Isotope effects on plasma species of Ar/H2/D2 plasmas

Abstract

The authors studied the influence of isotopes on the Ar/H 2 and Ar/D 2 plasmas using Langmuir probe and ion mass analyzer measurements at several pressures relevant to low temperature plasma surface processing. As up to 50% H 2 is added to Ar plasma, electron energy distribution functions show an increase in electron temperature (from 2.5 eV to 3 eV for 30 mTorr with 50% addition) and a decrease in electron density (2.5 Â 10 11 cm À3 ! 2.5 Â 10 10 cm À3 at 30 mTorr with 50% addition). At lower pressures (5 and 10 mTorr), these effects are not as pronounced. This change in electron properties is very similar for Ar/D 2 plasmas due to similar electron cross-sections for H 2 and D 2 . Ion types transition from predominantly Ar þ to molecular ions ArH þ /H 3 þ and ArD þ /D 3 þ with the addition of H 2 and D 2 to Ar, respectively. At high pressures and for the heavier isotope addition, this transition to molecular ions is much faster. Higher pressures increase the ion-molecules collision induced formation of the diatomic and triatomic molecular ions due to a decrease in gaseous mean-free paths. The latter changes are more pronounced for D 2 addition to Ar plasma due to lower wall-loss of ions and an increased reaction rate for ion-molecular interactions as compared to Ar/H 2 . Differences in plasma species are also seen in the etching behavior of amorphous hydrocarbon films in both Ar/H 2 and Ar/D 2 plasma chemistries. D 2 addition to Ar plasma shows a larger increase in etch rate than H 2 addition.

Measurement and modeling of neutral, radical, and ion densities in H2-N2-Ar plasmas

“…One of the main result of Refs. 22,23 , namely the ion species distribution, is in reasonable agreement with recent publications of Fox-Lyon et al 24 and Jimenez-Redondo et al 25 studying H 2 -Ar plasmas at comparable pressures. The H 2 -Ar plasma can be considered as a model system with a much lower complex plasma chemistry than a H 2 -N 2 -Ar plasma.…”