Effects of deposition rate and substrate temperature on the orientation and the growth of YBa2Cu3Ox thin films

The authors report in situ studies of film growth by sputtering using synchrotron X-rays. The structure and growth habit of YBa₂ Cu₃O₇ (YBCO) thin films deposited on (100) SrTiO₃ in a miniature, faced-magnetron sputtering system have been investigated. A combination of the substrate temperature and the deposition rate determines whether the film grows along the a, c, or multiple axes. At low substrate temperatures and low deposition rates, the films grow preferentially along the a-axis, In contrast, higher substrate temperatures and high deposition rates favor c-axis-oriented film growth with some admixture of (220). The X-ray diffraction peaks were monitored in real time, revealing that a-axis- and c-axis-oriented grains nucleated on the surface of the (100) SrTiO₃ between 625° and 765°C, although the volume fraction of each orientation was temperature dependent. The structural quality of the a-axis films is superior to that of the c-axis films. The best a-axis films (deposited at 685°C) had a rocking curve width of 0.08°, which is 10 times smaller than that for the c-axis films (deposited at 800°C). A shift of the (007) and (200,) peak positions during deposition was observed. The shift in the (007) peak is larger than that for the (200) peak. Defects in the c-axis films were observed, not only at the interface between the film and the substrate, but also on the upper surface of the (final) film; the latter seems to be inherent and is more severe in the films considered