Off-axis magnetron sputtering of YBCO films: the influence of atomic oxygen

It is pointed out that in situ off-axis magnetron sputtering of superconducting Y-Ba-Cu-O (YBCO) is the simplest method for producing high-quality thin films. However, the method is not completely understood and the properties of films can vary widely among similarly configured systems and even from run-to-run in a given system. The authors have performed a series of experiments aimed at understanding and controlling the off-axis sputtering process. Film properties such as lattice parameter, T_c, and surface morphology were measured as a function of substrate temperature, oxygen pressure, and substrate position. A method to accurately measure the substrate surface temperature has been developed, thus eliminating this as an unknown parameter. Under certain conditions, good films can be deposited at oxygen partial pressures well below the Hammond-Bormann oxygen-pressure-vs.-temperature stability curve for superconducting YBCO, showing the importance of the generation of activated oxygen in the sputtering chamber. Optical emission has confirmed the presence of atomic oxygen. Additional studies of the oxidation of YBCO films in molecular and atomic oxygen generated by an electron cyclotron resonance plasma show that the presence of atomic oxygen creates an equivalent pressure more than two orders of magnitude greater than molecular oxygen at that pressure