Electron-impact Excitation Processes Research Articles

Observations of Recombination Population ofn=2Excited States ofAr16+in Tokamak Plasmas

Results from the first radial measurements of the $n=2$ to $n=1$ x-ray transitions of high-$Z$ elements in deuterium tokamak plasmas are presented. The observed line intensity ratios cannot be explained by electron-impact excitation and dielectronic recombination processes. Radiative and charge-transfer recombination are proposed as additional population mechanisms. The emission lines emitted in the cascade following capture constitute a unique diagnostic probe of the neutral component of plasmas.

Simulation of Spatially Dependent Excitation Rates and Power Deposition in RF Discharges for Plasma Processing

AbstractIn low pressure, radio frequency (RF) discharges of the type used in plasma processing of semiconductor materials, the rate of electron impact excitation and energy transfer processes depends upon both the phase of the RF excitation and position in the discharge. Electron impact collisions create radicals that diffuse or drift to the surfaces of interest where they are adsorbed or otherwise react. To the extent that these radicals have a finite lifetime, their transport time from point of creation to surface of interest is an important parameter. The spatial dependence of the rate of the initial electron impact collisions is therefore also an important parameter. The power that sustains the discharge is coupled into the system by two mechanisms: a high energy “e-beam” component of the electron distribution resulting from electrons falling through or being accelerated by the sheaths, and by “joule heating” in the body of the plasma. In this paper, we will discuss the spatial dependence of excitation rates and the method of power deposition in RF discharges of the type used for plasma processing. The basis of that discussion will be results from a Monte-Carlo plasma simulation code for RF discharges. Preliminary results from a model for the etching of silicon in SF6 /O2 plasmas will be presented and evidence for long term changes in the manner of energy deposition will be discussed.

Excitation of Helium-Like Ions by Electron Impact in the First-Order Exchange Coulomb Approximation

Usefulness of the first-order exchange Coulomb approximation has been examined by applying it to the electron impact excitation processes of helium-like ions. Collision strengths for the excitation from the ground state to the n =2 states (2 3 S, 2 1 S, 2 3 P and 2 1 P) for Li + , C 4+ , O 6+ and Si 12+ have been calculated at energies up to five times threshold energies. It is found that the present approximation improves the Coulomb-Born-Oppenheimer approximation remarkably and gives results comparable with the five-state close-coupling calculation of Wyngaarden et al. (1979). It is also found that the short range distortion effect is largely taken care of in the present first-order approximation.

Electron-impact excitation and dissociation processes inH2

The electron-impact excitation and dissociation cross sections for the C 1Πu, c 3Πu, B′ 1Σu+, and E(F) 1Σg+ states of H2 have been calculated within the distorted-wave approximation. The distorted waves are obtained as solutions of the static-exchange potential field of the ground electronic state. Both differential and integral inelastic cross sections are reported and compared with other calculated results and available experimental data.