Dynamic interactions in the physical properties of magnetron deposition systems

Abstract

The traditional approach to magnetron sputter deposition is to describe the plasma, the sputtering and bombardment processes, atom transport and film deposition individually as separate non-interacting processes. In reality, however, strong interactions exist between most of these phenomena. As an example, the bombardment process at the cathode can lead to energetic bombardment of the sample through energetic neutrals or neutralized negative ions. Also, the density of the background gas and the subsequent sputtered atom-gas atom collisions result in changes in atom transport as well as changes in the energy distribution of the sputtered atoms. The collisional rarefaction of the background gas results in a host of other changes, including changes in the plasma impedance, the film stress and composition, the relative arrival rates of energetic and condensing species and the optical emission levels. Several experiments have shown the magnitude of these various effects. The neutral density near the cathode has been measured and found to be strongly dependent on the discharge current, as well as the sputter yield and the thermal conductivity of the gas. The flux of energetic neutrals has been experimentally measured at the sample surface during sputtering as a function of pressure, power and the particular species involved. The relative ion to neutral arrival rate can be measured as a function of pressure. As a function of increasing pressure the reduction in the deposition rate of sputtered atoms is more significant than changes in the flux of high energy neutrals due to scattering. The gas rarefaction effect can be shown to modify the transport process of the sputtered atoms, as well as the resultant composition and stress of films deposited on both the cathode and the sample. © 1991.