AVS 53rd International Symposium
    Plasma Science and Technology Tuesday Sessions
       Session PS2-TuM

Paper PS2-TuM3
Studies of Oxygen and Chlorine Atom Recombination Reactions on Anodized Aluminum in O@sub 2@/Ar, Cl@sub 2@ and Cl@sub 2@/O@sub 2@ Plasmas by a Spinning Wall Method

Tuesday, November 14, 2006, 8:40 am, Room 2011

Session: Plasma Surface Interactions I: Joint AVS-AIChE Session
Presenter: J. Guha, University of Houston
Authors: J. Guha, University of Houston
V.M. Donnelly, University of Houston
Correspondent: Click to Email
We have studied reactions of O and Cl atoms on a room temperature anodized aluminum substrate in O@sub 2@/Ar, Cl@sub 2@, and Cl@sub 2@/O@sub 2@ plasmas by the "spinning wall" technique. In this method, a rotating cylindrical substrate is periodically exposed to the plasma and then analyzed in a differentially pumped chamber by mass spectrometry (MS), and for the first time, by Auger electron spectroscopy (AES). By varying the %O@sub 2@ in Ar, O atom recombination has been studied over a wide range of O atom flux. In 600 W, 5 mTorr plasmas, the O@sub 2@ desorption signal decays in a "stretched" exponential manner over a 40 ms period by a factor of 8 for pure O@sub 2@ and by a factor of ~2 for 2% O@sub 2@/Ar. When a single desorption product is observed (e.g. O@sub 2@ in oxygen plasmas), we find that the pressure rise in the MS chamber as a function of increasing rotation frequency is directly proportional to the MS signal. Consequently, absolute fluxes of O@sub 2@ and Cl@sub 2@ could be obtained from a calibration of the pumping speed and ion gauge sensitivity. For the above example, the yields extrapolated to t=0 are 0.35 and 6 x 10@super 14@cm@super -2@s@super -1@, respectively. In pure chlorine plasmas, the Cl@sub 2@ desorption signal decays in a similar non-exponential manner, but by a larger factor of ~25 over 40 ms in a 5mTorr, 600W plasma, and with a higher yield of 3 x 10@super 15@cm@super -2@s@super -1@ extrapolated to t=0. Unlike O@sub 2@ or Ar, a substantial desorption of physisorbed Cl@sub 2@ is observed over 40 ms with the plasma off. Competitive recombination of Cl and O was also studied in Cl@sub 2@/O@sub 2@ plasmas. Formation of ClO and ClO@sub 2@ peak at ~80% O@sub 2@ and exceed O@sub 2@ and Cl@sub 2@ yields. In all experiments, chemisorbed O and Cl are detected by AES, and showed little dependence on substrate rotation frequency. A sub-surface diffusion-recombination model has been developed to explain these observations.