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• Bent beam structures are used to find Ta thermal coefficient of expansion. • Oxygen interstitial diffusion in Ta is studied using bent beam structures. • An activation energy of E a = 0.53 eV/atom is found in air. • The effect of oxygen diffusion on stress is modeled. • Oxidation is suppressed up to 400 °C in high vacuum. Sensors and actuators constructed from freestanding tantalum thin films show promise for micromachining applications and for the study of thin film mechanical behavior. To assess this promise, it is necessary to gain further understanding of the performance of Ta as a structural material. We first evaluate the coefficient of thermal expansion, α T a , using micromachined bent beams, which amplify displacement compared to linear expansion. The value for α T a is 6.8 × 10−6 m/m °C, in good agreement with the bulk value. This validation enables the study of interstitial oxygen diffusion in Ta, for which literature values of activation energy vary widely, from 0.60 to 1.98 eV. Displacement in air due to oxygen diffusion becomes measurable after 30 min exposure at 180 °C. We extract an activation energy for interstitial oxygen in Ta of 0.53 eV/atom. Analysis indicates that lattice rather than grain boundary diffusion is the associated mechanism. To inhibit the oxidation, we construct a thermal stage that controls specimen temperature in 10−5 Pa vacuum. Then, after a 24 h hold, oxidation is suppressed up to 400 °C. This result is discussed in terms of O dissolution from its native oxide, coupled with further absorption from background gases. [ABSTRACT FROM AUTHOR]

Biosensor development has relied on the process of anodization of sputtered aluminum‑tantalum thin films to develop specific optical properties for interference color generation. The anodization of thin sputtered films of aluminum (140 nm) on tantalum (230 nm) on silicon was completed in 0.4 M phosphoric acid under potentiostatic conditions (4 V) and with various additives: 0.1 M and 0.4 M citric acid, 3% (v /v) and 10% (v/v) of a commercial anodizing solution consisting of glycerol and glycolic acid, and 0.1 M and 0.4 M oxalic acid. The microstructural and optical properties of these films were analyzed using scanning electron microscopy, X-ray diffraction, and ellipsometry. The interference colors produced by the anodic aluminum and tantalum oxides on top of the tantalum metal layer were also observed. The addition of 0.1 M citric acid, 3% (v /v) glycerol and glycolic acid-based solution, and 0.1 or 0.4 M oxalic acid all produced changes to the porous microstructure of the anodic alumina, including lower roughness and more homogeneous surfaces by inhibition of the dissolution from phosphoric acid. Oxalic acid acted as the strongest inhibitor and significantly reduced surface roughness and pore size, increased the composite refractive index of the anodized film, and significantly changed the interference colors compared to films where no additive was used. • Porous anodization of Al Ta thin films is important in the field of biosensors. • Tailored thin film optical properties allow development of Al 2 O 3 -Ta 2 O 5 diagnostics. • Additives to a H 3 PO 4 anodization bath improve microstructure and optical properties. [ABSTRACT FROM AUTHOR]

Ta 3 N 5 belongs to the group of transition metal nitrides with the cation in a high oxidation state. These are typically challenging to synthesize owing to the low reactivity of nitrogen. This applies similarly to Ta 3 N 5 that crystallizes only in the presence of oxygen during synthesis. Typical preparation methods are ammonolysis of oxidized Ta or magnetron sputtering of a Ta target in an atmosphere of Ar, N 2 and O 2. However, the material typically obtained by either synthesis method is of varying degrees of crystallinity and the key parameter affecting the crystallinity remains elusive. In this study, we examine the role of oxygen for the crystallinity of Ta 3 N 5 samples by studying. Thin film samples prepared by magnetron sputtering reveal that oxygen is indeed the central driver for Ta 3 N 5 crystallinity. While little oxygen in the films yields the metallic δ-TaN phase, excess oxygen results in low crystallinity Ta 3 N 5 or Ta-O-N films. Ta 3 N 5 samples with a high degree of crystallinity are obtained by limiting the oxygen supply to the sample during the deposition. A comparison with other studies suggests a fundamental oxygen incorporation limit above which the crystallinity of Ta 3 N 5 is compromised. The most crystalline sample from this study contains 4.4 at.% of oxygen. It is grown onto a Si(100) substrate, covered with a 30 nm-thick metallic diffusion layer. For this sample, we observe Ta 3 N 5 grains between 80 and 120 nm in size. • The degree of crystallinity of Ta 3 N 5 thin films is determined by its oxygen content. • A fundamental limit of oxygen incorporation in Ta 3 N 5 crystalline films is suggested. • Ta interlayer between Si substrate and Ta 3 N 5 promotes crystallization. • Large Ta 3 N 5 grain sizes between 80 and 120 nm are obtained. [ABSTRACT FROM AUTHOR]

In this study, tantalum (Ta) thin films deposited (by magnetron sputtering) on CoCrMo alloy substrates were studied using X-Ray Diffraction, Scanning Electron Microscopy and Rockwell C indentation tests. The results show that α-Ta single phase thin films, the desired phase for orthopedic implant applications, with low adhesion forms at substrate temperature of 400 °C or above while a mixture of α-Ta and β-Ta forms at substrate temperature lower than 400 °C. A negative bias of 78 V applied to substrate results in development of adherent β-Ta thin film at room temperature. Based on the results, a multilayered gradient Ta thin film, β-Ta/β-Ta + α-Ta/α-Ta, with controlled structure has been developed on biomedical CoCrMo alloy sheets. The film shows high adhesion, which is promising for biomedical applications. [ABSTRACT FROM AUTHOR]

• Bipolar HiPIMS technique was used to form highly adhesive and ductile alpha-Ta films. • Alpha-Ta film was formed without substrate biasing or heating. • High adhesion strength (>45 MPa), broadened intermixed layer, dense films were achieved. In this study, a method for forming a highly adhesive and ductile α-phase tantalum film on 304 stainless steel using the bipolar high-power impulse magnetron sputtering (bipolar HiPIMS) technique was investigated. The growth of brittle β-phase tantalum, which is commonly formed when using conventional direct current magnetron sputtering methods (DCMS) at room temperature, was prevented by the high-energy ions directed toward the growing films. The results showed the formation of an extremely thin (<70 nm) α-phase tantalum film without any additional processes, such as substrate biasing or heating. In addition, a high adhesion strength exceeding 45 MPa, broadened intermixed layer, and nanocrystalline microstructure were achieved by the effect of positive voltage. These results indicate that the bipolar HiPIMS technique is a facile deposition method for modifying the substrate surface and forming high-quality crystalline films. Our tantalum films are optimized to protect substrates against corrosion in severely harsh mechanical, chemical, and thermal environments. To confirm the superiority of the bipolar HiPIMS technique over HiPIMS and DCMS, the properties of the films formed using the three methods were analyzed via X-ray diffraction, Auger electron spectroscopy, atomic force microscopy, scanning electron microscopy, and pull-off adhesion testing. [ABSTRACT FROM AUTHOR]

The device performance of amorphous In–Zn–O ( a -IZO) thin-film transistors (TFTs) with printed Cu contacts was significantly improved by the insertion of a diffusion barrier Ta layer and rapid thermal process (RTP) annealing. Furnace-annealed a -IZO TFTs with Cu/Ta contacts exhibited mobility values of 21.3 cm 2 /Vs, subthreshold gate swing ( SS ) values of 1.9 V/decade, and I ON / OFF of ~ 10 6 . In contrast, the SS , mobility, and I ON / OFF ratio of RTP-annealed a -IZO TFTs with Cu/Ta contacts were 30.6 cm 2 /Vs, 0.68 V/decade, and 3 × 10 7 , respectively. We attributed the performance improvement of devices with Cu/Ta contacts to the suppression of Cu in-diffusion within the a -IZO channel due to the rapid heating associated with RTP annealing. [ABSTRACT FROM AUTHOR]

In this work a systematic in situ annealing study of sputtered Cu–Ta alloys is reported. Under equilibrium conditions Cu and Ta are completely immiscible, the metastable Cu–Ta alloys hence undergo phase separation upon annealing. Using in situ X-ray diffraction the phase evolution at temperatures < 650 °C is studied over the entire composition range and the data is assembled in a phase map. It is shown that the presence of a surface oxide layer influences the β to α phase transformation temperature of Ta and thus determines the crystal structure of the Ta-rich phase formed upon phase separation. Surface segregation of Cu necessitates the use of an alumina capping layer on the Cu–Ta/SiN x /SiO 2 /Si samples. [ABSTRACT FROM AUTHOR]

• Thick, high-resistivity Au-80 at.% Ta films were sputtered onto rotating cylinders • Film properties varied with sputter configuration, gas pressure, and substrate bias • Incident atom angle distributions were insensitive to deposition conditions • Calculated incident atom energies were strongly linked to gas phase collisions Sputter deposition of gold-tantalum alloy coatings is a key process for manufacturing hohlraums for magnetically-assisted inertial confinement fusion implosions. Here, we describe direct current magnetron sputter deposition of ∼ 10 − μ ∼ 10 − μ m-thick films of Au-80 at.% Ta onto rotating sphero-cylindrical hohlraum and planar Si witness substrates. Emphasis is given to how film microstructure and properties are affected by main deposition parameters, including argon working gas pressure, substrate bias, and the source composition (a single alloyed target compared to co-sputtering from two elemental targets). Experimental findings are correlated with distributions of landing energies and incident angles of depositing species calculated by Monte Carlo simulations of ballistic collisions and gas phase atomic transport. Deposition conditions characterized by low energetics of depositing species favor the formation of a β -Ta-like phase. Implications of these results to hohlraum fabrication are discussed. [ABSTRACT FROM AUTHOR]

In present work, undoped and Ta-doped SnO 2 thin films were fabricated via a simple and cheap spray pyrolysis technique. The Ta-doping level was varied from 0 at.% to 5 at.% in the step of 1 at.%. Large pyramidal and small densely-packed tetragonal SnO 2 particles were observed by X-ray diffraction and scanning electron microscope. Atomic force microscope analysis indicated that root mean square roughness values of films changed from 26.7 nm to 51.6 nm with Ta-doping. The electrical and optical measurements revealed that the films had a degenerate n-type semiconductor property. The resistivity, sheet resistance, carrier concentration, mobility, and optical band gap values of films varied between 1.11 × 10 − 2 Ω cm–2.35 × 10 − 3 Ω cm, 130.66 Ω/□–26.97 Ω/□, 2.72 × 10 19 cm − 3 –1.12 × 10 20 cm − 3 , 20.68 cm 2 V − 1 s − 1 –30.78 cm 2 V − 1 s − 1 , and 3.43 eV–3.94 eV, respectively. As a result of this study, it is concluded that characteristic properties of SnO 2 can be greatly improved with Ta-doping. [ABSTRACT FROM AUTHOR]

We describe Ta underlayer thickness influence on thermal stability of perpendicular magnetic anisotropy in Ta/CoFeB/MgO/W stacks. It is believed that thermal stability based on Ta underlay is associated with thermally-activated Ta atom diffusion during annealing. The difference in Ta thickness-dependent diffusion behaviors was confirmed with X-ray photoelectron spectroscopy analysis. Along with a feasible Ta thickness model, our observations suggest that an appropriate seed layer choice is needed for high temperature annealing stability, a critical issue in the memory industry. [ABSTRACT FROM AUTHOR]

A dual hot-wire arrangement has been designed and investigated for the deposition of various thin film materials by the hot-wire chemical vapor deposition (HWCVD) technique. Tantalum and rhenium wires were used for silicon and silicon carbide depositions with hydrogen diluted silane and monomethylsilane, respectively. It is shown that the both types of filaments are mechanically stable after alternate depositions of silicon and silicon carbide with a total deposition time of about 80 h. Good material quality of the deposited films is demonstrated. By taking advantage of this dual hot-wire arrangement, it is possible to deposit both kinds of thin film materials with the individual optimum deposition conditions in a single HWCVD chamber. [ABSTRACT FROM AUTHOR]

• Ta, Nb, Ba, Sb-doped SnO 2 thin films were prepared by metal organic decomposition. • Structural deterioration occurred with increasing dopants concentrations. • Resistivity for Ta-, Nb- and Sb-doped SnO 2 samples decreased to ∼10−3 Ωcm. • No decrease in resistivity was observed for Ba-doped SnO 2 samples. • Increase of band gap relates to Burstein-Moss effect and structural deterioration. Ta-, Nb-, Ba-, and Sb-doped SnO 2 thin films were prepared by the metal organic decomposition (MOD) method using spin coating. The effects of dopant concentration on the structural, electrical, and optical properties were investigated. The growth of polycrystalline films with the tetragonal rutile structure was confirmed by X-ray diffraction and atomic force microscopy measurements. The resistivity of Ta-, Nb- and Sb-doped SnO 2 samples decreased to ∼10−3 Ωcm for dopant concentrations of around 1.5–3.0 at.%. The lowest resistivities were obtained for Ta- and Sb-doped SnO 2 samples. On the other hand, no decrease in resistivity was observed for Ba-doped SnO 2 samples. The band gap energy of Ta-, Nb-, Ba-, and Sb-doped SnO 2 samples appeared to be larger than for those prepared by other methods. It was suggested that the structural deterioration may be related to the increase in the band gap energy for MOD prepared samples in addition to the Burstein-Moss effect. [ABSTRACT FROM AUTHOR]

Abstract: We describe a combinatorial experiment investigating the Ta–Al–C material system, conducted with the aim of determining why the tantalum-containing M n +1AX n phases have so far proved to be not amenable to thin-film synthesis. Samples were deposited onto (0001) Al2O3 wafers at 850°C and characterized by X-ray diffraction wafer maps, scanning electron microscopy, and surface optical scattering. Elemental Ta, the binary phases TaC, Ta2C, and TaAl3, and the ternary phases Ta3Al2C and Ta5Al3C were identified. The morphology, phase composition and preferred orientation of the films deposited were found to be highly sensitive to the Ta fraction of the incident flux during deposition. No MAX phase material was observed, indicating that the Ta-containing MAX phases do not form under the deposition conditions investigated. Explanations associated with inadequate coverage of stochiometries, preferential sputtering, and thermodynamic instability have been ruled out. An explanation based on reduced surface diffusion of Ta during growth is proposed. A substantially higher substrate temperature during deposition is likely to be required to synthesize Ta-containing MAX phases. [Copyright &y& Elsevier]

In this study, tin oxide (SnO2) thin films doped with 1 cation percent tantalum were deposited on amorphous fused silica substrates by RF-magnetron sputter deposition. Electrical and optical properties were subsequently measured and analyzed as a function of deposition temperature (300 to 700°C) and oxygen ratio in the process gas (0 to 50%). In situ photoelectron spectroscopy was used to determine tantalum incorporation, sample stoichiometry, valence band electronic structure and Fermi level position. Samples were analyzed with respect to their optical and electrical characteristics by spectral transmittance and Hall measurement. Electrical resistivity reached values as low as 1.7×10−3 Ωcm with a charge carrier density of 3.3×1020 cm−3 and a mobility of 12cm2 V−1 s−1. Electrical transport properties were related to structural properties as determined by atomic force microscopy, scanning electron microscopy and X-ray diffraction. It was found that electrical properties are a strong function of substrate temperature, mainly due to a reduced charge carrier density for deposition temperatures below 700°C. This is thought to be caused by an intrinsic compensation mechanism which has not yet been identified. [ABSTRACT FROM AUTHOR]

Abstract: Tantalum (Ta) and tantalum nitride thin films are highly important as diffusion barriers and adhesion layers in microelectronics and hard coatings for cutting tools. In this study, the effect of the underlying substrate on the phase formation of Ta and the influence of a changing N2/Ar flow ratio on hardness, phase and composition of reactively formed tantalum nitride have been investigated. Ta is DC sputter deposited and forms β-Ta on amorphous diamond-like carbon and on the amorphous natural oxide layers of Ti and Si(100) while a 15nm TaN seed layer results in the formation of α-Ta. The chemical composition of the topmost layers of a substrate influences the formation of α- and β-Ta. With increasing N2/Ar flow ratios a transition from amorphous Ta-rich tantalum nitride over face-centered cubic tantalum nitride (fcc-TaN) to (100) textured fcc-TaN at flow ratios above 45% is observed. The hardness of the tantalum nitride thin film reaches a maximum at a flow ratio of 45%, followed by a decrease in hardness for higher N2/Ar flow ratios. The increase in hardness is associated with a decrease in grain size and shows a stronger correlation for a Meyers and Ashworth relationship than for a Hall–Petch relationship. [Copyright &y& Elsevier]

• Multilayer coatings (Ta/ZrN) n deposited using reactive magnetron sputtering. • The microstructure, hardness, roughness, and residual stress are investigated. • The tribocorrosion behavior has a close relationship with the design of the coating. Multilayer thin coatings (∼3 µm in thickness) were deposited using reactive radio frequency magnetron sputtering on Ti-6Al-4 V substrate for biomaterial applications. Films are a combination of hard zirconium nitride with pure tantalum, used to manage interfacial stress and to avoid crack growth. Alternating hard/ductile material is a biomimetic design inspired by nature (nacre-inspired materials). Tribocorrosion tests were performed in Hank's solution at 37 °°C, under open circuit potential by using a ball-on-disk reciprocating tribometer. A tendency to high resistance against corrosion was found for all the samples. Coatings with a top 100 nm thick ZrN layer showed more noble potential as well as a reduction of both the friction coefficient and the wear rate during the sliding phase. The principal wear mechanism is related to a tribocorrosion layer formation. [ABSTRACT FROM AUTHOR]

• Shadow effect and interfacial alloy impacting ultrathin film magnetic properties. • Unexpected exchange bias of Ta/NiFe/IrMn/Ta heterostructures. • Investigation of ultrathin dimension system allows sublayer resolution. Ultrathin Si(100)/Ta/Ni 80 Fe 20 /Ir 20 Mn 80 /Ta heterostructure deposited by oblique incidence in a confocal magnetron sputtering exhibits an unexpected exchange bias effect, despite the rotation of the sample holder and absence of external magnetic field during the deposition. Its magnetic loops have anomalous shifts along the field axis, whose features are non-uniform and strongly dependent on the orientation of the applied magnetic field. Structural, magnetic and thermal properties of the heterostructure were investigated using x-ray scattering and magnetic measurements to highlight the role of interfaces between ultrathin films and the related magnetic effects on the setting of the exchange bias. We show that the shadowing effect due to the oblique incidence of the sputtering flux combined to the atomic diffusion at the Ta/Ni 80 Fe 20 interface favors the emergence of a uniaxial anisotropy in the ferromagnetic layer formed by a Ni 80 Fe 20 sublayer at the top and a NiFeTa alloy at the bottom. The later increases the uniaxial anisotropy constant of the ferromagnet, which was strong enough to impose a well-defined direction for the spontaneous magnetization and, consequently, set the unidirectional anisotropy during the Ir 20 Mn 80 layer formation. The thermal processes can reversibly be applied up to 460 K and, for higher temperatures, there were the vanishing of the exchange bias at 600 K and a thickening of the NiFeTa alloy which led to a reduction in the saturation magnetization of the heterostructure. Therefore, our findings suggest that the role of the interfacial NiFeTa alloy is only revealed in the ultrathin dimension and is imperceptible in thicker samples. [ABSTRACT FROM AUTHOR]

In this work, the effect of substrate temperature (room temperature — 250°C) on the structural, morphological and electrical properties of tantalum films deposited on Si/SiO2 (100) substrate by electron beam evaporation technique was presented. The structural analysis of the deposited films was done using X-ray diffraction (XRD). The XRD patterns revealed the growth of tetragonal crystalline structure (β-Ta) and that the crystallinity of the films increased with the increase of substrate temperature. The field emission scanning electron microscopy (FESEM) images showed that the film morphology was smooth with fine spherical particles on the surface. The film thickness measured using a cross-sectional FESEM was found to increase from 97nm to 165nm with the increase in substrate temperature. The resistivity of tantalum films was found to decrease from ~350μΩ-cm to ~220μΩ-cm with increasing substrate temperature from room temperature — 250°C respectively. [ABSTRACT FROM AUTHOR]

Abstract: This study reports the utility of tantalum (Ta) coating for improving the surface hardness, in vitro bioactivity and biocompatibility of Co–Cr implants. The use of direct current sputtering allowed for the deposition of a dense and uniform Ta film onto a Co–Cr substrate, which was composed of β-phase Ta grains. This hard Ta coating significantly improved the surface hardness of the Co–Cr by a factor of >2.3. In addition, the Ta-deposited Co–Cr substrate showed a vigorous precipitation of apatite crystals on its surface after 4weeks of immersion in simulated body fluid, suggesting its excellent in vitro bioactivity. This bioactive Ta coating led to a considerable improvement in the in vitro biocompatibility of the Co–Cr, which was assessed in terms of the attachment, proliferation and differentiation of pre-osteoblasts (MC3T3-E1). [Copyright &y& Elsevier]

Abstract: To elucidate in details any possible influence of the adjacent layers on perpendicular magnetic anisotropy in very thin ferromagnetic CoFeB electrodes of CoFeB/MgO based stacks, we grew by sputtering BL/CoFeB (1nm) and BL/CoFeB (1nm)/MgO (2nm), being BL (buffer layer)=Ta (5nm) or Ru (1nm) multilayers, consisting of 30 repetitions of the bi- or tri-layers. Specular X-ray reflectivity (XRR) has been performed on both as grown and annealed (300°C in vacuum) multilayers. From XRR results, good reproducibility of each layer thickness is achieved, indicating a well-controlled film growth. Further, CoFeB/MgO interface is found to be quite smooth and stable with annealing, as shown by the limited interface width, while BL/CoFeB interface widens upon annealing, in particular when BL=Ta is used. We discuss the above findings, also considering the role of possible layer crystallinity in affecting the interface width, and tentatively relate them to the magnetic anisotropic behavior of the stacks. [Copyright &y& Elsevier]

Abstract: Ta(5nm)/CoFeB(1nm)/MgO(2nm) stacks have been deposited by magnetron sputtering on top of 8" Si/SiN/SiO2 substrates, where the effects of different passivation steps related to copper damascene processes have been simulated. It is shown that excellent thickness uniformity of the deposited stack is achieved on 8" areas, and strong uniaxial perpendicular magnetic anisotropy Ku up to 0.5–1×106 J/m3 develops in the 1nm CoFeB following thermal annealing at 300°C for 2h, irrespective of the adopted passivation treatment. The CoFeB coercive field varies from 0.21 to 0.51kA/m for substrate surface roughness in the range of 0.45–0.55nm. These results are of relevance in the view of integrating into standard complementary metal-oxide semiconductor process, advanced magnetic memory concepts based on perpendicular magnetic anisotropy in ultrathin layers. [Copyright &y& Elsevier]

Abstract: This study proposes that the corrosion resistance of copper film correlates well with underlying barrier''s orientation. To test the hypothesis, we performed X-ray diffraction, conducted copper removal rate experiments after chemical mechanical polishing, and tested static potentiodynamic polarization. The results all show that copper deposited on strongly (002) oriented β-Ta barrier layer demonstrated better chemical resistance against surface reaction with the slurry for strong copper (111) orientation. The findings were consistent with the result of the chronoamperometric test at 0.3V in which the more passive film formed on the composite film with (002) β-Ta underlying barrier. [Copyright &y& Elsevier]

Abstract: During the formation of the top electrode (T.E.) in spin-transfer torque magnetic random access memory, a slurry with a high polishing rate of SiO2 and a low polishing rate of metal (T.E. material) is required in the chemical mechanical planarization application area. We used a ceria-based slurry with a polymeric additive to maintain the high polishing rate of SiO2 while it suppresses the polishing rate of the T.E. material, tantalum and ruthenium. We found ruthenium showed a significantly higher selectivity than tantalum in the ceria-based slurry. X-ray photoelectron spectroscopy was used to investigate the adsorption characteristics of the polymeric additive on the T.E. material. Except for the adsorbed polymeric additive, we found that zeta potential of the T.E. material played a critical role in determining the polishing selectivity of SiO2-to-T.E. material. [Copyright &y& Elsevier]

Abstract: A multilayer thin film structure of ten alternate Ta and Si layers with approximately 18nm thickness for the combined (Ta+Si) layer, was evaluated to explore the individual layer thickness and the interface mixing behavior using different surface characterization techniques like Time-of-Flight Secondary Ion Mass Spectrometry (TOFSIMS), X-ray Reflectometry (XRR) and Kelvin Probe Force Microscopy (KPFM). These results were compared with measurements performed earlier using cross section Transmission Electron Microscopy (TEM). The TOFSIMS depth profile results indicate the individual thickness of Si and Ta layers to be 8.1nm and 5.9nm respectively which are less than the corresponding actual thickness measured by cross section TEM as 10.5nm and 7.5nm. The difference in thickness measurement has been explained in the light of ion bombardment induced atomic mixing in the interface during sputter depth profiling. A scanning electron micrograph shows the actual crater and its edges created due to the sputtering including the multilayer for real view of the structure. The XRR observations however reveal better agreement with the cross section TEM data, both being non-destructive in nature. Attempts were made to characterize the multilayer using KPFM technique which clearly elucidated the grating type cross section of the structure. [Copyright &y& Elsevier]

Abstract: Catalytic chemical vapor deposition (Cat-CVD) has been demonstrated as a promising way to prepare device-quality silicon films. However, catalyst ageing due to Si contamination is an urgency to be solved for the practical application of the technique. In this study, the effect of carbonization of tantalum catalyst on its structure and performance was investigated. The carbonized Ta catalyst has a TaC surface layer which is preserved over the temperature range between 1450 and 1750°C and no Si contamination occurs on the catalyst after long-term use. Si film prepared using the carbonized Ta catalyst has a similar crystal structure to that prepared by uncarbonized Ta catalyst. Formation of the TaC surface layer can alleviate the ageing problem of the catalyst, which shows great potential as a stable catalyst for Cat-CVD of Si films. [Copyright &y& Elsevier]

Abstract: Ta-doped SnO2 films were deposited on glass substrate (either unheated or heated at 200°C) by reactive magnetron sputtering with a Sn–Ta metal-sintered target using a plasma control unit (PCU) and mid-frequency (mf, 50kHz) unipolar pulsing. The PCU feedback system precisely controlled the flow of the reactive and sputtering gases (O2 and Ar, respectively) by monitoring either discharge impedance or the plasma emission of the atomic O* line at 777nm. The planar target was connected to the switching unit, which was operated in unipolar pulse mode. Power density on the target was maintained at 4.4Wcm−2 during deposition. The lowest obtained resistivity for the films deposited on heated substrate was 6.4×10−3 Ωcm, where the deposition rate was 250nmmin−1. [Copyright &y& Elsevier]

Abstract: Chemical mechanical planarization (CMP) of tantalum nitride is an essential step of material processing in the fabrication of integrated circuits. This CMP step often involves the chemical formation of a structurally weak oxide-complex film on the wafer surface, followed by selective removal of the film with mechanical abrasion under reduced loading. The present work investigates certain chemical aspects of this strategy of TaN-CMP by using guanidine carbonate (GC) as a surface complexing agent, and employing electrochemical experiments. The experiments are designed to study the chemical and electrochemical origins of the CMP-specific surface complex films formed on a TaN wafer in acidic solutions of GC and hydrogen peroxide. Open circuit potential, polarization resistance, and electrochemical impedance measurements are employed to probe the surface effects that facilitate material removal in chemically prevailing CMP of TaN. The results are discussed in view of designing slurry variables to support barrier layer planarization with reduced roles of mechanical abrasion. [Copyright &y& Elsevier]

Abstract: Metal–Insulator–Metal (MIM) capacitors are one of the most essential components of radio frequency devices and analog/mixed-signal integrated circuits. In order to obtain high capacitance densities in MIM devices, high-k materials have been considered to be promising candidates to replace the traditional insulators. The challenging point is that the dielectric material must demonstrate high capacitance density values with low leakage current densities. In this work, SrTiO3 based MIM capacitors have been investigated and the electrical performance of the devices have been optimized by using bilayered systems of Sr2Ta2O7−x/SrTiO3 with different thicknesses of Sr2Ta2O7−x. Sputtering X-Ray photoelectron spectroscopy (XPS) measurements have been applied to investigate the interfaces between the thin film constituents of the MIM stacks. The optimized bilayered system provides a leakage current density of 8∗10−8 A/cm2 at 2V (bottom electrode injection) and a high capacitance density of 13fF/μm2. [Copyright &y& Elsevier]

Abstract: Ta–Ru and Mo–Ru alloy coatings with phases of intermetallic compounds are often used as protective coatings on die materials. After annealing under an oxygen containing atmosphere, the internal oxidation phenomenon resulted in the preferential oxidation of Ta or Mo in the coatings. This process created a phase separated structure consisting of continuous and alternative oxygen rich and deficient layers with a nano scale period beneath the free surface. The experiments in this study deposited Ta–Ru and Mo–Ru coatings with a Cr interlayer by direct current magnetron co-sputtering at 400°C. Annealing treatments were conducted at 600°C for short durations under controlled atmospheres consisting of 50 or 10,000ppm oxygen with residual nitrogen or argon gas. The internal oxidation behavior in the initial stage was determined by evaluating the variations in crystalline structure, surface morphology and chemical composition. The laminated structure was examined by transmission electron microscopy. Results show distinct oxidation behaviors for Ta47Ru53 and Mo46Ru54 coatings. Internal oxidation phenomena appeared in Ta47Ru53 coatings annealed in both 50 and 10,000ppm O2 containing atmospheres. The Mo46Ru54 coatings exhibit external oxidation at 50ppm O2 containing atmosphere, and internal oxidation at 10,000ppm O2 containing atmosphere. Finally, this study proposes an internal oxidation mechanism for alloy coatings with an orientated structure. [Copyright &y& Elsevier]

Abstract: N-type hydrogenated nanocrystalline silicon thin film piezoresistors, with gauge factor −28, were deposited on rugged and flexible polyimide foils by Hot-wire chemical vapor deposition using a tantalum filament heated to 1750°C. The piezoresistive response under cyclic quasi-static and dynamical (up to 100Hz) load conditions is reported. Test structures, consisting of microresistors having lateral dimensions in the range from 50 to 100μm and thickness of 120nm were defined in an array by reactive ion etching. Metallic pads, forming ohmic contacts to the sensing elements, were defined by a lift-off process. A readout circuit for the array consisting in a mutiplexer on each row and column of the matrix is proposed. The digital data will be processed, interpreted and stored internally by an ultra low-power micro controller, also responsible for the communication of two-way wireless data, e.g. from inside to outside the human body. [Copyright &y& Elsevier]

Abstract: We grow silicon films by hot-wire/catalytic chemical vapor deposition using a new filament material: TaC-coated graphite rods. The filaments are 1.6mm diameter rigid graphite rods with ~30μm thick TaC coatings. Whereas heated W or Ta wire filaments are reactive and embrittle in silane (SiH4), the TaC/graphite filament is stable. After >2h of exposure to SiH4 gas at a range of filament temperatures, the full length of a TaC/graphite filament retains its shiny golden color with no indication of swelling or degradation. In comparison, a W wire exposed to SiH4 under the same conditions becomes swollen and discolored at the cold ends, indicating silicide formation. Scanning electron microscopy images of the filament material are nearly identical before and after SiH4 exposure at 1500–2000°C. This temperature-independent chemical stability could enable added control of the gas phase chemistry during deposition that does not compromise the filament lifetime. The larger surface area of the 1.6mm diameter TaC coated graphite filament (compared to the 0.5mmW filament) allows for a ~2× increase in the deposition rate of Si thin films grown for photovoltaic applications. [Copyright &y& Elsevier]

Abstract: Tantalum nitride (TaNx) films are usually used as barriers to the diffusion of copper in the substrate for electronic devices. In the present work, the TaNx coating plays an extra role in the iron catalyzed chemical vapor deposition production of carbon nanotubes (CNT). The CNTs were grown at 850°C on TaNx films prepared by radio frequency magnetron sputtering. The correlation between the CNT morphology and growth rate, and the pristine TaNx film nature, is investigated by comparing the evolution of the nano-composition, roughness and nano-crystallinity of the TaNx films both after annealing and CVD at 850°C. [Copyright &y& Elsevier]

Abstract: Three synthesized stable phases for TaN are studied by the first-principles calculations. We confirm that TaN undergoes a phase transition from the hexagonal є phase to the hexagonal θ one with a volume collapse of 5.25% when the applied pressure is 3.2GPa. The obtained phase transition pressure is in good agreement with the experimental results. An analysis of the calculated results shows that this phase transition is mainly caused by the higher bulk modulus and lower electron states on the Fermi level of the hexagonal θ phase for TaN. The superior elastic properties indicate that TaN in the hexagonal θ phase is an ultra-incompressible and hard material. [Copyright &y& Elsevier]

Abstract: Metal–insulator–silicon structures containing Hf-doped Ta2O5 dielectric films sputtered on rapid thermally nitrided Si are shown to have very good reliability properties. Stress-induced leakage currents are low, both at low and at high-fields. It is found that charge trapping during the stress is the dominant wear-out mode for very long stress times of 500s even for injected current densities J s as high as 100mA/cm2. Stress curves approach saturation at long stress time, indicating that the trap generation rate is very low, even compared to the observed reduced trapping at pre-existing traps. Applying a trapping kinetics model, two trapping sites with characteristic trapping times τ1 =3.2s and τ2 =49s were determined and attributed to pre-existing defects in the bulk Hf:Ta2O5 layer and not in the interfacial SiOxNy layer. It was found that both τ1 and τ2 do not depend on J s, which may be explained by the presence of a mechanism of charging the active sites through field activated emission of charge from them. [ABSTRACT FROM AUTHOR]

Abstract: Ta3N5 thin-film photoelectrodes were prepared using a reactive sputtering technique, and their properties for photoelectrochemical water splitting under visible light were investigated. The crystal phases of the films were dependent on the sputtering conditions, such as the N2/O2 ratio of the sputtering atmosphere and the substrate temperature (T s). Single-phase Ta3N5 films were obtained by sputtering at N2/O2 =30 and T s =1013K with post-annealing in an NH3 flow. The Ta3N5 photoelectrodes had an anodic photoresponse in water photoelectrolysis, although the photocurrent rapidly decreased because of self-oxidation of the photoanode by photogenerated holes. However, modification of the NH3-treated Ta3N5 films with IrO2 promoted the oxidation of water and suppressed the self-oxidation of Ta3N5. [ABSTRACT FROM AUTHOR]

Abstract: Thermo chemical computing validates the stability of different nitrides against Co, Mo, and methane up to 1150K, showing the highest chemical stability against carburization for ZrN and TaN under static conditions. Single zirconium and tantalum nitrides layers have been sputtered onto WC–Co substrates as diffusion barriers and buffer layers under specific reactive sputtering conditions. To improve the nuclei density of diamond during CVD processing, a thin Mo extra layer has been added (<500nm). In this study, two bilayer systems have been tested: TaN–Mo and ZrN–Mo. Nano crystalline diamond has been grown under negative biased substrates. After diamond deposition, a massive carburization of molybdenum and tantalum nitride is observable whereas zirconium nitride is not. Nevertheless, a small amount of cobalt has migrated through the ZrN layer. The better efficiency of the ZrN layer to prevent diffusion of the Co element, leads to expect an increased adhesion of diamond on ZrN–Mo bilayer coating. A TEM study is done to improve understanding of phenomena occurring at the interfaces during process. [ABSTRACT FROM AUTHOR]

Abstract: Tantalum nitride based thin films have been deposited on p-Si (100) and SiO2/Si by thermal Atomic Layer Deposition (ALD) using either the Ta(=N t Bu)(NEt2)3 or a derivative, in which one dialkylamido ligand is substituted by a η5-cyclopentadienyl (η5-Cp), as metal organic precursors with ammonia as reducing agent. TaNxCy self-limiting temperature dependent ALD growth was achieved for the TaCp(=N t Bu)(NEt2)2/NH3 process with a growth rate of 0.51–0.91Å cycle−1 in the 400–425°C temperature range while between 240 and 280°C, the growth of TaN based films from the Ta(=N t Bu)(NEt2)3 was accompanied by a partial decomposition of the precursor. The η5-cyclopentadienyl type compound allows lower nitrogen content in the precursor and thereafter in the deposited film. Although N/Ta ratio is close to one at temperatures of 390 and 400°C, as analyzed by Rutherford Back Scattering and Nuclear Reaction Analysis, films were amorphous independently of the deposition temperature. Since Ta–C bonds are present in the Cp derivative, the TaCp(=N t Bu)(NEt2)2 tends more likely to form tantalum carbide compared to Ta(=N t Bu)(NEt2)3, which leads to lower thin film resistivity. For both precursors, employed in their respective ALD window, films were smooth with a root-mean-square roughness close to 1nm. [ABSTRACT FROM AUTHOR]

Abstract: This study focuses on the synthesis of tantalum (Ta) coatings on high strength steel by plasma assisted chemical vapor deposition using tantalum pentachloride (TaCl5) as a preferred precursor and hydrogen (H2) as a reducing agent. The interrelationships governing the growth kinetics, compositions, and coating properties are discussed as a function of deposition temperature, total pressure, and gas composition. The synthesized tantalum coatings are shown to be essentially pure with trace amounts of oxygen, carbon, and chlorine. The coatings are found to be dense and to exhibit conformal coverage. Preferential formation of the α-Ta phase is noted to occur when coatings are grown sequentially and in-situ on a TaN x seed layer. [Copyright &y& Elsevier]

Abstract: We discuss the fabrication of highly conductive Ta-doped SnO2 (Sn1− x Ta x O2; TTO) thin films on glass by pulse laser deposition. On the basis of the comparison of X-ray diffraction patterns and resistivity (ρ) values between epitaxial films and polycrystalline films deposited on bare glass, we proposed the use of seed-layers for improving the conductivity of the TTO polycrystalline films. We investigated the use of rutile TiO2 and NbO2 as seed-layers; these are isostructural materials of SnO2, which are expected to promote epitaxial-like growth of the TTO films. The films prepared on the 10-nm-thick seed-layers exhibited preferential growth of the TTO (110) plane. The TTO film with x =0.05 on rutile TiO2 exhibited ρ =3.5×10−4 Ωcm, which is similar to those of the epitaxial films grown on Al2O3 (0001). [Copyright &y& Elsevier]

Abstract: Deposition of MoSi2 films on silicon and tantalum substrates applying pulsed laser deposition technique has been performed. Crystalline, hexagonal symmetry, MoSi2 films were prepared directly from stoichiometric MoSi2 tetragonal target on room temperature and heated substrates (500°C). Textured MoSi2 films having privileged (110) and (115) orientations and average crystallite size of about 105nm were grown on Si(111) substrates with a good degree of axial texture (rocking curve full width half maximum of 1.5°). MoSi2 films grown on Ta(211) substrates, instead, turned out to be polycrystalline, with an average crystallite size of about 100nm and 50nm on substrates kept at room temperature and at 500°C, respectively. Vickers hardness for 1.2μm thick MoSi2 films on Si(111) substrates resulted to be 15GPa both at room temperature and 500°C, while for 0.4μm thick MoSi2 films on Ta(211) substrates — 26GPa at room temperature and 30GPa at 500°C. [Copyright &y& Elsevier]

Abstract: Thermal helium desorption spectrometry has been used to study the interaction of helium with defects in Cu films (5–300 Å) deposited on Ta(110) and Ta(100) single crystals by ultrahigh vacuum electron beam evaporation. The thermal stability of the Cu films was also investigated. Cu films on Ta(110) and Ta(100) at room temperature are metastable and on heating, the films transform into islands. The temperature at which this takes place is strongly dependent on the Cu film thickness and for a given thickness (>40 Å) occurs at a lower temperature on Ta(100) than on Ta(110). The activation energy for island formation is 1.6±0.4 eV for 50 Å Cu/Ta(110) and 0.8±0.1 eV for 100 Å Cu/Ta(100) obtained by Kissinger analysis. The geometry of the Cu islands resulting from annealing 50 Å Cu films at 1000 K for 10 s depends strongly on the Ta substrate orientation. There is evidence for the stressed states of both the Cu films and the Ta substrates. Helium release from monovacancies and vacancy clusters in Cu films (>75 Å) on Ta(110) and Ta(100) was detected at ~750 K and ~800–1000 K respectively. The sublimation of the Cu films from the Ta substrates could be observed by the release of retained helium at ~1300 K. [Copyright &y& Elsevier]

Abstract: Ru thin films were sequentially deposited onto TaN (5 nm) by plasma enhanced atomic layer deposition using Ru(EtCp)2 and NH3 as precursors. The effect of growth temperature on the electrical resistivity and morphology of the Ru films were studied. It was found that the Ru films can achieve a low resistivity of 14 µΩ cm and a low root-mean-square roughness at a growth temperature of 270 °C. The thickness of the underlying TaN film was found to affect the Ru film growth. The oxidation of the very thin TaN film was correlated with the island growth of Ru. Ex and in-situ X-ray diffraction was employed to verify the copper diffusion barrier properties of a Ru (3 nm)/TaN (5 nm) bi-layer structure. [Copyright &y& Elsevier]

Abstract: In this work, the influence of sputter conditions and film thickness on both the morphology and the resistivity of tantalum (Ta) thin films will be investigated. Glass wafers were used as substrates. With increasing back pressure level ranging from 0.3 to 6 Pa at a fixed plasma power of 100 W, the microstructure changes from a dense to an open porous characteristics. At a moderate back pressure level of 0.9 Pa, the stable α-phase is detected when the film thickness exceeds a value of about 1.3 µm. Besides the impact of phase composition, the microstructure influences in addition the electrical performance of the Ta films. Therefore, the room-temperature resistivity can be varied within two orders of magnitude by applying different parameters for film deposition. [Copyright &y& Elsevier]

Abstract: Reliability properties of 30-nm thick insulating films grown by thermal oxydation of Ta deposited on plasma nitrided Si for times varying from 5 to 15 s were studied for the case of constant current stresses. Stress-induced leakage currents of thus obtained Ta2O5/SiOxNy stacked layers with the stress were monitored by the evolution of the parameters extracted with the use of our recently developed comprehensive model for leakage currents. It is concluded that the nitridation of the substrate prior to the Ta2O5 formation, simultaneously with the increase of the dielectric constant of the stack and the decrease of the leakage currents in fresh samples, improves the reliability properties against constant current stress. The increased charges to breakdown and the decreased trapping in the insulating film were explained by the improved resistance of the interface with substrate to the stress due to the incorporation of a small amount of nitrogen atoms. Since the N atoms are much stronger bonded to the Si substrate, the nitrided interface becomes more resistant to the stress. The optimum observed for nitridation times of about 10 s was explained by the strengthening of the interface with N-atoms without excessive growth of the SiOxNy–Si interfacial layer and without excessive lowering of its injection barriers. [Copyright &y& Elsevier]

Abstract: The thermal radiation which generated from the patterned Ta/Pt/Ta thin heater achieved a high temperature up to 1010 °C under applied current of 2.4 A. In order to reduce an electromigration at high current of 2 A, a Ta capping layer was placed on the Pt layer instead of conventional capping layer, such as SiNx and CoWP. Under the thermal radiation at the applied current of 2 A in the Ta/Pt/Ta thin heater, the Ta capping layer enhanced the lifetime of the Pt thin heater up to 5 h. A stamping process for the crystallization of a-Si was performed for 40 samples using the Ta/Pt/Ta thin heater. For all samples, a-Si has been selectively crystallized and Raman peaks were located near 519 cm− 1. These results indicated that the thermal radiation of the Ta/Pt/Ta thin heater was maintained constantly due to the Ta capping. [Copyright &y& Elsevier]

Abstract: The filament in a hot-wire chemical vapour deposition (HWCVD) reactor is an important component. When tantalum (Ta) filaments are used for the deposition of thin silicon films, strong degradation takes place: there is a large amount of silicon not only at the surface but also in the bulk of the tantalum catalyst. Ta–Si phases form on the filament surface and in the bulk, which can lead to a porous structure of the catalyst filament. Filament contamination (silicide formation and thick silicon deposits (TSDs)) is the reason for the changes in filament resistance. It also reduces filament lifetime, which is a serious concern for HWCVD deposition technology. A cleaning procedure for the filament at high-temperatures in a vacuum (about 2000 °C) can neither remove the thick silicon deposits nor fully restore the filament surface properties. In order to decrease the silicon content in the tantalum catalyst and suppress TSD formations on the filament surface, we use radio-frequency alternating current (RF, 13.5 MHz) instead of direct current (DC) to heat the filament. The skin effect of the RF current reduces the formation of TSDs on the surface and silicon diffusion into the filament. We show that it is possible to clean the filament surface of TSDs by means of a high-frequency current. Combined RF+DC filament heating allows us to increase the lifetime of the catalyst (almost twofold) and to improve HWCVD process reproducibility without any deterioration in the quality of the deposited film. [Copyright &y& Elsevier]

Abstract: This paper presents a method for multi-component three dimensional nanostructuring during physical vapor deposition, termed simultaneous opposite glancing angle deposition (SO-GLAD), which exploits atomic shadowing effects to control both the shape and the composition of nanorods parallel (in-plane) and perpendicular to the rod-axis. Periodic arrays of ~200-nm-wide Si–Ta two-component rods are grown by SO-GLAD onto monolayers of self-assembled close-packed 260-nm-diameter silica spheres. Simultaneous deposition of Si and Ta from opposite sides on a stationary substrate yields nanorods consisting of laterally separated Si and Ta components, since atomic shadowing causes deposition only onto the sphere-sides that are exposed to the respective deposition fluxes. Sequential deposition with a stationary and rotating substrate results in zigzag two-component nanosprings and vertical multilayer nanorods, respectively. A checkerboard arrangement is achieved by simultaneous deposition with intermittent 180° substrate rotations. [Copyright &y& Elsevier]