Growth of (Ba,Sr)TiO 3 Thin Films in a Multi-wafer MOCVD Reactor
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Growth of (Ba,Sr)TiO3 Thin Films in a Multi-wafer MOCVD Reactor P. Ehrhart1, F. Fitsilis1, S. Regnery 1,2, C. L. Jia1, H.Z. Jin1, R. Waser1, F. Schienle2, M. Schumacher2, and H. Juergensen2 1) IFF-Forschungszentrum Jülich, D-52425 Jülich, Germany 2) Aixtron AG, D-52072 Aachen, Kackertstr.15-17, Germany
ABSTRACT We report on the performance of a planetary multi-wafer MOCVD reactor which handles 5 six inch wafers simultaneously. The reactor is combined with a liquid delivery system which mixes the liquid precursors from three different sources: 0.35 molar solutions of Ba(thd)2 and Sr(thd)2 and a 0.4 molar solution of Ti(O-i-Pr)2(thd)2. The microstructure and the film stress were investigated by X-ray diffraction and the composition of the films was determined by X-ray fluorescence analysis. As a direct consequence of the reactor design we obtain a high uniformity of the films over 6 inch wafers, as well as high efficiencies for the precursor incorporation. Film growth is discussed within a wide parameter field and the finally achieved electrical properties, e.g., permittivity, loss tangent, leakage current, are discussed in relation to the microstructural properties.
INTRODUCTION (BaxSr1-x)TiO3, (BST), is one of the prime candidates as a high-k-dielectric in integrated highdensity capacitors for future multi-GBit DRAM memory cells1 as well as for dielectric tuneable devices and remarkable progress has been achieved in the metal-organic chemical vapor deposition (MOCVD) of thin BST films2-5. Most of the experimental reactors used for the development of mass production tools presently have a single wafer showerhead design3-5 and we report as a comparison on the performance of a planetary multi-wafer reactor offering extremely high throughput due to possible batch mode processing which results in low cost of ownership. We report on the properties of BST films which were deposited on Pt/TiO2/SiO2/Si wafers. The composition and microstructure of the films were routinely investigated by X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis using different calibration standards prepared by chemical solution deposition. Additional substrates without Ti adhesion layer were used for the XRF analysis since the penetration depth of the X-ray beam is too large to distinguish the Ti of the BST from the Ti of the adhesion layer. The electrical properties were investigated after sputter-deposition and structuring of Pt top electrodes. BST properties depend critically on the stoichiometry, the microstructure, as well as on the films thickness. For the present discussion we select films of a composition around (Ba0.7Sr0.3)TiO3. Through process variations we grew a broad field of BST thin films with different stoichiometry, i.e. different ratios of the Group-II/Ti content. We first discuss the thickness dependence of the film properties and concentrate then on films with a thickness of 30nm, which is close to envisaged application for DRAMS. We selected films which are slightly Ti rich to discuss the influence of the growth te
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