Deposition of Sno₂ Coatings Using a Rectangular Filtered Vacuum Arc Source

An arc discharge was sustained between a rectangular Sn cathode and an anode with a rectangular aperture, both 66 × 440 mm. Magnetic fields in the vicinity of the cathode directed the retrograde motion of the cathode spots in a racetrack pattern along the surface of the cathode. Sn plasma generated by the cathode spots passed through the anode aperture into a rectangular plasma duct having two 45° bends, and baffles to prevent macroparticle bouncing. A magnetic field of ∼26-38 mT parallel to the duct walls directed the plasma flow. Either a substrate or a multi-element Langmuir probe was placed on a carriage in a 60-cm-wide rectangular vacuum deposition chamber at the duct outlet. Oxygen was fed into the vacuum chamber at a rate of approximately 200 sccm, and regulated to maintain a constant pressure of approximately 0.7 Pa in the chamber. The saturated ion current to individual probe elements was measured, and tin oxide coatings were deposited on either stationary or moving substrates of glass polycarbonate. The saturated ion current density at the center of the duct exit at the substrate plane was measured to be J=55 mA/cm², with an arc current of 400 A. The coating thickness distribution was approximately triangular in the direction perpendicular to the cathode axis, with a maximum deposition rate of 37 nm/s in the center, and a base length of 9 cm. The thickness distribution along the long axis could be fit to a parabolic function. Coatings were deposited on glass and polycarbonate substrates transported perpendicular to the long axis with dynamic deposition rates of 80-100 nm-m/min. Sheet resistances between 70-400 Ω/□ were measured. The relative optical transmission at a wavelength of 500 nm of a polycarbonate sample with a coating thickness of 420 nm was 83% with a standard deviation of less than 2% in the central 10 cm of the sample. Microwave power transmission at 10 GHz was attenuated by as much as 9 db.