In-situ particle detection during optical coating process

Small particles generated during various stages of the optical coating process can result in defects incorporated in the coatings and lead to premature failure and compromise both quality and yield. In-situ monitoring of small particles during the coating process and optimization of the coating procedures to minimize particulate formation and deposition is therefore crucial. In this work, an in-situ method for detecting micron-sized particles during optical coating processes using laser light scattering and camera-based imaging is presented. Various optical configurations, including endoscopic and in-vacuum arrangements, and different camera sensors, CMOS and event-based, were evaluated and optimized during laboratory testing under process-relevant conditions. The in-situ method using an event-camera was validated in multiple industrial coating platforms, including electron-beam evaporation and ion-beam sputtering systems. These measurements revealed that particle generation is process-dependent and that most of the particle activity occurs during pump-down and venting phases, while significantly lower particle counts were observed during deposition. These observations were qualitatively confirmed by ex-situ wafer inspection techniques and with particle counter measurements.