Paper PS-ThM6
Oxygen and Chlorine Atom Recombination on TiO₂, SiO₂, and SiO_xCl_y-Coated Plasma Chamber Wall Surfaces

Thursday, October 21, 2010, 9:40 am, Room Aztec

Recombination and other possible reactions of Cl and O on chamber walls in chlorine and oxygen plasmas were studied by the “spinning wall” technique. With this method, a small cylinder (1”dia. x 1”high) in the chamber wall was rapidly rotated, periodically exposing its surface to the plasma and then to the differentially pumped diagnostic chamber housing an Auger electron spectrometer for in-situ surface analysis. The plasma chamber also contained a silicon electrode that can be rf-biased and sputtered in an inert (Ar) plasma, or etched in a chlorine plasma. Using this technique, we previously measured Cl and O atom recombination on plasma-conditioned anodized Al and stainless steel surfaces by monitoring desorption of Cl₂ and O₂ with a mass spectrometer or through a pressure rise. We also previously found a substantial increase in O atom recombination probabilities due to trace amounts of Cu deposited in-situ by thermal evaporation. In the current study, a smooth Ni-coated Al substrate was used. This substrate was exposed to Si sputtered from the rf-biased electrode and was then oxidized and conditioned by long exposure to oxygen plasma. Traces of Ti were deposited on this surface with the evaporator, followed by the oxygen plasma conditioning (Ti:Si:O::5:47:48 atomic percents, averaged over the ~10 nm depth probed by Auger). The O atom recombination probability on this Ti-contaminated substrate was found to be ~30% lower than on the Ti-free substrate, i.e. the opposite to that observed for Cu contamination. Ti was then etched away in the chlorine plasma, leaving an oxy-silicon-chloride surface (Si:O:Cl:: 47:39:14). The Si electrode was then etched in the chlorine plasma while rotating the substrate, coated the rotating substrate with etching products changing the substrate surface composition to Si:O:Cl :: 54:19:27. Immediately after extinguishing the rf bias to the Si electrode, the Cl atom recombination probability was found to be lower than on the more oxygen-rich Si surface. During rf bias, however, the total product yield is higher, indicating that other products (i.e. SiCl_x) could also be desorbing from the substrate as a result of the etching of the Si electrode.