Effect of low-energy ion assistance on the properties of sputtered ZrB2 films

Zirconium diboride (ZrB2) films have been deposited by direct current magnetron sputtering (DCMS) from a ZrB2 compound target on Al2O3 (0001) substrates held at 600, 700, 800, and 900 °C, and with two different axial magnetic field strengths, 34 and 104 G, generated using a coil surrounding the substrate. Plasma probe measurements show an increase of the ion fluxes on floating-potential substrates of the two different configurations by a factor of 2.8 for 104 G compared to 34 G, while the ion energy remained relatively constant at ≈12 eV. Time-of-flight elastic recoil detection analysis (ToF-ERDA) show that films deposited with a magnetic field of 34 G are highly overstoichiometric with B/Zr ratios ≈2.4, while films deposited with 104 G exhibit a B/Zr ratios ≈2.1. The levels of oxygen and carbon in the films are below 1 at. % irrespective of growth conditions. X-ray diffraction (XRD) θ/2θ scans, complemented by pole figure measurements, reveal that all deposited films are 0001-oriented. XRD θ/2θ scans of the 000ℓ peak intensities and ω (rocking-curve) widths show increased ZrB2 crystal quality with increasing temperature for both magnetic field strengths. Minimum electrical resistivity of ≈100 μΩcm is achieved for an axial magnetic field of 104 G, independent of temperature.