Arc behaviour during filtered vacuum are deposition of Sn-O thin films

Abstract

Sn−O transparent, conductive thin films were produced in a filtered vacuum-arc deposition system, consisting of a 90 mm diameter cathode, 122 mm diameter annular anode, and a magnetic quarter torus macroparticle filter. Arc current was in the range 30–200 A and the toroidal magnetic field (BT) was in the range 0–25 mT. A radial magnetic field (Br) at the cathode surface was produced by a coil placed inside a cavity in the cathode. Cathode spot motion, plasma jet motion through the toroidal field, and the characteristics of the deposited Sn−O films were studied as a function of arc current, applied magnetic fields and oxygen pressure. Cathode spot motion on the cathode surface was controlled by BT. Random spot motion on the entire cathode surface was obtained in vacuum when Br was less than 2 mT. The spots were forced to move on a circular path with average radius of 25 mm when Br was larger than 2 mT. Cathode surface oxidation occurred when oxygen was introduced into the system, and its rate increased with the gas pressure. The extent of the oxidized area on the cathode surface was affected not only by gas pressure, but also by the magnitude of arc current and the magnetic fields Br and BT. With Br smaller than 2 mT, oxidized surface regions appear on the cathode, and cathode spot activity on them is disturbed. Random cathode spot motion continues undisturbed on non-contaminated regions of the cathode surface. Cathode spots were hardly observed on the oxidized regions, yet visual examination of the cathode surface used in the arc revealed the existence of cathode spots erosion tracks on them. Transparent and conductive tin oxide films were produced at oxygen pressures of 0.8 Pa when arc operation and the plasma jet in the filter were stable. The stability of the arc and the plasma jet were found to depend on the combination of gas pressure, arc current and magnetic fields. When the plasma jet was not stable poorly conductive films were produced, containing the non-conductive oxide SnO.