Al Alloy Films Research Articles

Solid state reaction at the interface between Heusler alloys and Al cap accelerated by elevated temperature and rough surface

We have investigated the solid state reaction at the interface of Co2Cr0.6Fe0.4Al, Co2FeSi, and Ni2MnGa Heusler alloy films and Al cap layers using x-ray absorption spectroscopy in transmission and total electron yield mode. At elevated temperatures and at rough surfaces the deposited Al severely reacts with the surface of a Heusler alloy indicated by changes of the absorption spectra. Microspectroscopy using photoemission electron microscopy reveals that the reaction proceeds inhomogeneously with reaction nuclei separated on a micron length scale.

A method for AlCu interconnect electromigration performance predicting and monitoring

The physical properties of (bottom)Si/SiO2/Ti(top) and (bottom)Si/SiO2/Ti/TiN/Al(0.5wt.% Cu)(top) structures by different processes were compared and studied. The resistivities of thin Ti films and the reflectivities of thin Al alloy films were found to correlate to their microstructure as well as the mean time to fail (MTTF) in electromigration (EM) testing. A method to predict and monitor the EM performance of the AlCu interconnects was proposed.

Temperature Dependence of Internal Stress and Crystal Growth of Dilute Cu Alloy Films

Annealing behavior of dilute Cu-X alloys (adding element X = transition metal and rare-earth metal with less than 3 at %) was investigated in terms of resistivity, internal stress, grain growth and hillock formation. The resistivity increases with addition of impurities regardless of kinds of adding elements. Generally, resistivity starts to decrease on annealing above 200 °C. Among present Cu dilute alloys, Sn addition shows the lowest resistivity 2.5 μΩcm on annealing at 400 °C. However, compared with a pure Cu film, salient grain growth of present dilute alloys does not takes place even at temperatures above 300 °C , where the grain size is nearly the same as that of as-deposited films. In-situ surface observation using an atomic force microscope (AFM ) revealed that hillocks did not grow on cooling stage (under tension), but started to form on heating stage (under compression). The scanning electron microscopy (SEM) observation of hillocks thus formed in present dilute alloy films shows that the external appearance of these defects was quite different from those observed in Al and Al alloy films. They most likely grow with a preferential crystal plane, not irregular growth like Al and Al alloy films. The internal stresses in most of the present as-deposited dilute Cu alloy films were nearly zero or compression of –25 to –100MPa, and upon annealing, they started to increase in tensile manner due to thermal stresses induced by the mismatch of the thermal expansion between substrates and deposited films. A large stress relaxation started to occur above 250°C, associating with a large number of hillock formation.

Preparation of Thin-Film Capacitor with High Reliability by Anodization of Zr–Al Alloy Film

We have prepared Zr–Al thin-film capacitors by anodizing a sputter-deposited Zr–Al alloy film with 46 at. % Al, and examined their properties before and after heat treatment and their leakage current mechanism. In addition, anodized Zr–Al films were characterized by X-ray diffraction (XRD) analysis and Auger electron spectroscopy (AES). It is revealed that the reliability of an anodized pure-Zr capacitor is markedly improved by substituting the anodized Zr–Al film for anodized pure-Zr, because the crystallization of anodized Zr–Al amorphous films hardly occurs. In addition, it is clarified that the leakage current mechanism of the anodized Zr–Al capacitor is due to Schottky emission and that the thermal degradation observed after heat treatment above 350 °C is triggered by the diffusion of Zr atoms from the underlying unoxidized alloy layer into the anodized Zr–Al layer.

Annealing effects on microstructure and properties of Ta–Al thin film resistors

The Ta–Al thin film resistor has been used as a heating element of the thermal bubble inkjet printhead with several millions of thermal cycle operations between room temperature and about 350 °C. In this paper, the thermal stability of Ta–Al alloy films was investigated by the variation of phase transformation, microstructure and resistivity at annealing temperatures of 450–650 °C for 1 h. Three kinds of Ta–Al films were prepared with average Ta/Al atomic composition ratios of about 2/1, 1/1 and 1/2, respectively. The Ta–Al film with composition ratio of about 1/1 exhibits amorphous-like microstructure with nanocrystalline grains embedded in an amorphous matrix. The thermal stability is strongly related to the composition and microstructure in Ta–Al alloy. The best thermal stability of Ta–Al films occurs in Ta-rich alloy up to 650 °C and the worst occurs in Al-rich alloy with phase transformation as low as 450 °C. The amorphous-like Ta–Al alloy is stable up to 550 °C, but then exhibits polycrystalline multiphase formation at 650 °C. The resistivity of Ta–Al films is also related to the annealing temperature. The resistivity of Ta-rich Ta–Al film increases to about 13.5% from as-deposited to after annealing at 450 °C while that is doubled in the Al-rich Ta–Al film. In contrast, the resistivity of the amorphous-like Ta–Al film increased by about 6.1% at 450 °C and then remains nearly stable at 1.5% variation on annealing at 450–550 °C. The as-deposited amorphous-like Ta–Al film has the merits of high resistivity, smooth morphology and good thermal stability at annealing temperatures of up to 550 °C. These attributes are beneficial for the thermal bubble inkjet application with thermal cycling at maximum temperatures below 400 °C.

The influence of substrate bias in I-PVD process on the properties of Ti and Al alloy films

The effects of substrate bias power on the microstructure, physical and electrical properties of thin Ti films prepared by ionized physical vapor deposition (I-PVD) process were studied. The influence of Ti underlayer with substrate bias power ranging from 0 to 400 W on the subsequent TiN/AlCu films deposited by conventional PVD process in a multilayer structure was further investigated. Decreasing substrate bias power led: (1) better Ti(002) texture, smoother surface, and lower resistivity in Ti films, and (2) better Al(111) texture, narrower grain size distribution, smoother final surface, better-defined TiN/AlCu interface, and lower residual stress in AlCu alloy films in the corresponding Ti/TiN/AlCu stacks. In both cases, lower substrate bias power resulted in films with desirable microstructures and properties, compared to higher bias powers, for use as Al-based interconnects in IC manufacturing.

Electrodeposition of Ho and Electrochemical Formation of Ho–Al Alloys from the Eutectic LiCl–KCl

The electrochemistry of a melt at inert and reactive electrodes has been studied at temperatures between 673 and . At a W electrode the electroreduction of Ho(III) proceeds in a single step and electrocrystallization plays an important role. Experimental current-time transients followed the theoretical models based on instantaneous nucleation with three-dimensional growth of the nuclei whatever the applied overpotential. Mass transport toward the electrode is a diffusion process, and the validity of the Arrhenius law was verified. For an Al electrode, the electroreduction of Ho(III) takes place at less cathodic potential values than at the inert W electrode which indicated the formation of Ho–Al intermetallic compounds. Ho–Al alloy films were obtained by potentiostatic electrolysis, and the samples were characterized by X-ray diffraction and scanning electron microscopy. The activity of Ho in the aluminium phase as well as the standard Gibbs energy of formation for were estimated from open-circuit chronopotentiometric measurements.

Film growth arising from the deposition of Au onto ani-Al–Pd–Mn quasicrystal: a medium energy ion scattering study

The room temperature deposition of 7 ML of Au onto the fivefold symmetric surface oficosahedral Al–Pd–Mn leads to the formation of a several monolayers thick Au–Al alloyfilm. An AlAu film with 1:1 stoichiometry is formed, which shows no evidenceof ordered structure, being either amorphous or polycrystalline. Annealing to325 °C causes more Al to diffuse into the film, producingAl2Au but still with no indication of structure. Experiments using 0.5 ML of pre-deposited Indemonstrated a surfactant effect as the In ‘floated’ on the surface during growth andproduced a reduction in film roughness. However, contrary to previous findings the film wasstill either amorphous or polycrystalline, with no evidence of quasi-crystalline or aperiodicstructure. Experiments were also conducted using smaller doses of Au to look for theformation of an epitaxial layer and, if formed, determine the registry with the substrate.However, no change in the Pd blocking curves for the surface could be seen, suggesting thatthe Au does not adsorb in well defined sites. This result is not surprising whenconsidering that even for these low doses Al is drawn into the film, changing thecomposition and probably the structure of the topmost layers of the substrate,so that the potential adsorption sites on the clean surface may no longer exist.

Structural and magnetic properties and tunnel magnetoresistance for Co2(Cr,Fe)Al and Co2FeSi full-Heusler alloys

We have investigated the structure and magnetization of Co2(Cr1−xFex)Al (0 ⩽ x ⩽ 1) and Co2FeSi full-Heusler alloy films deposited on thermally oxidized Si (SiO2) and MgO (001) single crystal substrates by ultra-high vacuum sputtering at various temperatures. The films were also post-annealed after deposition at room temperature (RT). Magnetic tunnel junctions with a full-Huesler alloy electrode were fabricated with a stacking structure of Co2YZ (20 nm)/Al (1.2 nm)-oxide/Co75Fe25 (3 nm)/IrMn (15 nm)/Ta (60 nm) and microfabricated using electron beam lithography and Ar ion etching with a 102 µm2 junction area, where Co2YZ stands for Co2(Cr1−xFex)Al or Co2FeSi. The tunnel barriers were formed by the deposition of 1.2 nm Al, followed by plasma oxidization in the chamber. The x-ray diffraction revealed the A2 or B2 structure depending on heat treatment conditions and the substrate, but not L21 structure for the Co2(Cr1−xFex)Al (0 ⩽ x ⩽ 1) films. The L21 structure, however, was obtained for the Co2FeSi films when deposited on a MgO (001) substrate at elevated temperatures above 473 K. The maximum tunnelling magnetoresistance (TMR) was obtained with 52% at RT and 83% at 5 K for a junction using a Co2(Cr0.4Fe0.6)Al electrode. While the junction using a Co2FeSi electrode with the L21 structure exhibited the TMR of 41% at RT and 60% at 5 K, which may be improved by using a buffer layer for reducing the lattice misfit between the Co2FeSi and MgO (001) substrate.

Influence of thickness and band structure of insulating barriers on resistance and tunneling magnetoresistance properties of magnetic tunnel junctions with Al-oxide and Ti-alloyed Al-oxide barriers

Abstract We investigated the influence of insulating barrier thickness and the Ti composition dependence of the band structure of Al-oxide on the resistance and tunneling magnetoresistance (TMR) behavior of the magnetic tunnel junction (MTJ). Low resistance × area (RA) value (1.1 MΩ μm2) was achieved by decreasing the Al-oxide thickness down to 1.0 nm. However, this led to the partial oxidation of the bottom ferromagnetic (FM) electrode of the junction and non-continuous thin barriers by the occurrence of pinholes, with low TMR ratio of 8.3%. For an alternative for low RA value, we developed a new Ti-alloyed Al-oxide (TiAlOx) that had lower band gap than Al-oxide as an insulating barrier of MTJ. As the Ti concentration increased up to 5.33 at.% Ti in Al, the RA value of the MTJs was reduced from 9.5 to 0.69 MΩ μm2, owing to the band-gap reduction of TiAlOx caused by the formation of extra bands, mainly composed of Ti-3d orbitals, within the band gap. It was analyzed that TiAlOx has localized d states in the band gap below the conduction band. In addition, the TMR ratio increased with the Ti concentration and reached a maximum of 49% at 5.33 at.% Ti owing to the microstructural evolution of Ti–Al alloy film in the pre-oxidation state.

Amorphization of Ta–Al films using magnetron sputtering

Amorphous films of alloys generally have different properties from the crystalline ones in the microstructure, resistivity and morphology. In this paper, we study the Ta/Al composition ratio effect on the formation of amorphous Ta–Al alloy films, which are used as heating materials in inkjet printhead or micro-thermal actuator. Three kinds of Ta/Al atomic composition ratios of about 2/1, 1/1 and 1/2 are prepared by different powers of Ta and Al targets in a magnetron sputtering system. The microstructure of Ta–Al film becomes amorphous at medium Al composition ratio of about 50%, while they are polycrystalline at low Al composition ratio of about 33% and at high Al composition ratio of about 67%. The amorphous TaAl film also has better properties than the others. It has the highest resistivity of 163.73 μΩ cm than the others of 125.46 and 120.71 μΩ cm, respectively. It also has the smoothest morphology with average roughness of 0.12 nm than the others' roughness of 0.39 and 7.2 nm, respectively. The smooth morphology of TaAl film with high resistivity is good for the application of micro-thermal actuator as the heating element.

Electrical Properties of a Thin Anodized Capacitor Made of Y-Doped Al Alloy Film

We have prepared an Al–Y anodized capacitor using sputter-deposited Al–Y alloy film with 5 at. % Y atoms, and evaluated the capacitor properties and the leakage current properties before and after heat treatment. In addition, the characterization of Al–Y anodized films was examined by X-ray diffraction, Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy analyses. As a result, it is revealed that the thermal stability of an Al–Y anodized capacitor is superior to that of a pure Al anodized capacitor because of its excellent passive nature, and the loss properties can be improved by increasing the heat treatment temperature in air because of the reduction of the equivalent series resistance. Furthermore, it is clarified that the cause of the short-circuited state observed at 550°C is the formation of a narrow capillary-like conduction path of metallic Al atoms as a result of the interdiffusion of Al.

Electrochemical analysis of zincate treatments for Al and Al alloy films

Electrochemical behavior of Al and Al alloy films in zincate solution was investigated to elucidate the effect of the zincate pretreatment for electroless NiP deposition, which is used for under bump metallization for LSI interconnects. The immersion potential for AlCu and AlSiCu, immediately reached to constant, which was almost equal potential to zinc reference electrode. The corrosion current for the AlCu and AlSiCu films was larger than that of the Al and AlSi films in the zincate solution. It was also confirmed that the deposited Zn at the surface of AlCu and AlSiCu films possessed smaller grain size and larger amount of nucleation, resulted in the formation of flat NiP films.

Creep-resistant aluminum alloys for use in MEMS

Creep is expected to be a reliability issue in MEMS where high temperatures and stresses are present in the moving part. In this paper, we describe a method of measuring the creep parameters, ΔF and τ, in metal thin films. Substrate curvature measurements were used to study different Al alloys—Al98.3Cu1.7, Al99.7V0.2Pd0.1, Al93.5Cu4.4Mg1.5Mn0.6 and Al99.6Cu0.4 films—during isothermal tensile stress relaxation. We show that there is a direct relation between the measured creep parameters and the coherency, size and spacing of precipitates observed by TEM and SEM in the alloys. Furthermore, we confirm that the plastic deformation is controlled by the motion of dislocations inside grains in the Al alloy films. A strengthening process called precipitation hardening was used to create stronger precipitates within the grains in Al99.6Cu0.4 to hinder the movement of dislocations more effectively and thus to make the alloy more creep resistant.

Band structure modification of Al oxide by Ti-alloying and magnetoresistance behavior of magnetic tunnel junctions with Ti-alloyed Al oxide barrier

We investigated the composition dependence of the band structure of Ti-alloyed Al oxide (TiAlOx), tunneling magnetoresistance (TMR) behavior of the magnetic tunnel junctions (MTJs) with TiAlOx barrier, and the microstructural evolution of Ti–Al alloy films. X-ray absorption spectroscopy indicated that TiAlOx had localized d states in the band gap below the conduction band. As the Ti concentration increased, the resistance×area value and effective barrier height of the MTJs were reduced owing to the band-gap reduction of TiAlOx caused by the formation of extra bands, mainly composed of Ti3d orbitals, within the band gap. The TMR ratio increased up to 49% at 5.33at.% Ti. Ti alloying enhanced the barrier∕electrode interface uniformity and reduced microstructural defects. These structural improvements enhanced not only the TMR effect but also the thermal stability of the MTJs.

Chemical–mechanical polish of aluminum alloy thin films: slurry chemistries and polish mechanisms

This study discusses experimentally the effects of slurry formulation and passivating rate on the chemical mechanical polish removal mechanism of aluminum (Al) alloy films. Two regions of material removal with different slurry pH values, namely, one, non-passivating region (pH<4), and the other, passivating region (pH≥4) are investigated. The removal rates of Al alloy films decline with increasing slurry pH. In the non-passivating region (pH=2) where the material removal is a competition between the passivation and mechanical abrasion plus chemical etching, an optimal removal rate occurs in the slurry with hydrogen peroxide (H2O2) concentration ranging from 0 to 15 vol.%. While the slurry pH is increased to 4 arriving in the passivating region where the material removal is a competition between the passivation and mechanical abrasion only, the material removal has weak dependence to the H2O2 concentration. Too low a slurry, pH results in metal loss and scratching, while too high a slurry, pH leads to oxide residue and insignificant removal rate. Furthermore, removal selectivity and performance of Al/barrier metals and Al/oxide are discussed as well.

Creep characterization of Al alloy thin films for use in MEMS applications

Creep is expected to be a major reliability problem in some MEMS, as for example RF-MEMS switches, especially at high RF powers. For this reason it should be avoided to use creep sensitive materials in these devices. In this paper we report on creep studies on Al-alloys, materials that are often used for the bridge in RF MEMS switches. Substrate curvature measurements were used to study Al98.3Cu1.7, Al99.7V0.2Pd0.1 and Al93.5Cu4.4Mg1.5Mn0.6 films during isothermal tensile stress relaxation. It is shown that to all studied aluminum compositions dislocation glide describes the relaxation data well for temperatures up to 110 °C. The paper discusses a very simple way of characterizing creep in thin Al-alloy films by the activation energy ΔF and the athermal flow stress τ. A large difference in creep sensitivity of the studied alloys is measured: Al–Cu–Mg–Mn is found to be very creep resistant while Al–Cu is creep sensitive. It is shown that there is a direct relation between the measured creep parameters and the coherency, size and spacing of precipitates observed by TEM and SEM in the alloys. There is also a direct link between the creep-sensitivity and the obstacle strength of the precipitates.

Comparison of texture evolution in Ag and Ag(Al) alloy thin films on amorphous SiO2

The thermal stability of Ag metallization on SiO2 was improved by using Ag(Al) alloy films instead of pure Ag thin films which agglomerate at high temperature. X-ray diffraction techniques were used to study the texture evolution of Ag and Ag(Al) films. Different behaviors were observed in texture evolution of Ag and Ag(Al) films. Detailed information about the texture of Ag and Ag(Al) films was obtained by performing pole-figure analysis. Two different changes in texture are explained using a grain-growth mechanism and an agglomeration phenomenon, both of which work to reduce the total free energy of the system at high temperature. Based on the data obtained in this study, the texture evolution of Ag film, induced by agglomeration, and Ag(Al) film is discussed.

The electroformation of Zr metal, Zr–Al alloy and carbon films on ceramic

A method of electroforming Zr metal, Zr–Al alloy and carbon film on ceramic substrates has been developed. Using this method, it is possible to apply these films to ceramic substrates, which are complicated in structure. Zr metal and alloy film are formed in the LiCl–KCl melt containing Zr(II), whereas carbon film is formed in the molten carbonate. The electrode consists of a metal part and the ceramic substrate. The films develop between the metal part and the ceramic substrate and propagate along the surface. To form the film there has to be sufficient initial current density to deposit dendritic Zr, carbon whiskers or cubic carbon particles on the metal part.

Influence of thermal treatment on the structure of Ti–Al films

Titanium aluminides based on TiAl and Ti 3Al are potential materials for high temperature aerospace application. Their low density, high temperature creep resistance and strength, high oxidation resistance, make them excellent potential engine materials. It is reasonable to develop processing strategies for protective and high temperature coatings based on them. On magnetron sputtering the Ti–48% Al alloy films, the composition of which corresponds to the target’s one, have been obtained. When annealed, the aluminium atoms have been discovered to diffuse into the substrate. The redistribution and the leveling of the films’ compositions in the volume take place. After annealing the film contains a higher titanium concentration. On sputtering the formation of the Ti 3Al-based metastable phase in the films has been observed. This phase is the main one in the films and has a different morphology on different substrates. It is stable and doesn’t decompose at annealing. During annealing the new intermediate metastable phases, which are stable only within a definite temperature and concentration range, have developed. The structure, kinetics of phase transformation and evolution of the film microstructures depend on the structure and morphology of the substrate.