| AVS 56th International Symposium & Exhibition | |
| Plasma Science and Technology | Thursday Sessions |
| Session PS1-ThA |
| Session: | Fundamentals of Plasma-Surface Interactions II |
| Presenter: | V.M. Donnelly, University of Houston |
| Authors: | V.M. Donnelly, University of Houston J. Guha, University of Houston |
| Correspondent: | Click to Email |
Plasma and surface diagnostics of Cl2/O2 mixed-gas inductively coupled plasmas are reported. Using trace rare gas optical emission spectroscopy (TRG-OES) and Langmuir probe analysis, electron temperatures (Te) and number densities for Cl atoms (nCl), electrons (ne), and positive ions were measured as a function of percent O2 in the feed gas and position in the plasma chamber. Adsorbates on, and products desorbing from a rotating anodized aluminum substrate exposed to the plasma were detected with an Auger electron spectrometer and a quadrupole mass spectrometer. Te and ne increased with increasing percent O2 in the plasma, while nCl fell off with O2 addition in a manner reflecting simple dilution. Cl atom recombination probabilities (γCl) were measured and were found to be a nearly constant 0.036±0.007 over the range of Cl2/O2 mixing ratios and Cl coverage. Large yields of ClO and ClO2 were found to desorb from the surface during exposure to the plasma, ascribed predominantly to Langmuir-Hinshelwood reactions between adsorbed O and Cl. In addition, the transient surface composition of an anodized aluminum surface was determined as the gas was switched from Cl2 to O2 and vice versa. When the surface was first conditioned in an O2 plasma and then exposed to Cl2 plasmas, a rapid uptake of Cl was found in the first tens of seconds, followed by a slow approach to a steady state value within ~5 minutes of plasma exposure. Conversely, when the surface was exposed to a Cl2 plasma for a long time and then switched to an O2 plasma, the anodized aluminum surface underwent a rapid de-chlorination in the first few seconds and then a slow approach to steady state over ~3 minutes. The buildup and decay of Cl coverage is well described by a stretched exponential function, reflecting a range of binding sites for Cl. Throughout these treatments, the coverages of Si (from erosion of the quartz discharge tube) and O was nearly constant.