OPTICAL-EMISSION DIAGNOSTICS OF AN RF MAGNETRON SPUTTERING DISCHARGE

An rf planar magnetron discharge in argon has been studied by optical emission spectroscopy. The cathode is an aluminium base alloy. The deposition rate is determined by a quartz microbalance. Atomic and ionic emission lines from Ar and from sputtered particles are studied as a function of the rf power (50-200 W) and the discharge gas pressure (7-150 mtorr). An effective electron temperature is calculated from two Ar lines. By an appropriate choice of emission line, it is shown that the dependence of the atomic and ionic sputtered species on the rf power is identical within the experimental error whatever the excitation level. It is deduced that the sputtered particles are excited to an emitting state by an electron-atom collision and that the ionic lines are produced in a two-step mechanism: first, ionization by electron-atom collision and second, excitation by direct electron collision from the ground state of the ion.