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Photoresist roughness characterization in additive lithography processes for the fabrication of phase-only optical vortices

The roughness on the surface of phase-only micro-optical elements can limit their performance. An optical vortex phase element was fabricated by using additive lithography with an optimized process to have minimal surface roughness. Thick photoresist was used in order to obtain the appropriate dynamic range for the desired phase profile. We investigated the effects of both post applied and post exposure baking processes, as well as the effects of surfactant in the developer. We found the resist surface roughness to be a function of both the temperature and the time of the respective bakes, as well as the developer surfactant content.