A generation of hydrogen atoms in DC-RF ExB plasma source for advanced material processing applications

Electron beam-generated plasmas enable precise control over the flux of species and the ion energy at surfaces making such low temperature plasmas attractive for advanced material processing applications including, but not limited to atomic layer etching and processing of ion energy-sensitive materials and atomically thin 2-D materials [1]. In the ExB Penning plasma system [2], energetic electrons are extracted from the RF plasma cathode to a cylindrical geometry chamber by applying a DC bias voltage between the cathode and the chamber. It is experimentally shown that in operation with argon-hydrogen gas mixtures at 1-10 mtorr, this plasma source can sustain efficient dissociation of hydrogen molecules and ionization of argon and hydrogen atoms. Spatially resolved measurements of the absolute density of hydrogen atoms using two-photon absorption laser-induced fluorescence diagnostic revealed that the density of hydrogen atoms in the chamber substantially increases with the magnetic field. This result and its practical implications for materials processing will be discussed. For example, this source was successfully applied for a high coverage graphene hydrogenation with a minimized irreversible damage to the 2-D substrate [3].  [1] S. G. Walton et al., ECS J. Solid State Sci. Technol. 4, N5033 (2015); [2] E. Rodriguez, V. Skoutnev, Y. Raitses, A. Powis, I. Kaganovich, and A. Smolyakov, Physics of Plasmas 26, 053503 (2019); [3] F. Zhao, Y. Raitses, X. Yang, A. Tan, C. G. Tully, Carbon 177, 244 (2021).