A comparison of titanium-based films produced by pulsed and continuous DC magnetron sputtering

Abstract

In the field of magnetron sputtering, it is well established that mid-frequency (20–350 kHz) pulsed processing offers many advantages over continuous DC processing for the reactive deposition of dielectric films. By periodically reversing the target voltage, arc events at the target are suppressed and the reactive sputtering process is stabilised. However, recent studies have shown that pulsing the discharge also significantly modifies the characteristics of the magnetron plasma. Specifically, increased plasma density and electron temperatures, and therefore increased ion energy fluxes to the growing film, have been measured. Clearly, this will have an impact on the properties of both insulating and conductive films. In this study, therefore, titanium dioxide and titanium nitride coatings were deposited by pulsed (asymmetric bipolar, 20-kHz pulse frequency) and continuous DC reactive sputtering. The coatings were characterised in terms of their structures and properties using a range of analytical and measurement techniques, including scanning electron microscopy, electron probe microanalysis, X-ray diffraction, micro-hardness testing, scratch adhesion testing, wear testing and surface profilometry. The optical properties of the TiO2 films were also investigated. In this case, the pulsed films showed increased refractive index and peak transmission values in comparison to the DC films, while the tribological properties of both coating types were superior when pulsed processing was used in comparison with continuous processing.