End-boundary sheath potential, electron and ion energy distribution in the low-pressure non-ambipolar electron plasma

Abstract

The end-boundary floating-surface sheath potential, electron and ion energy distribution functions (EEDf , IEDf ) in the low-pressure non-ambipolar electron plasma (NEP) are investigated. The NEP is heated by an electron beam extracted from an inductively coupled electron-source plasma (ICP) through a dielectric injector by an accelerator located inside the NEP. This plasma's EEDf has a Maxwellian bulk followed by a broad energy continuum connecting to the most energetic group with energies around the beam energy. The NEP pressure is 1-3 mTorr of N 2 and the ICP pressure is 5-15 mTorr of Ar. The accelerator is biased positively from 80 to 600 V and the ICP power range is 200-300 W. The NEP EEDf and IEDf are determined using a retarding field energy analyser. The EEDf and IEDf are measured at various NEP pressures, ICP pressures and powers as a function of accelerator voltage. The accelerator current and sheath potential are also measured. The IEDf reveals mono-energetic ions with adjustable energy and it is proportionally controlled by the sheath potential. The NEP end-boundary floating surface is bombarded by a mono-energetic, space-charge-neutral plasma beam. When the injected energetic electron beam is adequately damped by the NEP, the sheath potential is linearly controlled at almost a 1 : 1 ratio by the accelerator voltage. If the NEP parameters cannot damp the electron beam sufficiently, leaving an excess amount of electron-beam power deposited on the floating surface, the sheath potential will collapse and become unresponsive to the accelerator voltage.

Beam-plasma discharge in a dielectric cavity by electron beam injection

“…A large amount of research on physics and applications of beam plasma produced by an energetic (several keV) cylindrical or sheetlike magnetically-confined electron beams formed by plasma-cathode electron sources at much higher gas pressures of up to tens of Pa, have been performed by the research group of US Naval Research Laboratory [12][13][14][15], which demonstrated that such beam plasma has typically low (<1 eV) electron temperature due to electrons cooling in collisions with gas atoms and molecules [12,13], and employed this plasma for effective nitriding [14] and atomicprecise etching [15,16]. Chen et al [17] have investigated 80-600 eV dc electron beam injection in cylindrical volume having large positive potential with a floating dielectric end plate, at N 2 or Ar pressure of 0.1-0.4 Pa; authors demonstrated that energy of ions, incident to end plate, can be nearly mono-energetic, controllable by e-beam accelerating voltage, and at such low pressures, e-beam energy dissipation due to collective interaction prevails over dissipation in collisions with gas.…”

Experimental study of transition from electron beam to rf-power-controlled plasma in DFCCP in argon with additional ionization by an electron beam

“…To further decrease ion energies, different alternative approaches have been proposed. One of the possible methods is the application of a nonselfsustained low-pressure rf plasma with additional ionization by an electron beam (EB) [18][19][20][21][22][23][24][25]. There are few results on the processing of materials in such plasma, for example, silicon [18] or graphene [26], which is easily damaged in conventional rf discharges.…”

“…In [24], layerby-layer etching of p-Si at ε i ∼ 25-50 eV using a cycling process (cycling of gas and EB, radical source power), as well as continuous etching of epi-grown µ-Si in Cl 2 -based plasmas, are demonstrated. Various EB sources and discharge configurations have been applied: a cold cathode electron gun source with single frequency rf plasma in [18,23], a hollow cathode EB source [19,20,26], an electron source based on ICP plasma [21] and an EB source together with an additional ICP radical source [24,25].…”

Excitation of a global plasma mode by an intense electron beam in a dc discharge

“…This is especially important for advanced plasma processing applications in order to produce high-aspect ratio nano-features of electronic devices. [14,15] One way to control the beam energy deposition in plasma is by profiling the background plasma density. [6] Conditions favorable for development of the beam-plasma instabilities depend on parameters such as the beam and plasma densities, plasma temperature, and plasma density gradients.…”