Impact of Antenna Length on Microwave Transmission Characteristics of Flat Cutoff Probes

Real-time and precise monitoring of plasma parameters has become a critical requirement in advanced semiconductor and display manufacturing processes.Among various diagnostic tools, the flat cutoff probe stands out due to its ability to provide non-invasive, real-time electron density measurements near the plasma-sheath boundary.In this study, we investigate the influence of antenna structure on the microwave transmission characteristics of flat cutoff probes using electromagnetic (EM) wave simulations.EM wave simulations under vacuum conditions demonstrate that structural resonance arises when antenna length equals a quarter of the incident wavelength.In plasma environments, antenna-induced structural resonance frequencies approaching the plasma frequency obscure cutoff frequency detection, leading to unreliable electron density measurements.These results demonstrate that cutoff frequency detection is only achievable when the antenna length remains below the quarter-wavelength corresponding to the plasma frequency.Based on these results, we propose guidelines for antenna design to optimize the flat cutoff probes, which could enhance the accuracy and reliability of in-situ electron density measurements in plasma processing environments.