Studies of Plasma Etching of High Temperature Superconducting Thin Films
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STUDIES OF PLASMA ETCHING OF HIGH TEMPERATURE SUPERCONDUCTING THIN FILMS M. R. Poor* and C. B. Fleddermann* * Center for High Technology Materials, University of New Mexico, Albuquerque, New Mexico 87131 ABSTRACT The fabrication of devices in high-temperature superconducting ceramics will require the development of suitable techniques for patterning thin films of these materials. We report the plasma etching of Y-Ba-Cu-oxide thin films using techniques adapted from the semiconductor industry. The etching reactor consists of a dc hollow cathode discharge using a chlorine/helium mixture as the working gas. The Y-Ba-Cu-oxide films are deposited on alumina substrates using ion-beam sputtering. We have investigated the etching of these films over a broad range of gas pressures, substrate temperatures, and input powers, using both asdeposited and oxygen annealed films. Substrates were held at ground potential to minimize ion bombardment during etching in order to separate the chemical aspects of the etching process from ion-bombardment effects. The etch rate of these films was found to be highly dependent on the substrate temperature, the system pressure, and on whether the films are annealed. Annealed films etch nearly an order of magnitude more slowly than unannealed films. The film stoichiometry, measured using energy dispersive spectroscopy (EDS), varies greatly with temperature. The copper in the films is removed at the lowest temperature, followed by barium and then yttrium. INTRODUCTION The potential applications for high-temperature superconducting thin films may include devices such as Josephson junctions, radiation detectors, magnetometers, wire interconnects for semiconductor circuits, and perhaps ultimately all-superconducting computer circuitry. In order to fabricate these devices, techniques for patterning thin films into devices must be developed. The extensive research taking place worldwide investigating deposition techniques for high Te superconducting thin films has yet to be matched by comparable research efforts investigating device patterning techniques. Many different candidate techniques for superconductor patterning have been studied: wet chemical etching, 1] laser ablation, 12-4] laser "de-annealing" (in which a laser is used to selectively remove oxygen from a film, altering its electrical characteristics), 15,6] direct laser writing, [7-9] laser assisted chemical etching, [10] and ion-beam high-temperature patterning. 111-13] Another candidate technology for patterning superconductors which has many potential advantages over those mentioned above but which By analogy with semiconductor has not yet been extensively studied is plasma etching. fabrication, plasma etching of superconductors can be expected to lead to very sharp pattern definition in superconducting thin films and high packing densities of devices as well as the successful integration of high temperature ceramics with existing high density semiconductor circuits. Some limited study of plasma-based etching focussing mainly on RIE te
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