On the importance of excited state species in low pressure capacitively coupled plasma argon discharges

De Qi Wen*, Janez Krek, Jon Tomas Gudmundsson, Emi Kawamura, Michael A. Lieberman, Peng Zhang, John P. Verboncoeur

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


In the past three decades, first principles-based fully kinetic particle-in-cell Monte Carlo collision (PIC/MCC) simulations have been proven to be an important tool for the understanding of the physics of low pressure capacitive discharges. However, there is a long-standing issue that the plasma density determined by PIC/MCC simulations shows quantitative deviations from experimental measurements, even in argon discharges, indicating that certain physics may be missing in previous modeling of the low pressure radio frequency (rf) driven capacitive discharges. In this work, we report that the energetic electron-induced secondary electron emission (SEE) and excited state atoms play an important role in low pressure rf capacitive argon plasma discharges. The ion-induced secondary electrons are accelerated by the high sheath field to strike the opposite electrode and produce a considerable number of secondary electrons that lead to additional ionizing impacts and further increase of the plasma density. Importantly, the presence of excited state species even further enhances the plasma density via excited state neutral and resonant state photon-induced SEE on the electrode surface. The PIC/MCC simulation results show good agreement with the recent experimental measurements in the low pressure range (1-10 Pa) that is commonly used for etching in the semiconductor industry. At the highest pressure (20 Pa) and driving voltage amplitudes 250 and 350 V explored here, the plasma densities from PIC/MCC simulations considering excited state neutrals and resonant photon-induced SEE are quantitatively higher than observed in the experiments, requiring further investigation on high pressure discharges.

Original languageEnglish
Article number064001
JournalPlasma Sources Science and Technology
Issue number6
Publication statusPublished - Jun 2023

Bibliographical note

Publisher Copyright:
© 2023 The Author(s). Published by IOP Publishing Ltd.

Other keywords

  • electron dynamics
  • electron-induced secondary electron yield
  • excited state atoms
  • low pressure capacitively coupled plasmas
  • plasma-surface interaction
  • resonance photons
  • simulation validation against experiments


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