Experimental and modeling study of O and Cl atoms surface recombination reactions in O2 and Cl2 plasmas

In low-pressure plasmas commonly used in materials processing, plasma–wall inter-actions play a crucial role in the evolution of the plasma properties both over time and across large-area wafers. We have recently studied the heterogeneous recombination of O and Cl atoms on reactor walls in O and Cl plasmas through both experiments and modeling. The Langmuir–Hinshelwood (i.e., delayed) recombination was investigated using a “spinning-wall” technique in which a portion of the substrate surface is periodically exposed to an inductively coupled plasma and to a differentially pumped chamber where either Auger electron spectroscopy (AES) or line-of-sight mass spectrometry (MS) is used to detect surface and desorbing species. In this paper, a review of the various effects driving the O and Cl atoms recombination dynamics on anodized aluminum (AA) and stainless steel (SS) surfaces is presented. It is shown that recombination probabilities, , can vary following plasma exposure due to surface conditioning. In Cl plasmas, was also found to depend on the Cl-to-Cl number density ratio, a mechanism ascribed to a competition for adsorption sites between Cl and Cl . We have also determined the recombination rates of Cl atoms in Cl high-density plasmas sustained by electromagnetic surface waves by comparing the measured degrees of dissociation of Cl to those predicted by an isothermal fluid model. For a reactor with large SS and quartz surfaces exposed to the plasma, values and their dependence on the Cl-to-Cl number density ratio were consistent with those obtained from the rotating substrate technique. Similar values were obtained for plasmas sustained in a quartz discharge tube. It is expected that for plasmas sustained in or adjacent to a silica tube or plate, the Cl atoms recombination coefficient becomes independent of chamber wall material due to reactor seasoning, producing a silicon-oxychloride layer.