Two-layer resist process for printing thick patterns by exploiting a maskless projection exposure system using a liquid-crystal-display panel

To utilize maskless lithography using a liquid-crystal-display (LCD) panel for printing thick resist patterns, a novel two-layer resist process was developed. In the past research, simple and low-cost maskless exposure system was developed using an LCD panel in place of a reticle. However, commercial LCDs were fabricated not to irradiate short-wavelength light rays for protecting human eyes. Therefore, only thin g-line resists have been applicable for printing patterns. Nevertheless, patterning in 10–100 μm thick resist is frequently required for fabricating fluidic devices, lens arrays, and others. For this reason, a conventional g-line resist was coated on a thick UV resist, and patterns of g-line resist formed using the LCD maskless lithography was used as exposure masks of the bottom layer UV resist. As a result, various test patterns with widths of down to 40 μm and almost vertical side walls were successfully printed in the 70 μm thick UV resist.