An Improved Process for Fabricating Microlens Array With High Fill Factor and Controllable Configuration

Abstract

An improved process has been developed for the efficient fabrication of a microlens array with high fill factor and controllable configuration. The microlens mold for patterning transformation was fabricated by using the processes of glass wet etching, nickel electroplating, photoresist spin coating, and encapsulated air heating. The convex microlens shape resulted from the photoresist compressed by the thermal expansion of sealed air to form a semispherical shell. By adjusting the heating temperature and the sealed air volume, the curvature and size of the shell are controllable. In addition, the microlens mold or plano-convex micromirror can be fabricated by depositing a metal film on the surface profile of swelled photoresist. An analytical model was established to predict the surface profile of a single microlens and was experimentally verified. A typical microlens mold made from nickel with different fill factors and various configurations was also fabricated and characterized. The polysiloxine microlens array was also fabricated by mold pressuring, and its optical properties were measured to identify the focusing capability. Experimental results reveal that various configurations of microlens array could be formed, such as semielliptical and M-character, by defining the pitch sizes of via holes. High fill factors approaching 100% can also be achieved. The fabrication provides an effective way to manufacture a microlens mold to serve as the master element for replication.