AVS1997 Session TF-FrM: Electronic Ceramic Thin Films

Friday, October 24, 1997 8:20 AM in Room B3/4

Friday Morning

Start	Invited?	Item
8:20 AM		TF-FrM-1 Structure and Properties of Thin ZnO Films R.N. Lamb, A.J. Hartmann, N. Tran, L.G. Mar, M.H. Koch (The University of New South Wales, Australia) Crystalline and c- axis oriented ZnO thin films have been grown using single source chemical vapour deposition (CVD) of basic zinc acetate. The growth was carried out under high vacuum conditions in a background of H₂O vapour. The film crystallinity is found to be highly dependent on the ambient H₂O pressure. In this work the influence of chemical growth parameters on the film structure and their properties have been investigated. The structure of crystalline ZnO films have been analysed using X-ray Diffraction (XRD) while amorphous films were examined with extended X-ray absorption fine structure (EXAFS). Quantitative information concerning the film crystallinity (grain size and orientation, density of crystallographic defects) are presented and correlated with the results of high resolution electron microscopy. As an example the influence of chemical film growth parameters on the film properties the ZnO film resistivity has been analysed. The resistivity can be varied many orders of magnitude by doping the films with copper ions. Cu⁰ or Cu¹⁺ ions effectively reduce film resistivity while Cu²⁺ has the opposite effect. Doping was performed both in situ during film growth via co-deposition or ex situ after film growth via implantation In situ doped and crystalline films with high copper concentrations (5 atm. %) where successfully prepared whereas in the case of implantation comparable high copper dopant concentrations were found to destroy the film crystallinity and thus significantly alter the film resisitivity. The origin of this behaviour will be discussed.
8:40 AM		TF-FrM-2 Efficient Investigations of Processing/Property/Performance Relationships for Metal/Oxide Sensing Films Using Micromachined Platforms M.J. Nystrom, F. DiMeo, R.E. Cavicchi, S. Semancik, J.S. Suehle (National Institute of Standards & Technology); J. Kelliher (Microelectronics Research Laboratory) Gas sensor researchers have long recognized that the microstructure of a sensing film can have a profound influence on its sensing performance. In this presentation, we describe a novel approach for the direct and efficient exploration of processing/property/performance relationships of sensing films useful in gas sensing. The technique involves the use of Si-based micromachined arrays (of individually-addressable "microhotplates"), and is particularly advantageous for developing multiple active film types for use in gas sensor arrays. Functionality designed into our 100 micron x 100 micron microhotplate elements allows heating to 500 C, temperature measurement, and conductance monitoring of over-deposited films (during and after deposition). We discuss results obtained for SnO₂, ZnO, and WO₃, deposited by self-lithographic chemical vapor deposition (CVD), as well as for overlayers (on the oxides) of CVD- or evaporation-deposited Pt and Pd. To illustrate the power of using heatable microsubstrate arrays in processing/property/performance surveys, we discuss SEM, electronic transport, and gas sensing results associated with microstructure and performance examinations of: effective parameter spaces for deposition conditions; initial nucleation behavior; coverage dependence of catalytic additives; rapid thermal cycling and annealing; and, film seeding. The generalization of the approach to other classes of materials is also discussed.
9:00 AM		TF-FrM-3 Microstructure-Dependent Ferroelectric Properties in SrBi₂Ta₂O₉ Thin Films Fabricated by the Radio Frequency Magnetron Sputtering Techniques J.-K. Lee, K.-J. Cho, S.-H. Lee, Y.B. Park (Korea Institute of Science and Technology); J.-W. Park (Hanyang University, Republic of Korea); K.H. Yoon (Yonsei University, Republic of Korea); H.-J. Jung (Korea Institute of Science and Technology) Nonvolatile memories based on ferroelectric capacitors show much promise because they exhibit a spontaneous polarization that can be reversed by an electric field. Ferroelectric materials, such as Pb(Zr,Ti)O₃ ; PZT offer significant advances over silicon based devices for potential use in semiconductor nonvolatile memories. But, there is still problems in ferroelectric thin film for microelectronics device applications. The solution for this problem is the oxide electrode. In this case, the oxide electrode helps to control the presence of oxygen vacancies at the interface between the ferroelectric thin film and the electrode. But, using the oxide electrodes make the capacitor more leaky. Alternative candidate ferroelectric material to control the fatigue problem in ferroelectric capacitors is the layered perovskite structured ferroelectrics such as SrBi₂Ta₂O₉ ; SBTO. It has been demonstrated that Pt/SBTO/Pt capacitors present practically no polarization fatigue up to about 10¹² switching cycles. SBTO is mainly fabricated by the sol gel technique and the pulsed laser ablation deposition technique. Recently, radio frequency magnetron sputtering techniques are used to grow the SBTO thin films. In this research, r.f. magnetron sputtering technique was used to fabricate the thin film. Crystallographic orientations were changed as the sputtering pressure was increased. Crystal orientation was controlled by using the various substrates such as MgO, SrTiO₃ single crystal. Interfacial analysis will be done by using AES, SIMS, RBS, SEM, TEM, AFM. Long term properties of the Pt/SBTO/Pt capacitors were depend on the interfacial state between the electrode and SBTO and the crystal orientations of the ferroelectrics. By these characteristics, we can observe the relationships between the ferroelectric properties and the morphologies and the crystal orientations. The ferrolelectric properties were measured by the Standard Ferroelectric Tester (RT66A Tester). The morphologies of the SBTO thin films show irregular shaped grains. The c-axis oriented thin films show that the remnant polarization and the coercive field were 10.4µC/cm² and 50 kV/cm, respectively.
9:20 AM		TF-FrM-4 Preparation and Properties of Ferroelectric SrBi₂Ta₂O₉ Thin Films On SrTiO₃ and MgO Substrates By Radio Frequency Magnetron Sputtering Z.J. Huang, Q.D. Jiang, C.L. Chen, P. Jin, L.M. Dezaneti, C.W. Chu (University of Houston) We have synthesized ferroelectric SrBi₂ Ta₂O₉ (SBTO) thin films on SrTiO₃, MgO substrates and SBTO/Pt/SrTiO₃ multi-layer thin films by using radio frequency (rf) magnetron sputtering technique with substrate temperature ranging from 600 to 800 C, O₂/Ar ratio from 5:95 to 40:60, and total pressure from 50 to 200 mTorr. X-ray diffraction, scanning probe microscope (SPM) and scanning electron microscope (SEM) are used to study the influence of processing gas pressure, substrate temperature, and sputtering power density on the micro-structure, compositions and surface morphology. By controlling the deposition parameters, thin films with various orientations and textures have been obtained. Effects on dielectric constant, P-E characteristics of the multi-layer thin films will be presented.¹ ¹This work is supported in part by NSF Grant No. DMR 95-00625, the T. L. L. Temple Foundation, the John and Rebecca Moores Endowment, and the State of Texas through the Texas Center for Superconductivity at the University of Houston.
9:40 AM	Invited	TF-FrM-5 Compositional Effect on Sputtered Multicomponent Oxide Thin Films. U. Helmersson (Linkoping University) The composition of a multicomponent oxide thin film sputter deposited from a compound target often deviates from that of the target. This is often taken to be due to different sputtering rate of different target constituents. However, the composition of the flux of deposition atoms are always equal to that of the target after a period of target presputtering unless extensive target diffusion occurs. The reason for deviation in stoichiometry is instead mainly due to a difference in incorporation probability of different elements in the growing film as well as difference in the gas phase transport. Examples of compounds that deviate from target are SrTiO₃ which usually becomes Sr deficient and KNbO₃ that often becomes K deficient. One very important reason for this is different desorption rates, from the growth surface, for different elements. By estimating the bonding strength of the different elements in bulk SrTiO₃ we find that the Sr ion bond energy is only 0.35 eV while it is 5.05 eV for the Ti ion. The situation on the surface will of course be different but these values gives a hint on the reason for the selective loss of Sr. A way of avoiding desorption is otherwise often to ensure that the metallic constituents are rapidly and thoroughly oxidized to become chemisorbed to the surface. Ba in YBa₂Cu₃O₇ is such an example where Ba in metallic form is likely to desorb from the surface. Using a more efficient oxidizing agents then O₂, such as N₂O reduces the Ba desorption and target stoichiometry is maintained.
10:20 AM		TF-FrM-7 XPS Study of TiN Films Produced with TDMAT and Selected N-Containing Precursors on SiO₂ J.P. Endle, Y.-M. Sun, J.M. White, J.G. Ekerdt (University of Texas, Austin) Low pressure chemical vapor deposition (LPCVD) TiN films were produced on SiO₂ by co-dosing tetrakis(dimethylamido)titanium with selected N-containing precursors. The films were grown at total pressures ranging from 10^-4 to 10^-3 Torr and temperatures between 573 and 723 K. Film composition and chemical states were determined, without exposure to ambient pressure, using X-ray photoelectron spectroscopy (XPS). The primary goal was to evaluate how precursor ligands affect the C and N incorporation into TiN films. To this end, dimethylhydrazine (DH) and 1-aminopiperidine (AP) were chosen for their steric differences, and aniline was chosen to compare the effect of the C-N bond strength in aniline to the N-N bond strength in AP on C and N incorporation. At all growth temperatures, when compared to TDMAT alone, a decrease in the carbon concentration and an increase of N concentration were observed for the DH and AP cases, while an increase of C content was observed for aniline. Growth temperature affected film compositions and the chemical states of C, N, and Ti. At 673 K, DH and AP reduced the C/Ti ratio from 1.16 with TDMAT alone to 0.18 and 0.94, while aniline increased C/Ti to 1.99. The addition of the N-containing precursors causes the XPS C 1s peak to shift to higher binding energy and become broader, and the N 1s peak broadened suggesting that, compared to TDMAT alone, more C-N bonds are formed. Furthermore, the Ti 2p peak shifted to higher binding energy and became broader upon co-dosing. This is evidence of the incomplete conversion of Ti (IV) to Ti (III) in the TiN film.
10:40 AM		TF-FrM-8 Preparation of High Quality RuO₂ Electrodes for High Dielectric Thin Films by Low Pressure Metal Organic Chemical Vapor Deposition J.M. Lee, J.C. Shin (Seoul National University, Korea); C.S. Hwang (Samsung Electronics Co. Ltd., Korea); C.-G. Suk (APEX Co. Ltd., Korea); H.J. Kim (Seoul National University, Korea) Highly conductive RuO₂ thin film recently attracts considerable intererst because it is one of candidate electrode materials for high dielectric constant (Ba,Sr)TiO₃ thin film, which is also the most possible candidate material for a capacitor of ULSI DRAM. For higher than 1 giga bit DRAM a capacitor must have a 3-dimensional structure, even though the BST thin films are used as a dielectric material, because of its extremely small size. Therefore, conformal deposition techniques such as MOCVD for the deposition of electrode materials as well as the BST thin film are essentially required. In this study, high quality RuO₂ thin films with a good electrical conductivity were deposited at 250 - 450°C by MOCVD using Ru(C₁₁H₁₉O₂)₃ [Ru-TMHD], which is first adapted for the deposition of RuO₂ thin films. Deposition behavior and properties of RuO₂ thin film were affected by both the substrate temperature and the added amount of oxygen during deposition. Oxygen addition should be essential to deposit RuO₂ thin films because no films were deposited without oxygen. The deposited RuO₂ thin films with smooth crack free surfaces showed very low resistivities of 45 - 50µOHM cm. At lower deposition temperature and smaller amount of oxygen addition, RuO₂ thin films showed smoother surface morphologies and better step coverage. The BST capacitors of using MOCVD RuO₂ thin films show good electrical properties, indicating that the MOCVD process for RuO₂ thin films can be applied for the deposition of electrode for high dielectric constant thin films used as dielectric materials for ULSI DRAM.
11:00 AM		TF-FrM-9 Magnetoresistance Effect in as-grown La-Ca-Mn-O Films Prepared by MBE Co-evaporation Technique A. Brazdeikis, A. Miniotas, U.O. Karlsson (Royal Institute of Technology, Sweden) Thin films of La-Ca-Mn-O have been grown on (100)-oriented LaAlO₃ and SrTiO₃ substrates by a molecular beam epitaxy co-evaporation technique. The films were found to grow along the c-axis both on LaAlO₃ and SrTiO₃ substrates. Zero-field resistance measurements of La_0.68Ca_0.32MnO₃ films on LaAlO₃ showed that a insulator-metal transition occur in the range of 220 K-230 K. In an applied magnetic field of 5.0 T the resistance decrease, calculated as (R(H)-R(0))/R(H), by more than 1500% at 214 K. The magnetoresistance effect values are similar to those reported for as-grown La-Ca-Mn-O films synthesized either by so-called "block-by-block" or "layer-by-layer" MBE techniques but the effect appear at significantly higher temperatures. In addition, for La-Ca-Mn-O films grown on SrTiO₃ a 200% resistance suppression at 1.0 T was observed. Although atomic force microscopy studies showed film surfaces with typical rms values of 10 nm, the MBE co-evaporation approach which is characterized by relatively high growth rates, may provide new insights in La-Ca-Mn-O film properties. In the paper, we will extend the discussion by providing a detailed study of La-Ca-Mn-O film processing conditions and how they affect film microstructure and transport properties.
11:20 AM		TF-FrM-10 Abstract Epitaxial Growth and Surface Morphology of Ferroelectric BaTiO₃ Thin Films. Q.D. Jiang, C.L. Chen, Z.J. Huang, P. Jin, L.M. Dezaneti, C.W. Chu (University of Houston) Atomically flat single crystal SrTiO₂ (001) surfaces prepared by two-step annealing, first in flow oxygen at 1100 C, and then in ultra high vacuum at 950 C, are used as substrates for thin film deposition. The surfaces so generated are uniformly TiO₂ terminated on the top layer, and are very stable in oxygen and in air. Ferroelectric BaTiO₃ thin films have been epitaxially grown onto so engineered SrTiO₃ (001) substrates with high quality SrRuO₃ bottom electrode. Thin films have been characterized with x-ray diffraction, scanning electron microscope, and scanning probe microscope. In order to achieve atomically smooth surfaces for heterostructure fabrication, observation of ferroelectric domain structure and nano-scale poling, we systematically investigate effects of the deposition parameters and post annealing in flow oxygen on the surface morphology of thin films. Ferroelectric properties of BaTiO₃ thin films, and results of local poling using scanning probe microscope will be presented. This work is supported in part by NSF Grant No. DMR 95-00625, the T. L. L. Temple Foundation, the John and Rebecca Moores Endowment, and the State of Texas through the Texas Center for Superconductivity at the University of Houston.
11:40 AM		TF-FrM-11 Characterization and Thickness Effects on Sputtered Ba_{0.5√sub 0.5}TiO₃ Thin Films P.Y. Chu, S. Zafar, B.E. White, B. Melnick, B. Jiang, P. Zurcher, D.J. Taylor, R.E. Jones, S.J. Gillespie, M. Kottke, R. Liu, W. Chen, D. Werho, R. Gregory (Motorola) Barium strontium titanate ceramic thin films have shown great potential for many microelectronic applications, such as on chip capacitors, sensors, and high k dielectrics. In this work, Ba_{0.5√sub 0.5}TiO₃(BST) capacitors in the thickness range of 10-200 nm were prepared by RF magnetron sputtering on Pt electrodes at 300-600 C in Ar/O₂ gas. The sputtered films show dense and smooth surface with a root mean square of roughness less than 2.5 nm and decreases with film thickness. Thickness uniformity better than 3.5% has been achieved across a 5" wafer. The refractive index of the BST films, deposited above 500 C, is close to the bulk value at 2.2-2.3, indicating good film quality. Auger spectroscopic analysis shows uniform composition throughout the film and possible Ti diffusion into the Pt electrode. The BST capacitors exhibit a high dielectric constant up to 350 and a low leakage current of ~10^-9 A/cm² at room temperature. Even at 125 C, the leakage current is still below 10^-7A/cm². Results on BST films with different thickness indicate the presence of an interfacial layer of ~100 fF/um², which reduces the overall capacitance. This interfacial capacitance becomes important for films thinner than 40 nm. The intrinsic film dielectric constant was calculated to be 462. Effects of film thickness on capacitor properties will be presented.