Chemical Vapor Deposition Route to the Fabrication of thin Films of High Temperature Oxide Superconductors
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CHEMICAL VAPOR DEPOSITION ROUTE TO THE FABRICATION OF THIN FILMS OF HIGH TEMPERATURE OXIDE SUPERCONDUCTORS Alain E. Kaloyeros,* Kenneth C. Brooks," Aiguo Feng,* and Jonathan Garhart* Physics Department, State University of New York at Albany, Albany, NY 12222 **Chemistry Department, University of Illinois at Urbana-Champaign, Urbana, IL 61801 ABSTRACT High quality Y-Ba-Cu-O thin films were produced by metal-organic chemical vapor deposition (MOCVD) using metal chelates of A-diketonate ligands. The films were grown in a cold-wall CVD reactor at a reactor pressure of 10 torr and substrate temperature in the range 450-550 0 C. Characterization studies were performed using Rutherford Backscattering (RBS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDXS). These studies showed that the films were uniform, continuous, adherent and highly pure--carbon and fluorine contents were below the detection limits of the techniques used. Four point resistivity measurements showed that the films had a sharp superconducting transition at 90K and exhibited current densities of -3x10 5 2 A/cm (B=0, T=65K). The Y-Ba-Cu-O films thus grown were subsequently compared to radio-frequency (rf) sputtered Y-Ba-Cu-O films. It was found that the MOCVD-produced films were superior in terms of uniformity, adherence, and electrical properties. INTRODUCTION In very recent years, the level of sophistication achieved by MOCVD has allowed to produce electronic materials with excellent degrees of perfection 1 2 and purity. , At present, almost all silicon-based and III-V compound 3 4 semiconductors are grown by MOCVD processes. , The advantages of MOCVD include its relative simplicity, controllability, good adherence, high uniformity over a large area, and reduced susceptibility to interfacial mixing and cross-contamination effects. These unique features make MOCVD a very attractive technique for the fabrication of high temperature superconductor thin films. This paper is the second in a series of reports by the present authors on the successful preparation of superconductor5 thin 2 5 showing a sharp transition at 90K and a current density of 3xl0 A/cm films, (B=0), by MOCVD from 0-diketonate precursors, followed by in-situ postdeposition annealing. In particular, we compare microstructural and microchemical analyses results from MOCVD-produced Y-Ba-Cu-O films to similar findings from rf sputtered films. Our results show that the MOCVD films are superior in terms of uniformity, adherence and electrical properties. EXPERIMENTAL
TECHNIQUE
Three metal chelate precursors of the P-diketonate ligand 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, abbreviated as fod, were chosen as the source compounds for the Y, Ba and Cu. A cold wall type CVD apparatus was used for MOCVD of the 123 thin films. A detailed description of the experimental apparatus has already been reported by the 6 present authors. The source compounds were heated, in separate bubblers, to 0 0 0 45 C, 125 C, and 175
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