Chemical Vapor Deposition of Ruthenium and Osmium Films from Mono- and Bis-(Cyclopentadienyl) Complexes as Precursors
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ABSTRACT We have investigated cyclopentadienyl (Cp) complexes of Ru and Os as precursors for low temperature CVD of pure ruthenium and osmium films. Films were grown on a variety of substrates in a warm-walled CVD reactor, equipped with a resistively heated wafer chuck, massflow controllers for carrier gas regulation, and a mechanically-backed oil-vapor diffusion pump. Typical depositions were done under ca. 1 Torr total pressure. Use of air or oxygen as a carrier gas and Cp2M (M = Ru or Os) as precursors gave high purity, conformal films of ruthenium and osmium at temperatures as low as 275°C and 350"C, respectively. Under these conditions, the only observable by-products were C02 and H20, indicating that surface-catalyzed, complete oxidation of the ligands was involved in the decomposition process. Growth rates, film purities, resistivities and conformality were measured. INTRODUCTION Ruthenium, which is nearly as chemically inert as platinum, but is much cheaper, is potentially useful for a variety of microelectronics applications. In addition to chemical inertness, it is a hard metal, has a fairly high melting point (2450°C) and has a bulk resistivity of 7.6 p..Qcm at room temperature. The oxide of ruthenium, RuO2, is also highly conductive, with a bulk resistivity of 35.2 ptfcm. These properties make ruthenium and/or ruthenium oxide candidates for use as barrier layers [1-5] or in contact applications [6,7]. For these applications, a conformal deposition technique may be desirable. Although osmium is not as chemically inert as ruthenium, it is similarly hard, and among pure elements is surpassed only by carbon, tungsten and rhenium in melting point. Because of this, and its high electron work function, osmium has been used as a coating material for thermionic electrodes, where current densities are very demanding [8,9]. In addition, osmium has been implicated as the ohmic contact material of choice for certain field effect transistors [10]. Osmium is also highly conductive, with p = 8.8 pgcncm at room temperature. Chemical vapor deposition (CVD) of thin films of ruthenium using bis(cyclopentadienyl)ruthenium(II) (commonly called ruthenocene) as an organometallic precursor has been reported, using hydrogen [11] or oxygen [6] as a carrier gas. In neither case were ruthenium films grown at temperatures lower than 500"C. When oxygen is used in the carrier gas, RuO2 films have been grown using ruthenocene and substrate temperatures above 550°C [5,6]. Other precursors have been used for CVD of ruthenium at similarly high substrate temperatures [6,12,13]. Reports of CVD of osmium are scarce [8,14-16], and it is notable that in no case are clean osmium films deposited at temperatures lower than 500"C. We report here conditions under which ruthenium and osmium films can be grown by CVD at substrate temperatures as low as 275"C and 350'C respectively. For ruthenium, we have used ruthenocene and cyclopentadienyl dicarbonylruthenium(II) dimer (abbreviated Rp-dimer) as precursors. This is the first report of the use of the
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