UV-LED Lithography System and Characterization

This paper presents a design, system setup, characterization, and microfabrication of high-intensity UV-LED microlithography. Since the high enough intensity of the UV light enables even a millimeter thick SU-8 photoresist process, an array of high-intensity UV-LEDs has been optimized as a light source of the microlithography system. A simple waveguide with a single optical lens has made light collimation without high attenuation of the light intensity while the rotation of the light source provides uniform light distribution. Adopting the x-y-z-r stage to the light source enables a mask aligning function together with light intensity and exposure time controllers. The maximum intensity of 448 mW/cm2 has been measured and the light collimation has been achieved within 5°. The uniform light distribution was measured without and with light rotation. The rotating light source resulted in approximately 29% better than the no-rotation case. The LED source has been stable over 100 hours of operation. The test microstructures include 3 μm lines, high-aspect-ratio micropillars, and 2-mm tall SU-8 pillar array. The proposed system has great flexibility and versatility as a mask aligner system that can be used as both conventional and MEMS microfabrication.