Preparation of Strontium Bismuth Tantalate Thin Film by Liquid-Delivery Metalorganic Chemical Vapor Deposition
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Preparation of Strontium Bismuth Tantalate Thin Film by Liquid-Delivery Metalorganic Chemical Vapor Deposition M. Silinskas1, M. Lisker1, B. Kalkofen1, S. Matichyn1, B. Garke2, and E. Burte1 1 Institute of Micro and Sensor Systems, Otto von Guericke University Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany 2 Institute of Experimental Physics, Otto von Guericke University Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany ABSTRACT Thin films of BiOX, SrXTaYO, and SrXBiYTaZO (SBT) were deposited by liquid-delivery metalorganic chemical vapor deposition (MOCVD). The substrate temperature and the deposition pressure were varied from 300 to 600°C and from 0.35 to 7 mbar, respectively. Triallylbismuth (Bi-1), triphenylbismuth (Bi-2) or alkyl bismuth (Bi-3) and strontium bispentaethoxy-methoxyethoxy tantalate (Sr-Ta) were used as Bi precursors and as Sr-Ta precursor, respectively. X-ray photoelectron spectroscopy (XPS), ellipsometry, and scanning electron microscopy (SEM) were carried out to characterize the film properties. The growth rates of the MOCVD of BiOX and SrXTaYO were compared to the growth rate of SBT to obtain information about mutual interaction between the precursors. The growth rate of bismuth oxide thin films deposited from Bi-1 and Bi-2 was low (~10 nm/h at 0.35 mbar). The growth rate of strontium tantalate films was higher (up to 50 nm/h) and depended strongly on the temperature. Eight times higher (~400 nm/h) growth rates of BiOX and SBT films were observed for the Bi-3 precursor. The deposition rate of the SBT films was quite similar to the rate of the bismuth oxide. However, the deposition rate of SBT was always lower than the deposition rate of the single Bi precursors. The growth rate significantly depended on the deposition pressure. A decrease of the deposition pressure in the reactor chamber reduced the deposition rate of BiOX, SrXTaYO, and SBT, but on the other hand, it improved the uniformity of the film thickness over the entire 150 mm wafer surface. The XPS measurements showed a deficit of bismuth in the SBT films even though the concentration of the Bi-1 or Bi-2 precursor was several times higher compared to the Sr-Ta precursor. This problem disappeared when Bi-3 source was used. INTRODUCTION Ferroelectric thin films have attracted great interest for non-volatile ferroelectric random access memory (FeRAM) applications [1-3]. These materials have some advantages over silicon based memories such as faster write speed and lower operating voltage [4]. Pb(ZrXTi1-X)O3 (PZT) has been the most intensively studied material for this application. However, PZT thin films especially in combination with Pt electrodes exhibit a serious degradation of the remanent polarization with increasing number of hysteresis cycles, which is known as polarization fatigue [3,5]. Recently, alternative SrBi2Ta2O9 materials have been widely used because of their excellent fatigue endurance [3,6] and the lead free technology. In the recent years, the MOCVD of SBT thin films was constrained by a lack
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