| Understanding the structure and dynamics of the plasma within magnetron sputtering systems is important to the continued and extended exploitation of this deposition technique for the production of novel and industrially valuable thin films. To achieve this goal, it is necessary to understand how electrons, as a critical constituent of the plasma, respond, in terms of spatial densities and temperatures, to process conditions such as pressure, gas mixture, and cathode current.;In this investigation, a combination of experimental and simulation techniques are utilized. An electrostatic or Langmuir probe is used to observe basic plasma parameters including electron density (up to 6 x 1016 cm-3), plasma electrical potential (typically 1 to 3 volts), floating potential (down to below -12 volts), and electron temperature (typically 0.5 to 5 eV), as functions of process conditions. The results indicate that electron transport throughout the magnetron reactor is not due to a simple or obvious mechanism. The electron density and temperature spatial profiles are strongly dependant on the magnetic field and the neutral gas species type and density profile. A Monte-Carlo simulation technique has also been used to study those dependencies. Such a technique involves following the three dimensional trajectories of electrons and accounts for an-isotropic and inelastic or elastic collisions with neutral gas atoms. The simulations demonstrate that the magnetic field and density of neutral gas species are important to the evolution of electron densities and temperatures. Additionally, the sputtered atom density (Ag in this case) seems to play a role in electron temperature profiles because of the lower ionization threshold for Ag. It also appeared that cathode voltage was not a major factor in the spatial electron temperature distribution. Finally, it appears that the presence of a group of hot electrons detected with the Langmuir probe, which are not in equilibrium with the bulk group of electrons, may result as the evolution of electrons originating from the cathode or within the sheath. |
