Liquid-delivery Metalorganic Chemical Vapor Research Articles

A ferroelectric capacitor with an asymmetric double-layered ferroelectric structure comprising a liquid-delivery MOCVD Pb(Zr, Ti)O3 layer and a sputter-deposited La-doped Pb(Zr, Ti)O3 for highly reliable FeRAM

We have developed a double-layered ferroelectric capacitor comprising a liquid-delivery metal–organic chemical vapor deposition-based Pb(Zr, Ti)O3 (PZT) lower layer and a sputter-deposited La-doped Pb(Zr, Ti)O3 (PLZT) upper layer. This structure is designed to achieve a large polarization in the stacked-type capacitor of FeRAM. Ferroelectric capacitors with noble metal electrodes, which are patterned by sputter-etching due to the difficulty of standard chemical reactive etching typically exhibit sloped sidewalls. Consequently, their polarization values, determined by the actual capacitor area, depend on their geometric shape. Our developed capacitor exhibits a 35% increase in polarization compared to an all-sputter-deposited PLZT capacitor. This improvement is due to the reduced total thickness of the developed capacitor achieved by simplifying the bottom electrode structure, which results in steeper capacitor sidewalls. Furthermore, our developed capacitor demonstrates excellent retention margin even after 3000 h of baking at 150 °C, and with a potential endurance of 1014 cycles as predicted by voltage acceleration measurements.

Intermolecular interaction between rare earth and manganese precursors in metalorganic chemical vapor deposition of perovskite manganite films

AbstractThe gas‐phase reaction mechanism was investigated in liquid delivery metalorganic chemical vapor deposition (MOCVD) of praseodymium and lanthanum manganite films. We studied the gas‐phase behavior of praseodymium, lanthanum, and manganese precursors under actual CVD conditions by in situ infrared absorption spectroscopy. The rate of the decrease of the infrared absorbance due to Pr(DPM)3 was almost constant even if Mn(DPM)3 was added, indicating that the intermolecular interaction between Pr and Mn precursors in the gas phase is relatively weak in MOCVD of praseodymium manganite films. On the other hand, the temperature dependence of the infrared absorption indicates that the thermal decomposition of La(DPM)3 was promoted in the presence of Mn(DPM)3. The significant intermolecular interaction occurs between La and Mn precursors in the gas phase in MOCVD of lanthanum manganite films. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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.

Formation Mechanism of Oriented Pb(Zr,Ti)O3 Thin Films on Platinum Bottom Electrodes from Amorphous Films Prepared by Liquid Delivery Metalorganic Chemical Vapor Deposition

Ferroelectric Pb(Zr,Ti)O3 (PZT) thin films with 111- and 001/100-orientations were fabricated on silicon substrates covered with platinum (Pt). Amorphous PZT (a-PZT) films were deposited on Pt bottom electrodes by liquid delivery metalorganic chemical vapor deposition and subsequent postannealing by a special heating stage equipped with an X-ray diffraction system. Variations in the 111 d-space of Pt and the crystallization behavior of PZT layers were in situ measured in postannealing processes. The existence or absence of lead platinum intermediates in a-PZT layers near Pt bottom electrodes at the beginning of crystallization are suggested to be the key factor for obtaining 111- or 001/100-oriented crystalline PZT thin films.

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.

Interfacial and electrical properties of ZrxTi1−xO4 (x=0.66) films deposited by liquid-delivery metal organic chemical vapor deposition to be used as high-k gate dielectric

Zr x Ti 1 − x O 4 (x=0.66) films were deposited on p-type Si (100) substrate using liquid-delivery metal organic chemical vapor deposition using Zr(O–C3H7)2{(C11H19O2)2} and Ti(O–C3H7)2{(C11H19O2)2} precursors. Postdeposition rapid thermal annealing was performed in N2 ambient to improve the electrical characteristics of the films. The postdeposition annealed samples show excellent electrical characteristics, such as low values of effective oxide charge density, flatband voltage, hysteresis, oxide trap charge density, and interface state density. No metal silicides were found in the films. A minimum leakage current density of the order of ∼10−5A∕cm2 at a bias voltage of −1V has been obtained even after annealing at 800°C.

Effect of substrate temperature on structural and electrical properties of liquid-delivery metal organic chemical vapor deposited indium oxide thin films on silicon

Indium oxide conducting films were deposited on p-type Si (100) substrates at various temperatures by a liquid-delivery metal organic chemical vapor deposition technique using indium (III) tris(2,2,6,6-tetramethyl-3,5-heptanedionato) (dpm)3 precursors. The structural, morphological, and chemical bonding features of these films were studied by x-ray diffraction, scanning electron microscopy, and x-ray photoelectron spectroscopy. The effect of substrate temperature on the electrical and structural properties has been investigated to obtain a high mobility and highly conducting In2O3 film. All deposited films within the temperature range of 200–400°C have a [111] preferred orientation and exhibit an increase of grain size from 21to33nm with increasing deposition temperature. In this range of deposition temperature, there is no metallic indium phase in deposited films. It was observed that the electrical properties of the films are closely related to the microstructure of the films. Hall mobility and electrical resistivity values of the films are comparable to most of the presently investigated transparent conducting oxide films.

MOCVD of Strontium Tantalate Thin Films using Sr[Ta(OEt)5(OC2H4OMe)]2 as Precursor

The strontium tantalate (STaO) films were deposited on silicon substrates by liquid delivery (LD) metalorganic chemical vapor deposition (MOCVD) using Sr[Ta(OEt)5(OC2H4OMe)]2 as a single strontium-tantalum 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 values of process temperature, pressure, and concentration of the precursor. As- deposited STaO films were completely amorphous. Crystallization occurs only after annealing at higher temperatures (~1000{degree sign}C). Additionally, annealing reduced the interface state density and the leakage current but a SiO2 interlayer grew too.

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.

Fabrication of 3-Dimensional PbZr1−x TixO3 Nanoscale Thin Film Capacitors for High Density Ferroelectric Random Access Memory Devices

PbZr(x)Ti(1-x)O3 (PZT) thin films were deposited on 3-dimensional (3D) nano-scale trench structures for use in giga-bit density ferroelectric random access memories. PZT thin films were deposited by liquid delivery metalorganic chemical vapor deposition using Pb(thd)2, Zr(MMP)4, and Ti(MMP)4 precursors dissolved in ethyl cyclohexane. Iridium thin films were deposited by atomic layer deposition, and they exhibited excellent properties for capacitor electrodes even at a thickness of 20 nm. The trench capacitor was composed of three layers, viz. Ir/PZT/lr (20/60/20 nm), and had a diameter of 250 nm and a height of 400 nm. Almost 100% step coverage was obtained at a deposition temperature of 530 degrees C. The PZT thin film capacitors with a thickness of 60 nm on a planar structure exhibited a remnant polarization (Pr) of 28 microC/cm2, but the Pr value of the 3D PZT capacitors decreased slightly with decreasing 3D trench pattern size. The transmission electron microscope analysis indicated that the PZT thin films had compositional uniformity in the 3D trench region. Both columnar and granular grains were formed on the sidewalls of the trench capacitors, and their relative proportion exhibited strong size dependence. The trench capacitors with more columnar PZT grains showed good switching behavior under an external bias of 2.1 V and had a remnant polarization of 19-24 microC/cm2.

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.

Investigation of the Deposition Behavior of a Lead Oxide Thin Film on Ir Substrates by Liquid Delivery Metallorganic Chemical Vapor Deposition

Lead oxide thin films were deposited on Ir/IrO 2 /SiO 2 /Si substrates by liquid delivery metalorganic chemical vapor deposition at 525 °C in order to understand its influence on Pb-based ferroelectric film growth. The Ir substrates were variously pretreated in situ to control the surface oxidation state. Fully oxidized lead oxide films were grown on a nonoxidized Ir or fully oxidized IrO 2 surface. The lead oxide film growth on partially oxidized IrO x (x < 2) was hampered resulting in metallic Pb incorporation which may largely degrade the electrical properties of the film. IrO x oxidizes quickly consuming the supplied oxygen.

Metalorganic chemical vapor deposition of lead-free ferroelectric BiFeO3 films for memory applications

We have grown BiFeO3 thin films on SrRuO3∕SrTiO3 and SrRuO3∕SrTiO3∕Si using liquid delivery metalorganic chemical vapor deposition. Epitaxial BiFeO3 films were successfully prepared through the systematic control of the chemical reaction and deposition process. We found that the film composition and phase equilibrium are sensitive to the Bi:Fe ratio in the precursor. Fe-rich mixtures show the existence of α-Fe2O3, while Bi-rich mixtures show the presence of β-Bi2O3 as a second phase at the surface. In the optimized films, we were able to obtain an epitaxial single perovskite phase thin film. Electrical measurements using both quasistatic hysteresis and pulsed polarization measurements confirm the existence of ferroelectricity with a switched polarization of 110–120μC∕cm2, ΔP(=P*−P̂). Out-of plane piezoelectric (d33) measurements using an atomic force microscope yield a value of 50–60pm∕V.

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.

Epitaxial Pb(Zr,Ti)O3 Capacitors on Si by Liquid Delivery Metalorganic Chemical Vapor Deposition

La0.5Sr0.5CoO3/Pb(Zr x Ti1−x)O3/La0.5Sr0.5CoO3 capacitors have been successfully fabricated by liquid delivery metalorganic chemical vapor deposition on Si wafers using SrTiO3 thin layer (20 nm) as a template. Zr(dmhd)4 in tetrahydrofuran was used as Zr precursor for compatible thermal behavior with Pb(thd)2 and Ti(OiPr)2(thd)2 precursors. The dependence of the ferroelectric film composition on the precursor mixing ratio and growth temperature has been systematically studied by Rutherford Backscattering (RBS). Ferroelectric and piezoelectric properties at the composition close to morphotropic phase boundary region (Pb(Zr0.5Ti0.5)O3) have been investigated for application in nonvolatile ferroelectric random access memories and microelectromechanical system (MEMS). These capacitors show desirable ferroelectric properties, which proves that this approach is very promising for both fundamental study and potential applications. The changes of spontaneous polarization (P s ) and piezoelectric coefficient (d33) with Ti/(Zr + Ti) ratio are also presented and compared with theoretical values.