High-T C Yba 2 Cu 3 O 7 Thin Films Produced by Multilayer Sputter Deposition
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HIGH-Tc YBa2 Cu 3 O7 THIN FILMS PRODUCED BY MULTILAYER SPUTTER DEPOSITION MARK S. DIIORIO*, KAI-YUEH YANG*, ANDREW N. ERICKSON*, PATRICIA K. TSAI**, and M. BRIAN MAPLE** * Biomagnetic Technologies, Inc., 9727 Pacific Heights Blvd., San Diego, CA 92121 ** Dept. of Physics, University of California San Diego, La Jolla , CA 92093 INTRODUCTION Attractive applications for thin films with high superconducting transition temperatures include input coupling coils for SQUIDs as well as Josephson junctions and SQUIDs themselves. Such applications place many demands on the films, including reproducible composition, good electrical transport properties, uniformity over large substrate areas, short deposition turnaround times, high-quality film surfaces and interfaces, and film stability. Consequently, we are developing a multilayer deposition technology to fabricate thin films of YBa 2 Cu3 O7 . The films are produced by sequential sputtering from three metallic targets onto substrates attached to a rotating table controlled by a programmable stepping motor. Presently, all of our films require post-annealing outside the deposition system to form the high-Tc superconductor structure, although our eventual intention is to produce films by an entirely in-situ method. The multilayer technique1-5 is well-suited for obtaining reproducible film composition as the substrates remain over each target for a long enough time to average out the small fluctuations in the sputter deposition rate. The composition, post-annealing profile, and details of the layering are the primary factors determining the microstructure and transport properties of the films. Note that sputter deposition is intrinsically capable of producing layers of uniform thickness over substantial areas (> two inches in diameter for our two-inch diameter targets at a target-to-substrate distance of 6.5 inches). The deposition system is also load-locked to decrease pumpdown time and to prevent deterioration of the targets, especially the Ba, thereby reducing the presputtering needed to clean the targets. FILM FABRICATION The films are deposited from three two-inch US magnetron sputter guns in a cryopumped vacuum system capable of reaching 1 x 10 -8 Torr, although the typical base pressure before deposition is 7 x 10 -8 Torr. The Cu target is dc sputtered, the Ba target is rf sputtered, and the Y target is either de or rf sputtered, depending on the sputtering gas mixture. The three sputter guns are outfitted with custom shielding cans to prevent coating of the vacuum chamber. Each sputter gun has its own rate monitor that can be connected to the gun power in a feedback loop, although the latter is generally unnecessary because of the inherent stability of sputter deposition. Since the argon is introduced directly into the gun shield can the pressure measured in the vacuum chamber (typically 5 x 10 -4 Torr) is about an order of magnitude lower than the pressure in each can. For Mat. Res. Soc. Symp. Proc. Vol. 169. c1990 Materials Research Society
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many depositions, oxyg
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