Mass spectrometric and Langmuir probe measurements in inductivelycoupled plasmas in Ar, CHF3/Ar and CHF3/Ar/O2 mixtures

Abstract

Absolute fluxes and energy distributions of ions in inductivelycoupled plasmas of Ar, CHF3/Ar, and CHF3/Ar/O2 have been measured.These plasmas were generated in a gaseous electronics conference cell modifiedfor inductive coupling at pressures of 10-50 mTorr and 100-300 W of13.56 MHz radio frequency (RF) power in various feed gas mixtures. In pure Arplasmas, the Ar+ flux increases linearly with pressure as well asRF power. In mixtures, the Ar+ flux decreases with increase in pressureand CHF3 concentration in the mixture. The loss mechanism for Ar+ isattributed to resonance charge exchange(Ar+ + CHF3→products). Total ion flux in CHF3 mixturesdecreases with increase in pressure and also CHF3 concentration. Relativeion fluxes observed in the present studies are analysed with the help ofavailable cross sections for electron impact ionization and charge-exchangeion-molecule reactions. Measurements of plasma potential, electron and ionnumber densities, electron energy distribution function, and mean electronenergy have also been made in the centre of the plasma with an RF-compensatedLangmuir probe. Plasma potential values are compared with the mean ionenergies determined from the measured ion energy distributions and areconsistent. Electron temperature, plasma potential, and mean ion energy varyinversely with pressure, but increase with CHF3 content in the mixture.