Adjustable Refractive Index Method for Complex Microstructures by Automated Dynamic Mode Multidirectional UV Lithography

A method to use a liquid-state refractive index matching medium is introduced to overcome the limit of the inclined angle for the three-dimensional (3D) microstructures by dynamic mode multidirectional ultraviolet (UV) lithography. The proposed approach uses an isolated container for an index matching medium without direct contact between the index matching medium and the sample, reducing the chance of contamination, simplifying the fabrication process, and broadening the selection of an index matching medium. In addition, the liquid container is designed to allow in-situ adjustable refractive index matching performance during a dynamic mode operation. A refracted angle of 58.5° for an incident angle of 67.5° has been obtained for an SU-8 structure using glycerol as an index matching medium. UV lithography using water, solvent, acid, oil, and starch syrup as an index matching medium has been demonstrated. Various microstructures with large inclined or flare angles such as a chevron shape, an ellipsoidal horn, and a chained wind vane are successfully demonstrated with dynamic mode multidirectional UV lithography.