SYNTHESIS AND CHARACTERIZATION OF HIGHLY TEXTURED POLYCRYSTALLINE ALNTIN SUPERLATTICE COATINGS/

AlN/TiN multilayer coatings were synthesized by sputtering Al and Ti m etal targets simultaneously in an Ar+N-2 plasma using a dual-cathode u nbalanced de magnetron sputtering system. Two different power sources, rf and pulsed-de, were employed for substrate bias. It was found that under a critical thickness for the AW layer, the AlN/TiN coating with the AlN layers below a critical thickness exhibit a highly textured [ 111]-oriented superlattice structure. However, the rf-biased films hav e poor mechanical properties. Transmission electron microscopy (TEM) s tudies of the rf-biased films show columnar structure of large grains with weak links (amorphous-like material) between different columnar g rains. In the pulsed-de-biased films, however, we noticed a twofold in crease in hardness, when the bilayer thickness is under similar to 5 n m. The increase of the hardness coincides with the structure phase tra nsition from a randomly oriented polycrystalline AlN/TiN thin film to a highly [111]-textured AlN/TiN thin film. X-ray diffraction and TEM s tudies indicate that in the highly [111]-textured multilayer films, Al N is in a nanostabilized cubic form. The critical thickness for AlN to form a nanostabilized cubic structure along [111] is less than about 2.5 nm. TEM studies on the highly textured films deposited with pulsed -de bias showed a coherent growth of an AlN/TiN layered structure acro ss the film and highly dense grain boundaries, which was achieved by u sing the low-energy ion bombardment induced by the pulsed-de bias. The high hardness value of the coating with small bilayer thickness depos ited with pulsed-de bias is not only due to the formation of the nanom eter-scale multilayer structure and nanometer-stabilized cubic form of AlN, but also due to the strongly bonded high-angle grain boundaries between different columnar grains. (C) 1998 American Vacuum Society. [ S0734-2101(98)02406-3].