Time-averaged and time-resolved ion fluxes related to reactive HiPIMS deposition of Ti-Al-N films

Abstract

Time-averaged and time-resolved ion fluxes during reactive HiPIMS deposition of Ti1-xAlxN thin films are thoroughly investigated for the usage of Ti1-xAlx composite targets – Al/(Ti + Al) ratio x = 0.4 and 0.6. Ion mass spectroscopy analysis revealed, that increasing x in the target material or reducing the N2 flow-rate ratio leads to a proportional increase of the Al+-ion count fraction, whereas that of Tin+-ions (n = 1, 2) remains unaffected despite of comparable primary ionisation energies between Al and Ti. In fact, energetic Ti2+-ions account for the lowest flux fraction incident on the substrate surface, allowing for a high Al-solubility limit in cubic-structured Ti1-xAlxN thin films (xmax ~ 0.63) at low residual stresses. In addition, time-resolved plasma analysis highlights the simultaneous arrival of metal- and process-gas-ions throughout the entire HiPIMS pulse duration. These ion-bombardment conditions, which were dominated by gas-ion irradiation with a significant contribution of Al+-ions (up to ~20 %) and negligible energetic Ti2+-ions, allowed for the growth of cubic Ti0.37Al0.63N coatings exhibiting high indentation hardness of up to ~36 GPa at a low compressive stress level (σ = −1.3 GPa).