Inductively coupled plasmas in low global-warming-potential gases

Many high-density discharges used in microelectronics fabrication use fluorocarbon gases with coincidentally high global-warming potentials (GWPs). We have determined the identities, fluxes, and energy distributions of ions produced in high-density discharges generated in two low GWP gases, CF3I and CF3CH2F (HFC-134a), which have attracted interest for plasma processing applications. Measurements were made using a combined ion energy analyser-mass spectrometer that samples ions through an orifice in the lower electrode of an inductively coupled Gaseous Electronics Conference (GEC) rf reference cell. The effects of plasma operating conditions and Ar dilution on ion fluxes and energies were examined. Nearly complete dissociation of CF3I occurs in CF3I discharges and I+ comprises almost all of the ion yield. Mean ion energies range from 5 eV to 10 eV for the operating conditions investigated. Discharges generated in mixtures of CF3I with Ar have ion fluxes and energies resembling those in pure CF3I discharges. Pure HFC-134a discharges produce several ions of significant intensity, with HF+ and Si+ bring the most abundant. Mean ion energies range from 20 eV to 35 eV, and decrease as HFC-134a is diluted with Ar. Higher discharge powers result in greater dissociation in HFC-134a discharges, shifting the ion composition towards higher fluxes of lighter ions.