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Plasma-Surface Interactions at a Spinning Wall Vincent M. Donnelly Department of Chemical Engineering University of Houston Houston, Texas Students: Joydeep Guha (now at Lam Research), Rohit Khare Postdocs: Peter Kurunczi (now at Varian), Luc Stafford (now at Univ. Montreal) Visiting Professor Yi-Kang Pu (Tsinghua University, Beijing, China) Supported by the National Science Foundation, the Department of Energy, the American Chemical Societys Petroleum Research Fund, the University of Houston, and Lam Research Corp.

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Classes of Catalytic Reactions on Plasma Chamber Walls (Catalytic means walls are not consumed) Ion Neutralization and Fragmentation Knowledge / Treatment Neutral Recombination and Reactions Good / Unit probability for this channel. Poor / Usually ignored or adjustable parameter Fair to poor / A few published coefficients. Usually an adjustable parameter Poor / A handful of studies. Usually ignored or an adjustable parameter.

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plasma spinning cylinder surface exposed to plasma to pump to differentially-pumped mass spectrometer, or Auger Electron spectrometer high- speed motor SPINNING WALL Method for Studying Plasma-Surface Interactions 10 -3 P 10 -6 P pres.=P

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differential pumping differential pumping differential pumping Feed gases (Cl 2 or Cl 2 /O 2 in this talk) mass spectrometer (Extrel) tuning fork chopper PLASMA REACTOR, SPINNING WALL AND MASS SPEC. anodized Al reactor Line-of-sight gas from spinning surface = Chopper open signal chopper closed signal Ionization gauge

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Wall is Al y Si x O z with ~5% Cl, O, or N in Cl 2, O 2 or N 2 plasmas Cl in Cl 2 corresponds to ~1-2 x 10 14 cm -2 Cl at the surface. Si from erosion of quartz discharge tube; ~1% Ag from Ag-plated gaskets. Large amount of Cl in N 2 plasmas, compared to O 2 plasmas. AUGER SPECTRA OF SEASONED REACTOR WALL DURING LONG EXPOSURES TO Cl 2, O 2, OR N 2 PLASMAS, 5 mTorr, 600 W

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Cl 2 MASS SPECTROMETER SIGNALS: PLASMA ON OR OFF Plasma-ON signals are a result of desorption of Cl 2 formed by recombination of Cl on the spinning wall surface. Plasma-OFF signal is a result of desorption of physisorbed Cl 2. J. Guha, V. M. Donnelly, Y-K. Pu, J. Appl. Phys. 103, 013306 (2008);

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Plasma (e.g. Cl 2 plasma) Eley-Rideal (E-R) product (Cl 2 ) (if occuring, not detectable) Langmuir-Hinshelwood (L-H) product (Cl 2 ) Cl atoms ATOM RECOMBINATION: Experiment Detects Delayed (L-H) Recombination, not prompt (E-R) Mass Spec. Reaction time 1/(2f)

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ABSOLUTE Cl 2 DESORPTION FLUXES FROM ANODIZED-Al EXPOSED TO A Cl 2 PLASMA (plasma off removed) Cl (g) Cl (ads) in plasma, followed by 2Cl (ads) Cl 2 in mass spec.

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TIME-RESOLVED AUGER SPECTRA OF SPINNING WALL DURING Cl 2 PLASMA EXPOSURE, 5 mTorr, 600 W E b = 1.5 keV

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TIME-RESOLVED PEAK-TO-PEAK AUGER INTENSITIES Cl 2 plasma, 5 mTorr, 600 W, E b = 1.5 keV Dashed line corresponds to time-independent Cl coverage. CONCLUSION: Cl undergoing recombination accounts for