Constraints on particle growth in plasmas

Summary form only given. Estimates were made of the various effects caused by particles in processing plasmas. Negative ions have long residence times and can contribute to clustering, and external sources of particles, such as aerosols and sputtering, also will be causes of contamination. The particles have to satisfy charge balance and their floating potential acts like a mass filter, allowing only the larger particles to grow in the higher electron temperature regions of the discharge. The presence of large numbers of negative ions permits the formation of smaller particles by reducing the floating potential. At higher ion densities and modest pressures, rapid growth can occur by pyrolysis on the hot surface of the particles which are heated by ion bombardment, and by recombinations of charged and neutral species. The position of the particles in the plasma is determined mainly by a balance between the electric field forces and the gravitational force. Calculations show that the particles will locate in low field regions of a few volts per centimeter for typical plasma RF reactor conditions. The spatial distribution will be influenced by the particle masses and by any spatial changes in the electron energy distribution (reflecting the excitation conditions)