Abstract A two-dimensional self-consistent fluid model integrated with finite-difference time-domain Maxwell solver is developed to investigate the electromagnetic effects in large-area very-high-frequency capacitive hydrogen discharges. Through systematic investigation of the discharge properties under various powers and interelectrode gaps at 150 MHz, interactions between the electromagnetic effects and plasmas are presented. The results indicate that as power increases, the electron density profile evolves from center-peaked to multi-peak or edge-high distributions, and this is governed by the competition between electromagnetic wave propagation and edge-localized electrostatic field effects. At small gaps (2 cm), edge-dominance emerges above 350 W. While, larger gaps (3-4 cm) amplify the standing wave effect, and suppress the electrostatic edge effect and evanescent wave skin effect, so higher power is required for multi-peak or edge-peak formation. Besides, it is also revealed that addition of a low-frequency source is an effective strategy for plasma uniformity control. By introducing a moderate low-frequency power, the standing wave effect is suppressed due to the longer wavelength. Accompanied by the enhanced electrostatic edge effect and evanescent wave skin effect, the plasma radial uniformity is effectively improved. These results provide comprehensive understanding of the electromagnetic effects on the plasma distributions, and demonstrate the effectiveness of low-frequency modulation on the plasma radial uniformity, which is significantly important for optimizing the performance of large-area very-high-frequency discharges in industry.
Li et al. (Mon,) studied this question.