Gray-scale lithography using mask-less exposure system

A fabrication process of precisely controlled three-dimensional patterns using a gray-scale lithography is presented. Multi-layered exposure patterns digitally generated by a mask-less exposure system are superposed on a photoresist-coated substrate layer by layer. Changing the exposure patterns and the exposure time of each exposure make the precise control of the profile of ultraviolet dose possible. The mask-less exposure system realizes fabrication of variable three-dimensional patterns at low cost with saving time. Photoresist patterns of spherical and aspherical microlens array of 100 μm in each diameter are fabricated. The patterns are successfully transferred into silicon substrates with reactive ion etching.