FABRICATION OF SUBMICRON STRUCTURES VIA DOUBLE EXPOSURE UV LITHOGRAPHY

Keywords: ring resonators, double-exposure UV lithography, SU-8.
Ring resonators are essential components in biosensors, optical sensor systems, integrated circuits, and telecommunication devices, as well as in enhancing laser coherence. Their fabrication requires high precision, typically achieved using electron beam lithography (EBL). However, EBL is slow and complex, prompting interest in UV lithography as a faster, more accessible alternative. Conventional UV lithography faces challenges due to diffraction effects, limiting feature sizes to approximately 1 µm when using a 375 nm wavelength source. Creating small gaps is particularly difficult, as closely spaced structures tend to merge due to optical diffraction. This research explores a double-exposure UV lithography method to fabricate submicron ring resonators using SU-8, aiming to achieve gap sizes as small as 20–100 nm. To enhance alignment precision, metalized markers were used for overlaying the two lithographic exposures. The fabricated structures were analyzed using a scanning electron microscope (SEM) to evaluate gap profiles and tested for optical resonance by coupling laser light into the resonators. Additionally, COMSOL modeling was performed to optimize the ring resonator design and predict expected optical behavior. Achieving submicron structures using UV lithography would represent a significant advancement, offering a faster and more scalable alternative to traditional EBL-based fabrication. This method has the potential to simplify production while maintaining the precision needed for photonic applications.