Electron-Beam Generated Plasmas: Modeling and Comparison to Experiments

Electron beam (e-beam) generated plasmas are being investigated for use in atomic precision processing applications as they have several useful characteristics. Because the electron-impact cross section for ionization is much larger than the cross section for dissociation at the e-beam energies (> 1 keV), e-beam plasmas are characterized by large ion densities and modest radical densities. The inherently low electron temperature (around 1 eV) leads to low plasma potential and thus a flux of low energy ions to surfaces. With low energy ions and few radicals, e-beam plasmas limit damage at surfaces, making them well-suited for atomic layer processing. The 2D Hybrid Plasma Equipment Model (HPEM) is used to examine e-beam plasmas in pure Ar and Ar/N₂. The model includes magnetic field coils that create a magnetic field of 200 G on axis, confining the electrons. Benchmarking of the model is achieved by comparing the results of HPEM to experimental measurements of electron density and temperature as a function of gas composition and pressure. Additional results of the model include the ion species (Ar⁺, Ar⁺², N₂⁺, N⁺) produced inside the bulk plasma and their relative densities outside of the e-beam volume.

 

This work is partially supported by the Naval Research Laboratory base program.