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 Society’s Petroleum Research Fund, the University of Houston, and Lam Research Corp.
Transcript
Slide 1
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.
Slide 2
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.
Slide 3
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
Slide 4
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
Slide 5
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
Slide 6
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);
Slide 7
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)
Slide 8
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.
Slide 9
TIME-RESOLVED AUGER SPECTRA OF SPINNING WALL DURING Cl 2 PLASMA
EXPOSURE, 5 mTorr, 600 W E b = 1.5 keV
Slide 10
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