Optical emission spectroscopy in an inverted cylindrical magnetron plasma

Optical emission spectroscopy was performed on a novel inverted cylindrical magnetron (ICM) sputtering system. This ICM technique offers the advantage of depositing insulating films such as alumina. Initial data were acquired for two conditions: titanium targets with argon (85 sccm) at 0.27 Pa and 6.5 kW; aluminum targets with argon (85 sccm) also at 0.27 Pa and 6.5 kW. For both plasma conditions, emission scans were acquired from 400 to 825 nm. After calibrating our spectroscopy system's optical response, we generated electronic Boltzmann plots using argon lines to evaluate the relative population of five specific excited states. From the Boltzmann plots, we calculated a Boltzmann temperature for each condition. Results indicate a higher temperature (5200 K) for the Ti conditions than for the Al conditions (2100 K), though the population of the argon excited states was higher for the Al conditions. These results are generally consistent with a two-temperature electron energy distribution function where the high energy electrons (responsible for the initial excitation of argon ground state atoms) have more energy for the Al plasma (producing more excited states) but where the low energy electrons and/or neutrals and ions (responsible for the relative distribution of excited states which are close in energy) have lower energy (producing a lower Boltzmann temperature).