Nucleation and growth of thin (Ba,Sr)TiO3 films in a MOCVD reactor
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Nucleation and growth of thin (Ba,Sr)TiO3 films in a MOCVD reactor S. Regnery 1,2, Y. Ding1, P. Ehrhart1, F. Fitsilis1, C.L. Jia1, K. Szot1, R. Waser1, F. Schienle2, M. Schumacher2, T.McEntee2 1) IFF Forschungszentrum Jülich, D-52425 Jülich, Germany 2) Aixtron AG Aachen, Kackertstr. 15-17, D-52072 Aachen, Germany
ABSTRACT (BaxSr1-x)TiO3 thin films were deposited on Pt electrodes in a planetary multi-wafer MOCVD reactor combined with a liquid delivery system. The nucleation behavior and the size of the stable nuclei were investigated by different SPM techniques and by XPS. Characteristic differences were observed between deposition temperatures of 565°C and 655°C, i.e. a homogeneous nucleation of small BST grains on the larger Pt grains (100 – 200 nm in-plane size) at low temperatures and a dominating nucleation at the grain boundaries at high temperatures. Further film growth was investigated for nominal film thickness between 5 and 100 nm and details of the grain structure are revealed by HRTEM, e.g., randomly oriented grains (typical in-plane size 10-20nm) with a high density of twins at 565°C and (100)-oriented defect free grains of slightly increased size at 655°C. As the electrical properties like permittivity and also leakage current depend on film thickness the final discussions of the electrical properties are based on thickness series and evaluated within the phenomenological dead layer model. INTRODUCTION High-K perovskite thin films, such as (BaxSr1-x)TiO3, (BST), have been proposed for a very broad application area, including capacitor dielectrics for future dynamic random access memories (DRAMs), embedded capacitors, tunable devices, as well as gate oxides for field effect transistors [1]. For capacitor applications of BST films, i.e., metal-insulator-metal (MIM) structures, Pt is considered as a standard metal electrode [2] and with MOCVD (metal organic chemical vapor deposition) different textures of the films have been observed for different deposition temperatures, e.g. typically BST-(100) on Pt-(111) for temperatures above 600°C and more randomly orientated grains at lower temperatures [3]. However, details of the nucleation and growth behavior are still unknown. In this study a broad spectrum of analytic methods including different types of scanning probe microscopy (SPM), high resolution transmission electron microscopy (HRTEM), and x-ray photoelectron spectroscopy (XPS) were used to get a more quantitative understanding. As electrical properties such as permittivity and also leakage current depend on film thickness [4] the final discussions of the electrical properties are based on thickness series and evaluated within the phenomenological dead layer model. EXPERIMENTAL DETAILS (Ba0.7Sr0.3)TiO3 films were deposited in an AIXTRON 2600G3 Planetary Reactor, which can handle five 6-inch wafers simultaneously. This reactor is characterized by a central gas inlet which provides a pure horizontal gas flow and makes this reactor a radial flow system as described previously [3]. The main proce
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