Ta Capping Research Articles

TaN∕Ta as an Effective Diffusion Barrier for Direct Contact of Copper and NiSi

In this letter, the bi-layered structure of TaN/Ta is revealed to be an effective diffusion barrier for copper (Cu)/NiSi direct contact application. Comparing with the conventional Cu/Ta/TaN/NiSi contact structure, the proposed Cu/TaN/Ta/NiSi contact structure can significantly increase the contact failure temperature over 100°C. It is demonstrated that the NiSi morphological stability is effectively enhanced by Ta capping, which is crucial to improve the performance of Cu/TaN/Ta/NiSi contact. For TaN/Ta diffusion barrier, the Cu diffusion through TaN/Ta layers is revealed to be a diffusion-controlled process with an activation energy of 0.95 eV.

Time-Resolved Magnetization Dynamics and Damping Constant of Sputtered Co/Ni Multilayers

Co/Ni multilayers with a stack of Ta (2 nm)/[Co ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Co</sub> )/Ni ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ni</sub> )] <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> /Ta (30 nm) were prepared by dc magnetron sputtering, and their magnetization dynamics were measured by time-resolved magneto-optical Kerr effect (TRMOKE). The total thickness of the multilayer and perpendicular anisotropy were varied by changing the bilayer period <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> = <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Co</sub> + <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ni</sub> and number of repeats <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> while <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Ni</sub> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Co</sub> was kept at a constant of 2.5. The TRMOKE measurements show clear damped oscillation of the magnetization of Co/Ni multilayers after the pump pulse illumination, and the damping constant α of the Co/Ni multilayers was estimated from the TRMOKE waveform. The estimated α was found to be independent both on total thickness and anisotropy field of the multilayer and was estimated to be ~ 0.035 for all the multilayers. This means that the use of Ta capping and buffer layers is effective to evaluate intrinsic damping constant of the Co/Ni multilayer, and that independent control of α and perpendicular anisotropy are possible for the magnetic multilayers.

Chemical stability of highly (0001) textured Sm(CoCu)5 thin films with a thin Ta capping layer

With the highest magnetocrystalline anisotropy constant (Ku) among practical magnetic materials, SmCo5 could be a very attractive candidate for future high areal density magnetic recording. However, its corrosion resistance is always a concern in recording media applications. In this paper, the chemical stability and microstructures of highly (0001) textured Sm(CoCu)5 thin films with and without a 3 nm Ta capping layer were reported. For Sm(CoCu)5 thin films without a capping layer, the coercivity decreases significantly (from 8kOe to 1kOe) within one month. Sm(CoCu)5 thin films capped with a thin Ta layer (3 nm) behave differently. Even exposed to a laboratory environment (25 °C) over 3 years, the Ta-capped Sm(CoCu)5 thin films are stable in terms of structural and magnetic properties, i.e., there were no changes in X-ray diffraction peaks and vibrating sample magnetometer hysteresis loops. Microstructure of Ta-capped Sm(CoCu)5 thin films showed that Sm(CoCu)5 formed a domelike particle assembly structure on a smooth Ru underlayer and were well covered by partially oxidized Ta capping layer, as shown by TEM cross-section micrographs. Accelerated corrosion treatment (130 °C, 95% relative humidity, 6 h) was performed on Ta-capped Sm(CoCu)5 thin films. X-ray photoelectron spectroscopy (XPS) results showed that no Co was detected on the sample surface before the corrosion treatment, but strong XPS signals of CoOx and Co(OH)x were observed after treatment. Therefore, none of our Sm(CoCu)5 thin films can pass the accelerated corrosion test. Hcp-phased CoPt-alloys are proposed as better capping materials for Sm(CoCu)5 thin films in future high-density magnetic recording applications.

Effects of Cu Self-Capping and Ta Capping on Nanometer-Sized Cu Films Sputter-Deposited on &amp;beta;-Ta

Effects of Cu Self-Capping and Ta Capping on Nanometer-Sized Cu Films Sputter-Deposited on &amp;beta;-Ta

Influence of [formula omitted] ion irradiation on thermal relaxation of exchange bias field in the IrMn-based magnetic tunnel junctions

The IrMn/CoFe/AlO x /CoFe magnetic tunnel junctions (MTJs) were deposited by magnetron sputtering on the surfaces of thermally oxidized Si substrates. The thermal relaxation of both non-irradiated and Ga + ion irradiated IrMn/CoFe/AlO x /CoFe MTJs has been investigated by means of holding the films in a negative saturation field. As the ion dose increases the exchange bias field shows a maximum at a dose of 1×10 13 ions/cm 2, resulting from the change of interface roughness induced by irradiation. The irradiation-induced intermixing at the interface of free ferromagnetic (FM) layer and Ta cap layer as well as the Ga + implantation into free FM layer causes the decrease of the magnetization of free FM layer. The results also showed that exchange bias field decreases with increasing period of holding time for both non-irradiated and Ga + ion irradiated MTJs, which is owing to the immediate nucleation of reversed AF domains after the reverse field is applied driven by thermal activation over an energy barrier distribution. With ion dose increasing the thermal stability of H e x is enhanced.

Nano-sized disorders in hard magnetic grains and their influence on magnetization reversal at artificial Nd/Nd 2Fe 14B interfaces

We have investigated the effect of lattice disorders near the surface of hard magnetic Nd 2Fe 14B grains on coercivity using artificial interfaces created by sputter depositing Nd on polished surface of Nd–Fe–B sintered magnets. The interfacial structure was manipulated by annealing the coated samples at 550 °C in vacuum with and without Ta cap. Nano-beam electron diffraction revealed a few nm thick disordered layer within the Nd 2Fe 14B phase at the Nd/Nd 2Fe 14B interface of a low coercivity sample, while a high coercivity sample showed a well-defined crystal structure of Nd 2Fe 14B near the NdO x /Nd 2Fe 14B interface.

Magnetic tunnel junctions with large tunneling magnetoresistance and small saturation fields

There is a continuing need for greater sensitivity in magnetic tunnel junction (MTJ) sensors. We have found a new approach to achieving large tunneling magnetoresistance (TMR) with a very soft free layer. The high TMR is achieved by conventional means of annealing a bottom pinned MTJ that has Ta and Ru capping layers. The soft free layer is achieved by etching almost to the MgO tunnel barrier and depositing a thick soft magnetic film. The results are far superior to annealing the MTJ with the thick soft layer already deposited.

Inter-diffusion study in MgO tunneling magneto-resistive (TMR) system by XPS

In this paper, we investigated the elemental inter-diffusion in MgO TMR system, namely, between MgO barrier and free layer (CoFeB, NiFe or their combination) interface and the oxygen diffusion into the capping layers (Ta, Ru, TaN) at elevated temperatures using simple sheet film stack to simplify the results interpretation. Boron, cobalt, iron, and nickel show various diffusion tendencies into the MgO barrier after annealing the sheet film stack. Oxygen has different penetration depth into single CoFeB free layer upon annealing under N 2 + Ar protective atmosphere for different capping layers. Ru and TaN capping layer provide much better O 2 diffusion barrier, compared with Ta capping layer. This could potentially change the boron segregation tendency at free layer and capping layer interface and thus affect the interface crystallization process and lattice matching between the crystallized CoFeB free layer and the MgO(0 0 1) barrier layer. All these effects will impact the overall TMR performance.

Magnetic Properties Optimization for Amorphous Soft Underlayers

Magneto-optical Kerr effect (MOKE) microscopy and vibrating sample magnetometer (VSM) were used to investigate the magnetic properties of CoFeTaZr and CoTaZr soft magnetic underlayers (SULs). When comparing the CoTaZr with the CoFeTaZr amorphous thin films, the CoFeTaZr films yielded superior magnetic properties. Pre-sputtering substrate Ar-ion milling and sputtering processing pressure were varied to control the magnetic properties of the amorphous films. Furthermore, it was discovered that the magnetic properties of the amorphous thin film strongly depended on the thickness of the SULs, seed layers and capping layers. The experimental results indicated that above a certain thickness, the media noise could be substantially reduced and the magnetic properties of the CoFeTaZr SULs would be optimized. It was also shown that CoFeTaZr SULs with a Ta capping layer and Ru seedlayer had lower coercivity.

New Crystallization Method of Amorphous Silicon by Selective Area Heating for Stamp Process

We propose a new crystallization technique called selective area heating. In this study, we investigated a new technique for high-reliability selective area crystallization of a-Si films that does not cause thermal damage to glass substrates. We reduced the crystallization time as compared to the conventional solid phase crystallization method using a stamp-type isolated thin heater. The thin heater was fabricated with a layer of Pt on a quartz substrate via Ta adhesion and capping layers. A crystalline transverse optic phonon peak at about 519 cm−1 was seen in Raman scattering spectra, showing that the films were crystallized. The poly-Si grain size was found to be smaller than 100 nm, and the dendritic structure was found using scanning electron microscopy.

Specular electron scattering at single-crystal Cu(001) surfaces

Epitaxial copper layers, 20 nm to 1.5-μm-thick, were grown on MgO(001) by ultrahigh vacuum magnetron sputter deposition at 80 °C. In situ electrical resistivity measurements indicate partial specular scattering at the Cu vacuum interface with a Fuchs–Sondheimer scattering parameter p=0.6±0.1. In situ deposition of 0.3 to 7.0-nm-thick Ta cap layers on the Cu surfaces leads to a resistivity increase, which is independent of the Ta thickness and is associated with a transition to completely diffuse surface scattering with p=0.0±0.1. The diffuse scattering is attributed to a “rough” electron potential at the Cu–Ta interface as well as to scattering into localized interface and surface states.

Reduction in critical current density by tuning damping constants of CoFeB for spin-torque-transfer switching

Different capping layers were deposited on 2.5 nm Co72Fe8B20 to investigate their effects on damping constants and critical current density (JC0) for spin-torque-transfer switching. The damping constant of CoFeB is affected by the interfacial conditions and the spin-pumping effects. The Cu capping layer significantly suppresses intermixing and possesses the lowest damping constant of 0.009. The micromagnetic simulations reveal that the low damping constant of CoFeB may result in the nucleation of domains at lower current density, and thus reduces JC0. A reduction of 27% in JC0 can be achieved by replacing the conventional Ta capping layer with a Cu layer.

Lower-temperature crystallization of CoFeB in MgO magnetic tunnel junctions by using Ti capping layer

Effects of capping materials on magnetoresistance (MR) properties of MgO magnetic tunnel junctions (MTJs) with a CoFeB free layer were investigated. MR ratios of samples with various capping materials showed a difference in annealing temperature dependence. MTJ with a Ti capping layer annealed at 270°C showed a MR ratio 1.4 times greater than that with a conventional Ta or Ru capping layer. Secondary ion mass spectroscopy and high-resolution transmission electron microscopy images revealed that crystallization of CoFeB was remarkably affected by adjacent materials and the Ti capping layer adjoining CoFeB acted as a boron-absorption layer. These results suggest that the crystallization process can be controlled by choosing proper capping materials. Ti is one of the effective materials that accelerate the crystallization of CoFeB layers at lower annealing temperature.

Tantalum capping on platinum thin heater for selective area heating

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.

Effect of deposition pressure and post deposition annealing on SmCo thin film properties

AbstractIn this article we report on the effect of the deposition pressure and the post deposition annealing conditions on the structural and magnetic properties of SmCo thin films deposited on Si(100) wafers employing Ta buffer and capping layers. The films were deposited by DC magnetron sputtering and annealed in vacuum at various temperatures. The films under investigation were isotropic with high remanence magnetization, maximum coercive field of 8 kOe and a squareness ratio of coercivity higher than 0.9. It was found that the Ar pressure during the deposition is a key factor in controlling the stoichiometry and the structural and magnetic properties of the SmCo films, while the effect of the annealing temperature is crucial in optimizing the magnetic properties of the films. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Magnetic dead layers in sputtered Co40Fe40B20 films

The magnetic moment of Co40Fe40B20 electrodes has been investigated as a function of thickness for films prepared by magnetron sputtering on Si∕SiO2∕MgO and Si∕SiO2 substrates. On MgO, the metal film becomes discontinuous and superparamagnetic with no stable ferromagnetic moment below 1.0nm, whereas on Si∕SiO2, there appears to be a 0.7nm dead region for all film thicknesses. The dead layer is attributed to an interdiffusion region at the interface with the substrate where there are weakly coupled noncollinear spins and a 0.2nm dead layer associated with the Ta cap. The discontinuous ferromagnetic films maybe useful for the wide-range linear field sensors.

保護層材料による層間交換結合型スピンバルブＧＭＲ膜の耐熱性向上

Interlayer-exchange-coupled (IEC) type spin-valve giant magnetoresistive (SVGMR) films in which the pinning layer does not contain an anti-ferromagnetic layer have been investigated. The IEC-type SVGMR films had good SV properties with a 10% MR ratio as deposited. However, the MR ratio decreased with increasing annealing temperatures over 310°C. From cross sectional TEM observation, interfacial roughness between the free and pinned layers was increased by annealing, and such roughness causes the degradation of SVGMR properties. Thermal stability of SVGMR films was improved when the thickness of Ta capping layer was 5 nm. In order to reduce the thickness of capping layer, various materials of Ru, Cu, and NiFeCr were investigated instead of Ta. No degradation in SV properties after 320°C annealing was achieved with the 2 nm of Ru capping layer.

Improvement of Transport Properties in Magnetic Tunneling Junctions by Capping Materials

The capping effects on the properties of magnetic tunneling junctions (MTJs) have been investigated to improve the magnetoresistive (MR) ratio [Nagamine , Applied Physics, vol. 99, p. 08K703, 2006] and thermal stability [Fukumoto , Japanese Journal of Applied Physics, vol. 45, p. 3829, 2006. In this paper, MgO/Mg and MgO capping layers for MTJs were used to replace our previously used Ta and Ru capping layer [Yen , IEEE Transactions on Magnetics, vol. 42, no. 10, p. 862, 2004]. The MTJs with NiFe and CoFeB free layers were patterned to ellipses of 0.36 mum times 0.72 mum. The MR ratios of the MTJs with an NiFe free layer were enhanced from 26% to about 33% by capping MgO/Mg bilayers. A great improvement was also found on the MTJs with the CoFeB free layer, where the MR ratio was 50.4% with the MgO cap layer enhanced from 44.7% of Ru-capped MTJs. In addition, the influences of those capping layers included Ta, Ru, MgO, and MgO/Mg on thermal stability were also discussed

The Effects of Ruthenium and Grain Size on Spin Valves With Ultra Thin Antiferromagnetic Pinning Layers

Improvements in exchange-biased spin valves have come from control of the grain size and the addition of a ruthenium layer. In this work the GMR ratio, the exchange field and blocking temperature for three sets of spin valves with varying IrMn thickness were measured. Two sets of samples with grain sizes of 10 nm, and one with a grain size of 30 nm were studied. One of the 10 nm grain size sets has a Ru layer separating the antiferromagnet from the Ta capping layer. The GMR ratio at 5 K depends on the grain size, but shows no dependence on the presence of the Ru layer, with larger grain samples having a higher GMR ratio. The exchange fields at 5 K are independent of grain size. However, the samples with the Ru layer show a higher exchange field at 5 K than those without. The blocking temperature for the small grain sets with and without Ru correlate very well with the exchange field. Ta in contact with the IrMn causes a magnetically "dead" region

Improvement of Switching Field in Magnetic Tunneling Junction Using Ru/Ta Capping Layer

A Ru/Ta capping layer for magnetic tunneling juctions (MTJs) was used to replace the routinely used Ta capping layer. The MTJs with CoFeB used as the free layer were shaped to ellipses of 0.36 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$times$</tex> 0.60 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$mu$</tex> m. The magnetoresistive (MR) ratio of Ru/Ta capped MTJs was found to be 47.3%, slightly lower than the value of 52.8% of Ta capped MTJs. In the meantime, the switching field of Ru/Ta capped MTJs with 30 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$ AA$</tex> of Ru was found to be 37.7 Oe, greatly reduced from 63 Oe of Ta capped MTJs. The switching field varition of Ru/Ta capped MTJs was 6 Oe, also better than the value of 11 Oe of Ta capped MTJs. The different switching behaviors of Ru/Ta and Ta capped MTJs were discussed from the aspects of oxygen diffusion, intermixing, and magnetostriction.