Absolute argon excited-state population measurements from emission spectroscopy in an inverted cylindrical magnetron plasma

An inverted cylindrical magnetron sputtering system operating at 6.5 kW, 85 sccm argon, and 0.27 Pa was used to produce a mid-frequency AC (40 kHz) Al–Ar plasma. Optical emission spectroscopy was used to monitor the plasma emission from 680 nm to 830 nm. Absolute calibration of the emission data was performed to find the population density of excited-state argon atoms in the 4p electron energy level for six transitions. The excited-state densities were on the order of 1013 m− 3 for each transition. For comparison, an argon collisonal-radiative model was used to simulate the excited-state densities. The model used non-Maxwellian electron energy distribution functions obtained from the commercially available software ELENDIF. Good agreement between the measured and predicted Ar4p excited states was observed.