On the Determination of Energy and Particle Fluxes Towards Surfaces in Plasma Processing by “Non-Conventional” Probes

The diagnostics of electrons and ions in plasmas and the fluxes of charged and neutral species toward plasma-facing surfaces along with their energy and momentum transfer will be discussed. The focus is laid on the fundamentals of “non-conventional” calorimetric (CP) and force probes (FP) [1] as well as their combination with common Langmuir probes (LP) and retarding field analyzers (RFA) for application to non-equilibrium plasmas and ion beams. These rather simple methods are useful tools for the measurement of overall, not species resolved, ions and neutral species and energy fluxes toward surfaces. Although the diagnostics have their roots in the beginnings of plasma research, they were gradually refined to match the requirements of plasma environments in industry, such as rf-discharges, reactive plasmas, dusty plasmas, and atmospheric pressure plasmas.<br/>Of particular interest is the combination of different types of probes, e.g. retarding field analyzer (RFA) and passive thermal probe (PTP) [2]. The PTP serves as collector, in front of which three centrally aligned grids are operated as the retarding field system. In this setup the collector does not only measure the incoming ion current depending on the voltage applied to the grids of the RFA, but also the incoming energy flux density of the impinging ions or neutrals, respectively. The ion energy distribution (IED) is determined regarding the energy exchange of the neutral background gas with the ions extracted from the plasma source (charge exchange collisions) and the measured energy influx can even deliver information about fast neutrals and chemical reactions, recombination and secondary electrons.<br/>The current trend in the miniaturization of sensors, adopted from the manufacturing of MEMS, will allow measurements with high spatial resolution in miniaturized plasma sources, like plasma jets or micro discharges [3], respectively.<br/><br/><b>Keywords</b>: probe measurements, plasma diagnostics, calorimetric probe, force probe, plasma surface interaction, plasma processing<br/><br/><br/>[1] J. Benedikt, H. Kersten, A. Piel, Plasma Sources Sci. Technol., <b>30</b>(2021), 033001.<br/>[2] F. Schlichting, H. Kersten, Eur. Phys. J. Techniques Instrument. <b>10</b>(2023), 19.<br/>[3] L. Hansen, N. Kohlmann, U. Schürmann, L. Kienle, H. Kersten, Plasma Sources Sci. Technol, <b>31</b>(2022), 035013.