Structure and surface morphology of highly conductive RuO 2 films grown on MgO by oxygen-plasma-assisted molecular beam
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Structure and surface morphology of highly conductive RuO2 films grown on MgO by oxygen-plasma-assisted molecular beam epitaxy Y. Gaoa) Pacific Northwest National Laboratory, P.O. Box 999, MS K2-12, Richland, Washington 99352
G. Bai Argonne National Laboratory, 9700 S. Cass Ave., Argonne, Illinois 60439
Y. Liang, G. C. Dunham, and S. A. Chambers Pacific Northwest National Laboratory, P.O. Box 999, MS K2-12, Richland, Washington 99352 (Received 1 November 1996; accepted 11 February 1997)
Metallic RuO2 (110) thin films were grown by oxygen-plasma-assisted molecular beam epitaxy (MBE) on MgO(100) and (110) at 425 ±C. RuO2 films on MgO(100) are epitaxial with two variants, while RuO2 films on MgO(110) are highly oriented with the (110) face parallel to the substrate surface. The two variants in the RuO2 (110) epitaxial films resulted in a twofold mosaic microstructure. The RuO2 (110) epitaxial films are very smooth and exhibit a low resistivity of ,36 mV-cm. In contrast, the RuO2 (110) textured films are very rough, and consist of small grains with a poor in-plane alignment. A slight higher resistivity (49 mV-cm) was found for the RuO2 (110) textured films grown on MgO(110).
I. INTRODUCTION
Ruthenium dioxide (RuO2 ) exhibits a variety of interesting properties such as low bulk metallic resistivity (,35 mV-cm1 ) and very high thermal and chemical stability.2 These properties have made RuO2 widely used as corrosion-resistant electrodes2 and as positive temperature coefficient (PTC) resistors.3 Recently, RuO2 thin films have been investigated as a diffusion barrier between Al and Si in very large scale integrated circuits4,5 and as a stable electrode for ferroelectric thin films.6–8 Interdiffusion between Al and Si is significantly reduced by a thin RuO2 layer between Al and Si during annealing at temperatures as high as 600 ±C.9 Ferroelectric thin films grown on RuO2 electrodes have excellent resistance to polarization fatigue, compared to those on Pt electrodes.6–8 However, RuO2 electrodes are polycrystalline, and use of epitaxial RuO2 thin films as the bottom electrodes could further enhance their resistance to polarization fatigue, as well as reduce capacitor leakage by eliminating grain boundaries. Many groups have used a variety of thin film techniques including reactive sputtering4–8,10 metal-organic vapor deposition,9,11 and pulse laser deposition (PLD)12 to synthesize RuO2 thin films. Most of the resulting RuO2 films are polycrystalline, and show a relatively high resistivity of ,100 mV-cm. Thus far, the only occurrence of epitaxial growth of RuO2 films with excela)
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http://journals.cambridge.org
J. Mater. Res., Vol. 12, No. 7, Jul 1997
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lent electrical properties (r 35 mV-cm) was obtained on LaAlO3 by PLD. However, high deposition temperatures (,700±) were required.12 Recently, oxygenplasma-assisted molecular beam epitaxy (MBE) has been shown to be exceptionally well suited for epitaxia
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