Role of sputtered Cu atoms and ions in a direct current glow discharge: Combined fluid and Monte Carlo model

The Cu atoms sputtered from the cathode and the corresponding Cu ions in an argon direct current glow discharge are described by a combination of two models: a fluid model for their overall behavior (diffusion and migration) in the entire discharge and a Monte Carlo model for the explicit transport of the Cu ions in the cathode dark space. The models are combined with other models described previously for the electrons, Ar ions, fast Ar atoms, and Ar metastables, in order to obtain an overall picture of the glow discharge. Results of the fluid model are the densities and fluxes of the Cu atoms and ions. At 100 Pa and 1000 V the Cu atom and ion densities are of the order of 10(12)-10(13) and 10(10)-10(11) cm(-3), respectively. The ionization degree is hence about 1%, which is much higher than for Ar. The Cu ion to Ar ion density is about 6% and the Cu ion to Ar ion flux is about 5%. The energy distribution of the Cu ions bombarding the cathode is calculated with the Monte Carlo model and shows good agreement with experiment. It is characterized by a peak at maximum energy, in contrast to the energy distribution of Ar ions and fast atoms. Since sputtering increases with the bombarding energy, the amount of self-sputtering is significant, although still clearly lower than the contribution of Ar ions and fast atoms. The influence of pressure, voltage, and current on all these quantities is investigated. (C) 1996 American Institute of Physics.