Influence of Ar and N2 Pressure on Plasma Chemistry, Ion Energy, and Thin Film Composition During Filtered Arc Deposition From Ti3SiC2 Cathodes

Arc plasma from Ti₃SiC₂ compound cathodes used in a filtered dc arc system has been characterized with respect to plasma chemistry and charge-state resolved ion energies. In vacuum, the plasma composition is dominated by Ti ions, with concentrations of 84.3, 9.3, and 6.4 at% for Ti, Si, and C ions, respectively. The reduced amount of Si and most notably C compared with the cathode composition is confirmed by analysis of film composition in corresponding growth experiments. The deposition of light-element deficient films is thus related to plasma generation or filter transport. The ion energy distributions in vacuum range up to 140, 90, and 70 eV for Ti, Si, and C, respectively. Corresponding average ion energies of 48, 36, and 27 eV are reduced upon introduction of gas, down to around 5 eV at 0.6 Pa Ar or 0.3 Pa N₂ for all species. In vacuum, the charge state distributions of Si and C are shifted to higher values compared with corresponding elemental cathodes, likely caused by changed effective electron temperature of the plasma stemming from compound cathode material and/or by electron impact ionization in the filter. The average ion charge states are reduced upon addition of Ar, ranging between 1.97 and 1.48 for Ti, 1.91 and 1.46 for Si, and 1.25 and 1.02 for C. Similar effects are observed upon introduction of N₂, though with more efficient charge state reduction with pressure. It is conceivable that the pressure-induced changes in ion energy and charge state are crucial for the film synthesis from a microstructure evolution point of view, as they affect the ion-surface interactions through supply of energy, especially when substrate biasing is employed during arc deposition from a compound cathode.