Ionization of sputtered material in a planar magnetron discharge

Emission spectra in the visible and near ultraviolet have been recorded for the magnetron sputtering of titanium by argon at pressures between 0.5 and 100 Pa. Intense emission lines from both atomic and ionic material were detected, and comparison of line intensities yielded an ionization fraction of over 10% and an electron temperature of the order of 1 eV for the sputtered material. The ionization fraction decreased with increasing magnetron power, and an optimal operating pressure was found for maximum ion content of the sputtered flux. Scaling laws of emission line intensity with magnetron power indicated the incomplete thermalization of sputtered metal with the sputtering plasma, and spatially resolved measurements of ionization profiles were used to investigate the transport and collisional ionization of sputtered material. Penning ionization of sputtered titanium by metastable argon was found to be the dominant ionization process, and the effect of diffusion of metastable argon was noted. Control of ion content in sputtered fluxes is of interest for the deposition of thin films and for metallization of semiconductors.