Thermal Stability and Electrical Properties of RhO 2 Thin Films
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Thermal Stability and Electrical Properties of RhO2 Thin Films Yoshio Abe, Kiyohiko Kato, Midori Kawamura and Katsutaka Sasaki Department of Materials Science, Kitami Institute of Technology 165 Koen-cho, Kitami 090-8507, Japan
ABSTRACT RhO2 belongs to the family of conducting oxides with a rutile structure, which have attracted attention as capacitor electrode materials for memory devices. In this study, effects of thermal treatment under various oxygen pressures on structural and electrical properties of RhO2 thin films prepared by reactive sputtering were investigated. The RhO2 films were found to be stable up to 700°C under oxygen pressure of 1 atm and a metallic conduction property with a resistivity of about 80 µΩcm was obtained. However, the RhO2 films decomposed to semiconducting Rh2O3 at 750°C. The decomposition temperature decreased to 500°C under oxygen pressures of 0.5-5 mTorr.
INTRODUCTION The family of conducting metal oxides with a rutile structure, such as RuO2 and IrO2, has attracted attention as electrode materials for dynamic random access memories (DRAMs) and ferroelectric RAMs (FeRAMs) [1, 2]. In FeRAMs, the ferroelectric capacitor is a key component, and these conducting oxide films are considered to be promising as capacitor electrodes because of their low resistivity, high chemical stability and low degradation of their ferroelectric films. RhO2 belongs to the family and was reported to exhibit metallic behavior with resistivity below 1
×10
-4
Ωcm [3, 4]; however, thin films of Rh oxides, except for PtRhOx [5], have scarcely been
investigated. We have reported results on the formation of Rh oxide thin films by reactive sputtering [6]. In this study, the thermal stability and electrical properties of RhO2 films were studied in order to clarify the applicability of such films to memory devices.
C5.7.1
EXPERIMENTAL RhO2 thin films with a thickness of about 200 nm were deposited on thermally grown SiO2 (100 nm)-coated Si(001) substrates using an rf magnetron sputtering system. The sputtering target was a 2-in.-diameter Rh disk (99.9% purity). To obtain fully oxidized RhO2 thin films, reactive sputtering was carried out in 100% O2 gas. The rf power, substrate temperature and sputtering gas pressure were 15W, room temperature and 5 mTorr, respectively. Post deposition annealing of the RhO2 thin films under oxygen pressures of 0.5-50 mTorr and in a vacuum (below 10-6 Torr) was performed using the sputtering chamber at temperatures between 100°C and 500°C for 1 h, and that under oxygen pressure of 1 atm was performed using an electronic furnace at temperatures between 200°C and 800°C for 1 h. The film thickness was measured by multibeam interferometry. The crystal structure was examined by X-ray diffraction (XRD) with Cu Kα radiation. Resistivity was measured by a four-point probe method at room temperature.
RESULTS AND DISCUSSION XRD patterns of the films annealed in oxygen at a pressure of 1 atm are shown in Fig. 1 (a). Diffraction peaks of (101) and (002) RhO2 with a rutile structure are
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