Towards defect-free lithography: study of process instabilities for efficient lithography-based patterning

Features are patterned onto a photoresist layer in optical lithography using light to define high-resolution structures. Optical elements such as Metasurfaces, notch filters, and diffractive gratings require high-precision, defect-free fabrication at the sub-micron scale. However, fabrication at this scale often encounters defects due to thermal, mechanical, and fluidic instabilities within photoresist during processing, which limits the dimensions of the fabricated structures by optical lithography. This study investigates the process-induced instabilities observed in photoresist during the fabrication of submicron structures. We focus particularly on SU-8 6000.5, a negative tone photoresist, to study the arising instabilities during the fabrication with optical lithography. Our study is further extended to investigating how the observed instabilities vary with different photoresist materials and lithography methods. Finally, we investigate the behavior of the observed instabilities as a function of feature geometry, focusing on trends such as width versus wavelength, width versus amplitude, spacing, length dependence, and rotational variance. Understanding and mitigating these instabilities is essential for improving pattern fidelity and enabling the reliable fabrication of advanced photonic and electronic components.