High concentration effects in dusty plasmas

Dust generation in plasma reactors used for PECVD is a general limiting effect which occurs when trying to obtain high deposition rates in the fabrication of thin films. In such dust-forming processes, for instance silane discharges, very high concentrations of submicrometre sized particulates are readily produced. The theoretical approach and the modelling of these dusty dense plasmas suggest that they have very peculiar properties with spectacular effects concerning the plasma equilibrium and the behaviour of the particulate cloud. Well characterized dusty dense plasma situations have been obtained in argon-silane or in pure argon RF discharges and experimental data obtained in these situations are reported here, in connection with the theoretical predictions. In terms of plasma properties the drastic modification of the free electron population, induced by the presence of the particles, is one of the most important results, with significant effects on the chemical equilibrium of the plasma. In terms of the particle cloud behaviour the strong electrostatic interaction between the negatively charged particulates is shown to be an order of magnitude higher than their kinetic energy and this particle cloud has to be described as a 'Coulomb liquid'. An overview of our experimental studies of these effects in a dusty dense plasma situation is given, including the most recent results.