AVS 49th International Symposium
    Plasma Science Wednesday Sessions
       Session PS+BI-WeA

Paper PS+BI-WeA4
The Role of Reactive Neutral and Ionic Species in the Deposition of Organic Thin Films from an Isopropyl Alcohol and Argon Plasma

Wednesday, November 6, 2002, 3:00 pm, Room C-103

Session: Plasma Processing for Biocompatible Surfaces
Presenter: D.C. Guerin, National Research Council, Canada
Authors: D.C. Guerin, National Research Council, Canada
V.A. Shamamian, Naval Research Laboratory
Correspondent: Click to Email
We present the measurements of neutral species in an argon/isopropyl alcohol (iPrOH) plasma, using appearance potential mass spectrometry. IPrOH is a potential precursor for the cost-effective plasma deposition of non-fouling surfaces. This work complements previous research on the ionic character of the plasma. It had been discovered that tuning the plasma pressure and power caused large variations in the dominant ionic reactions. The resulting changes in the chemical nature of the ionic flux were reflected in the functional character of the deposited films. A significant flux of neutral radicals was detected at the deposition surface at low plasma pressure. However, at higher pressures the plasma region was more remote and the neutral radicals were completely attenuated. The attenuation mechanism was determined to be reaction with the precursor. For example, the methyl radical abstracts hydrogen from iPrOH. Thus, as the pressure increases, the methyl radical flux evolves into a flux of methane. Mean free path (MFP) calculations for hydrogen abstraction agree with the experimental results. At low pressures, the reactive MFP is larger than the chamber geometry. At higher pressures, the reactive MFP is much smaller than the distance between the plasma and deposition surface. The ability of the reactive ions to diffuse from the remote plasma to the deposition surface is explained as being due to charge exchange limitations. The radical species generated have lower ionization energies than iPrOH or argon. Thus, the radical ions are energetically unable to react with the main species in the plasma. In contrast, the flux of ions with ionization energy greater than that of iPrOH, such as argon and methane, is highly attenuated at higher pressures. These results provide some context to competing claims as to the importance of neutrals and ions in deposition from molecular plasmas.