AVS 52nd International Symposium
    Plasma Science and Technology Tuesday Sessions
       Session PS-TuP

Paper PS-TuP16
Time-Dependent Recombination Reactions of Oxygen Atoms on an Anodized Aluminum Plasma Reactor Wall, Studied by a Spinning Wall Method

Tuesday, November 1, 2005, 4:00 pm, Room Exhibit Hall C&D

Session: Plasma Science and Technology Poster Session
Presenter: J. Guha, University of Houston
Authors: P.F. Kurunczi, University of Houston
J. Guha, University of Houston
V.M. Donnelly, University of Houston
Correspondent: Click to Email
We have studied the pressure, power, and time dependence of recombination of O atoms on an anodized Al surface, using a new "spinning wall" technique. With this method, a cylindrical section of the wall of the plasma reactor is rotated, and the surface is periodically exposed to the plasma and then to a differentially pumped mass spectrometer (MS). By varying the substrate rotation frequency (f), we vary the reaction time, t@sub r@ i.e. the time between exposure of the surface to O-atoms in the plasma and MS detection of desorbing O@sub 2@ (t@sub r@=1/2f). At 600 W and 5 mTorr, the O@sub 2@ desorption signal decreases by a factor of 6 as t@sub r@ is increased from 0.7ms to 40ms. (The signal is zero at f=0.) The O@sub 2@ signal decay rate is highly non-exponential, slowing at longer times. As power is lowered, the signal decreases more strongly at short t@sub r@ than at long t@sub r@. For constant power, signals also decrease at pressures above or below 5 mTorr. The shape of the decay curve is determined solely by the O@sub 2@ desorption signal extrapolated to t@sub r@=0, which is determined by the absolute O flux in the plasma. We have also studied the time dependence of recombination by spinning the substrate at a rapid rate and then turning the plasma on and off. The rate of rise and decay in signal is again highly non-exponential; O@sub 2@ desorption decays by 1/e in ~30ms and is still detectable ~200ms after the discharge extinguishes. When the plasma is turned on, the rise time in O@sub 2@ signal mirrors the decay (~30ms and ~200ms components) if the plasma was recently operated (within the last minute) and is much longer (~2s) if the plasma was off for more than 1 hr, indicating some initial conditioning of the surface. Mechanisms and modeling of O-atom recombination will be compared with these time-dependent results. Supported by ACS-PRF. @FootnoteText@ P.F. Kurunczi - Present affiliation: Varian Semiconductor Equipment, Gloucester, MA 01930.