Study on UV Energy Effects in High Aspect Ratio Patterning via the Self-propagating Photopolymer Waveguide (SPPW) Method

This study quantitatively examines the impact of ultraviolet (UV) intensity and energy on the formation of high aspect ratio (HAR) microstructures using the Self-Propagating Photopolymer Waveguide (SPPW) process. This mechanism relies on the self-focusing of UV light within a refractive index gradient, allowing the light to propagate and polymerize vertically beyond the initial exposure zone. Experiments were performed at UV intensities of 7.5, 12.5, and 17.5 mW/cm2, with energy levels ranging from 0.0375 to 13.5 J/cm2. The results indicated that a lower UV intensity of 7.5 mW/cm2 produced uniform and vertically elongated structures, achieving a maximum aspect ratio of 12.26 at 0.9 J/cm2. In contrast, higher UV intensities led to lateral over-curing, base expansion, and shape distortion, primarily due to rapid polymerization and the oxygen inhibition effect. These findings emphasize the importance of precisely controlling both UV intensity and energy to produce uniform, vertically aligned HAR microstructures, offering valuable insights for optimizing the SPPW process in future microfabrication applications.