Preparation of YBa₂Cu₃O_y thin films using induction-coil-coupled sputtering

YBa₂Cu₃O_y (YBCO) superconducting thin films were deposited on MgO single crystals by induction-coil-coupled sputtering. The effects of the induction coil on the qualities of YBCO thin films are examined. Uniformity of film thicknesses below ±5% was obtained over an area of 40 mm diameter using a 50 mm diameter target by the condition of the substrate-target distance of 90 mm. Even in the area of 60 mm diameter which was wider than that of the target, the uniformity of thickness within ±17% was obtained. In order to clarify the effects of the induction-coil, we studied the dependence of the critical temperature (T_c) and the full width at half maximum (FWHM) of the films on the applying power of coil. T_c and FWHM showed optimum values at the applying coil power of 70W. It is confirmed from these results that the induction-coil operated effectively to fabricate high quality films. The epitaxial relations of YBCO films on MgO single crystal substrates were examined by X-ray pole figure measurements. Basically film of YBCO was aligned with the c-axis perpendicular to the substrate surface. The film deposited at the coil power of 70W exhibited well single-oriented grains with the a- or b-axis parallel to the a-axis of MgO. However, films deposited at the applying coil power of 0W contained grains with two different orientations which were rotated by 45°. Scanning electron microscopy (SEM) of the film surface showed the films to consist of a smooth background surface and a distribution of particles. Energy dispersive X-ray analysis (EDAX) measurements showed that the Ba concentration was larger than that of exact stoichiometric composition. Auger electron spectroscopy (AES) revealed that the elements contained in the particles were richer in Ba than in the smooth background surface. The BaCuO₂ particles seemed to precipitate on the surface of the film.