Precise control of low-energy electron beam for selective radical density control

Abstract

The precise control of electron beam energy linewidth is a critical requirement for enabling selective electron-impact reactions in plasma-assisted processes. In this work, we investigate how the electron temperature (Te) of a source plasma governs the energy dispersion of a low-energy electron beam generated using a multiple DC-biased grid system in an inductively coupled plasma. The electron beam energy spread is successfully minimized by lowering the source Te. By regulating the source plasma Te is regulated in the range of 0.8-2.43 eV. A narrow energy linewidth of the extracted electron beam is observed at lower Te, showing an energy dispersion full width at half maximum of 2.54 V (at Te = 0.8 eV), compared to 5.85 V (at Te = 2.43 eV). Using first-derivative Langmuir probe analysis, we quantitatively demonstrate that the electron beam energy dispersion is directly determined by the electron energy distribution function of the source plasma. The generation of a narrow-linewidth electron beam is then applied to examine electron-impact dissociation characteristics of nitrogen by tuning the beam energy near the N2 dissociation threshold. The results reveal a clear threshold-activated dissociation signature, indicating that selective access to specific reaction channels becomes possible when the beam energy dispersion is sufficiently suppressed. These findings establish a physical framework for grid-based low-energy electron beams as an enabling platform for selective electron-driven plasma chemistry, with potential relevance to damage-sensitive plasma processes such as atomic layer etching and deposition.