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Fabrication of ellipticity-controlled microlens arrays by controlling parameters of double-exposure two-beam interference technique

Danh Bich Do, Ngoc Diep Lai, Cheng Yi Wu, Jian Hung Lin, Chia Chen Hsu, Appl. Opt. 50, 579-585 (2011)

We demonstrate a promising method to fabricate plastic microlens arrays (MLAs) with ellipticity- and structure-controlled, by using the combination of multiple-exposure two-beam interference and plastic replication techniques. Multiple-exposure of a two-beam interference pattern with wavelength at 442 nm into a thick positive photoresist (AZ-4620) was used to form different two-dimensional periodic structures. Thanks to the developing effect of the positive photoresist, fabricated structures consisting of hemi-elliptical- or hemi-spherical-shaped concave holes were obtained. By controlling the rotation angle between different exposures, both shape and structure of holes were varied. With adjusting 2 the dosages ratio between different exposures, the shape of holes was modified while the structure of holes was unchanged. The photoresist concave micro-structures were then transferred to plastic MLAs by employing replication and embossing techniques. The fabricated MLAs were characterized by scanning electron microscope and atomic force microscope measurements. We show that the ellipticity of microlenses can be well-controlled from 0 (hemi-spherical) to 0.96 (hemi-elliptical) by changing the rotation angle or dosages ratio between two exposures.

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