Ion chemistry in H2-Ar low temperature plasmas

A rate equation model is devised to study the ion composition of inductively coupled H-2-Ar plasmas with different H-2-Ar mixing ratios. The model is applied to calculate the ion densities n(i), the wall loss probability of atomic hydrogen beta(H), and the electron temperature T-e. The calculated n(i)'s of Ar+, H+, H-2(+), H-3(+), and ArH+ are compared with experimental results. Calculations were made for a total gas pressure of 1.0 Pa. The production and loss channels of all ions are presented and discussed in detail. With the production and loss rates, the density dependence of each ion on the plasma parameters is explained. It is shown that the primary ions H-2(+) and Ar+ which are produced by ionization of the background gas by electron collisions are effectively converted into H-3(+) and ArH+. The high density of ArH+ and Ar+ is attributed to the low loss to the walls compared to hydrogen ions. It is shown that the H+/H-2(+) density ratio is strongly correlated to the H/H-2 density ratio. The dissociation degree is around 1.7%. From matching the calculated to the measured atomic hydrogen density n(H), the wall loss probability of atomic hydrogen on stainless steel beta(H) was determined to be beta(H) = 0.24. The model results were compared with recently published experimental results. The calculated and experimentally obtained data are in fair agreement.