Low Temperature Tungsten, Tungsten Carbide and Tantalum Carbide Film Growth
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LOW TEMPERATURE TUNGSTEN, TUNGSTEN CARBIDE AND TANTALUM CARBIDE FILM GROWTH Y.-M. Sun, S.Y. Lee, E. R. Engbrecht, K. Pfeifer1, S. Smith1, J. M. White and J. G. Ekerdt Texas Materials Institute, The University of Texas at Austin, Austin, TX 78712 1 International Sematech Austin, TX 78741 ABSTRACT Low temperature chemical vapor deposition of tungsten, tungsten carbide and tantalum carbide films on SiO2/Si(100) surfaces was studied by X-ray photoelectron spectroscopy (XPS) and electron microscopy. Tungsten carbide films were deposited using the W(CO)6 precursor with and without ethylene over temperatures ranging from 250 to 500 °C. The films grown without ethylene contained approximately 13 % carbon and 6 % oxygen. Cross section scanning electron microscopy imaging of the films grown at various temperatures without ethylene shows a polycrystalline microstructure, and the grain size increases dramatically as the growth temperature increases. Introducing ethylene increased carbon incorporation and changed the microstructure to amorphous-like. The tungsten to carbon ratio was approximately 2 at growth below 500 °C, and reached ~ 1.2 above 500 °C. The tantalum carbide films were deposited in a plasma enhanced chemical vapor deposition (PECVD) process using methane. The PECVD tantalum carbide films were conductive with a resistivity of ~1000 µΩ cm, which is about one order of magnitude lower than thermally grown films from pentakisdimethylamino tantalum. INTRODUCTION Copper-based multilevel metallization schemes are expected to dominate system architectures for the next few microelectronic generations. While copper offers the advantages of better electromigration performance and lower thin film resistivity compared to Al, copper also places significant challenges on the materials and process technologies. A major problem is the strong tendency of copper to diffuse into adjacent materials, therefore a high performance barrier is necessary to prevent copper movement into the interlayer dielectric. The National Technology Roadmap for Semiconductors predicts the maximum allowable barrier thickness will be less than 1 nm for the 50 nm node and identifying new copper barrier materials is critical to achieving this goal. Various refractory material systems, primarily transition metals and their binary and ternary nitrides, have been extensively investigated for barrier applications in copper metallization [1-6]. Transition metal carbides and nitrides have many similarities, such as high melting point, high chemical and thermal stability and good electrical conductivity [7]. Imahori et al. have reported 5 nm PVD TaC films are effective Cu diffusion barriers [8]. In this paper we report our study of chemical vapor deposition (CVD) tungsten carbide and tantalum carbide films for use as copper diffusion barriers. Nearly stoichiometric tungsten carbide (W2C) and tantalum carbo-nitride films were deposited over a wide range of growth temperatures and flow ratios. In contrast to polycrystalline CVD tungsten films grown from W(CO)6, all c
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