Time-averaged and time-resolved ion fluxes related to reactive HiPIMS deposition of Ti-Al-N films
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).
L. Zauner, A. Bahr, T. Kozák, J. Čapek, T. Wojcik, O. Hunold, S. Kolozsvári, P. Zeman, P.H. Mayrhofer, H. Riedl
Surface and Coatings Technology