Properties Of Ta2O5 Thin Films Research Articles

Study on microstructure, optical and tribological properties of self-formed Ta oxide films

Ta2O5 films were deposited on glass and silicon substrates by magnetron sputtering with different power. The microstructure of Ta2O5 films was studied by XRD, SEM, EDS, XPS and AFM. The mechanical and tribological properties of Ta2O5 thin films were studied by ultraviolet–visible spectrophotometer, nanoindentation and friction and wear tester. The sputtering power has a significant effect on the surface morphology of Ta2O5 films. The transmittance of the film decreases with the increase of sputtering power. The optical band gap of the film fluctuates with the change of sputtering power. This is related to the packing density of the sputtered particles and the oxygen vacancies in the film. The wear forms of Ta2O5 films prepared under different sputtering power conditions are mainly fatigue wear and adhesive wear. The optical properties of Ta2O5 films are more sensitive to the change of sputtering power. Ta2O5 films with good optical and tribological properties can be obtained under appropriate process conditions.

Fabrication of tantalum oxyfluoride and oxynitride thin films via ammonolysis of sol–gel processed tetraethoxo (β-diketonato) tantalum (V) precursors for enhanced photocatalytic activity

In the present report, the generation of Tantalum oxyfluoride and oxynitride upon ammonolysis of the gel obtained from modified tantalum-alkoxo complexes is reported. To the best of our knowledge, this is the first report of the formation of tantalum oxyfluoride thin films via ammonolysis of the β-diketone modified tantalum-alkoxo complex [Ta(OEt)4(CF3COCH2COCH3)]m. The integration of nitrogen and fluorine in lattice sites of metal oxides leads to significant reduction in the bandgap, resulting in their activation under visible light. Moreover, in this report the effect of the modified alkoxide precursors and ammonolysis on the photophysical properties of Ta2O5 thin films have also been investigated and compared with the results obtained from films fabricated from unmodified tantalum (V) ethoxide. 1H NMR, 13C NMR and elemental analyses confirmed successful modification of tantalum (V) ethoxide to [Ta(OCH2CH3)4(CH3COCHClCOCH3)]m (1), [Ta(OCH2CH3)4(CF3COCH2COCH3]m (2) and [Ta(OCH2CH3)4 (CH3COC(CH3)2COCH3))]m (3). The fabrication of Ta2O5 thin films involved the spin casting of the gels of modified tantalum alkoxo complexes (processed by sol–gel method) on to glass substrate. X-ray photoelectron spectroscopy results show that nitrogen was incorporated into the ammonolyzed films fabricated from complex precursors (1) and (3), while the presence of fluorine as tantalum oxyfluoride was confirmed in the ammonolyzed film fabricated from complex (2) precursor. The optical characterization insinuate bandgap narrowing from 3.55 eV for undoped film prepared from tantalum (V) ethoxide to 3.47 eV for undoped film prepared from [Ta(OEt)4(CF3COCH2COCH3)]m and 3.05 eV for ammonolyzed film obtained from [Ta(OEt)4(CF3COCH2COCH3)]m precursor. Furthermore, enhanced photocatalytic efficiency of the films is demonstrated by degradation of methylene blue dye.

Influence of ammonolysis, Cu-incorporation and film thickness on structure, optical and photocatalytic properties of Ta2O5 thin films fabricated via sol–gel: a comparative study

Thin films fabricated by spin coating of the gels obtained from tantalum (V) ethoxide precursor were subjected to ammonolysis at 500 °C. Cu-incorporated gels obtained from the same precursor were also spin coated and calcined at 500 °C to give thin films. The optical, structural and photocatalytic properties and their dependence on the thicknesses of these thin films were compared with undoped Ta2O5 thin films fabricated by the same precursor. All the thin films were deposited on glass substrate by spin coating with the thicknesses (d) ranging from 150 to 300 nm. The structure and optical properties of the films were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, spectroscopic ellipsometry, atomic force microscopy, and UV–Vis–NIR spectroscopy. The experimental results insinuated that not only ammonolysis at 500 °C and Cu-doping drastically affect the properties of tanatala films but a variation in their thickness also has significant influence. Small intensity peaks of TaOxNy phase were also detected by X-ray diffraction in the ammonolysed thin films. XPS analysis showed that nitrogen and copper were successfully incorporated in to the Ta2O5 lattice of the respective films. Lower refractive indices and significant narrowing of band gaps (Eg) (i.e. form 3.49 to 3.27 eV for N doped and to 2.92 eV for Cu doped) were observed as compared to the undoped and oxygen-calcined Ta2O5 films. Photocatalytic efficiency of the films was demonstrated by photo-degradation of methylene blue (MB) under UV irradiation. Maximum MB degradation of 86.87% was observed for the Cu-doped Ta2O5 film, while 72.01% of MB concentration was degraded by N-doped Ta2O5 film as compared to only 59.12% MB degradation exhibited by undoped Ta2O5 thin film.

热处理对离子束溅射Ta2O5薄膜特性的影响

热处理对离子束溅射Ta₂O₅薄膜特性的影响

Properties of Ta2O5 thin films prepared by ion-assisted deposition

Tantalum penta-oxide (Ta2O5) thin films were deposited onto highly polished and clean, fused silica glass substrates via ion beam-assisted deposition at room temperature using a high-vacuum coater equipped with an electron beam gun. The effects of ion beam parameters, oxygen flow rate, and deposition rate on the optical and structural properties as well as the stress of Ta2O5 films were studied. It has been revealed that Ta2O5 thin films deposited at 300eV ion beam energy, 60μA/cm2 ion current density, 20sccm oxygen flow rate and 0.6nm/s deposition rate demonstrated excellent optical, structural and compressive stress.

Properties of pulsed reactive DC magnetron sputtered tantalum oxide (Ta2O5) thin films for photocatalysis

Tantalum oxide (Ta2O5) is a wide band gap semiconductor, known for a wide range of applications in many areas. The present investigation reports the effect of pulsing on the physical and photocatalytic properties of Ta2O5 thin films. The samples are prepared at room temperature on quartz and ITO substrates by pulsed reactive direct current (DC) magnetron sputtering. The pulsing frequency is varied between 5kHz and 100kHz. The photocatalytic activity is measured by the Rhodamine B dye. The thicknesses of all films were kept constant of ~500nm. The microstructure obtained by X-ray diffraction is amorphous for all the samples. A lowest surface roughness of 4.62nm for 50kHz pulsing frequency is seen in atomic force microscopy measurements. The calculated relative density, optical band gap and the surface work function varies with the pulsing frequency. The sample prepared at 50kHz pulsing frequency shows high photocatalytic activity: 2.59×1013 number of Rhodamine B molecules were oxidized per an incident photon flux of 1.78×1016photons/s at 254nm. The pulsed-Ta2O5 thin films were compared with continuous DC-Ta2O5 films and showed that pulsing (target power) gives the enhanced film properties, leading to better photocatalytic properties.

原子层沉积制备Ta2O5薄膜的光学特性研究

原子层沉积制备Ta2O5薄膜的光学特性研究

Effect of Underlayer in the Growth of Ta2o5 Films Prepared using MOCVD Method for Metal-Insulator-Metal Capacitors in RF-BiCMOS Technology

AbstractThe properties of Ta2O5 thin films with respect to different underlayer stack have been investigated. At first, a set of samples were produced at various conditions as an underlayer of Ta2O5 film deposition. Then, Ta2O5 films were grown using a MOCVD method with Ta(OC2H5)5 pre-curser at 440 °C. The Process parameters for Ta2O5 films were remained same through the preparation of the sample set. The results were analyzed using various methods including thickness measurement, SEM, stress measurement, X-ray diffraction (XRD), and electrical property measurements. Different grain structures and growth rates were observed with respect to the different underlayer preparation condition mainly as a function of deposition temperature. The deposition rate varied from 0.6 Åsec to 1.8Åsec depend on different underlayer. Crystalline Ta2O5 films with large-grain-size were obtained on Aluminum/TiN underlayer stack. Films with crystalline structure show better leakage current characteristics than the amorphous one.

Change in Radiative Optical Properties of Ta2O5 Thin Films due to High-Temperature Heat Treatment

Thin films (0.85μm, 3μm) of Ta2O5 deposited on Si and SiO2 were heated to 900°C. Their reflectance in the infrared was measured using a Fourier transform infrared spectrometer equipped with a multiple angle reflectometer before and after exposure to the high-temperature heat treatment. An interfacial layer (TaSixOy) formed by the diffusion of Si from the substrate into the deposited film was observed using Auger depth profiling, and the effect of this interfacial layer on the reflectance was measured. Using a least squares optimization technique coupled with an optical admittance algorithm, the multiple angle reflectance data were used to calculate the optical constants of the as deposited Ta2O5 film, crystalline Ta2O5, and the interfacial layer in the 1.6 to 10μm range. The interfacial layer formed due to exposure to high temperature was found to be more absorptive than the crystalline Ta2O5.

Improvement of interfacial and dielectric properties of sputtered Ta2O5 thin films by substrate biasing and the underlying mechanism

The use of tantalum pentoxide (Ta2O5) thin films as advanced gate dielectrics in integrated circuits has been hampered by thermodynamic instability at the Ta2O5/Si interface. We have demonstrated the fabrication of crystalline Ta2O5 thin films on n-type Si (100) at lower substrate temperature by means of substrate biasing. In the work reported here, the influence of the substrate bias on the interfacial and dielectric characteristics of the Ta2O5 thin films is investigated in details. Our results show that by applying a suitable bias to the Si substrate, the dielectric properties of Ta2O5 thin films can be improved. Using a substrate bias of −200 V, the thin film has a permittivity of 34 and leakage current density of 10−7A∕cm2 at an electric field of 800 kV/cm. The effects and mechanism of the bias on the interfacial and dielectric characteristics are described.

Effects of postannealing on the electrical properties of Ta2O5 thin films deposited on TiN/T

The effects of postannealing on the structural and leakage current characteristics of Ta2O5 thin films deposited on a TiN/Ti bottom electrode by chemical-vapor deposition at 350 °C were investigated. The Ta2O5 film of 50 nm thickness shows an amorphous phase and smooth surface morphology after annealing in N2O plasma at 350 °C, but the film treated with rapid thermal annealing in nitrogen (RTN) at 750 °C prior to N2O plasma annealing at 350 °C has an orthorhombic structure and rugged surface morphology. In addition, the TiSi phase also appears in the specimen of RTN-treated Ta2O5 film. Moreover, the residual carbon can be effectively eliminated and the oxygen deficiency can be well compensated by the N2O plasma annealing for both amorphous and crystalline Ta2O5 films. The I–V relation of the amorphous Ta2O5 films is asymmetric with respect to the biasing polarity, which indicates that the leakage current is primarily dominated by the Schottky emission. On the other hand, the crystalline Ta2O5 film has a symmetrical I–V relation, suggesting that the non-Ohmic leakage in the crystalline Ta2O5 film is related to the Poole–Frenkel effect. The barrier heights φB for the non-Ohmic leakage in the amorphous and crystalline Ta2O5 films, as evaluated from the temperature dependence of the I–V relation, are 0.52 and 0.82 eV, respectively.

Comparison of Ta2O5 Thin Films Deposited by “Off-axis” and “On-axis” Pulsed Laser Deposition Technique

The crystalline properties of Ta2O5 thin films deposited by an off-axis aperture-installation-type pulsed laser deposition (PLD) technique are investigated and the results are compared to those of films deposited by the conventional on-axis technique. When the repetition frequency is lowered, the X-ray diffraction intensity of (001) peak increases in both films. This tendency, however, is more pronounced in the off-axis films. The dielectric constant of off-axis films fabricated at 20 Hz indicates a high value of about 40, and is higher than the measured value of bulk Ta2O5. Therefore, it is concluded that the off-axis aperture-installation-type pulsed laser deposition technique is effective not only for decreasing the density of droplets, but also for obtaining high-quality crystalline films.

Properties of Amorphous and Crystalline Ta2O5 Thin Films Prepared by Metalorganic Solution Deposition Technique for Integrated Electronic Devices

AbstractWe report on the properties of Ta2O5 thin films prepared by the metalorganic solution deposition (MOSD) technique on Pt-coated Si, n+-Si, and poly-Si substrates. The effects of postdeposition annealing temperature on the structural, electrical, and optical properties were analyzed. The electrical measurements were conducted on MIM and MIS capacitors. The dielectric constant of amorphous Ta2O5 thin films was in the range 29.2-29.5 up to 600°C, while crystalline thin films, annealed in the temperature range 650–750°C, exhibited enhanced dielectric constant in the range 45.6–51.7. The dielectric loss factor did not show any appreciable dependence on the annealing temperature and was in the range 0.006–0.009. The films exhibited high resistivities of the order of 1012–1015 Δ-cm at an applied electric field of 1 MV/cm in the annealing temperature range of 500-750 °C. The temperature coefficient of capacitance was in the range 52-114 ppm/°C for films annealed in the temperature range 500-750°C. The bias stability of capacitance, measured at an applied electric field of 1 MV/cm, was better than 1.41 % for Ta2O5 films annealed up to 750°C.

Ta 2 O 5 thin-films deposited by off-axis and on-axis pulsed laser deposition techniques

The crystalline properties of Ta2O5 thin films deposited by an off-axis aperture-installation-type pulsed laser deposition technique are investigated and the results are compared with the results for films deposited by the conventional on-axis technique. No significant difference in the substrate temperature dependence is seen between films deposited on-axis or off-axis at a pulse repetition frequency of 30 Hz. When the repetition frequency is lowered, the degree of c-axis orientation is increased in both films. This tendency is more pronounced in the off-axis films. Therefore it is found that the off-axis aperture-installation-type pulsed laser deposition technique is effective not only for decreasing the density of droplets, but also for obtaining more highly c-axis-oriented crystalline films.

The effect of Al–Ta2O5 topographic interface roughness on the leakage current of Ta2O5 thin films

Amorphous Ta2O5 thin films were formed by radio-frequency magnetron sputtering at the substrate temperature of 200 °C. The electrical properties of Ta2O5 thin films were investigated as a function of the film thickness. The dominant conduction mechanism transited from the electrode-limited conduction (Schottky emission current) at low field to the bulk-limited conduction (Poole–Frenkel current) at high field. With increasing thickness of the thin films, the surface roughness increased, whereas the transition fields from the electrode-limited to the bulk-limited conduction process decreased. To verify the effect of this surface roughness on the electric conduction mechanism, a two-dimensional numerical simulator, MEDICI, was used to simulate the electric-field distribution at the bulk region of the thin film and the interface region between the thin film and the electrode.

Electrical properties of Ta2O5 thin films deposited on Ta

The electrical properties of reactively sputtered Ta2O5 thin films with Ta as the bottom electrodes were investigated. Ta films were deposited onto SiO2/n-Si substrates by sputtering in Ar and in situ annealed at 700 °C for 10 min in N2 at a chamber pressure of 20 mTorr. We compared the effectiveness of both as-deposited and annealed Ta bottom electrodes on the leakage characteristics of Ta2O5 thin films. We also envisaged the influence of the surface roughness and morphology of the Ta bottom electrode in modifying the resultant microstructure of the annealed Ta2O5 films. Present studies demonstrate the use of Ta as a potential bottom electrode material to replace the precious metal electrodes and to simplify the fabrication process of the Ta2O5 storage capacitor.

Monolayer‐Mediated Deposition of Tantalum(V) Oxide Thin Film Structures from Solution Precursors

Integration of oxide thin films with semiconductor substrates is a critical technology for a variety of microelectronic memory and circuit applications. Patterned oxide thin film devices are typically formed by uniform deposition followed by postdeposition ion‐beam or chemical etching in a controlled environment. This paper reports details of an ambient atmosphere technique which allows selective deposition of dielectric oxide thin layers without postdeposition etching. In this method, substrate surfaces are selectively functionalized with hydrophobic self‐assembled monolayers of octadecyltrichlorosilane by microcontact printing (μ‐CP). Sol‐gel deposition of ceramic oxides on these functionalized substrates, followed by mild, nonabrasive polishing, yields high‐quality, patterned oxide thin layers only on the unfunctionalized regions. A variety of micrometer‐scale dielectric oxide devices have been fabricated by this process, with lateral resolutions as fine as 4 μm. In this paper, we describe the solution chemistry, evolution of microstructure, and electrical properties of Ta2O5 thin films, as well as the stress‐related mechanism which enables selective de‐adhesion and resultant patterning. Selectively deposited, 80‐120 nm thick Ta2O5 thin film capacitors were crystallized on platinized silicon at 700‐800°C, and had dielectric constants of 18‐25 depending upon the processing conditions, with 1 V leakage current densities as low as 2 × 10−8 A/cm2. The ability to selectively deposit Ta2O5 and other electrical ceramics (such as LiNbO3 and PbTiO3) on a variety of technologically important substrate materials suggests broad potential for integrated circuit and hybrid microelectronics applications.

Leakage currents in amorphous Ta2O5 thin films

Tantalum oxide (Ta2O5) is an important material for future dynamic random access memory application owing to its high dielectric constant. This work examines the structural and electrical properties of Ta2O5 thin films deposited by plasma-enhanced chemical vapor deposition using a penta ethoxy tantalum Ta(OC2H5)5 liquid source. The x-ray diffraction patterns indicate that the as-deposited thin films are amorphous and become polycrystalline after rapid thermal annealing above 650 °C. The level of carbon contamination is below that which can be detected by Auger electron spectroscopy measurement. Electrical measurements performed on amorphous Ta2O5 using a Au/Ta2O5/Pt/Ti/Si metal-tantalum oxide-metal structure exhibit a low leakage current, reasonable breakdown field (5.4 MV/cm), and high dielectric constant (23–25). The leakage current is 2×10−8 A/cm2 at 1 MV/cm. In addition, the leakage current mechanism of amorphous Ta2O5 capacitors is investigated by plotting the ln(J) vs E1/2 curves at a low electric field (<2 MV/cm) and plotting ln(J/E) vs E1/2 curves at a high electric field (>2 MV/cm). The dominant conduction mechanism is due to Schottky emission at low electrical field and Poole–Frenkel emission at high electrical field. According to our results, the Ta2O5 thin films annealed in N2 or O2 at 800 °C exhibit a much higher leakage current than amorphous Ta2O5 , possibly due to the out-diffusion of Ti during high temperature annealing.

The effects of substrate and annealing ambient on the electrical properties of Ta2O5 thin films prepared by plasma enhanced chemical vapor deposition

Ta2O5 thin films were deposited onto p-Si, n +-Si, RTN (rapid thermal nitridation) nitride and HSG (hemispherical grain) Si substrates by plasma enhanced chemical vapor depostion (PECVD). The physical and electrical properties were characterized after annealing in the temperature range 600–900°C in N2 or O2 ambient. Fourier transform IR analysis revealed that an interfacial oxide which affected the electrical properties of Ta2O5 thin film was formed at the Ta2O5-Si interface during annealing above 800°C. The electrical properties of the Ta2O5 thin film were strongly dependent on annealing conditions. The Ta2O5 thin films showed 1.5 times higher capacitance, but higher leakage current owing to the edge effect, on the enlarged surface area of HSG Si than on the flat p-Si or n+ -poly Si. RTN treatment of Ta2O5 thin films on the Si substrate reduced the leakage current without loss of the high dielectric constant.