Gray-scale photolithography using maskless exposure system

Abstract

Three-dimensional (3D) photoresist patterns of which shape is precisely controlled are fabricated using a gray-scale photolithography. We utilize a maskless exposure system to achieve the precise gray-scale photolithography at low cost. Multilayered exposure patterns digitally generated by the maskless exposure system are superposed on a photoresist-coated substrate layer by layer. Changing the exposure patterns and the exposure parameters such as the exposure time and the scanning speed of the stage of each exposure make the precise control of the profile of UV dose possible. The exposure process does not require any hard masks such as expensive gray-scaled hard masks; therefore, a fabrication of variable 3D patterns at low cost can be achieved, which is an advantage for developing microelectromechanical systems devices. A spherical and an aspherical microlens and its arrayed patterns of 100μm in diameter and 6μm in height are fabricated by a superposition of sixteen-layered exposure patterns. The profile of the fabricated microlens pattern deviates from that of the designed microlens pattern by less than 0.2μm.