Growth and characterization of chromium oxide thin films prepared by reactive ac magnetron sputtering

CrO _x thin films were prepared on single crystal silicon (111 orientation) and glass substrates by midfrequency (41 kHz) ac sputtering technique in an Isoflux ICM-10 sputter deposition system consisting of two hollow cylindrical targets of Cr in an argon-oxygen plasma at a discharge power of 5 kW and without any deliberate substrate heating. X-ray diffraction studies showed that the coatings were of hcp rhombohedral α-phase chromium oxide. CrO _x coating samples were found to grow preferentially towards the (110) crystal orientation of α-Cr ₂O ₃. Texturing was found to depend on the orientation of the substrates relative to the targets and also on the nature of substrates. One coating sample grown on Si substrate was annealed in air up to 1173 K. Whereas heat treatment increased the crystallite size, CrO _x coating was thermally stable and did not show any structural transformations. Scanning electron microscopy studies showed differences in the surface morphology of the coatings grown on glass and silicon substrates. Dynamic secondary ion mass spectrometry measurements performed on one CrO _x coating deposited on silicon showed that the O/Cr ratio in the films was 1.38. Ar and H impurity concentrations were also measured in this coating as a function of film thickness. Alumina coatings were prepared on Si substrates by reactive sputtering technique using CrO _x coating as template layers. X-ray diffraction studies showed that CrO _x template layers improved the crystallinity of alumina coatings grown on top of it and also facilitated the formation of the thermodynamically stable α-alumina phase.