Photoresist-Based Evaluation of Ultraviolet Exposure under Yellow Lighting in Academic Cleanrooms

Unintentional ultraviolet (UV) exposure during photolithography poses a significant risk to pattern fidelity, particularly in academic cleanrooms where lighting conditions are rarely verified due to the lack of specialized instruments. In this study, we present a simple and low-cost diagnostic technique that evaluates ambient UV exposure by observing the development behavior of standard photoresist films. By employing a masked-exposure geometry, we directly visualized and quantified resist degradation under various cleanroom lighting configurations. This method revealed a problematic yellow-room lighting system that allowed sufficient residual UV to fully develop the resist, despite its intended UV filtering function. Through systematic testing and geometric modeling, we demonstrated that replacing the original lighting with spectrally filtered alternatives—such as UV filtered fluorescent lamps or filtered light-emitting diodes—effectively mitigated the UV exposure risk. We further developed a physically grounded dose-response model based on a combination of the Dill and Mack formulations, allowing users to estimate UV dose rates without spectroscopic tools. This resist-based method offers an intuitive, accessible, and quantitative framework for ensuring photolithography reliability, especially in educational or resource-constrained environments.