Modeling of microsphere photolithography

Microsphere photolithography (MPL) is a fabrication technique that combines the ability to self-assemble arrays of microspheres with the ability of a microsphere to focus light to a photonic jet, in order to create highly ordered nanoscale features in photoresist. This paper presents a model of photoresist exposure with the photonic jet, combining a full-wave electromagnetic model of the microsphere/photoresist interaction with the sequential removal of exposed photoresist by the developer. The model is used to predict the dose curves for the MPL process based on the photoresist thickness, illumination conditions, and development time. After experimental validation, the model provides insight into the process including the resolution, sensitivity, and effects of off-normal illumination. This guides the fabrication of sub-100 nm hole/disk arrays using lift-off, and superposition is shown to predict the geometry for split-ring resonators created using multiple exposures. This model will assist synthesizing fabrication parameters to create large area scalable metasurfaces with sensing and energy management applications.