Mass Spectrometric and Langmuir Probe Measurements in Inductively Coupled Plasmas in Ar, CHF3/Ar and CHF3/Ar/O2 Mixtures

Absolute fluxes and energy distributions of ions in inductively coupled plasmas of Ar, CHF 3 /Ar, and CHF 3 /Ar/O 2 have been measured. These plasmas were generated in a gaseous electronics conference cell modified for inductive coupling at pressures of 10-50 mTorr and 100-300 W of 13.56 MHz radio frequency (RF) power in various feed gas mixtures. In pure Ar plasmas, the Ar + flux increases linearly with pressure as well as RF power. In mixtures, the Ar + flux decreases with increase in pressure and CHF 3 concentration in the mixture. The loss mechanism for Ar + is attributed to resonance charge exchange (Ar + + CHF 3 → products). Total ion flux in CHF 3 mixtures decreases with increase in pressure and also CHF 3 concentration. Relative ion fluxes observed in the present studies are analysed with the help of available cross sections for electron impact ionization and charge-exchange ion-molecule reactions. Measurements of plasma potential, electron and ion number densities, electron energy distribution function, and mean electron energy have also been made in the centre of the plasma with an RF-compensated Langmuir probe. Plasma potential values are compared with the mean ion energies determined from the measured ion energy distributions and are consistent. Electron temperature, plasma potential, and mean ion energy vary inversely with pressure, but increase with CHF 3 content in the mixture.

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