Deposition of Ru Thin Films by MOCVD Using Direct Liquid Injection System
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Deposition of Ru Thin Films by MOCVD Using Direct Liquid Injection System Sang Y. Kang, Cheol S. Hwang and Hyeong J. Kim School of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea
ABSTRACT Ru thin films were deposited on SiO2/Si and (Ba,Sr)TiO3 [BST]/Pt/TiO2/SiO2/Si substrates using Ru(C2H5C5H4)2 [Ru(EtCp)2] by metal-organic chemical vapor deposition (MOCVD). To determine the effects of the solvent, C4H8O [tetrahydrofuran : THF], it was injected into the reaction chamber by the Direct Liquid Injection (DLI) system while Ru(EtCp)2 was input through the bubbler system. Also, Ru thin films were deposited using a liquid source, Ru(EtCp)2 dissolved in THF, delivered by the DLI system. The surface of the Ru thin films deposited on the BST substrate using only Ru(EtCp)2 through the bubbler system was very rough and milky, but the addition of THF made the surface of the films smooth and clean. In addition, Ru films deposited at 325°C using Ru(EtCp)2 dissolved in THF through the DLI system have a dense and smooth microstructure with resistivity as low as 15µΩcm.
INTRODUCTION The requirements for the chemical vapor deposition (CVD) of metal electrodes for the (Ba,Sr)TiO3 [BST] capacitor of dynamic random access memory (DRAM) devices have become more critical with the increase in storage node height. With the three dimensional geometry of the capacitor, the plate electrode needs to be deposited by CVD, as otherwise the device may suffer from a reliability problem due to electrical leakage or chemical reactions. The CVD-Ru thin film is one of the most appropriate candidate plate electrodes, since it has the good electrical performance as an electrode, such as ensuring low leakage current and large dielectric constant of the BST [1] as well as Ta2O5 [2] dielectric films, and good etching property compared to Pt [3]. Deposition of CVD-Ru thin films using Ru(EtCp)2 with the bubbler system has been already reported, but few researches on CVD-Ru thin films deposited with DLI system have been reported to date, since the vaporizer may be clogged due to the high viscosity of the Ru(EtCp)2 [5]. Therefore, a liquid source metal-organic chemical vapor deposition (LSMOCVD) technique, in which Ru(EtCp)2 dissolved in THF is used, is required to deposit Ru thin films in order to solve problems such as source decomposition and instability of the source delivery system. In this paper, to investigate the effect of the solvent, Ru films were first deposited using O3.18.1
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Ru(EtCp)2 through the bubbler system and THF through the DLI system. Then Ru thin films were prepared by LSMOCVD using Ru(EtCp)2 dissolved in THF through the DLI system.
EXPERIMENTAL DETAILS Figure 1 shows a schematic diagram of the MOCVD system which consist of a vertical warm wall reactor, a resistive substrate heater 6” in diameter, the bubbler system and the DLI system. The flow rate of the liquid source in the DLI system was controlled using a micropump. Both the source cylinder and micropump were kept at room temperature. The liquid
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