PLASMA CHARACTERIZATION OF A HIGH-PRESSURE D-SPUTTERING SYSTEM USED FOR THE IN-SITU PREPARATION OF HIGH-TC SUPERCONDUCTING THIN-FILMS

A characterization of the high-pressure dc-Sputtering system, used for the ''in situ'' preparation of high-quality high-T(C) superconducting thin films, was performed by plasma electrical measurements using a s ingle Langmuir probe. A correlation between plasma characteristics and thin film properties (transition temperature, T(C), transition width, DELTAT(C) and residual resistivity ratio RRR) is presented. The param eters of the plasma were obtained from measurements at pressures rangi ng from 2.0 to 4.0 mbar with unheated and heated substrates (around 75 0-degrees-C) during the ''in situ'' preparation of YBa2Cu3O7-x thin fi lms. We found that anode heating contributes to the formation of posit ive ions and reduces the formation of negative ions, which minimizes t he re-sputtering effects during film growth. Optimal superconducting p roperties of the films were obtained at an oxygen pressure of 3.25 mba r; at this pressure the plasma has the largest density of positive ion s and the lowest density of both electron and negative ions.