Reduction photolithography using microlens arrays: Applications in gray scale photolithography

This paper describes the application of reduction photolithography, using arrays of microlenses and gray scale masks, to generate arrays of micropatterns having multilevel and curved features in photoresist. This technique can fabricate, in a single exposure, three-dimensional microstructures (e.g., nonspherical microlens arrays) over areas of ∼2 × 2 cm². The simple optical configuration consisted of transparency film (having centimeter-sized features) as gray scale photomasks, an overhead projector as the illumination source, and arrays of microlenses as the size-reducing elements. Arrays of 40- and 100-μm lenses achieved a lateral size reduction of ∼10³ and generated patterns of well-defined, multilevel structures; these structures may find use in applications such as diffractive optics.