INFLUENCE OF GAS-PRESSURE ON THE ION CURRENT AND ITS DISTRIBUTION IN A FILTERED VACUUM ARE DEPOSITION SYSTEM

A filtered vacuum are deposition system consisted of a cathode, an ann ular anode, a quarter torus duct macroparticle filter, and a depositio n chamber. Arcs were sustained on a Ti cathode in the presence of nobl e background gases helium and argon, and reactive gases nitrogen and o xygen. The gas pressure was continuously varied from 3 x 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 i mposed for plasma guiding. The total saturation ion current was measur ed 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 distributi on. It was shown that in the presence of a noble gas the total saturat ion ion current at first increases with increasing the background gas pressure, then achieves a maximum at a pressure of 10 mTorr (1.3 Pa) f or 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 ma ximum 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 i ndividual probes of multi-probe, positioned towards the direction of t he plasma beam displacement. With increasing gas pressure, the distrib ution width decreases, and a displacement of the beam center is observ ed both in the -g direction and in the (B x g) direction, where B and g are vectors of the toroidal field and centrifugal acceleration, resp ectively. The present results show that proper substrate positioning i n the deposition chamber must take into account the beam displacement due to the background gas.