Growth of dense, hard yet low-stress Ti0.40Al0.27W0.33N nanocomposite films with rotating substrate and no external substrate heating

Abstract

W+ irradiation of TiAlN is used to demonstrate growth of dense, hard, and stress-free refractory nitride coatings with no external heating during reactive magnetron sputtering. Ti0.40Al0.27W0.33N nanocomposite films are deposited on Si(001) substrates using hybrid high-power impulse and dc magnetron cosputtering (HiPIMS and DCMS) in an industrial sputtering system employing substrate rotation during film growth from six cathodes. Two W targets powered by HiPIMS serve as a pulsed source of energetic W+ ions with incident fluxes analyzed by in situ time- and energy-resolved mass spectroscopy, while the remaining four targets (two elemental Ti targets and two Ti plates with Al plugs) are operated in the DCMS mode (W-HiPIMS/TiAl-DCMS) to provide a continuous flux of metal atoms and sustain a high deposition rate. A negative substrate bias Vs is applied only in synchronous with the W+-ion-rich portion of each HiPIMS pulse in order to provide film densification by heavy-ion irradiation of the TiAlN layers deposited between W+-ion exposures. W is selected for densification due to its high mass and relatively low reactivity with N2, thus minimizing target poisoning while enhancing gas rarefaction. Dense Ti0.40Al0.27W0.33N alloy films, grown with no external substrate heating (substrate temperature Ts lower than 150 °C due to heat load from the plasma) and Vs = 500 V, exhibit a nanoindentation hardness of H = 23.1 GPa and an elastic modulus of E = 378 GPa, which are, respectively, 210% and 40% higher than for reference underdense DCMS Ti0.58Al0.42N films grown under the same conditions, but without W+ irradiation. The W ion bombardment does not affect the film stress state, which is compressive and low at 1.2 GPa.