Thin Ta Research Articles

Relaxation of slow highly charged ions hitting thin metallic foils

We developed a method to determine the relaxation time of the innermost vacancies for highly ionized heavy ions moving through the bulk. The method compares the intensities of photons emitted through the front and back sides of a thin metal foil. Using foils with known thickness and x-ray absorption cross sections, we directly obtained the mean x-ray emission depth, and thereafter the mean relaxation time. We present data for the emission depth of highly charged $8.5q$ keV and $23.5q$ keV ${\mathrm{Pb}}^{q+}$ ions $(q=53--58)$ impacting on thin Ta foils. The mean relaxation time of $M$-shell vacancies is estimated to be between 22 and $68\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$, depending on charge state of the projectile, which is about five times longer relaxation time than reported by Hattas et al. [Phys. Rev. Lett. 82, 4795 (1999)]. The experimental results are supported by a model calculation that combines molecular-orbital calculation for the ${\mathrm{Pb}}^{54+}\text{\ensuremath{-}}\mathrm{Ta}$ interaction system with a rate-equation model for inner-shell relaxation.

Highly Oriented High-$B_s$Fe-Co Soft Underlayer for High-Density Perpendicular Recording Media

Two types of media with a high-B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> Fe-Co soft underlayer (SUL) were prepared to reduce the film thicknesses of the Ru intermediate layer and the SUL. The crystal orientation of the media was greatly changed by using a thin Ta underlayer. The magnetic properties of the SULs were similar, independent of the existence of the Ta underlayer. However, the media with high orientation have large H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c </sub> and squareness ratio. The Ru layer thickness for obtaining the maximum H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> and squareness ratio is 5-7 nm. This seems to be due to the imperfection of Ru orientation. From the read-write properties, the minimum of the Ru layer thickness is 7 nm. However, from vibrating-sample magnetometer measurements, the magnetic interaction between the recording layer and the Fe-Co SUL is broken by using an Ru layer of 1-3 nm. The intermediate layer thickness could be reduced down to about 1 nm if the orientation is improved

Growth of highly c-axis oriented aluminum nitride thin films on β-tantalum bottom electrodes

We have investigated the influence of tantalum (Ta) bottom electrodes on the crystallinity and crystal orientation of aluminum nitride (AlN) thin films. AlN thin films and Ta electrodes were prepared by using rf magnetron sputtering method. The crystal structure of the Ta electrodes was tetragonal (β-Ta, a metastable phase) at room temperature. The crystallinity and orientation of the AlN thin films and Ta electrodes strongly depended on sputtering conditions. Especially, the crystallinity and crystal orientation of the Ta electrodes were influenced by their film thickness and the substrate temperature. When the thickness of the Ta bottom electrodes was 200 nm and the substrate temperature was 100 °C, the AlN thin films indicated high c-axis orientation (the full width at half maximum of rocking curve of 3.9°). The crystal orientation of the AlN film was comparable to that of AlN thin films deposited on face centered cubic (fcc) lattice structure metal, such as Au, Pt and Al, bottom electrodes.

Influence of bias-temperature stressing on the electrical characteristics of SiOC:H film with Cu/TaN/Ta-gated capacitor

Experiments on bias-temperature stressing, capacitance-voltage measurements, current-voltage characteristics, and time-dependent dielectric breakdown were performed to evaluate the reliability of Cu and low-k SiOC:H integration. A high leakage current of ∼8 × 10−10 to 2 × 10−8 A/cm2 at 1 MV/cm in SiOC:H dielectrics in a Cu-gated capacitor, and a lower 2 × 10−10 to 5 × 10−10 A/cm2 at 1 MV/cm in a Cu/TaN/Ta-gated capacitor, were observed at evaluated temperatures. The drift mobility of the Cu+ ions in the Cu/TaN/Ta-gated capacitor was lower than that in a Cu-gated capacitor. A physical model was developed to explain the observed kinetics of Cu+ ions that drift in Cu-gated and Cu/TaN/Ta-gated capacitors. The electric field in the Cu-gated MIS capacitor in the cathode region is believed to be increased by the accumulation of positive Cu+ ions, which determines the breakdown acceleration. Good Cu+ ions drift barrier layers are required as reliable interconnects using thin TaN and Ta layers. Additionally, Schottky emission dominates at low electric fields, E 1.5 MV/cm.

Quantitative mapping of elastic properties of plasma-treated silica-based low-k films

A modulus mapping technique is described which provides quantitative information about the elastic properties of the near-surface region of both unpatterned and patterned silica-based low dielectric constant (low-k) thin films. The extent of oxygen plasma-induced damage has been studied using this method. Compared with quasi-static nanoindentation, the modulus mapping technique is more surface sensitive. This is first demonstrated for thin Ta layers on top of low-k films, where the effective modulus systematically increases with the Ta film thickness. Correspondingly, the effective modulus of the near-surface region of a plasma-treated low-k film is significantly higher than that measured on the same type of low-k film without treatment. Modulus mapping performed on integrated Cu/low-k structures showed that a sub-micrometer spatial resolution is clearly achievable. Furthermore, the effective modulus of patterned low-k material between inlaid copper interconnects was found to be considerably higher than the modulus measured on a blanked low-k film of the same type.

Effect of nitrogen content on the degradation mechanisms of thin Ta–Si–N diffusion barriers for Cu metallization

The effect of the nitrogen content on the thermal stability and degradation mechanisms of Ta–Si–N diffusion barriers was studied using methods that prove Cu interdiffusion. On the one hand, glancing angle X-ray diffraction was applied to detect Cu 3Si formation after annealing of Cu/Ta–Si–N/Si layer stacks. On the other hand, a combined secondary ion mass spectroscopy and transmission electron microscopy analysis of Ta–Si–N/Cu/Ta–Si–N/SiO 2/Si samples was performed. For a detailed investigation of the microstructure evolution, the crystallization behavior of both Cu-capped and uncapped Ta–Si–N/Si samples was analyzed using X-ray diffraction. In the case of an uncapped Ta 73Si 27 film, Si interdiffusion from the substrate precedes the layer crystallization. The substrate influence on the crystallization process decreases with increasing N content x N of the Ta–Si–N layer. Using Cu/Ta–Si–N/Si samples, a critical temperature for Cu silicide formation was determined. This temperature increases with increasing N content of the Ta–Si–N barrier. In the case of Ta–Si–N films with x N > 25 at.%, Cu interdiffusion into the substrate occurs before a significant barrier crystallization is observed. For Ta–Si–N layers with x N ≤ 25 at.%, no indications for Cu diffusion before crystalline phase formation were detected.

Effect of Ion Irradiation on α and β Phase Evolution of Sputtered Tantalum Thin Films

AbstractTantalum thin films were deposited by RF (13.56 MHz) magnetron sputtering on silicon and aluminum substrates with ion irradiation (~ 0.3 mA per sqaure cm) controlled by applying different DC bias voltages (0-300 V) to the substrate. The presence of two main crystallographic phases of Ta in deposited films was investigated. Results showed that only the tetragonal â-phase formed in thin Ta films on both Si &lt;100&gt; and Al substrates at zero bias voltage (ion energy ~10 eV), and only bcc α-phase of Ta formed at the ion irradiation energy to 150 eV. Both phases were present at the ion energy of 100 eV. With increase of the ion energy to 250 eV, or higher, â-phase Ta dominated the film structure on Si &lt;100&gt; but not on Al substrate. Ta films were deposited in compressive stress with the lowest stress measured for α-phase Ta films deposited with ion energy of 150 eV. A new set of deposition parameters, significantly different than those previously reported, for low temperature growth Ta films with bcc crystallographic structure, desired for most applications, was found. An advantage of the new deposition parameters is relatively simplicity of the required equipment, which can be easily scaled up for an industrial process.

Effects of Ta buffer layers on the ordering of equiatomic FePt thin films

The magnetic and microstructural properties of Ta/FePt/C thin films after annealing at various temperatures have been investigated. The results indicate that for a very thin Ta buffer with amorphous structure and relatively large roughness, defects and grain boundaries of high density are formed in the FePt film grown on it, which effectively lowers the energy barrier of the ordering with Ta interdiffusion into the grain boundaries of the FePt film during the annealing process. The formation of the L10 phase of FePt thin films is thus greatly promoted with the ordering temperature of FePt significantly reduced by introducing a thin Ta buffer layer. On the other hand, when Ta layer is relatively thick, its roughness accordingly reduces, and most of the interfacial Ta atoms are finally bounded with the advent of the crystalline structure of the Ta buffer. Therefore, Ta buffer layer at this thickness range has little effect on the ordering of FePt films.

Formation of Mo gate electrode with adjustable work function on thin Ta 2O 5 high- k dielectric films

Formation of Mo gate electrode with adjustable work function on thin Ta 2O 5 high- k dielectric films at low-temperature processing of 600 °C has been studied by using nitrogen implantation into the Mo gate electrode. For the sample without nitrogen implantation, a work function of about 4.85 V can be achieved for p-FET. By employing the nitrogen implantation into the Mo gate electrode, a work function of about 4.45 V can be achieved for n-FET. Though larger nitrogen implantation energy can lead to even lower work function as 4.25 V, much larger capacitor leakage is caused and capacitance value is considerably degraded, attributable to the penetration of nitrogen into Ta 2O 5 dielectrics. As a result, proper nitrogen implantation energy should be employed to make trade-off of capacitance value, capacitor leakage, and work function, for high-performance nanometer CMOS IC technology.

Femtosecond Laser Processing Using Subwavelength Thin Metal Slit Arrays

We have studied femtosecond laser processing using subwavelength thin metal slits patterned onto Si substrates. A thin Ta film (200 nm thickness) with a periodic-structured slit array (200–1000 nm width) was formed on the Si substrates. The ablation thresholds of the Ta and Si were investigated. Near-field enhancement effects were observed at the edge of the metal slit arrays. Ridge structures were created in the slits on the Si surfaces using a single laser shot. In addition, an interesting processing effect was observed that was dependent on the polarization of the beam; only a p-polarized beam could create grooves perpendicular to the slits on the Si substrate. The grooves were formed under the metal layer. Our experimental results concerning the enhancement of the electrical field at the edge of the slits were consistent with the results from finite-difference time-domain simulations.

Effect of barrier thickness on electromigration reliability of Cu/porous low k interconnects

The effects of Ta barrier thickness on electromigration reliability of dual-damascene Cu/porous methylsilsesquioxane interconnects were investigated. With decreasing Ta barrier thicknesses, the threshold product of current density and line length (jL)c was found to be reduced due to less structural confinement from thinner barriers. The effect can be accounted for by the effective modulus of the structure except for the 75-Å Ta barrier where the (jL)c product is reduced more than expected, probably due to the presence of defects in the barrier. Results from the early failure test structures revealed a bimodal failure distribution for samples with the 75-Å and l00-Å barriers. Focused ion beam microprobe and transmission electron microscopy observations revealed that the weak-mode early failure was caused by Cu outdiffusion through structural defects in the thin Ta barrier.

New (oxy)nitride pearlescent pigments

Thin ( d = 60 nm/140 nm) nanocrystalline Ta 3N 5 and Zr 2ON 2 films were synthesized in a rotary kiln and in a fluidized bed apparatus. The control of the reaction was performed by optimizing the ammonia flow, the temperature and the reaction time. Using fluidized bed technology, the reaction times were significantly reduced compared to a stationary oven and to a rotary kiln. Movement of the particles in the gas phase favors gas–solid interaction that enhances gas diffusion in the pores. In addition, complete reactions and homogeneous products were obtained in the fluidized bed and not in a rotary kiln, which resulted in pigments having a stronger interference color.

Incorporation of nitrogen in thin tantalum films using plasma immersion ion implantation

The incorporation of nitrogen into thin (10 nm) Ta layers using plasma immersion ion implantation (PIII) has been studied. PIII was carried out using a low-pressure (0.3 Pa) plasma and ion energies between 6 and 25 keV. The depth distributions of nitrogen were measured by Auger electron spectroscopy (AES) and compared with those obtained by numerical simulations (Profile Code). The experimental profiles do not show a maximum at the projected range of the implanted ions, but a high nitrogen concentration at the surface decreasing with depth. The influence of implantation parameters such as high-voltage pulse rise and fall times, voltage amplitude, and plasma pulsing on the shape of the nitrogen profile is investigated and discussed. Especially reduced fall time of the high-voltage pulse reduces the implantation with energies below the nominal value and therefore the high nitrogen concentration near the surface significantly.

Characterization of thin Ta–Si–N x layers of different nitrogen content using XPS, UPS and STM

Reactively sputtered Ta–Si–N x barrier systems of different nitrogen content on copper were investigated by photoelectron spectroscopy (XPS, UPS) and scanning tunnelling microscopy (STM). The measured photoelectron spectra (excitation He–I) showed a clear dependence of the electron state density near the Fermi edge on the content of nitrogen. These results correlate with the I(U) characteristics of the STM measurements and the electrical conductivity of these layers.

Ion beam etching of high resolution structures in Ta 2O 5 for grating-assisted directional coupler applications

An investigation on thin Ta 2O 5 films patterning using argon ion beam etching (IBE) is presented. The etch rates are characterised by varying the angle of incidence of the beam onto the substrate. Ta 2O 5 gratings with a period of 2.2 μm (1.1 μm linewidth) and 0.25 μm thickness are fabricated using an angle of incidence of 0°. The resulting Ta 2O 5 grating cross sectional profiles are analysed using AFM and SEM imaging. A fabrication method is thus demonstrated which could be used to implement wavelength selective gratings in applications such as grating-assisted directional couplers (GADCs).

Sintering of nanocrystalline Ta 2O 5 and ZrO 2 films compared to that of TiO 2 films

Thin ( d = 60 nm/140 nm) nanocrystalline Ta 2O 5 and ZrO 2 films were deposited onto SiO 2 flakes, using a liquid route synthesis. Their sintering behaviour was characterized and compared to that of the corresponding powders and the known equivalent TiO 2 film in terms of grain size, grain growth and layer porosity. The effect of the substrate was noticeable on crystallisation process but not on grain growth. The sintering behaviour was actually dictated by the initial size and the packing of the precipitated grains related to the synthesis of the film.

Surface characteristics and corrosion resistance properties of TiNi shape memory alloy coated with Ta

Ti-50.6 at.% Ni alloy samples were coated with tantalum by the arc ion plating method with the aim to improve their radiopacity. Surface characteristics and corrosion resistance properties were investigated in the present study. The results of XRD show that the film as-deposited was composed of a metastable tetragonal β-phase tantalum which can transform into α-phase tantalum after annealing at 700 °C, 800 °C, 900 °C for 1 h, respectively. TEM observations show that thin nano-structured Ta layers were obtained in the as-deposited samples. Mixture of microcrystallite (approx. 40 nm) and large-size crystal (approx. 150 nm) α-phase tantalum was formed in the film after annealing at 700 °C. When annealed at 900 °C, the film is composed of dominantly uniform large-size α-phase tantalum. The results of XPS survey and high resolution spectra show that a thin oxide film with Ta 2O 5 in the outmost layer and tantalum suboxides in the inner layer, are formed inside tantalum coating as a result of natural passivation of Ta in the atmosphere. The corrosion resistance was determined by electrochemical methods in 0.9% NaCl solution at 37 °C. Both the as-deposited and annealed samples exhibit excellent corrosion resistance property. Compared to the untreated coating samples, the annealed Ta coating samples exhibit higher open-circuit corrosion potential ( E corr), breakdown potential ( E br), and lower passive current density ( I p). The results indicate that the annealing treatment can improve the corrosion resistance property.

Landau-Pomeranchuk-Migdal effect for multihundred GeV electrons

Experimental results for the bremsstrahlung energy loss of 149, 207, and 287 GeV electrons in thin Ir, Ta, and Cu targets are presented. For each target and energy, a comparison between simulated values based on the Landau-Pomeranchuk-Migdal (LPM) suppression of incoherent bremsstrahlung is shown. For the electron energies investigated, the LPM effect enters the quantum regime where the recoil imposed on the electron by the emitted photon becomes important. Good agreement between simulations based on Migdal's theory and data from the experiment is found, indicating that the LPM suppression is well understood also in the quantum regime. Results from a comparison between simulations with the ``threshold'' energy ${E}_{\mathrm{LPM}}$ as a free parameter and the data are shown. This analysis reproduces the expected trend as a function of nominal radiation length, but yields values that tend to be low compared to Migdal's theory.

Coexistence of large Faraday rotation and high transmittance in magnetophotonic crystals with multi-cavity structures

Abstract Magneto-optical effects of one-dimensional magnetophotonic crystals composed of a Bi:YIG thin film and Ta 2 O 5 /SiO 2 multilayer film were theoretically investigated. The calculations revealed that the required optical isolator performance ( T >95% and θ F =45°) can be fulfilled when the periodic multilayer films have only two or three magnetic layers. This mechanism which satisfies the properties of an optical isolator can be thought of as a transmittance to improve; because the peak of one side piles up, though each of the circular polarizations of light has two peaks and a square bandpass.

Probing Effects of Etching Plasmas on the Properties of Porous Low-k Dielectrics

AbstractThe application of porous low-k interlayer dielectrics is needed for reducing the parasitical capacitance, especially at 65-nm node and beyond. The understanding of process-induced modifications to material properties is crucial for a successful integration of these low-k dielectrics. The dry etching processes of porous low-k materials are important modules in ULSI fabrication. In this study, the interaction between MSQ-based JSR LKD-5109 films (shown by PALS to have interconnected 2.8 nm size pores) with CF4/O2 plasma has been investigated. Various ratios of O2 content were designed to characterize its effects on the etch rate, formation of polymerization layer, and properties of the LKD-5109 film. Composition analysis was conducted by SIMS and FTIR. Moisture absorption and fluorine diffusion into low-k films after etch process are observed, along with carbon depletion near the surface region. The influence of etching chemistries on the morphological characteristics of thin Ta barrier layers (8-nm in thickness) deposited on etched low-k films were further investigated by SEM, and it is found that oxygen concentration has significant influences on the morphological characteristics of thin Ta barriers.