Papers

AVS2005 Session TF-TuM: Atomic Layer Deposition - Oxides

Tuesday, November 1, 2005 8:20 AM in Room 306

Tuesday Morning

Start	Invited?	Item
8:20 AM		TF-TuM-1 Atomic Layer Deposition of Titanium Oxide Thin Films using O₃ for MIM Capacitor of Next Generation Memory Devices S.K. Kim, K.M. Kim, C.S. Hwang (Seoul National University, Korea) TiO₂ films were deposited using a travelling-wave type ALD reactor on a bare-Si (100) wafer, sputtered and ALD Ru, and sputtered Pt electrodes at a wafer temperature of 250°C. TiO₂ thin films was grown using Ti(OC₃H₇)₄ and O₃ as the precursor and oxidant, respectively. The dielectric constants of these TiO₂ films are 83 between 100 for the films on Ru electrodes. Crystalline structure of TiO₂ films on various substrates was investigated to understand the origin of higher k values of TiO₂ films on Ru substrates. XRD results of TiO₂ films on various substrates show that the TiO₂ films on Si and Pt substrates have anatase structure whereas the films on Ru substrates have rutile phase grains. This means that the growth of rutile TiO₂ is related to the kind of substrate. The growth of rutile TiO₂ on Ru substrate is induced by the formation of RuO₂, which has almost identical ion arrangements in its rutile structure, at the TiO₂/Ru interface. For the application of the material and ALD process to DRAM devices, TiO₂ films were grown on contact hole structured Ru electrodes and the dielectric properties of Ru/TiO₂/Ru 3-D capacitor were investigated. The conformity in film thickness and dielectric properties over the entire structured surface was confirmed by capacitance variation vs. hole surface area experiments. Also, addition of Al as an acceptor in TiO₂ films was tried to improve the leakage properties of TiO₂ films due to a rather high leakage current density of TiO₂ films. Although toxeq. of doped-TiO₂ films is smaller than that of undoped-TiO₂ films, leakage current density of doped-TiO₂ films is much lower than that of undoped-TiO₂ films.
8:40 AM		TF-TuM-2 Characteristics of Atomic Layer Deposited TiO₂ Films and its Photocatalytic Activity D.H. Kim, R. Pheamhom (Chonnam National University, South Korea) Titanium dioxide has many attractive physicochemical properties and thus lends itself to various applications such as optical coatings for anti-reflection, high dielectric layers for electronic devices, biocompatible coatings for biomaterials, and photosensitive layers for photocatalysts and solar cells. In this work, tetrakis(dimethylamido) titanium (TDMAT) has been evaluated as a possible precursor for TiO₂ ALD using H₂O₂ as a counter-reactant. We have explored the effects of deposition temperature, reactants pulse and purging time on the film growth rate to optimize the ALD process for TiO₂ preparation using TDMAT. Self-limiting reaction was possible, as supported by saturated film growth rate and the linear property of the film growth depending on the number of cycles. Film growth rate, surface morphology, crystallinity, and conformality on the deposition temperature along with the photocatalytic activity of the ALD TiO₂ in decomposing methylene blue in aqueous solution will be presented.
9:00 AM		TF-TuM-3 Atomic Layer Deposition of SrTiO₃ Films Having a High Thickness- and Cation-Composition Conformality Over a Severe Contact Hole Structure O.S. Kwon, S.W. Lee, C.S. Hwang (Seoul National University, Korea) SrTiO₃ (STO) thin films were grown on Si wafer and Ru-coated Si wafers, respectively, by an atomic-layer-deposition (ALD) technique using conventional metal organic precursors, Sr(C₁₁H₁₉O₂)₂ (Sr(thd)₂) and Ti(Oi-C₃H₇)₄ (TTIP) as Sr- and Ti-precursors, respectively, with a remote-plasma activated and thermal H₂O vapor as oxidant. Although the each precursor exhibited ALD reaction with the remote-plasma activated H₂O vapor, STO exhibited quite different deposition behavior with the bubbling temperature of Sr(thd) ₂. The cation stoichiometry of STO films was dramatically improved when the bubbling temperature of Sr(thd) ₂ < 200°C (melting temperature of Sr(thd) ₂) irrespective of the type of oxidants. Furthermore, cation composition conformality over the severe contact hole structure (0.13µm opening diameter with an aspect ratio of 8) was highly improved when the Sr(thd)₂ bubbling temperature was 180°C. The thickness step coverage over the entire contact hole was >95%, and the variation of cation composition was very small (< 3%). The different degree of oligomerization of Sr(thd)₂ with the bubbling temperature was supposed to be the reason for these phenomena. Electrical properties of STO films grown by ALD were highly dependent on the amount of oxidant. Leakage current density of STO films with lower oxidant supply was too high to measure the dielectric properties. The high leakage property was directly related to the binding energy shift into high binding energy direction of Sr 3d peak position in the XPS analysis. The leakage current density of STO films with sufficient oxidant was reduced and the binding energy shift of Sr 3d peak was reduced. Equivalent oxide thickness < 1nm and leakage current density < 10^-6A/cm² at 1V were obtained by the optimized two step deposition and post-annealing processes.
9:20 AM		TF-TuM-4 Selective Atomic Layer Deposition (ALD) for Fabrication of Metal and Oxide Nanotubes J.Y. Kim, D. Jeong, S. Won, H. Shin, J. Lee (Kookmin University, Korea) In this study, we have fabricated various metal and oxide nanotubes using selective atomic layer deposition (ALD). We easily control the nanotubes shape and make high aspect ratio nanotubes by selective ALD using SAMs such as OTS(octadesyl-tetrachlorosilane). We avoid unnecessary deposition on top of nanotemplates such as poly-carbornate, which results in stand alone nanotubes without connection. The selective ALD is performed on sacrificial nanotemplates with pore sizes of 30 - 200nm. The template were commercial available polycarbonate (PC) and anodic aluminum oxide (AAO) with various hole sizes and thicknesses. After deposition, template was removed by wet etching. We successfully obtain metal (Cu,Co) and oxide(ZrO2,TiO2) single material nanotubes. In addition, metal/oxide double wall nanotubes are fabricated by sequential ALD process. We make metal oxide nanotubes and measure various properties using high resolution-transmission electron microscope (HR-TEM), field emission-scanning electron microscope (FE-SEM), selective area electron diffraction (SAED) patterns, X-ray diffractionmeter (XRD). We also characterize electrical properties of the nanotubes using conducting-atomic force microscope (AFM). The authors gratefully acknowledge the financial support through center for nanostructured materials technology by Korean ministry of science and technology (03K1501-02410).
9:40 AM		TF-TuM-5 Laterally Graded Films and Multilayers Using Atomic Layer Deposition with a Slit Doser and Substrate Translation F.H. Fabreguette, S.M. George (University of Colorado) Laterally graded multilayers have a bilayer spacing that continuously changes versus spatial position. These graded multilayer structures are important for x-ray collimation and x-ray focusing. Recently, optimized W/Al₂O₃ superlattices grown using atomic layer deposition (ALD) displayed an excellent x-ray reflectivity (XRR) of 96% at λ=1.54 Å. To obtain laterally graded W/Al₂O₃ multilayers, the normal conformality of ALD must be circumvented by preventing ALD on the entire substrate. Laterally graded multilayers can be fabricated using a slit doser to localize reactant delivery in a viscous flow gas stream. The substrate is then translated relative to the slit doser with a magnetic linear translator. Since the viscous flow entrains the reactants and moves them downstream, substrate translation upstream of the slit doser prevents ALD on the entire substrate. A laterally graded Al₂O₃ ALD film was initially demonstrated by translating the substrate relative to the slit doser during Al₂O₃ ALD reaction cycles. Variable angle ellipsometry and XRR quantified a varying Al₂O₃ film thickness grown on a Si(100) wafer with a length of 6 inches. Changes in leakage current density and capacitance confirmed the Al₂O₃ thickness gradient. In addition, a laterally graded ZnO/Al₂O₃ multilayer was grown and characterized using XRR. The angle of the first Bragg peak revealed a bilayer spacing that changed as expected versus spatial position.
10:00 AM		TF-TuM-6 Coating Nanoparticles by Atomic Layer Deposition in a Rotary Fluidized Bed Reactor: Al₂O₃ ALD on ZrO₂ J.A. McCormick, A.W. Weimer, S.M. George (University of Colorado at Boulder) Ultrathin and conformal Al₂O₃ films have been grown by atomic layer deposition (ALD) on ZrO₂ particles with diameters of 60 nm and 400 nm using sequential exposures of trimethylaluminum and H₂O. This Al₂O₃ ALD on gram-scale quantities of high surface area ZrO₂ nanoparticles was performed in a novel rotary fluidized bed reactor. The rotary fluidized bed reactor consisted of a stainless steel porous metal cylinder that rotated inside a vacuum system. The nanoparticles were contained inside the porous metal cylinder and the gaseous reactants and products could easily diffuse through the porous walls without particle loss. A magnetically coupled rotary motion feedthrough rotated the porous metal cylinder and provided a fluidization-like mixing between the particles and the reactants. The Al₂O₃ ALD films were deposited on the ZrO₂ nanoparticles at 180°C with a growth rate of 1.8 Å/cycle. The composition of the Al₂O₃ ALD coating was verified using Auger electron spectroscopy, x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Transmission electron microscopy and BET surface area analysis were utilized to determine the conformality of the Al₂O₃ ALD coating and to check for particle coalescence. The Al₂O₃ ALD film uniformly coats the primary ZrO₂ particles and there was no evidence for any particle coalescence.
10:20 AM		TF-TuM-7 The Atomic-Layer-Deposited HfO₂ Gate Dielectric Films; Chemistry of Interface and Electrical Performances T.J. Park, M.J. Cho, S.H. Hong, M.H. Seo, J.H. Kim, J.H. Park, C.S. Hwang (Seoul National University, Korea) HfO₂ thin films were deposited on HF-dipped Si wafers at temperatures ranging from 250 to 300°C using an atomic-layer-deposition technique with N-containing Hf[N(CH₃)₂]₄, Hf[N(CH₃)(C₂H₅)]₄ or Hf[N(CH₃)(₂H₅)]₃[OC(CH₃)₃] and H₂O or O₃ as the precursor and oxidant, respectively. A thin interfacial SiN_x layer was spontaneously formed at the HfO₂/Si interface during film growth. This interfacial SiN_x layer played a critical role in improving the thermal stability and interfacial trap (D_it) property. D_it of < 5 x 10¹⁰ cm^-2eV^-1 near the mid-gap energy states was obtained from most of the process conditions but it usually suffer from the degradation by high temperature post-deposition annealing (PDA) at temperatures > 800°C. The adoption of O₃ oxidant reduced carbon impurity concentration and made the film more amorphous compared to the films grown using H₂O as oxidant. Although ozone was effective in reducing the impurity concentration, the higher concentration slightly deteriorated the dielectric performance. Investigation of the interface states using X-ray photoelectron spectroscopy revealed that the excessive oxygen incorporated during the film growth made the interfacial sub-oxide species (SiO, Si₂O₃ and silicate) and SiO₂ coordinate more with oxygen. This was further confirmed by the MOSFET performance comparison fabricated with HfO₂ gate dielectrics using different O₃ concentration. An electron effective mobility of ~ 65% of the MOSFET with SiO₂ as gate dielectric was obtained from the stoichiometric HfO₂ gate dielectric film. The effective mobility from the MOSFET with the oxygen excess HfO₂ film was only ~ 45 %.
11:00 AM		TF-TuM-9 Atomic Layer Deposition for the Modification and Stabilization of Localized Surface Plasmon Resonance Nanosensors J.W. Elam, M.J. Pellin (Argonne National Laboratory); A.V. Whitney, R.P. Van Duyne, P.C. Stair, G.C. Schatz, S. Zou (Northwestern University) Noble metal nanoparticles serve as optical biosensors and chemosensors because of the localized surface plasmon resonance (LSPR) effect. The optical properties of LSPR sensors are strongly influenced by the size, shape and dielectric environment of the nanoparticles. Atomic layer deposition (ALD) can deposit dielectric films with atomic layer precision onto a variety of substrates including noble metals. Consequently, the optical properties of LSPR sensors can be tailored using ALD coatings. In this study, ordered arrays of Ag nanoparticles were coated with ALD Al₂O₃ and the resulting changes in the physical properties of the nanoparticles were explored. Initial experiments examined the nucleation and growth of ALD Al₂O₃ on flat Ag surfaces using quartz crystal microbalance and ellipsometry measurements. Surprisingly, these measurements demonstrated that the Al₂O₃ ALD proceeds on Ag without any nucleation delay. Next, ordered arrays of Ag nanotriangles fabricated using nanosphere lithography were coated using ALD Al₂O₃ at 50 °C. Optical absorption measurements revealed a 6 nm red shift in the LSPR peak for an Al₂O₃ thickness of only 1.6 Å. The LSPR peak continues to red shift with increasing Al₂O₃ thickness up to ~600 Å. These changes are explained well by theoretical analysis using finite element electrodynamics. The Ag nanotriangles were also examined using atomic force microscopy and scanning electron microscopy and these measurements demonstrated that the ALD Al₂O₃ conformally coats the nanotriangles while preserving their initial shape. Preliminary experiments reveal that thin ALD Al₂O₃ layers significantly improve the thermal stability of Ag nanoparticles while retaining strong Raman enhancement, suggesting that ALD coatings will broaden the range of applications for LSPR nanosensors.
11:20 AM		TF-TuM-10 Atomic Layer Deposition (ALD) of Nickel Films Using Amidinate Precursors V.R. Pallem, K. Kim, J.S. Park, R.G. Gordon (Harvard University) Atomic layer deposition (ALD) of nickel thin films was demonstrated by using new nickel-amidinate precursors. Here we present a dozen nickel N,N'-Dialkyl-2-alkyl/aryl-amidinate derivatives as potential precursors for ALD. Their physical properties (volatility, thermal stability and chemical reactivity) were tuned by altering the alkyl groups. Nickel-bis(N,N'-di-tert-butylacetamidinate) showed the best overall properties as an ALD precursor. With NH₃ as a reducing agent at 270°C, self-limiting growth was achieved at a rate of 0.4 Å/cycle. Analyses of the deposited films showed only nickel. Nickel films grown on silicon nitride substrate had resistivity of 81 µΩ-cm. Post-deposition annealing of nickel films on HF-last silicon showed the formation of nickel silicide.