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 /spl mu/m in each diameter are fabricated. The patterns are successfully transferred into silicon substrates with reactive ion etching.