High rate reactive sputtering in an opposed cathode closed-field unbalanced magnetron sputtering system

Abstract

An opposed cathode sputtering system was constructed with the ability to coat parts with a size up to 15 cm in diameter by 30 cm long, but initial trials with this system revealed very low substrate bias currents. When the AlNiCo magnets in the two opposed cathodes were arranged in a mirrored configuration, the plasma density at the substrate was low, and the substrate bias current density was less than 1 mA cm -2. If the magnets were arranged in a closed-field configuration where the field lines from one set of magnets were coupled with the other set, the substrate bias current density was as high as 5.7 mA cm -2 when NdFeB magnets were used. In the closed-field configuration, the substrate bias current density was related to the magnetic field strength between the two cathodes and to the sputtering pressure. Hard, well-adhered TiN coatings have been reactively sputtered in this opposed cathode system in the closed-field configuration, but the mirrored configuration produced films with poor adhesion because of etching problems and low plasma density at the substrate.