MOCVD of SrTa 2 O 6 Thin Films for High-k Applications
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MOCVD of SrTa2O6 Thin Films for High-k Applications Stephan Regnery 1,2, Reji Thomas1, Hans Haselier1, Peter Ehrhart1, Rainer Waser1, Peer Lehnen2, Stefan Miedl2, Markus Schumacher2 1) IFF - Institut für Festkörperforschung and CNI - Center of Nanoelectronic Systems for Information Technology, Forschungszentrum Jülich, D-52425 Jülich, Germany 2) AIXTRON AG Aachen, Kackertstr. 15-17, D-52072 Aachen, Germany ABSTRACT SrTa2O6 thin films with thickness between 6 and 150nm were deposited in a multi-wafer planetary MOCVD reactor combined with a TRIJET® liquid delivery system using a single source precursor, strontium-tantalum-(methoxyethoxy)-ethoxide dissolved in toluene. A rather narrow process window for the deposition of stoichiometric SrTa2O6 was found for this precursor at low pressures and a susceptor temperature around 500°C. Films were grown on Pt/TiO2/SiO2/Si, TiNx/Si, and SiO2/Si substrates. The as-deposited films were X-ray amorphous and could be crystallized by post-annealing at a temperature ≥700°C. The SrTa2O6 phase was dominating within a broad range of compositions (Sr/Ta: 0.4–0.7) and a perovskite type phase was observed for Sr/Ta > 0.7. The electrical properties have been investigated with MIM and MIS capacitors after sputter deposition of Pt top electrodes. The amorphous films had a relative permittivity, ε, in the range of 25–45, and low leakage currents. Crystallized films were investigated with Pt MIM capacitors. For stoichiometric SrTa2O6 the dielectric permittivity reached values of ε = 100–110, but the leakage currents were increased. Remarkably, the permittivity is not very sensitive to deviations from the exact stoichiometry of the SrTa2O6 phase (Sr/Ta: 0.4– 0.7), but a decrease to values of ε = 30–40 is observed along with the phase transition at high Sr contents. INTRODUCTION Along with the ongoing miniaturization of electronic devices high-k thin films are needed for a very broad application area, including capacitor dielectrics for future dynamic random access memories (DRAMs), embedded capacitors, tunable devices, as well as gate oxides for field effect transistors [1]. The spectrum of materials includes medium k binary oxides like ZrO2, HfO2, Ta2O5 with a relative permittivity, ε, between 20 – 40, as well as crystalline perovskites, STO, BST, which reach values of several 100. In addition SrTa2O6, (STA), has been discussed recently as it has promising properties as well in amorphous form (ε = 40) as in crystalline form (ε = 100). Chemical deposition methods are straightforward as the precursors developed for the deposition of ferroelectric SBT (SrBi2Ta2O9) are available and films have been deposited by chemical solution deposition [2,3], MOCVD (metal organic chemical vapor deposition) [4] and atomic layer deposition [5]. We report on MOCVD of STA thin films on different substrates, Pt/TiO2/SiOx/Si and TiNx/Si, which yield test structures for capacitor applications, i.e., metal-insulator-metal (MIM) structures, as well as on SiOx/Si(100) which yield test structures for gate oxide ap
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