Measurements of neutral plasma species in an argon/isopropyl alcohol plasma for the deposition of organic films

Abstract

The neutral gas-phase chemistry of an isopropyl alcohol/argon pulsed plasma was investigated. Appearance potential mass spectrometry was used to identify the neutral species present in the plasma. This article complements the previously published study of the positive ion flux to the deposition surface. Of particular interest was the identification of the reactive species in the plasma that exist as neutrals as well as ions. We determined that neutral radicals were produced by hydrogen-exchange mechanisms as well as electron-impact dissociation reactions. The electron-impact dissociation ionization of the precursor in the plasma resulted in reactive ions that did not occur as neutral species. A byproduct of this reaction was a large concentration of the neutral methyl radical. At low pressures, the methyl radicals diffuse to the surface and are incorporated into the deposited films. At elevated pressures, the neutral methyl radicals abstract hydrogen from gas-phase isopropyl alcohol molecules to form methane. Furthermore, as the pressure increases, the plasma becomes more remote from the deposition surface. Molecular ions created in the remote discharge preserve their chemical identity while diffusing to the surface, since the energies of charge-exchange limit the extent of reaction with the precursor.