Plasma distribution and SnO 2 coating deposition using a rectangular filtered vacuum arc plasma source

Abstract

A rectangular filtered vacuum arc plasma deposition system was used to deposit SnO 2 coatings on stationary or moving 400×420 mm substrates. The system consisted of a rectangular plasma gun, a rectangular macroparticle filter, a vacuum deposition chamber, a substrate carriage and a transport mechanism. An arc discharge was ignited in the plasma gun between a rectangular cathode and an anode with a rectangular aperture, both 66×440 mm. A Sn plasma jet produced by cathode spots passed through the anode aperture into the rectangular macroparticle filter, which had two 45° bends. A magnetic coil located in the vicinity of the cathode produced a magnetic field that confined the cathode spot motion to a defined trajectory on the cathode surface. Three magnetic coils, located around straight sections of the filter, produced a magnetic field, which guided the plasma through the filter to the substrate positioned on the substrate carriage in the deposition chamber. A stationary multi-element Langmuir probe situated opposite the filter outlet was used to measure the saturated ion current density distribution, as a function of the arc current, the magnetic field strength, and the oxygen pressure. The SnO 2 coatings were fabricated by deposition of the Sn plasma in low-pressure (≤0.73 Pa) oxygen background gas, either on stationary substrates, to determine the coating thickness distribution, or on moving substrates to determine dynamic deposition rate (DDR). The ion current at first increased with the arc current, I arc, in the range of 300–450 A and then saturated with further increasing of I arc up to 700 A. For coatings deposited on stationary substrates at I arc=400 A and oxygen pressure of 0.7 Pa, the coating thickness distribution could be fit by a parabolic function in the direction of the long aperture axis, and was almost triangular in the perpendicular direction, with a maximum deposition rate of 37 nm/s in the beam center. The coatings deposited on moving substrates with I arc=350 A had a DDR of ∼100 nm-m/min, 250–450 nm thickness, a relative visual light transmission of 83% or larger, and a sheet resistivity of 100–170 Ω/□. Higher current experiments suggest that a DDR of 190 nm-m/min or larger could be achieved.