Junwoo Lee, Yifan Liu, Ming Xu, Zhen Qiu, Qi Hua Fan, Michigan State University, East Lansing, MI
High- and low-refractive index thin films are fundamental components for engineering the optical interference to manipulate light transmission, reflection, and phase in high-performance coatings. In this study, niobium pentoxide (Nb₂O₅, high index) and silicon dioxide (SiO₂, low index) thin films were deposited through MetaMode sputtering in combination with an innovative beam plasma source (BPS). A primary challenge in reactive sputtering is target poisoning, which conventionally leads to significant reductions in deposition rates and the disappearing anode effect. On the other hand, the BPS can generate a high-density plasma and directionally deliver reactive species to the film, facilitating the film oxidation at low oxygen concentrations that keep the target in a metallic state. Consequently, the deposition rates increased by 2.8 to 3.3 times compared to conventional reactive sputtering. In addition, the BPS allows independent control over the ion energy and ion flux, resulting in greatly reduced film roughness and enhanced refractive indices. Lastly, by maintaining the target in a semi-metallic state rather than fully oxidized, the sputtered species remain semi-conductive, thereby preventing chamber insulation and extending the systems operational time. These results demonstrate that the use of a beam plasma source not only enables high-throughput fabrication of high-quality optical-grade oxide thin films but also provides a robust solution for maintaining stable processes.