Liquid-delivery Metalorganic Chemical Vapor Deposition Research Articles

Influence of Na on the structure of Bi 4Ti 3O 12 films deposited by liquid-delivery spin MOCVD

Thin Na-substituted Bi 4Ti 3O 12 films were grown by the liquid-delivery spin metal-organic chemical vapor deposition (MOCVD) method with different concentrations of sodium bis(trimethylsilyl)amide [Na(TMSA)] as Na precursor. At a substrate temperature of 600 °C the original Aurivillius structure was preserved, however high resolution x-ray diffraction (HRXRD) studies indicate that the Na-substituted phase exhibits a slightly smaller lattice parameter compared to the pure Bi 4Ti 3O 12 phase. From additional x-ray photoemission spectroscopy (XPS) results, we have concluded that monovalent Na + ions have been incorporated on Bi 3+ sites in the perovskite units. The proposed charge compensation for this aliovalent substitution is explained by a shift of the valence state of Bi 3+ ions in the vicinity of the incorporated Na + ions from 3+ to 5+. Due to the small ionic radius of the Bi 5+ ions, the incorporation efficiency amounts to a few atomic percent only.

The Structure and Characterization of ZrO2 Thin Films Prepared by Liquid Delivery-MOCVD

In this study, 50 nm-thick ZrO2 thin films have been prepared on Si substrate by liquid delivery metal-organic chemical vapor deposition(LD-MOCVD) at 650°C. The structural characteristics of the samples were investigated by X-ray diffraction analysis and SEM respectively, showed a tetragonal phase and a high uniformity of ZrO2 films. The electrical properties were studied by C-V and I-V measurements on Au/ZrO2/Si Metal-Insulator-Semiconductor (MIS) structure. The dielectric constant of ZrO2 films was 15. The leakage current-voltage dependence showed 3 different conduction mechanisms, which were Poole-Frenkel conduction mechanism, Schottky emission mechanism or ohmic emission.

Characterization of Pt/BiFeO3/ZrO2/Si Capacitors for Memory Applications

BFO film was fabricated on ZrO2 insulating buffer by sol-gel method. The ZrO2 was deposit on Si substrate by liquid delivery metal-organic chemical vapor deposition (LD-MOCVD) process. The microstructure and the electric properties of the Pt/BFO/ZrO2/Si capacitors were studied. ZrO2 demonstrates excellent insulating properties on Si substrate. The MFIS structure showed clockwise capacitance-voltage hysteresis loops due to the ferroelectric polarization of BFO. The maximum memory window is 2.26V. The leakage current density of the capacitor was of the order of 10−7 A/cm2 at an applied voltage of 8V.

Characteristics of Pt/BiFeO3/TiO2/Si capacitors with TiO2 layer formed by liquid-delivery metal organic chemical vapor deposition

Metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with 250 nm thick BiFeO3 (BFO) ferroelectric film and 150 nm thick TiO2 layer on silicon substrate have been fabricated and characterized. TiO2 was deposited on Si substrate by liquid delivery metal-organic chemical vapor deposition (LD-MOCVD) process. The microstructure and the electrical properties of the Pt/BFO/TiO2/Si capacitors were studied. TiO2 demonstrates excellent insulating properties on Si substrate. The MFIS structure showed clockwise capacitance-voltage hysteresis loops due to the ferroelectric polarization of BFO. The maximum memory window is 3.51 V. When sweeping voltages decreased from ±14 to ±6 V, the memory window width decreased from 3.51 to 1.11 V. The leakage current of the film was of the order of 10−8 A/cm2 at an applied voltage of 4 V.

Silver Films Deposited by Liquid-Delivery MOCVD using (Tertbutylcarboxylate)(Triethylphosphine)Silver with Toluene as the Solvent

Silver metallic films are prepared by liquid-delivery metal organic chemical vapor deposition (MOCVD) using (tertbutylcarboxylate) (triethylphosphine)silver ((Ag(OOCCH2tBu)(PEt3))n) solved 1M in toluene. The deposition of Ag thin films was carried out on different substrates at different pressures and temperatures within 300-550oC range. The reaction kinetics, film composition, film morphology and electrical properties of deposited Ag films were investigated. All the films were polycrystalline metallic silver as analyzed by X-ray diffraction with a preferred crystalline orientation (111). The surface structure investigation indicated that silver island formation takes place when Si and Si/SiO2 substrates were used, leading to a resistivity of the films from few MΩ/□ to infinity. In case of the silver films deposited on Si/SiO2/TiO2 substrates the films are rough but continuous showing a low resistivity (down to 3 mΩ/□) and offering potential applications in storage-capacitor or for solar cells technology.

Deposition of SrZrO3 Thin Films Using Liquid Delivery Metal–Organic Chemical Vapor Deposition

Proton-conductive SrZrO3 films were successfully deposited on Pt/SiOx/Si and porous stainless-steel substrates by liquid delivery metal–organic chemical vapor deposition (LD-MOCVD). The as-deposited films deposited on the Pt/SiOx/Si substrate at 600 °C showed good crystallinity and post-annealing at temperatures below 800 °C resulted in improved crystallinity. A 200-nm-thick film deposited on the porous stainless-steel substrate was flat and solid and did not show any gas leakage. We consider this deposition technique to be applicable for the fabrication of a new solid oxide fuel cell structure with intermediate-temperature operation.

FABRICATION AND PROPERTIES OF METAL-PZT-METAL CAPACITORS BY LIQUID DELIVERY MOCVD

ABSTRACT Pb(Zr1−x,Tix)O3(PZT) thin films were prepared on 8-inch and 4-inch Pt or Ir-electroded Si wafers by liquid delivery metal-organic chemical vapor deposition (LD-MOCVD) using cocktail sources of Pb, Zr and Ti. The processing conditions were optimized in order to obtain high-performance PZT films. The thickness uniformity of PZT films on 8-inch substrate was about ± 3.24%. The deposition rate of Pb (15.8 nm/min) and Ti (17.9 nm/min) deposited on Si substrate were faster than that of Zr (2.5 nm/min). The growth temperature of PZT film was adjusted to 570–630°C depending on the substrates used. The properties of metal/PZT/metal capacitors were also studied. The PZT films based on Pt substrate showed no good ferroelectric properties. By contrast, the ferroelectric properties of Ir/IrO2/PZT/IrO2/Ir capacitors were excellent. At an applied voltage of 5 V, the remanent polarization (Pr) and coercive field (Ec) values were about 36 μ C/cm2 and 50 kV/cm, respectively.

The Microstructure and Ferroelectric Properties of Ce-Doped Bi4Ti3O12Thin Films Fabricated by Liquid Delivery MOCVD

Ferroelectric Ce-doped Bi₄Ti₃O₁₂ (BCT) thin films were deposited by liquid delivery metal organic chemical vapor deposition (MOCVD) onto a Pt(111)/Ti/SiO₂/Si(100) substrate. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to identify the crystal structure, the surface, and the cross-section morphology of the deposited ferroelectric films. After annealing above 640℃, the BCT films exhibited a polycrystalline structure with preferred (00l) and (117) orientations. The BCT film capacitor with a top Pt electrode showed a large remnant polarization (2P r ) of 44.56 μC/㎠ at an applied voltage of 5 V and exhibited fatigue-free behavior up to 1.0×10¹¹ switching cycles at a frequency of 1 ㎒. This study clearly reveals that BCT thin film has potential for application in non-volatile ferroelectric random access memories and dynamic random access memories.

+Capacitance-voltage characteristics of BiFeO3∕SrTiO3∕GaN heteroepitaxial structures

The authors report the integration of multiferroic BiFeO3 films with the semiconductor GaN using liquid-delivery metal-organic chemical-vapor deposition. Epitaxial BiFeO3 films were deposited via interface control using SrTiO3 buffer/template layers. The growth orientation relationship was found to be (111)[11¯0]BiFeO3‖(111)[11¯0]SrTiO3‖(0001)[112¯0]GaN, with in-plane 180° rotational twins. The C-V characteristics of a Pt∕BiFeO3∕SrTiO3∕GaN capacitor exhibited hysteresis with a memory window of ∼3V at a sweeping voltage of ±30V.

Investigation of strontium tantalate thin films for high-k gate dielectric applications

Strontium tantalate (STO) films were grown by liquid-delivery (LD) metalorganic chemical vapor deposition (MOCVD) using Sr[Ta(OEt) 5(OC 2H 4OMe)] 2 as precursor. The deposition of the films was investigated in dependence on process conditions, such as substrate temperature, pressure, and concentration of the precursor. The growth rate varied from 4 to 300 nm/h and the highest rates were observed at the higher process temperature, pressure, and concentration of the precursor. The films were annealed at temperatures ranging from 600 to 1000 °C. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and ellipsometry indicated that the as-deposited and the annealed films were uniform and amorphous and a thin (>2 nm) SiO 2 interlayer was found. Crystallization took place at temperatures of about 1000 °C. Annealing at moderate temperatures was found to improve the electrical characteristics despite different film thickness (effective dielectric constant up to 40, the leakage current up to 6×10 −8 A/cm 2, and lowest midgap density value of 8×10 10 eV −1 cm −2) and did not change the uniformity of the STO films, while annealing at higher temperatures (∼1000 °C) created voids in the film and enhanced the SiO 2 interlayer thickness, which made the electrical properties worse. Thus, annealing temperatures of about 800 °C resulted in an optimum of the electrical properties of the STO films for gate dielectric applications.

EVALUATION OF METALORGANIC PRECURSORS FOR PREPARING BiFeO3 THIN FILMS BY LIQUID DELIVERY CHEMICAL VAPOR DEPOSITION

ABSTRACT The metalorganic precursors to fabricate multiferroic BiFeO3 thin films by liquid-delivery metalorganic chemical vapor deposition were investigated. Among the evaluated compounds, the combinations of Bi(p-Tol)3 and iron β -diketonates were suitable to control the metal composition in BiFeO3 films. The films obtained using the precursor solution with the molar ratio of Bi:Fe = 1:1 included excess bismuth. The films with only BiFeO3 phase could be fabricated at the substrate temperatures of 500°C and 525°C by using the precursor solution of Bi(p-Tol)3 and Fe(IBPM)3 with the molar ratio of 2:1. Though the remnant polarization of the film obtained at 525°C was very small, it was confirmed that the BiFeO3 film had ferroelectricity.

Fabrication of Ferroelectric Pb(Zr,Ti)O3 Thin Films by Liquid Delivery Metalorganic Chemical Vapor Deposition Using a Novel Titanium Source Ti(OEt)2(DPM)2

Ferroelectric Pb(Zr,Ti)O3 (PZT) thin films were fabricated on platinized silicon substrates by liquid delivery metalorganic chemical vapor deposition (MOCVD) using Pb(DPM)2, Zr(DIBM)4 and Ti(OEt)2(DPM)2, and subsequent post annealing. Approximately 30% higher deposition rates were attained and the variation in the composition of the deposited films with changing substrate temperature was significantly suppressed using Ti(OEt)2(DPM)2 instead of Ti(OiPr)2(DPM)2. Although the films deposited at 400 and 450 °C were amorphous with PbPtx alloy as a secondary phase, they were crystallized into a perovskite PZT single phase with preferential 111 and 001/100 mixed orientations, respectively, by post annealing at 600 °C in air for 15 min. The 111-oriented PZT film with a thickness of 153 nm showed well-saturated and symmetric hysteresis properties with a twofold remanent polarization of 64.4 µC/cm2 and a twofold coercive field of 133.6 kV/cm. These results suggest that Ti(OEt)2(DPM)2 is a more suitable source than Ti(OiPr)2(DPM)2 for liquid delivery MOCVD of PZT thin films.

Improvement in Step Coverage of Pb(Zr,Ti)O3 Thin Films Deposited by Liquid Delivery Metalorganic Chemical Vapor Deposition

Ferroelectric Pb(Zr,Ti)O3 (PZT) thin films were deposited on trenched SiO2/Si substrates at various substrate temperatures by liquid delivery metalorganic chemical vapor deposition (MOCVD) using Pb(DPM)2, Zr(DIBM)4 and Ti(OiPr)2(DPM)2 as precursors. Their step coverage increased from 38 to 80%, while their deposition rate decreased with decreasing the substrate temperature from 600 to 400°C. In the deposition on planar Pt/Ti/SiO2/Si substrates, the as-grown PZT films deposited under the substrate temperature of 450°C were confirmed to be amorphous; they crystallized into perovskite PZT single phase and showed ferroelectric properties after post annealing at 600°C in air for 15 min. From these results, we concluded that the combination of low-temperature deposition and post annealing is effective in improving the step coverage of PZT thin films deposited by liquid delivery MOCVD although composition control is severe in such a case because the self-regulation of lead atoms is not realized at low temperatures.

Iridium Electrodes for Ferroelectric Capacitors Deposited by Liquid-Delivery MOCVD

AbstractThin iridium films are required as electrode material for ferroelectric capacitors. SBT or PZT are often used as ferroelectric material in such capacitors. The PZT based non-volatile ferroelectric random access memories show better fatigue characteristics if platinum is replaced by iridium as electrode material. Metalorganic chemical vapor deposition (MOCVD) was used for the deposition because of the superior step coverage on three-dimensional structures compared to the conventional physical vapor deposition processes of metal layers. Particularly, in memory fabrication, good step coverage is essential. The iridium films were deposited on different substrates at temperatures of 300 – 500 °C by liquid-delivery MOCVD. The precursor Ir(EtCp)(1,5COD) [iridium(ethylcyclopentadienyl)(1,5-cyclooctadiene)] was diluted in toluene (0.1 M concentration) for the deposition experiments. The iridium films were deposited onto TiO2/SiO2/Si-, SiO2/Si-, and Si-substrates to compare the iridium film properties on different substrates. The growth conditions like oxygen flow, growth temperature, and reactor pressure were varied. The growth rates were in a range between 0.05 and 4.6 nm per minute. We found that the growth rates were highly influenced by the oxygen flow and the substrate material. Oxygen assisted the decomposition of the precursor, and carbon and hydrogen of the organic source were oxidized, which suppressed its incorporation into the iridium layer. Annealing in an oxidizing ambient at temperatures above 700 °C resulted in an increased oxidation of the films as proved by XRD analyses. The resistivity of the films was determined by the Van-der-Pauw method. Low resistivities of 7 – 70 µΩcm were obtained for the as-deposited iridium films.

Improvement of electrochemical properties in LiCoO2 cathode films grown on Pt∕TiO2∕SiO2∕Si substrates by liquid-delivery metalorganic chemical vapor deposition

The structural and electrochemical properties of LiCoO2 cathode films grown on Pt∕TiO2∕SiO2∕Si substrates at 500°C by liquid-delivery metalorganic chemical vapor deposition (LDMOCVD) were investigated as a function of Li∕Co mol ratio. The electrochemical properties such as initial discharge capacity and cyclic retention were improved through the study of Raman spectra of as-grown and annealed LiCoO2 films. The deposition temperature of 500°C was chosen to characterize the films because films grown at 500°C showed a typical high temperature hexagonal phase without Co3O4 impurities in the films. The optimum annealing condition of as-grown samples with Li∕Co=2.0 and 3.0 was at 700°C for 30min in an oxygen ambient. The highest initial discharge capacity and capacity retention were obtained in Li‖LiCoO2 cells grown with Li∕Co=3.0 and 2.0, respectively, and were approximately 38μAhcm−2μm and 77%, respectively. The compositional window for an optimum electrochemical property exists in the range of Li∕Co=2.0to3.0 in an as-grown temperature of 500°C and annealing temperature of 700°C for 30min in O2.

Improvement in Structural and Electrical Properties of (Ba0.5Sr0.5)TiO3 Capacitors Using (Ba0.5Sr0.5)RuO3 Conductive Layers at (Ba0.5Sr0.5)TiO3/Pt Interface

BST thin films and BSR interlayers were deposited by pulsed laser deposition (PLD) and liquid-delivery metalorganic chemical vapor deposition (LDMOCVD) onto Pt/TiO2/Si substrates, respectively. Ultrathin BSR conductive layers were inserted at the BST/Pt interface to improve the dielectric properties of BST thin films. BST films deposited on ultrathin BSR interlayers showed an improvement in roughness and microstructure compared with those without BSR layers in an overall range of BST film thickness. The temperature-independent interface capacities in BST/Pt and BST/BSR/Pt structures are approximately 8.9 and 20 µF/cm2, respectively. The dielectric properties of BST films were improved by the increase in interface capacity as well as roughness and microstructure using the BSR conductive layer which is similar to BST in crystal structure and chemical composition.

X-ray diffraction residual stress calculation on textured La2/3Sr1/3MnO3 thin film

Residual stresses and texture in La2/3Sr1/3MnO3 (LSMO) thin films have been investigated. The films were deposited on (100) LaAlO3 (LAO) and (100) MgO single crystals by liquid delivery-metal organic chemical vapor deposition (LD-MOCVD). X-ray diffraction (XRD) pole figures showed (001)LSMO//(001)LAO and (001)LSMO//(001)MgO preferred orientation. Residual stresses were calculated using a modified sin2ψ method, crystallite group method (CGM), assuming a biaxial stress state. Compressive stresses on the order of 224 and 1150MPa were obtained for LSMO films deposited on LAO (LSMO/LAO) and MgO (LSMO/MgO), respectively.

Semiconducting and ferromagnetic properties of Ti[sub 1−x]Co[sub x]O[sub 2] thin films grown by liquid-delivery metalorganic chemical vapor deposition

We have used liquid-delivery metalorganic chemical vapor deposition to grow polycrystalline Ti1−xCoxO2 anatase films with various Co concentrations onto SiO2/Si(100), and have measured the elemental distribution, magnetic properties, and chemical bonding states of the resulting films. The ionic states of Co in ferromagnetic Ti1−xCoxO2 films have the +2 formal oxidation states. Co-rich clusters on the Ti1−xCoxO2 film surface were formed above the limit of solubility of approximately x=0.05. Co-rich clusters formed in Ti1−xCoxO2 films decreased the value of Hc (coercive field) and increased the value of Ms (saturation magnetic field). The Ms and Hc of Ti0.97Co0.03O2 thin films were approximately 20 emu/cm2 and 250 Oe, respectively. The Curie temperature (Tc) of Ti0.97Co0.03O2 thin films is estimated to be higher than 300 K.

Preparation of Strontium Bismuth Tantalate Thin Film by Liquid-Delivery Metalorganic Chemical Vapor Deposition

ABSTRACTThin films of BiOX, SrXTaYO, and SrXBiYTaZO (SBT) were deposited by liquid-delivery metalorganic chemical vapor deposition (MOCVD). The substrate temperature and the deposition pressure were varied from 300 to 600°C and from 0.35 to 7 mbar, respectively. Triallylbismuth (Bi-1), triphenylbismuth (Bi-2) or alkyl bismuth (Bi-3) and strontium bis-pentaethoxy-methoxyethoxy tantalate (Sr-Ta) were used as Bi precursors and as Sr-Ta precursor, respectively. X-ray photoelectron spectroscopy (XPS), ellipsometry, and scanning electron microscopy (SEM) were carried out to characterize the film properties.The growth rates of the MOCVD of BiOX and SrXTaYO were compared to the growth rate of SBT to obtain information about mutual interaction between the precursors. The growth rate of bismuth oxide thin films deposited from Bi-1 and Bi-2 was low (∼10 nm/h at 0.35 mbar). The growth rate of strontium tantalate films was higher (up to 50 nm/h) and depended strongly on the temperature. Eight times higher (∼400 nm/h) growth rates of BiOX and SBT films were observed for the Bi-3 precursor. The deposition rate of the SBT films was quite similar to the rate of the bismuth oxide. However, the deposition rate of SBT was always lower than the deposition rate of the single Bi precursors. The growth rate significantly depended on the deposition pressure. A decrease of the deposition pressure in the reactor chamber reduced the deposition rate of BiOX, SrXTaYO, and SBT, but on the other hand, it improved the uniformity of the film thickness over the entire 150 mm wafer surface.The XPS measurements showed a deficit of bismuth in the SBT films even though the concentration of the Bi-1 or Bi-2 precursor was several times higher compared to the Sr-Ta precursor. This problem disappeared when Bi-3 source was used.

Preparation of Pb(ZrxTi1 - x)O3 Films on Trench Structure for High-Density Ferroelectric Random Access Memory

The growth characteristics of Pb(ZrxTi1 - x)O3 thin films on three-dimensional (3D) electrodes were investigated for the application to high-density ferroelectric random access memory (FeRAM) devices. PZT films have been grown on Ir coated trench structures having aspect ratio of 1.2 by liquid delivery-metal organic chemical vapor deposition (LD-MOCVD). Atomic layer deposited (ALD) Ir electrode showed good step coverage and electrical properties. MOCVD PZT films showed step coverage of 90% at the deposition temperature of 500°C, while it is decreased to 63% at 550°C. Compositional non-uniformity of PZT along the sidewall was greatly affected by the types of the metal organic sources.