Plasma PVD by small spiral Ta hollow cathodes

Abstract

Spiral hollow cathodes represent interesting options for local PVD applications. Radio frequency powered small diameter spiral hollow cathodes made from 0.45 mm diameter Ta wire rolled around 0.5 mm diameter rod were tested in PVD regimes on silicon substrates at the gas pressure of 400 Pa (3 Torr). The PVD of Ta and reactive PVD of Ta-N resulted in deposition rates of about 130 nm/min with maximum thickness in the center of the coating spots. However, part of the coating spots can be heavily eroded. At higher RF powers droplets from the melted Ta tip of the spiral can damage the coating and melt the Si substrate. The PVD rates of Ta in argon were similar as those for TaN. However, lower number of droplets of the melted Ta were formed in argon. The heating of the spiral outlet and its effect on the coating was also more intense in nitrogen than in argon. The temperature of the Si substrate table reached about 500 °C in 20 min in the nitrogen plasma and up to 400 °C in argon. This heating was higher on electrically grounded substrates than on the floating substrates. The effect of sharp outlet on possible eroding of the sample was confirmed by a sharp ended 1 mm diameter stainless steel medical needle used as a hollow cathode.