Physics of Plasma

Nature of Plasma

  • A plasma is a partially ionized gas consisting of electrons, ions and neutral atoms or molecules
  • The plasma electrons are at a much higher temperatures than the neutral gas species, typically around
    104 K, although the plasma gas as a whole is at near ambient temperature
  • The plasma electron density is typically around 1010 cm-3

Plasma Formation

  • An RF oscillating electric field is generated in the gas region, either through the use of capacitive plates or through magnetic induction
  • At sufficiently low pressures the combined effect of the electric field acceleration of electrons and elastic scattering of the electrons with neutral atoms or field lines leads to heating of the electrons
  • When electrons gain kinetic energy in excess of the first ionization threshold in the neutral gas species, electron-neutral collisions lead to further ionization, yielding additional free electrons that are heated in turn

Plasma-Surface Interaction

  • The energy of plasma electrons and ions is sufficient to ionize neutral atoms, break molecules apart to form reactive radical species, generate excited states in atoms or molecules, and locally heat the surface
  • Depending on the process gases and parameters, plasmas are capable of both mechanical work, through the ablative effect of kinetic transfer of electrons and ions with the surface, and chemical work, through the interaction of reactive radical species with the surface
  • In general, plasmas can interact with and modify a surface through several mechanisms: ablation, activation, deposition, cross-linking and grafting - see Plasma-Surface Interaction