A review of metal-ion-flux-controlled growth of metastable TiAlN by HIPIMS/DCMS co-sputtering.

We review results on the growth of metastable Ti 1− x Al x N alloy films by hybrid high-power pulsed and dc magnetron co-sputtering (HIPIMS/DCMS) using the time domain to apply substrate bias either in synchronous with the entire HIPIMS pulse or just the metal-rich portion of the pulse in mixed Ar/N 2 discharges. Depending upon which elemental target, Ti or Al, is powered by HIPIMS, distinctly different film-growth kinetic pathways are observed due to charge and mass differences in the metal-ion fluxes incident at the growth surface. Al + ion irradiation during Al–HIPIMS/Ti–DCMS at 500 °C, with a negative substrate bias V s = 60 V synchronized to the HIPIMS pulse (thus suppressing Ar + ion irradiation due to DCMS), leads to single-phase NaCl-structure Ti 1− x Al x N films ( x ≤ 0.60) with high hardness (> 30 GPa with x > 0.55) and low stress (0.2–0.8 GPa compressive). Ar + ion bombardment can be further suppressed in favor of predominantly Al + ion irradiation by synchronizing the substrate bias to only the metal-ion-rich portion of the Al–HIPIMS pulse. In distinct contrast, Ti–HIPIMS/Al–DCMS Ti 1 − x Al x N layers grown with Ti + /Ti 2 + metal ion irradiation and the same HIPIMS-synchronized V s value, are two-phase mixtures, NaCl-structure Ti 1− x Al x N plus wurtzite AlN, exhibiting low hardness (≃ 18 GPa) with high compressive stresses, up to − 3.5 GPa. In both cases, film properties are controlled by the average metal-ion momentum per deposited atom < p d > transferred to the film surface. During Ti–HIPIMS, the growing film is subjected to an intense flux of doubly-ionized Ti 2+ , while Al 2+ irradiation is insignificant during Al–HIPIMS. This asymmetry is decisive since the critical < p d > limit for precipitation of w -AlN, 135 [eV-amu] 1/2 , is easily exceeded during Ti–HIPIMS, even with no intentional bias. The high Ti 2 + ion flux is primarily due to the second ionization potential (IP 2 ) of Ti being lower than the first IP (IP 1 ) of Ar. New results involving the HIPIMS growth of metastable Ti 1− x Al x N alloy films from segmented TiAl targets are consistent with the above conclusions. [ABSTRACT FROM AUTHOR]