Structural Resonance Characteristics of Ceramic-Shielded Cutoff Probe in Low-Pressure Plasmas

To facilitate precise plasma density measurements in processing plasma and high-density plasma environments, a ceramic-shielded cutoff probe (CSC) has been developed, and studies on the structure of the ceramic shield have also been conducted. However, the periodic resonance signals commonly observed in previous CSC studies can cause difficulties in precisely measuring plasma density. [1,2] In this study, we investigated the mechanisms and suppression of periodic resonance signals of the CSCs. Through electromagnetic simulations and experiments, it was confirmed that structural resonance effects lead to the formation of standing waves inside the CSC ceramic body, resulting in the generation of periodic resonance signals. It was also confirmed that the structural resonance effect can be eliminated by electrically connecting the metal shields of the coaxial cable near the antennas. These results are expected to contribute to more accurate electron density measurements in harsh plasma environments using CSCs.