Influence of gas flow rate and entry point on ion charge, ion counts and ion energy distribution in a filtered cathodic arc

We report the results of an investigation in which we measured ion charge, ion counts and ion energy distributions of a titanium cathodic arc operated in a nitrogen atmosphere, using a Hiden mass selected ion energy analyser. Measurements were taken under standardised conditions of arc current and magnetic confinement. Two different gas entry points (over the cathode and in the main chamber close to the Hiden port), three different background gas pressures (2, 4 and 7.5 mtorr) and two different flow rates (23 and 71 sccm) were investigated. Counts were taken at 14, 24, 28, 48 and 62 amu, representing N+ or N22+, Ti2+, N2+, Ti+ and TiN+, respectively. Ion energy was measured up to a maximum of 80 eV relative to vessel wall potential. Multiple data sets were collected for each combination of gas entry, gas pressure and flow rate. Ion counts, ion energy and mean charge all decrease as flow rate increases. For cathode entry, Ti ion counts increase greatly, N ion counts decrease slightly, mean ion energy increases and mean ion charge does not show a clear trend. Similarly, the responses of ion counts, ion energies and mean ionic charges to increases in pressure do not show a single, clear trend. The results of the study are reported and some implications for PBII processing are discussed.