Y-Ba-Cu-O thin films composition formation during magnetron sputtering

The presence of various precipitations of secondary phases in Y-Ba-Cu-O films is extremely undesirable for many applications. Occurrence of yttrium-rich and copper-rich secondary phases in our films prepared by inverted magnetron sputtering is the result of the film composition deviations from "123" stoichiometry during in-situ growth. We have simulated and investigated in detail the processes causing the film composition deviations from stoichiometry. First, long-term changes (up to 50%) in the target composition due to the diffusion mass transfer inside the target are possible. Second, the distinctions in the modes of scattering by the background gas and in diffusive travelling of sputtered atoms to the substrate can lead to deviations (up to 15%) of film composition from the target composition. Third, the deviations (up to 30%) may be caused by significant nonstoichiometric currents of desorbed YBCO components from coated elements of the sputtering system to the substrate and from the growing film on substrate. These currents are a result of selective redeposition of the growing film by bombardment of positive plasma ions accelerated (up to 1 eV) through the floating potential voltage. The films with optimized properties show a zero resistance temperature of 92 K and a critical current density of 3/spl middot/10/sup 6/ A/cm/sup 2/ (at 77 K).