The plasma properties adjacent to the target in a magnetron sputtering source

Using a simple 1D fluid model of the bulk plasma, the distribution of plasma density, ion and electron velocity and space potential have been determined above the 'race-track' of a magnetron sputtering source. ions generated by electron impact ionization are unaffected by the source magnetic field as they fall to the sheath-edge; however, the electron motion is mobility-limited, in the mutually perpendicular electric and magnetic fields. The results show a peak in the plasma concentration in front of the cathode sheath, the height and position of which is governed by the magnetic field strength and discharge current. With increasing magnetic field, sheath-edge ion fluxes greater than the usual value prescribed by the Bohm criterion are found. For a set of discharge conditions, a reversal in the electron current flow is predicted, indicating a limit in the operating parameters for which physical solutions can be generated. The predicted plasma profiles give good agreement with Langmuir probe measurements made in the magnetron target pre-sheath, demonstrating the usefulness of the simple model approach.