In Situ Real-Time Studies of Oxygen Incorporation in Complex Oxide Thin Films Using Spectroscopic Ellipsometry and Ion S
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A.H. MUELLER, Y. GAO, E.A. IRENE 0. AUCIELLO*, A.R. KRAUSS* J.A. SCHULTZ** Department of Chemistry, University of North Carolina at Chapel Hill * Material Science and Chemistry Division, Argonne National Laboratory **Ionwerks Inc., Houston, Texas
ABSTRACT The surface termination of c-axis oriented YBa 2Cu 3OT7 _ (YBCO) and the oxygen incorporation mechanism has been investigated using a unique combination of spectroscopic ellipsometry (SE) and time of flight ion scattering and recoil spectrometry (ToF-ISARS). The high surface sensitivity of the ToF-ISARS technique combined with the bulk oxygen sensitivity of SE are shown to yield complimentary information. The SE provided the film orientation and quality, while ToF-ISARS supplied surface compositional and structural information and enabled isotopic 180 tracer studies. It was determined that the 0 content of the film had little effect on the surface termination of the film, indicating a lack of labile Cu(l) sites at the c-axis oriented YBCO surface. Also, strong evidence for a Ba or BaO terminated structure is shown. The data related to the 180 tracer studies indicate that 0 from the reaction ambient incorporates only into the labile Cu(l) sites during both deposition and annealing, while stable 0 sites were populated with 0 from the sputtered target, indicating either the need for sputtered atomic 0 or sputtered YCuO complexes to occupy the stable Cu(2) sites. INTRODUCTION Complex oxide materials in thin film form exhibit appropriate properties for use in technologies such as high K DRAM capacitors, Josephson junctions, SQUIDS, and ferroelectric devices. The properties of these films have shown a critical dependence on their oxygen content, such as loss of the superconducting properties by YBa 2Cu 30 7 8 (YBCO) depending upon the exact oxygen content, and the lowering of the dielectric constant of the high K material BaSrTiO 3 (BST) under oxygen depleted conditions. The objective of this study is to elucidate the mechanism of oxygen incorporation, as well as the structural implications using real time, in-situ spectroscopic ellipsometry (SE) and time-of-flight ion scattering and recoil spectrometry (ToF-ISARS). It has been shown that oxygen incorporation into complex oxide thin films can be followed in real time using SE1' 2, and that chemical and structural information such as oxygen adsorbtion and bonding sites are obtained using the ToF-ISARS techniques 3 . These complementary techniques are applied in real-time, and as such yield a wealth of information not only about the incorporation of oxygen, but also about the mechanism and structural effects relative to film function.
141 Mat. Res. Soc. Symp. Proc. Vol. 619 © 2000 Materials Research Society
The oxygen in- and out-diffusion within the YBCO film, and the unit cell substructure of these films have been studied thoroughly by many groups (see for examples ref's 1-7). While there are some minor differences in the anisotropic diffusion constants reported, the mechanisms of diffusion are generally agreed upon
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