Influence of gas pressure on the ion current and its distribution in a filtered vacuum arc deposition system

A filtered vacuum arc deposition system consisted of a cathode, an annular anode, a quarter torus duct macroparticle filter, and a deposition chamber. Arcs were sustained on a Ti cathode in the presence of noble background gases helium and argon, and reactive gases nitrogen and oxygen. The gas pressure was continuously varied from 3 × 10^-5 Torr (4 mPa) to 0.1 Torr (13.3 Pa). A toroidal magnetic field of up to 20 mT, and a straight field in the deposition chamber of up to 10 mT were imposed for plasma guiding. The total saturation ion current was measured with a 130 mm diameter probe. The ion current density distribution was measured with a nine-segment multi-probe, and the individual probe element currents were fitted to a two-dimensional Gaussian distribution. It was shown that in the presence of a noble gas the total saturation ion current at first increases with increasing the background gas pressure, then achieves a maximum at a pressure of 10 mTorr (1.3 Pa) for He, and at 2 mTorr (0.26 Pa) for Ar, where its value is 1.4-2 times greater than in vacuum. With further increase in the pressure the ion current strongly decreases. In the presence of reactive gases this maximum is not observed, and the total ion current strongly decreases at pressures greater than 2-3 mTorr (0.26-0.4 Pa). In contrast to this, a maximum is observed in the ion current collected on small diameter individual probes of multi-probe, positioned towards the direction of the plasma beam displacement. With increasing gas pressure, the distribution width decreases, and a displacement of the beam center is observed both in the -g direction and in the (B×g) direction, where B and g are vectors of the toroidal field and centrifugal acceleration, respectively. The present results show that proper substrate positioning in the deposition chamber must take into account the beam displacement due to the background gas.