Oxidation Resistance of TaSiN Diffusion Barriers for Stacked Capacitors
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OXIDATION RESISTANCE OF TaSiN DIFFUSION BARRIERS FOR STACKED CAPACITORS * F. LETENDU (1), * M.C. HUGON (1),* B. AGIUS (1), ** I VICKRIDGE, *** F. AYGUAVIVES, *** A.I. KINGON * LCFIO, bat 503, Université Paris Sud, 91405 Orsay cedex, France. ** GPS, Tour 23, Université Paris 6 et 7, 75251 Paris, France. *** Dept. of Materials Science and Engineering, North Carolina State University, Raleigh, NC, USA. (1) Present address: LPGP , bat 210, Université Paris sud, 91405 Orsay, France.
ABSTRACT Due to its resistance to oxidation, TaSiN is a promising candidate as an electrically conductive barrier layer for integration of high permittivity oxides in advanced memory devices. In this study we report on the properties and the resistance to oxidation of TaSiN thin films deposited by reactive magnetron sputtering and processed by rapid thermal annealing (RTA) in 18O2 at 650°C. In order to determine the composition, RBS (Rutherford Backscattering Spectroscopy) and NRA (Nuclear Reaction Analysis) techniques have been used. 18O depth profile concentrations were measured after RTA using the narrow (fwhm=100eV) resonance at 151 keV in the nuclear reaction 18O(p,α)15N. INTRODUCTION The use of ferroelectric (FeRAM) and high dielectric constant (DRAM) perovskite oxides, in advanced memory devices, requires the presence of a diffusion barrier between the capacitor's bottom electrode layer and the poly-Si plug. This barrier must prevent chemical electrode/plug interactions and plug oxidation, and must remain electrically conductive after annealing in oxygen. Al-Ta bilayers as well as a number of refractory metal nitrides have been proposed as oxygen diffusion barriers, including TiN, TaN and compositions of TaSiN and TiAlN. TaxSiyNz alloys (TaSiN in the following) are amorphous, ternary mixtures of the three elements which are electrically conductive over a wide range of compositions. A systematic study of this material as an oxygen diffusion barrier has not been extensively reported and only a few papers have been published. 1, 2, 3 In this paper, we report on the properties and the oxidation behavior of TaSiN thin films deposited by reactive magnetron sputtering of a TaSi2 target, using a new analytical tool in this field:18O tracer profiling. The composition of TaSiN films has been optimized in order to prevent oxidation of the underlying Si as well as to maintain a low electrical resistivity under high temperature oxidation, up to 650°C. EXPERIMENTAL PROCEDURE TaSiN films, with thicknesses ranging from 80 to 120 nm, were deposited at room temperature by reactive rf magnetron sputtering of a TaSi2 target in an Ar-N2 atmosphere. Thin film properties were studied as a function of rf power density (from 1.6 to 4 W/cm2) and N2 to Ar flow ratio for three different pressures (0.5, 1 and 3 Pa). The distance (z) between substrate and target was fixed at 7 cm. According to the kinetic theory of the gases4, we can consider, in our particular deposition conditions, that when the gas pressure is lower than 1 Pa, the mean free path of the atoms ej
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