Shape-controlled, high fill-factor microlens arrays fabricated by a 3D diffuser lithography and plastic replication method

This paper describes a simple and effective method to fabricate a plastic microlens array with controllable shape and high fill-factor, which utilizes the conventional lithography and plastic replication. The only difference from conventional lithography is the insertion of a diffuser that randomizes paths of the incident ultraviolet (UV) light to form lens-like 3D latent image in a thick positive photoresist. After replication of the developed concave microlens mold onto the polydimethylsiloxane ( PDMS), the focal length of the fabricated hemispherical microlens was observed to be 13-88 mum depending on the UV exposure dose. Two PDMS curing conditions were tested, where the elevated temperature of 85 degreesC resulted in smoother surface roughness of 2.6 nm in RMS value in the microlens mold. The proposed method can be extensively applied for microlens fabrication with other plastic materials due to its simplicity and versatility. (C) 2004 Optical Society of America.