AVS 52nd International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS-ThM

Paper PS-ThM2
Plasma-Surface Reactions at a Spinning Wall

Thursday, November 3, 2005, 8:40 am, Room 304

Session: Plasma-Surface Interactions II
Presenter: V.M. Donnelly, University of Houston
Authors: P.F. Kurunczi, University of Houston
J. Guha, University of Houston
V.M. Donnelly, University of Houston
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We report a new method for studying plasma-wall interactions in near-real time. A cylindrical substrate is embedded in the reactor wall. This "spinning wall" is rotated up to 200,000 rpm, allowing the surface to be periodically exposed to the plasma (40% of the time) and then analyzed by a chopped molecular beam mass spectrometer (MS) in as little as 150µs after plasma exposure. Skimmers on the plasma side and analysis side of the spinning wall, and 3 stages of differential pumping allow a pressure of 10@super -10@ Torr in the MS with a 10 mTorr plasma. We have used this method to study oxygen plasma reactions on anodized Al. With the plasma off and substrate at rest, we observe a small signal at m/e = 32, due to O@sub 2@. When the substrate is rotated (plasma off) this signal increases slightly. When the substrate is at rest and the plasma is turned on, no increase in signal is observed. When the substrate is spun with the plasma on, however, a large increase in signal is observed with increasing rotation frequency. We interpret these observations as follows: O-atoms that impinge on the surface when it is in the plasma recombine over the ~0.7 to 30 ms period probed by changing the rotation frequency. We rule out O@sub 3@ (cracking in the MS ionizer to form O@sub 2@) from the absence of its parent ion. Likewise, we rule out shallow implantation of O@sub 2@@super +@ or O@super +@ as a cause of the O@sub 2@ signal; the dependence of the signal on rotation frequency did not change when grids were positively biased to reject positive ions. No desorbing O was observed; a signal at m/e=16 was entirely from the cracking of O@sub 2@. Finally, no ions were observed with the MS ionizer off. Modeling of O@sub 2@ signal vs. rotation frequency indicates a range of recombination rate constants, suggesting a range of O-binding energies on anodized Al. Supported by ACS-PRF. @FootnoteText@ P.F. Kurunczi - Present affiliation: Varian Semiconductor Equipment, Gloucester, MA 01930.