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e thermal stability of RuO2/Si(100) films in air was studied using ex situ synchrotron x-ray scattering. The (110) textured RuO2 film showed good thermal stability due to the low surface and strain energies. However, the RuO2 films of high strain and surface energies were transformed to three-dimensional islands during annealing up to 800 °C. We also studied, during the post annealing process, the interface roughness of BaxSr1−xTiO3 (BST)/RuO2/Si(100) and BST/Pt/Ti/SiO2/Si(100) structures comparatively, using in situ synchrotron x-ray scattering. The interfaces of the BST/RuO2/Si were thermally stable up to 500 °C, and the deterioration of the interfaces above 500 °C was attributed to the crystallization of amorphous BST film. Meanwhile, the interfaces of the BST/Pt/Ti/SiO2/Si were significantly degraded even at the low temperature of 350 °C, mainly due to the formation of the Pt–Ti alloy and the Ti oxidation.

I. INTRODUCTION

BaxSr1−xTiO3 (BST) has been receiving great interest as a new dielectric material replacing SiO2 and/or Si3N4 dielectrics currently used in dynamic random-access memory (DRAM) because it exhibits a good insulating behavior with large values of the relative dielectric permitivity and small values of the dielectric loss.1 Most investigations were concentrated on the deposition techniques, the properties, and the microstructure of BST films.2 The electrical properties are related not only to the microstructure of BST films, but also to the interface roughness between electrode and ferroelectric film; the leakage current of BST films is greatly reduced as the interface roughness decreases.3 High annealing temperatures of 600–700 °C are usually required to obtain BST films of high quality. During annealing at these high temperatures, there occurred thermal degradation of bottom electrode and significant interface roughening.4,5 Up to the present the Pt/Ti bilayer has been the most commonly used electrode for ferroelectric capacitors due to the low resistivity and chemical stability.6 During the annealing in the oxygen ambient above 500 °C, however,

a)

Present address: Semiconductor Advanced Research Division, Hyundai Electronics Industries Co., Ltd., Ami-Ri, Bubal-Eup, I-chon, 467-701, Korea. b) Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 15, No. 9, Sep 2000

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the degree of oxidation and interdiffusion remarkably increased, resulting in the degradation of the electrical properties of BST films.7,8 Also the sputtered Pt electrode is known to have the disadvantage of hillock formation, which can electrically short the capacitor.9 There have been many studies to develop more stable electrodes at high temperature in oxygen ambient. Among them, RuO2, a conductive metallic oxide, is a highly promising electrode material due to its good properties, such as low resistivity, excellent diffusion barrier properties, good thermal stability, and high chemical corrosion resistance.10–13 However, there are few