Low-temperature synthesis of Al-rich rock salt Cr1−xAlxN films with selective metal ion bombardment by synchronized substrate bias pulsing

We demonstrate a two-stage low-temperature (<100 °C) growth process for obtaining Al-rich rock salt-structured Cr1−xAlxN films by high-power impulse magnetron sputtering (HiPIMS) with synchronized substrate bias pulsing. The first stage features selective ∼100 eV Al+ ion irradiation that promotes out-of-plane (002) texture in rock salt Cr0.3Al0.7N. Film thickness was limited to <∼230 nm above which wurtzite-AlN formation was observed. The second stage combines the synchronized bombardment of ∼100 eV Al+ and Cr+ ions, allowing the synthesis of rock salt Cr1−xAlxN with unprecedentedly high Al contents up to x ≈ 0.7 without wurtzite-AlN formation. Peening effects from heavier Cr+ ions stabilize rock salt Cr1−xAlxN with greater Al content, induce compressive stresses, and densify the film. In contrast, single-stage DC magnetron sputtering or HiPIMS using floating or continuous bias suffers from poor crystallinity, Ar entrapment, and film delamination. These findings establish that two-stage growth with selective ion bombardment is an attractive approach for tailoring stable single-phase Al-rich Cr1−xAlxN coatings with controlled properties for applications that do not allow high temperature processing.