Large Area IR Microlens Arrays of Chalcogenide Glass Photoresists by Grayscale Maskless Lithography

The ability to use chalcogenide glass thin films as photoresists for one-step maskless grayscale lithographic patterning is demonstrated. It is shown that the chalcogenide photoresists can be used to fabricate grayscale patterns with smooth and continuous profiles such as arrays of cylindrical and spherical microlenses, which are useful as optical structures for IR applications. The etching and exposure parameters are optimized to obtain smooth reproducible lens arrays of 150 μm periodicity and up to ∼170 nm height on large areas (∼1 cm(2)). The roughness is found to increase as a function of the exposure dose and is attributed to the selective dissolution of the As-Se, As-As, and Se-Se bonds present in the nanodistributed phases and the presence of the oxide phase. Thus, a minimum exposure dose produces optimally patterned lens arrays. The focal length calculated for the smooth microlens array is ∼9.3 mm, indicating the suitability of the lens arrays for focusing applications in the IR region.