Ar, N2, and Cl2 electron cyclotron resonance plasmas measured by time-of-flight analysis: Neutral kinetic energies and source gas cracking

Abstract

Effect of a metal-dielectric structure introduced in the plasma chamber of the Frankfurt 14 GHz electron cyclotron resonance ion source Rev.Measurement of ion charge state distributions inside electron cyclotron resonance neon and chlorine plasmas by x-ray spectroscopy Rev.Neutral mean kinetic energies, ion intensities, and neutral source gas cracking from Ar, N 2 , and Cl 2 electron cyclotron resonance ͑ECR͒ plasmas, are measured by modulated beam time-of-flight ͑TOF͒ analysis. The TOF distributions are characterized by a two component form consisting of an effusive Maxwell-Boltzmann distribution and a fast Gaussian component, that accounts for nonthermal species produced in the source. The mean kinetic energies of neutral species are found to range between 0.04 and 0.45 eV, depending on species and plasma conditions. Mean kinetic energies increase at a nearly constant rate, with decreasing pressure from 8.0ϫ10 Ϫ2 to 2.5 ϫ10 Ϫ2 Pa with constant applied microwave power. At pressures below 2.5ϫ10 Ϫ2 Pa, the neutral mean kinetic energies sharply increase. This sharp increase in neutral mean kinetic energy is attributed to an abrupt increase in the ion flux out of the source. The increase in kinetic energy can be separated into two contributions, ͑i͒ thermal at higher pressures and ͑ii͒ nonthermal at lower pressures. This effect is much stronger for atomic neutrals than for molecular neutrals, where internal degrees of freedom can accept energy in momentum transfer collisions. Cracking of N 2 and Cl 2 is also examined as a function of source pressure at constant microwave power. The N:N 2 flux ratio from the ECR source varies between 0.2 and 1.4. The Cl:Cl 2 flux ratio varies from 10 to 16, indicating a very high degree of dissociation in the plasma. Both flux ratios decrease with increasing source pressure. The total flux of Cl increases with increasing source pressure over the entire range, while the N atom flux peaks at ϳ1.3ϫ10 Ϫ2 Pa and decreases on either side of this pressure.