Reactive sputtering of hard nitride coatings using asymmetric-bipolar pulsed DC generator

Hard coatings of TiN, CrN, TiAlN and Si3N4, which exhibit a large variation in their electrical resistivities, have been prepared in an unbalanced magnetron sputtering system using an asymmetric-bipolar pulsed DC generator. TiN, CrN and TiAlN coatings, which exhibit fairly low electrical resistivities as compared to Si3N4, have also been prepared using a DC generator in the same sputtering system under identical deposition conditions. The properties of these coatings are compared with the pulsed deposited coatings. X-ray diffraction, X-ray photoelectron spectroscopy, nanoindentation tester, atomic force microscopy and potentiodynamic polarization have been used to characterize the coatings. We present in detail the effect of pulsed sputtering onto the plasma properties (e.g., cathode voltage, cathode current and ion current) and onto the properties of the coatings (e.g., growth rate, surface roughness, hardness, porosity). Our studies show that a variety of hard nitride coatings (including dielectric) with superior properties and low defect density can be prepared using asymmetric-bipolar pulsed DC generator.