Cobalt Alloy Films Research Articles

Layer-by-layer deposition of breakdown-strengthened Co(Ni) films by modulating termination time over the redox replacement

Seeking a material to replace copper (Cu) is essential because the high electron mean free path of Cu has remarkedly increased the resistivity of the interconnect when devices are continuously scaled down. This study aims to deposit a low electron mean free path cobalt (Co) alloy film strengthened by lightly doping nickel (Ni) in a layer-by-layer manner using an automatic electrochemical atomic layer deposition methodology. Through sequential underpotential deposition (UPD) of Co followed by surface-limited redox replacement (SLRR) of Ni, yielding an approximate monolayer, a film with a controlled composition of Co(Ni) can be deposited by modulating the termination time during the open circuit of SLRR-Ni. The nucleation mechanism correlated with the surface morphology was studied to elucidate electrical resistivity of the Co(Ni) film. The Co(Ni) film with 3.9 at.% Ni yields the low electrical resistivity of 27.72 μΩ-cm. The Co(Ni) film displays high breakdown strength, supporting its capability as an interconnecting material for next generation metallization beyond Cu.

Effects of stress and defects on hydrogenation and magnetic properties in (111) fiber-textured palladium cobalt alloy films

Effects of stress and defects on the hydrogenation and magnetic properties of (111) fiber-textured palladium cobalt Pd92Co8 (at.%) alloy films are investigated using post-annealing process. It is revealed that the hydrogen stabilization due to tensile stress induces various effects on hydrogenation. Defect removal results in an increased solubility limit for the metallic α-phase and an increased critical hydrogen pressure to form the hydride β-phase. It was demonstrated that the local strain can depict these effects using a linear function. The improved resistance against film buckling is also attributed to the defect removal. Thus, post-annealing is a powerful process to control hydrogenation; however, the effects are complicated because various effects work in conjunction. In contrast, the magnetic properties can be explained in simple terms. The saturation magnetization corresponds linearly to the defect concentration with a negative slope, and the magnetic anisotropy is proportional to the stress due to magnetoelastic coupling.

Controllable magnetic anisotropy and magnetostriction constant in palladium cobalt alloy films: Effects of composition, thickness, and stress

The magnetic anisotropy of sputter-deposited films of palladium cobalt Pd100 − xCox (x = 7, 15, and 28 at. %) alloy is investigated systematically. The exact anisotropy energies of all contributions, namely, surface, magnetocrystalline, magnetoelastic, and shape, are estimated. Using these energies, the main origin of the magnetic anisotropy is determined and summarized in maps of film thickness and film stress. Consequently, how composition, thickness, and stress affect the magnetic anisotropy is clarified. Accordingly, the controllability between longitudinal and perpendicular magnetic anisotropy is revealed. In addition, the magnetostriction constant λ111 is estimated from the change in the volume anisotropy energy due to the stress in the film, namely, the inverse magnetostrictive effect. The constant is a large negative number, −178 ppm at maximum, and agrees partially with a reference value measured under normal magnetostriction. The disagreement by 30% of the magnetostriction constant with respect to the expected value for Pd72Co28 films was elucidated by the magnetostriction enlargement by tensile stress.

Corrosion behaviour of super-hydrophobic electrodeposited nickel–cobalt alloy film

Hierarchical super-hydrophobic Ni–Co film with enhanced corrosion resistance was fabricated on a copper substrate by one-step electrodeposition process. The contact angle and water repellence properties of the Ni–Co film were measured to determine its wettability. The Ni–Co film exhibited excellent super-hydrophobic properties with a static water contact angle of 158° and a sliding angle of ≤5°. The corrosion performance of the super-hydrophobic surface (SHS) was investigated by electrochemical potentiodynamic measurements and electrochemical impedance spectroscopy in NaCl solution (3.5wt.%). Moreover, to study the long-term stability of the super-hydrophobic film, SHS samples were immersed into NaCl solution and their corrosion behaviour was investigated by the electrochemical impedance spectroscopy. Additionally, the changes of surface wettability were also monitored over the whole immersion time up to 11 days. Experimental results indicated that super-hydrophobic samples had much more corrosion resistance in comparison with freshly prepared samples or the bare substrate.

Preparation of CoP films by ultrasonic electroless deposition at low initial temperature

Electroless deposition technology has been considered as a kind of common ways to obtain cobalt alloy films. However, in order to get cobalt alloy films, high temperature (353K) is necessary during the electroless deposition process which will increase costs and energy consumption. Ultrasonic was introduced during electroless plating process to obtain cobalt alloy films at lower initial temperature. It was found that the cobalt thin films could be prepared at lower initial temperature (323K) with the introduction of ultrasonic. Therefore, different powers of ultrasonic were applied during the electroless deposition process to prepare CoP thin films on copper substrates from an alkaline bath in this investigation. The effects of different powers of ultrasonic on deposition rate, surface morphology, anticorrosion performance and magnetic property of films were studied. It was found that the deposition rate increased gradually with the rise in ultrasonic powers due to cavitation phenomenon. All the CoP films presented the typical spherical nodular structures with the impact of ultrasonic. Smaller and regular shaped structures could be observed when the films were deposited with higher power of ultrasonic which contributed directly to enhancement of anticorrosion performance. Saturation magnetization and coercivity of thin films increased gradually with the rise in ultrasonic powers during the electroless deposition process due to the higher amounts of cobalt.

CVD of cobalt–tungsten alloy film as a novel copper diffusion barrier

To reduce the resistivity of interconnects, to enhance electro-migration lifetime, and to improve the step coverage of the barrier layer, we deposited cobalt and cobalt-tungsten alloy films by chemical vapor deposition (CVD) using octacarbonyl dicobalt [Co2(CO)8] and hexacarbonyl tungsten [W(CO)6] as precursors, respectively. We demonstrated the formation of a conformal cobalt film on a trench pattern and confirmed that CVD cobalt-tungsten films have good barrier properties against copper diffusion.

Anderson-like localization in ultrathin nanocomposite alloy films on polymeric substrates

The resistivity–structure relationship is experimentally investigated for ultrathin chrome cobalt (CrCox) alloy films sequentially co-sputtered on pre-coated polymeric substrates. For a narrow range of concentrations, we determine the crystal structure to be predominantly body-centred cubic and in one case having an additional Ω-hexagonal close-packed phase. The alloy film with the Ω-hexagonal close-packed phase shows an anomalous resistivity–temperature relationship. This is consistent with the associated crystal structure change and is attributed to an Anderson-like localization of carriers.

On work function and characteristics of anomalous electrodeposited nickel–cobalt films

The anomalous cobalt content in the electrodeposited nickel–cobalt (Ni–Co) alloy films significantly influenced by the current density was related to the variation of morphology and electron work function (EWF) of the films. The characteristics and EWF of Ni–Co films were investigated by scanning electron microscope with an attached energy dispersive X-ray spectrometer, X-ray diffraction, ultraviolet photoelectron spectroscopy (UPS) and Kelvin probe technique, respectively. As the current density increased from 1 to 20 ampere per square decimeter (A/dm 2), the Co atomic concentration (at.%) in Ni–Co greatly decreased from 22.5 at.% to 13.2 at.% correspondingly. The surface morphology of film obtained at low current density became smoother than that at high current density. Both UPS and Kelvin probe results showed the same trend of EWF variation which increased with increasing current density from 1 to 10 A/dm 2 and kept nearly unchanged at 10–20 A/dm 2. The smooth Ni–Co film with low EWF could be achieved at low current density. In comparison, Kelvin probe operated at atmosphere ambient could be a good candidate for EWF measurement because of the lower cost and easier operation than UPS at ultra high vacuum.

High Perpendicular Coercivity Electroless Cobalt Alloy Films with 25 nm Thicknesses

This paper describes the development of Co alloy films thinner than 50 nm with high perpendicular magnetic coercivity using an electroless deposition process. In order to obtain these films, we used a Cu underlayer for a heteroepitaxial growth of the Co alloys and an optimized bath composition which included sodium hypophosphite and hydrazine as reductants. As a results, the perpendicular coercivity of the films turned to be higher 3000 Oe at the initial deposition stage with the thickness lower than 80 nm. In particular, the high perpendicular magnetic coercivity of the film as thin as 25 nm thick was obtained. These results indicate that electroless deposition is applicable for formation of the films with high perpendicular magnetic coercivity by optimizing the deposition conditions.

High Perpendicular Coercivity Electroless Cobalt Alloy Films with 25 nm Thicknesses

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A surface adsorption model for electroless cobalt alloy thin films

Thin cobalt alloy films have been obtained using electroless deposition solution with two reducing agents: dimethylamine borane (DMAB) and sodium hypophosphite. This system allows spontaneous and self-activated deposition of barrier layers on Cu lines and via contacts for ultra large scale integration (ULSI) interconnects applications. This work presents a study of the solution composition effects on the material properties and composition of the films. First, we present the deposition rates, the electrical resistance, the various element profiles in the thin film, and the thin film roughness. Next, we discuss the film’s composition and its dependence on the ratio between the reducing agents composition in the solution. The experimental results suggest that the film phosphorous and boron composition is determined by the surface adsorption rates of the reducing agents. Therefore, a surface co-adsorption model of the two reducing agents is proposed, formulated, analyzed, and compared to the experimental results. Finally, we discuss the model and its significance to the formation of high-quality ultra-thin barrier layers.

Fabrication and properties of macroporous tin–cobalt alloy film electrodes for lithium-ion batteries

The Sn-based intermetallic compounds possess a high specific energy density, but their most important challenge to be used as anodes in lithium ion batteries consists in the mechanical fatigue caused by volume change during lithium intercalation and extraction processes. The current paper presents a facile procedure to prepare macroporous Sn–Co alloy film electrode through a colloidal crystal template method together with electroplating on a Ni-coated Cu sheet substrate. The structure and electrochemical properties of the macroporous Sn–Co alloy films were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and galvanostatic cycling. The results illustrated that the macroporous Sn–Co alloy film electrode can deliver a reversible capacity as high as 610 mAh g −1 up to 75th cycle. In comparison with the Sn–Co alloy film directly deposited on Ni-coated Cu sheet substrate, the macroporous structure of the Sn–Co alloy electrode prepared by the present procedure has enhanced significantly the capacity and the cyclic performance. It has demonstrated that the macroporous structure has played an important role, in addition to the alloying effect, to overcome the effect of volume expansion during charge/discharge cycling of Sn-based alloy anodes.

Confirmation of hydroxide in electroless cobalt alloy films by GDOES

The objective of the present study was to confirm the presence of the hydroxide in electrolessly deposited cobalt alloy films. The existence of Mn hydroxide in Co–Mn–P films was confirmed by glow discharge optical emission spectroscopy (GDOES). The results of the electrical resistivity and magnetic coercivity measurements of the films are also consistent with the above results.

Porosity and its Effect on Barrier Performance of Thin Electroless Cobalt Alloy Caps

ABSTRACTPinhole densities of electroless cobalt alloy films on copper substrate are characterized using optical and electrochemical methods. The impact of pits or pinholes on deposit film barrier property is discussed. The improved film barrier property is shown by reduction of pits formation through deposition process optimization.

Microstructure and material properties of electroless CoWP films obtained from sulfamate solutions

This work describes the development of a thin film cobalt–tungsten–phosphorous (Co–W–P) alloy, deposited from an electroless deposition solution and the study of the effect of the solution composition and deposition parameters on the microstructure, electrical and magnetic properties of the deposits. Electroless deposition of CoWP was performed on copper surface from novel electroless bath with cobalt sulfamate Co(NH 2SO 3) 2 as a source of Co ions and sodium tungstate as a source of tungsten. The reducing agent and a source of phosphorous was sodium hypophosphite. The developed electroless solution produces high quality cobalt alloy films with the ability to form 2–2.5 μm thick soft magnetic layers. The CoWP deposition rate was found to decrease with the increase of sodium tungstate concentration. The maximum tungsten content in the film was about 1.9 at.%. The influence of the tungsten concentration in the solution and post-deposition vacuum annealing on film morphology, surface topography, composition, magnetic properties and resistivity was studied. The resistivity of the CoWP layers shows a strong non-linear dependence on the film thickness. The resistivity of the as-deposited films was in the order of 10 −4 Ω cm and it decreased by about a factor of two after vacuum annealing at 400 °C for 2 h. The corresponding evolution of the film structure and morphology is presented and discussed. The CoWP deposit demonstrated high temperature stability up to 350 °C during annealing in air.

Electrochemical deposition of macroporous magnetic networks using colloidal templates

Nanostructuring of magnetic materials, on a scale comparable to the dimensions of the magnetic domain boundaries, is known to have a significant effect on the magnetic properties of a material. Here we demonstrate a simple and versatile technique for the preparation of two- or three-dimensional highly ordered macroporous cobalt, iron, nickel, and nickel iron alloy films containing close packed arrays of spherical holes of uniform size (an inverse opal structure). The films were prepared by electrochemical deposition from aqueous solution within the interstitial spaces of pre-assembled templates. The templates were assembled from colloidal polystyrene latex spheres (0.20, 0.50, 0.75 or 1.00 µm in diameter) assembled onto gold electrode surfaces from aqueous solution by slow evaporation. Following the electrochemical deposition of the metal or alloy films the polystyrene templates were removed by dissolution in toluene. Scanning electron microscopy of the resulting films show well-formed two- or three-dimensional porous structures consisting of interconnected close packed arrays of spherical voids. X-Ray diffraction analysis confirms that the nickel iron alloy in the walls of the structure is polycrystalline fcc in structure with a grain size which is significantly smaller than the thickness of the walls. The diameter of the spherical voids within the structures can be varied by changing the diameter of the polystyrene latex spheres used to form the template. Studies of the magnetic properties of the macroporous films show a large coercivity enhancement in comparison to the corresponding plain films and we find that the coercive field gradually increases as the diameter of the spherical voids decreases for films of a constant thickness.

Origins of substrate-topography-induced magnetic anisotropy in sputtered cobalt-alloy films

Cr(001)/CoCrPt (112̄0) films, used in magnetic hard disks, exhibit in-plane magnetic anisotropy when grown over a substrate patterned with shallow grooves. In this experiment, Cr/CoCrPt films are grown over substrates that have been patterned using lithographic techniques to produce well-controlled topography. The in-plane anisotropy, which is of the order of 104 J m−3, increases with the groove height and frequency. This magnetic anisotropy is a result of anisotropic in-plane crystallographic orientation and anisotropic stress. Stress-induced anisotropy accounts for up to 25% of the total in-plane anisotropy, but the major contribution to the anisotropy is a preferential Co c-axis alignment parallel to the groove direction.

Effects of stacking faults on magnetic viscosity in thin film magnetic recording media

There is much interest in crystallographic defects in thin film magnetic recording media and their role in influencing recording performance such as media noise and thermal loss. In this article we report a correlation between the magnetic viscosity in CoPtCr thin film media, which is the origin of thermal loss effects, and the concentration of local fcc-like regions. The concentration of these defects (the type and density of stacking faults) was varied by growth on different underlayers (Cr and CrTa/Cr) and was measured with grazing incidence x-ray scattering using synchrotron radiation. We show that a substantial percentage of local fcc regions in an otherwise hcp cobalt alloy film leads to significant magnetic viscosity effects at quite modest magnetic fields. We find that the activation volume is reduced for a sample with a higher percentage of fcc-like regions and suggest that this can be understood in terms of the effect of weak links acting to stabilize local micromagnetic configurations.

The role of NiAl underlayers in longitudinal thin-film recording media

Longitudinal recording media made with chromium and with nickel-aluminum underlayers are compared. NiAl films have smaller grains and random crystallographic orientation, while Cr films have larger grains and either a {110} or a {200} preferred orientation depending on the deposition conditions. Cobalt alloy films grown on NiAl have nearly random crystallographic orientation and significant c-axis out-of-plane component, and lower hysteresis loop squareness and coercivity than films made on a heated Cr underlayer. NiAl-underlayer media do not exhibit in-plane magnetic anisotropy induced by the substrate texture lines. CoCrTaPt/Cr/NiAl media had higher overwrite than CoCrTaPt/Cr media due to higher coercive squareness and a sharper hysteresis loop closure.

Stress, Microstructure and Magnetic Properties of Thin Sputtered Co Alloy Films

ABSTRACTThe internal stress and magnetic properties have been measured for cobalt alloy films deposited using a range of sputter conditions. The sputter conditions affect the internal stress and the microstructure, both of which contribute to the magnetic properties of the films. Stress influences the magnetic properties via magnetostriction, while the microstructural effect on coercivity comes primarily from the degree of separation and size of the grains in the film. The effect of stress on coercivity was investigated separately by applying external stresses to the films, and magnetostriction coefficients were derived for different alloys. The change in coercivity with sputter parameters indicates that in alloys such as Co77Ni7Cr4Pt12, the microstructure has the dominant effect on coercivity.