An Investigation into the Optimization of Photolithography Process for Silicon Nitride Devices on the fab's 12-inch Production Line

The research and development of low-loss SiN silicon photonic devices are still in the laboratory stage, with only a handful of tape-outs having been conducted in 8-inch fabs. We are pioneering the development of SiN silicon photonic devices on 12-inch production line, thereby establishing a robust foundation for mass production. This study primarily focuses on the photolithography process utilized in the production of SiN devices [1], and investigates the impact of various factors, including stepper types, development conditions, temperature, and anti-reflection coatings. The photolithography of SiN devices mainly encounters problems photoresist (PR) residue and high line width roughness (LWR). It is found that when using a KrF [2] stepper, changing the development method has minimal impact on the photoresist residue. Raising the temperature from 120°C to 130°C can effectively mitigate the issue of residue in small line width patterns, however, residue defects persist in large line width patterns. Replacing the bottom anti-reflection coating (BARC) [3], [4] with bottom anti-reflection coating (TARC) can effectively improve PR residue, nonetheless, the issue of high LWR [5] remains pronounced. Switching to an Arf stepper [2] and utilizing both BARC and dielectric anti-reflection coating (DARC) can effectively reduce LWR. This study provides significant guidance for the exploitation of photolithography process in the production of SiN devices within 12-inch fab lines, thereby facilitating the advancement towards mass production of silicon optical devices.