condition for establishing enterocyte cell culture in vitro. From the cell culture results, we determined that the surface area of the 3D scaffold and a smooth surface contributed to cell proliferation. In addition, we used high-aspect-ratio microstructures to generate a 3D PDMS channel mold. The 3D PDMS channel mold reduced cell number and controlled their growth direction, and contributed to our understanding of the transmission mechanisms of neurons for further research on neural electrophysiology.