Source Metalorganic Chemical Vapor Deposition Research Articles

Impedance Spectroscopy of Manganite Films Prepared by Metalorganic Chemical Vapor Deposition

Polycrystalline Pr(1-x)CaxMnO3 (PCMO) films were prepared by liquid source metalorganic chemical vapor deposition using in situ infrared spectroscopic monitoring. The electric properties of the PCMO-based devices with Ni and Al electrodes (Ni-PCMO-Ni and Al-PCMO-Al devices) were studied by dc current-voltage (I-V) measurements and ac impedance spectroscopy. The current varied linearly with the applied voltage in Ni-PCMO-Ni devices, while nonlinear behavior was observed in I-V curves for Al-PCMO-Al devices. Impedance spectra were also different between Ni-PCMO-Ni and Al-PCMO-Al devices. The Cole-Cole plots for the Ni-PCMO-Ni devices showed only a single semicircular arc, which was assigned to the PCMO bulk impedance. Impedance spectra for the Al-PCMO-Al devices had two distinct components, which could be attributed to the PCMO bulk and to the interface between the PCMO film and the Al electrode, respectively. The bias dependence of the impedance spectra suggested that the resistance switching in the Al-PCMO-Al devices was mainly due to the resistance change in the interface between the film and the electrode. The metal electrode plays an important role in the resistance switching in the PCMO-based devices. The choice of the optimum metal electrodes is essential to the ReRAM application of the manganite-based devices.

BiFeO 3 thin films prepared using metalorganic chemical vapor deposition

BiFeO 3 thin films were grown on (001) SrTiO 3 and (001) ZrO 2(Y 2O 3) substrates by single source metalorganic chemical vapor deposition in the temperature range T = 500 ÷ 800 °C using Fe(thd) 3 and Bi(C 6H 5) 3 as volatile precursors. X-ray diffraction analysis shows cube-on-cube epitaxial growth of BiFeO 3 on (001) SrTiO 3. The strongly reduced bismuth transfer into the film due to the high thermal stability of Bi(C 6H 5) 3 was counterbalanced by the increase of the total pressure as well as of the residence time of the precursor flow in the reactor; the Bi/Fe ratio in the film thus becomes close to that in the precursor mixture. Optical second harmonic generation measurements have evidenced the ferroelectric ordering in BiFeO 3 films and the apparent decrease of the Curie temperature of the strained films as compared to BiFeO 3 single crystal.

Synthetic routes to colossal magnetoresistance manganites thin films containing unstable or highly volatile metal oxides

We demonstrate that the colossal magnetoresistance (CMR) manganites doped with the monovalent cations of the large ionic radius A (A = Na +, K +, Ag +) reveal enhanced sensitivity of the electrical resistance to the magnetic field near the room temperature. The main obstacle to their practical application is severe difficulty of the synthesis, in particular, that of the thin films because of the high volatility or low thermal stability of the oxides of these doping elements. But the preparation of the films in two steps allows for the materials with the superior CMR characteristics. At the first step, epitaxial single phase precursor La 1− x A y MnO 3 (0.3 ≥ x > y) is formed on the single crystal substrate due to the epitaxial stabilization by the single source MOCVD (metalorganic chemical vapor deposition) using thd-complexes. The second step is the isopiestic annealing with the powder mixture determining the high concentration of the volatile oxide in the gas phase resulting in the saturation of La 1− x A x MnO 3 ( x = y) films by the gas phase transport. The film transformations are studied with XRD and HREM. The high magnetoresistance MR and magnetotransmission MT with the linear magnetic field (H) dependence near the room temperature (dMR/dH up to 45%/T, dMT/dH up to 15%/T) are reported.

Magnesium hydrotris(1-pyrazolyl)borate as a promising single source MOCVD precursor of magnesium borate phases

The magnesium(II) hydrotris(1-pyrazolyl)borate, Mg[BH(pz) 3] 2, complex has been, for the first time, tested as a precursor for the metal organic chemical vapor deposition (MOCVD) of borate phase thin films. The thermal analyses of this source reveal high volatility and good thermal stability with a low residue left despite its relatively high melting point. In particular, the compound has been successfully applied to the MOCVD fabrication of Mg 2B 2O 5 films, and therefore it represents a suited and reliable single source precursor of borate phases. Mg[BH(pz) 3] 2 provides constant evaporation rates even for very long deposition times and, hence, highly homogeneous films of carefully controlled thickness.

Reaction mechanism of a lanthanum precursor in liquid source metalorganic chemical vapor deposition

The reaction mechanism of a lanthanum precursor, tris(dipivaloylmethanato)lanthanum (La(DPM) 3), was investigated in liquid source metalorganic chemical vapor deposition (MOCVD) of lanthanum oxide films. The behavior of La(DPM) 3 in the gas phase was analyzed under actual CVD conditions by in situ infrared absorption spectroscopy. The infrared band identification was performed using density functional theory calculations. We confirmed that the liquid source delivery using tetrahydrofuran as a solvent supplies a La(DPM) 3 molecule maintaining almost the whole molecular structure. The spectroscopic data on the gas-phase reactions were correlated with the characteristics of the deposited oxide films. The temperature dependence of the infrared absorption suggests that the thermal decomposition of La(DPM) 3 in the gas phase may trigger the film deposition. La(DPM) 3 was only partially decomposed in the gas phase under the actual deposition conditions, which indicates that surface reactions rather than gas-phase reactions control dominantly the film deposition.

In Situ Infrared Spectroscopic Study on a Titanium Source in MOCVD

The optimum deposition condition in liquid source metalorganic chemical vapor deposition (MOCVD) of films was significantly dependent on the chemical structures of titanium source molecules. To clarify the origin of this dependence, we investigated the reaction mechanisms of the individual titanium sources by in situ infrared absorption spectroscopy. A systematic study on the reaction mechanism of MOCVD source molecules was carried out using a novel titanium source molecule, [methylpentanediolbis(dipivaloylmethanato)titanium]. The obtained data on were discussed by comparing with those on the conventional titanium CVD sources such as [bis (tert-butoxy)bis(dipivaloylmethanato)titanium] and [bis(iso-propoxy)bis(dipivaloylmethanato)titanium]. is about as thermally stable as and more stable than The thermal stability of the organometallic molecules as a whole is determined by the stability of the moieties other than the DPM ligands. The addition of have little influence on the temperature dependence of the infrared absorption of in the gas phase under the actual CVD conditions. The competition between thermal decomposition and oxidation of titanium sources is also sensitive to the structures of their ligand groups other than DPM groups. © 2004 The Electrochemical Society. All rights reserved.

Reaction Mechanism of Alkoxy Derivatives of Titanium Diketonates as Source Molecules in Liquid Source Metalorganic Chemical Vapor Deposition of (Ba,Sr)TiO3 Films: A Study by In Situ Infrared Absorption Spectroscopy

The effect of the difference in the reaction mechanisms of the titanium source molecules on film quality was investigated in liquid source metalorganic chemical vapor deposition of (Ba,Sr)TiO3 (BST) films. The optimum deposition condition was significantly dependent on the alkoxy moiety of the mixed titanium alkoxide/diketonate compounds such as Ti(t-BuO)2(DPM)2 [bis(tert-butoxy)bis(dipivaloylmethanato)titanium] and Ti(i-PrO)2(DPM)2 [bis(iso-propoxy)bis(dipivaloylmethanato)titanium]. The liquid source delivery was found to be accompanied by local distortion and/or decomposition in the iso-propoxy moieties of Ti(i-PrO)2(DPM)2; no corresponding phenomena occurred in the case of Ti(t-BuO)2(DPM)2. In order to clarify the origin of this dependence, we analyzed the reaction mechanisms of the individual titanium sources by in situ infrared absorption spectroscopy. The chemical stability of the alkoxy moiety of the titanium source determines the reactivity of the whole molecule, which significantly influences on the crystallinity of the resultant BST films.

Liquid Delivery Metal-Organic Chemical Vapor Deposition of Pb(ZrxTi1-x)O3 Thin Films for High-Density Ferroelectric Random Access Memory Application

The growth characteristics of Pb(ZrxTi1-x)O3 (PZT) thin films were investigated for application to high-density ferroelectric random access memories (FeRAM) devices. Films were grown by the liquid source metal-organic chemical vapor deposition (LS-MOCVD) method with tmhd-family precursors, such as Pb(tmhd)2, Zr(tmhd)2(OiPr)2 and Ti(tmhd)2(OiPr)2, dissolved in octane. Film deposition was mainly performed at 560°C, because it is the highest temperature at which bottom electrode contact could be maintained against oxidation in our capacitor over bit-line (COB) structure. The control of Pb precursor supply plays the most critical role in realizing a reliable process for PZT thin film deposition. We have monitored the changes in the microstructure and electrical properties of films on increasing the Pb precursor supply into the reaction chamber. Under optimized conditions, Ir/IrO2/PZT(100 nm)/Ir capacitor shows well-saturated hysteresis loops with a remanent polarization (Pr) of ∼ 28 µC/cm2 and coercive voltage of 0.8 V at 2.5 V.

Highly (111)-oriented and conformal iridium films by liquid source metalorganic chemical vapor deposition

Highly (111)-oriented and conformal iridium (Ir) films were deposited by a liquid source metalorganic-chemical-vapor-deposition process on various substrates. An oxygen-assisted pyrolysis of (methylcyclopentadienyl) (1,5-cyclooctadiene) Ir precursor at a wide range of substrate temperatures (Tsub) between 300 and 700 °C was used. At a low Tsub of 350 °C, the randomly oriented polycrystalline films exhibited an I111/I200 x-ray intensity ratio of 6. However, the films deposited at Tsub = 700 °C on native SiO2 and amorphous SiO2 surfaces were highly oriented with the I111/I200 ratios of 277 and 186, respectively. The transmission electron microscopy study revealed continuous, dense, and faceted microstructures of Ir films. Also, the step coverage of Ir on TiN (64%) was higher than that on amorphous SiO2 (50%) surfaces.

Liquid Source-MOCVD of BaxSr1xTiO3 (BST) Thin Films with a N-alkoxy-β-ketoiminato Titanium Complex

AnN-alkoxy-β-ketoiminato titanium complex, (Ti(2meip)2 (2meip = 4-N-(2-methylethyoxy)imino-2-pentanoate), see Figure for molecular structure, was investigated as a Ti precursor for barium strontium titanate (BST) thin film growth by liquid source metal-organic chemical vapor deposition (LS-MOCVD). The BST films obtained have an ultra-smooth surface and the titanium composition is relatively independent of the deposition temperature.

Low temperature deposition of Ba1-xSrxTiO3 thin films by ECR plasma-enhanced metalorganic chemical vapor deposition

The deposition temperature dependence of Ba0.7Sr0.3TiO3 (BST) thin film physical and electrical properties was investigated. Films were deposited between 250 and 500°C by electron cyclotron resonance (ECR) plasmaenhanced liquid source metalorganic chemical vapor deposition (MOCVD). Depositions were carried out in an oxygen plasma using the precursors Ba(thd)2•(polyamine), Sr(thd)2•(polyamine), and Ti(O-i-Pr)2(thd)2. With a constant ECR plasma power, composition and growth rate were independent of temperature within the full range investigated, in contrast to most thermally-driven CVD BST processes. Films grown above 350°C were crystalline as-deposited on Pt, and were (100)-textured. The dielectric properties depended strongly upon BST crystallinity, with a sharp increase in dielectric constant and its field dependence observed above 350°C. For slightly Ti-rich, 800Å thick films, dielectric constants of 281 were obtained at 500°C, following a 550°C top electrode anneal in O2. Over the full deposition temperature range investigated, the leakage current density was less than 10-7 A/cm2 at 2.0 V and dielectric loss tangents varied between 0.003 and 0.013.

Deposition Characteristics of (Ba, Sr)TiO3 Thin Films by Liquid Source Metal-Organic Chemical Vapor Deposition at Low Substrate Temperatures

The deposition characteristics of (Ba, Sr)TiO3 (BST) thin films using a liquid source metal-organic chemical vapor deposition on a 6-inch-diameter Pt/SiO2/Si wafer were investigated. Ba(DPM)2 tetraglyme, Sr(DPM)2 tetraglyme and Ti(DPM)2(O-i-Pr)2, dissolved in n-butyl acetate, were used as the sources of Ba, Sr and Ti, respectively. Step coverage, within-wafer uniformities in composition and thickness of the BST films were investigated as a function of substrate temperatures ranging from 420° C to 570° C. As the substrate temperature decreased, the step coverage improved, whereas the within-wafer uniformities degraded. From BST films deposited in a temperature range from 450° C to 480° C, good step coverage (>80%), as well as good within-wafer uniformity were obtained. However, in that temperature range, hazy deposition was observed due to many humps on the surface. The humps are an agglomeration of crystalline grains and are a few hundred Å in diameter, which have a Ti-rich composition compared to flat film region.

Annealing effect on magnetic and electrical properties of epitaxial La0.8MnO3−δ thin films grown by chemical vapor deposition

A new liquid source metalorganic chemical vapor deposition process has been developed in order to control precisely the amount of precursors vapors that is produced. Films of self-doped La0.8MnO3−δ have been deposited on LaAlO3 (012) substrates. X-ray diffraction measurements reveal an epitaxial growth. The as-deposited films exhibit both a ferromagnetic (Tc=200 K) and a metal–insulator (Tρ=130 K) transition. Postannealing experiments have been carried out and the results indicate the resistivity is considerably reduced, the temperature of transitions is raised to 320 K, and a magnetoresistance Δρ/ρ0=20% per tesla is obtained at 300 K in the 0–2 T range.

Growth of epitaxial strontium barium niobate thin films by solid source metal-organic chemical vapor deposition

Strontium barium niobate (Sr x Ba 1− x Nb 2O 6) thin films have been epitaxially grown on (0 0 1)MgO, (1 1 0)MgO and (0 0 1)Sr 0.75Ba 0.25Nb 2O 6 substrates by solid source metal-organic chemical vapor deposition. Films became amorphous when the substrate temperature was below 535°C. The crystallinity of the film improved approximately with decreasing growth rate. Film compositions could be controlled by varying source compositions. Single crystalline films were deposited on (0 0 1)Sr 0.75Ba 0.25Nb 2O 6 single crystal substrates while films grown on (0 0 1)MgO and (1 1 0)MgO substrates revealed four in-plane orientations. Waveguiding behavior was demonstrated for both TE and TM modes with the films grown on (0 0 1)MgO substrates. The measured refractive indices were in agreement with those of bulk crystal.

In-SituEELS Analysis of Cobalt Valence in La1-xSrxCoO3-y

Transition and rare earth metal elements have played a vital role in synthesis of functional and smart materials because of their unique electronic structures and mixed valences. Experimental measurement of the valence states is thus important for understanding the mechanism which drives the functional properties. Lai1.xSrxCoO3-y(LSCO), for example, is an ionic conductor with potential applications in fuel cells and many other fields. In this type of materials, the anion deficiency is directly associated with the ratio of Co2+/Co3+ (or Co3+/Co4+) present in the specimen. It is known that the anion deficiency of the material depends on the operation temperature, but a direct measurement of anion deficiency is a challenge to existing microscopy techniques. In this paper, we present the in-situ analysis of Co valence in LSCO using electron energy-loss spectroscopy (EELS) in a transmission electron microscope.LSCO thin films (with x = 0.5) were grown on polished MgO(00l) substrate by liquid source metal-organic chemical vapor deposition (MOCVD) method [1].

SrBi2Ta2O9 thin films made by liquid source metal-organic chemical vapor deposition

A liquid source metal-organic chemical vapor deposition system was installed to deposit SrBi2Ta2O9 (SBT) thin films on sapphire and Pt/Ti/SiO2/Si substrates. The process parameters such as deposition temperature and pressure, and ratio of Sr: Bi: Ta in the precursor solutions were optimized to achieve stoichiometric films with good reproducible ferroelectric properties. It was found that the nucleation of SBT started at a deposition temperature close to 500 °C and grain growth dominated at 700 °C and higher temperatures. With increasing deposition temperatures, the grain size of SBT thin films increased from 0.01 μm to 0.2 μm; however, the surface roughness and porosity of the films also increased. To fabricate specular SBT films, the films had to be deposited at lower temperature and annealed at higher temperature for grain growth. A two-step deposition process was developed which resulted in high quality films in terms of uniformity, surface morphology, and ferroelectric properties. The key to the success of this process was the homogeneous nucleation sites at lower deposition temperature during the first step and subsequent dense film growth at higher temperature. The two-step deposition process resulted in dense, homogeneous films with less surface roughness and improved ferroelectric properties. SBT thin films with a grain size of about 0.1 μm exhibited the following properties: thickness: 0.16–0.19 μm; 2Pr: 7.8–11.4 μC/cm2 at 5 V; Ec: 50–65 kV/cm; Ileakage: 8.0–9.5 × 10−9 Acm−2 at 150 kV/cm; dielectric constant: 100–200; and fatigue rate: 0.94–0.98 after 1010 cycles at 5 V.

Effects of oxidants on the deposition and dielectric properties of the SrTiO3 thin films prepared by liquid source metal-organic chemical vapor deposition (MOCVD)

Abstract SrTiO3 thin films are deposited by a liquid source metal-organic chemical vapor deposition (MOCVD). The effects of oxidants on the deposition characteristics and dielectric properties of the films are mainly tested. O2, N2O and O2 + N2O gases are used as the oxidants and the films with Ti-rich and Sr-rich compositions are obtained when O2 and N2O is used, respectively. Deposition of thin initial layer under O2 atmosphere is very effective to obtain large dielectric constant of the SrTiO3 thin film when the main layer is deposited under O2 + N2O atmosphere. The dielectric constants of 40 nm thick SrTiO3 films with thin O2, N2O initial layers and without the initial layers are 235, 145 and 210, respectively.

Preparation and Electrical Properties of SrTiO3 Thin Films Deposited by Liquid Source Metal-Organic Chemical Vapor Deposition (MOCVD)

SrTiO3 thin films with thicknesses ranging from 30 nm to 60 nm were grown on 6-inch-diameter, platinized Si wafers by liquid source metal-organic chemical vapor deposition (MOCVD). The crystalline quality and cation concentrations of the films are strongly dependent on the deposition temperature with optimum temperatures ranging from 500° C to 550° C. Semi-conformal deposition on submicron-sized storage node patterns is obtained but further improvements in conformality and reproducibility are required. The dielectric constant is about 210 irrespective of the film thickness and leakage current densities are sufficiently small for the dynamic random access memory (DRAM) applications. SiO2 equivalent thickness (T ox) of the 30-nm-thick STO film is 0.51 nm. The finding that the leakage current density and dielectric constant are independent of the film thickness can be explained by a fully depleted model of the STO film.

Preparation and characterization of YBaCuO high T/sub c/ superconducting thin films

For thin film metalorganic chemical vapor deposition (MOCVD), a stoichiometric gas phase can be obtained from a mixture of the precursors in the desired mole ratios, in spite of differences in the volatilities of the individual compounds. Proper film composition is obtained by controlling the velocity of a carriage containing the precursors through the heating zone of a vaporizer. YBaCuO (YBCO) superconducting films were prepared on yttrium stabilized zirconia (YSZ) (001) crystal substrates by single source MOCVD using a mixture of powders of Y(thd)/sub 3/, Ba(thd)/sub 2/ and Cu(thd)/sub 2/ as sources. Nondestructive measurements of resistivity, critical current, composition, and surface morphology were performed on these films. A single crystal film with T/sub co/=89 K was made under optimum conditions. Its homogeneity was investigated by resistivity and T/sub co/ measurements and by atomic force microscopy (AFM) at several points of the surface along a diameter of this film. The roughness of the film is higher at the edge than at the center, and this appears to be correlated with the normal state resistivity. The c-axis and a-axis YBCO phases compete with each other at substrate temperatures ranging from 750 to 820/spl deg/C. The c-axis YBCO phase shows spiral growth structure and the spiral step height is about 12.

Crystalline quality and surface morphology of (100) CeO 2 thin films grown on sapphire substrates by solid source metalorganic chemical vapor deposition

(100)-oriented, cerium oxide epitaxial thin films, approximately 250 Å thick, were grown on r-plane sapphire substrates using a solid source MOCVD technique. Rocking curve FWHM values as low as 0.63° and AFM surface roughness on the order of 5 Å RMS were obtained with substrate temperatures near 680°C and growth rates of 0.13 Å/s. Lower substrate temperatures and higher metalorganic source feed rates resulted in rougher layers, which had broader XRD rocking curve widths, indicating poorer out-of-plane alignment. RBS channeling spectra showed that the best films had high crystalline quality: only at the film-substrate interface were slight distortions due to lattice or thermal expansion mismatch detected.