Aluminum Alloy Thin Films Research Articles

Cracking of Aluminum and Silver Alloy Thin Films on Polymer Thin Films

Cracking of Aluminum and Silver Alloy Thin Films on Polymer Thin Films

Coevaporation and structuring of titanium–aluminum alloy thin films

Intermetallic phases of binary material systems, such as TiAl, Ti3Al, RuAl, and Ni3Al have special physical properties such as a high oxidation resistance and low creep at high temperatures and a mechanical stability over wide temperature ranges. Due to new fields of application, such phases became increasingly important in the last two decades. In general, alloys can be sputtered very easily and reproducible. In surface acoustic wave (SAW) technology and microelectronics, the lift-off structuring technique is a fundamental process in the production of structured thin (<500 nm) metallic electrodes especially for low-cost fabrication of interdigital transducers (IDT). However, the structuring by standard lift-off technology only results in high quality IDTs for evaporated and not for sputtered layers. In order to investigate the intermetallic phases of the binary Ti-Al material system for IDT fabrication for SAW technology, a modified evaporator system for the simultaneous deposition of the low (Al) and the high (Ti) melting materials is presented.

Impact of the morphology and composition on the dealloying process of co‐sputtered silver–aluminum alloy thin films

Dealloying has been widely employed lately for the fabrication of nanoporous metals. However, in case of thin films, the impact of the initial morphology on the final porosity is still not well understood. In this work, we report on the influence of the initial morphology of silver–aluminum (Ag–Al) thin films on the dealloying process in hydrochloric acid. The films deposition was performed by a DC co‐sputtering process of silver and aluminum targets in a cofocal geometry using pure argon plasma; by tuning the deposition conditions such as the electrical powers applied to the targets and the deposition temperature, films with various compositions and morphologies can be obtained. The dealloying is then carried out using a free corrosion process applied in diluted (2 wt.%) hydrochloric acid in order to leach preferentially aluminum leaving behind a nanoporous skeleton of silver. We show that the dealloying process becomes faster when decreasing the initial silver content within the films. We further demonstrate that the dealloying kinetic is also dependent on the initial morphology of the Ag–Al films: it increases when decreasing the size of the columns forming the Ag–Al films.Top‐view SEM image of Ag–Al alloy thin film with 23 at.% of initial Ag content dealloyed for 5 min in 2 wt.% hydrochloric acid.

Optical, electrical, and structural properties of sputtered aluminum alloy thin films with copper, titanium and chromium additions

Aluminum alloys containing copper, chromium, and titanium were sputter deposited with the goal of maintaining the high bulk reflectance of aluminum while providing surface topography more suited for optical applications. Films were deposited at room temperature with no additional thermal processing. Results show that copper solute addition generates films that maintain much of the bulk reflectance of pure aluminum while refining surface morphology to create a more specular surface consisting of smaller, more uniform grains. X-ray diffraction studies revealed that copper addition into the aluminum lattice caused both a reduction in the preferred orientation of the film and change in the lattice parameter. Copper concentrations of 1.0% at. and above led to spatial variation in copper content within the films. The addition of titanium and chromium to Al-1.0%Cu films caused further microstructure refinement. Al-2.0%Ti-1.0%Cu and Al-2.0%Cr-1.0%Cu exhibited reflectivity spectra that differ significantly in both inter- and intraband absorption from that of pure aluminum. A dielectric function model combining a surface effective medium and a bulk Lorentz–Drude layer was applied to all alloy films to understand the observed reflectivity. Excellent agreement has been shown between the measured resistivity values and those obtained from the Drude model.

可動電気配線用アルミニウム合金薄膜

A Micro Electro-Mechanical System (MEMS) consist of a movable silicon substrate and static glass substrate. Two substrates are joined using an anodic bonding technique at 693 K for 1 h. A conductive thin film is deposited on to the silicon to provide the required electrical circuit. Thin film aluminum alloy is an appropriate material for MEMS, because it has low electrical resistance and is easy to etch using conventional acid techniques. Both electrical characteristics and mechanical characteristics of aluminum alloy film affect the MEMS device performance. Annealing at over 693 K will cause re-crystalization of the grain structure and hence the annealed aluminum alloy thin film has a large grain structure. With the addition of nitrogen and oxygen into the aluminum alloy, the grain growth will be inhibited during annealing, resulting in a fine grain structure of the annealed thin film. The dynamic hardness of the film with fine grain structure was approximately 1100 MPa and that of large one is 640 MPa, respectively. Both aluminum alloy thin films have been applied to yaw rate sensors. The static output of the sensors with the fine grain aluminum alloy thin film has been stable, but while those with coarse grain aluminum alloy thin film was found to be unstable.

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.

Thermal cycling fatigue and deformation mechanism in aluminum alloy thin films on silicon

Thermal cycling fatigue and deformation mechanism in aluminum alloy thin films on silicon

Material characteristics and chemical–mechanical polishing of aluminum alloy thin films

In the Damascene process, the need for separating plug and interconnect process steps is completely eliminated. This patterning scheme offers tremendous advantages, it will begin to emerge in the deep sub-micron generation and utilizes Al CMP as a critical part of the Al Damascene process. During Al CMP, the Al film surface reacts with slurry chemicals, resulting in passivation or dissolution reactions. Thus surface microstructure of Al films and slurry chemistry will determine the performance of metal CMP. Material characteristics of Al films have a great impact on its CMP behavior. Addition of Cu to Al generally increases the susceptibility to corrosion, thus leading to an increase in CMP removal rate. The grain size of Al film also affects its CMP performance. Films sputter-deposited at lower substrate temperature obtain higher removal rate due to increased grain boundary area and thus higher propensity to corrosion. In this study, Al-CMP characteristics are evaluated on Al alloy thin films of different compositions including: pure Al, Al–1.0% Si–0.5% Cu, Al–1% Cu, Al–0.5% Cu and Al–1% Si. Characteristics of the films such as alloy contents and grain size, and their effects on the CMP removal rates are investigated. The mechanism of Al CMP can be explained by the continuous formation and removal of a passivating layer formed on the Al surface during CMP. In this experiment, an Al2O3-based slurry is formulated with hydrogen peroxide added as the main oxidizer. CMP removal rates of various Al thin films with alterations in slurry pH and oxidizer concentrations were monitored to assess the role of chemical erosion and mechanical abrasion.

Comparison of Sputtered Titanium Nitride on Silicon Dioxide and Aluminum-Alloy Thin Films

Titanium nitride (TiN) films are used as anti-reflection coatings (ARC) on aluminum (Al) films to facilitate lithography processes during multilevel metallization for the manufacture of integrated circuits on silicon-based (Si) semiconductor devices. It is generally accepted in the literature that the microstructure of multilevel metal stacks is influenced by the texture of the substrate. For the case of interconnect materials used in the semiconductor industry, a typical metal stack is as follows: Titanium/Titanium Nitride/Al-alloy/ARC-Titanium Nitride. The Ti/TiN layer underneath the Al-alloy film is used as a barrier stack to prevent junction spiking. The Ti/TiN underlayer also determines the growth conditions (crystallography and orientation relationships) of the subsequent Al-alloy film.This study focuses on the microstructural characterization of the ARC-TiN layer on Si-oxide and Ti/TiN/Al-alloy substrates that are fabricated under similar conditions using conventional physical vapor deposition (PVD - sputtering) techniques. The ARC-TiN microstructure was investigated by transmission electron microscopy (TEM) using a Philips EM430 operating at 300 kV.

Surface Characteristics, Etching Behaviors and Chemicalmechanical Polishing of Aluminum Alloy thin Films

ABSTRACTEtching behaviors of various Al alloy thin films in H2O2-based acidic etchants are investigated in this study. The pH and H2O2 content in the etchant are varied in order to simulate the case where Al thin films are subject to chemical-mechanical polishing (CMP) using slurries of different compositions. Corrosion current and thickness of the native oxide on pure-Al, AI-1%Si, Al-0.5%Cu, AI-1%Si-0.5%Cu, and AI-1%Cu thin films are determined from Tafel and ESCA analyses respectively. Comparisons between etch rate and CMP polish rate data suggest that Al-CMP removal process depends strongly on the chemical reactions by the oxidizer (slurry). Mechanical abrasion by the abrasive particles plays only an auxiliary role during Al CMP. In addition, alloy composition (% Si and % Cu) influence both etching and polishing behaviors to a great extent. The underlying mechanisms for etching and polishing are discussed.

Influence of adding transition metal elements to an aluminum target on electrical resistivity and hillock resistance in sputter-deposited aluminum alloy thin films

Effects of adding group VIII transition metals (Fe, Co, and Ni) to an aluminum target on electrical resistivity and hillock suppression of sputter-deposited Al alloy films were studied. It was found that the group VIII transition metals and Al formed a complete series of metastable solid solutions in the as-deposited state. The solid solutions were decomposed into intermetallic compounds, and the microstructures of the Al alloy films changed during annealing up to 300 °C. The electrical resistivities of Al–Fe, Al–Co, and Al–Ni alloy films changed corresponding to the change in their microstructures, and markedly decreased to 5.0 μΩ cm at the precipitation points. The film stresses also changed corresponding to the change in the microstructure of the Al alloy films, and were abruptly relieved by precipitation of intermetallic compounds and grain growth. Since Al–Fe, Al–Co, and Al–Ni alloy films did not yield, they are highly resistant to hillock formation. The low electrical resistivity and the excellent resistance to hillock formation of Al–group VIII transition metal alloy films were explained on the basis of microstructural changes before and after annealing.

Elastic strain gradients and x-ray line broadening effects as a function of temperature in aluminum thin films on silicon

Grazing incidence x-ray scattering (GIXS) with a synchrotron source was used to measure elastic strain gradients as a function of temperature in aluminum and aluminum alloy thin films of different thicknesses on silicon. The stresses in the films are induced as a result of the difference in thermal expansion coefficient between film and substrate. Disregarding minor deviations at the surface, it is shown that there are no gross strain gradients in these films in the range of temperatures (between room temperature and 400 °C) considered. Significant x-ray line broadening effects were observed, suggesting an accumulation of dislocations on cooling the films and their annealing out as the films were being reheated. The variation of the dislocation density during thermal cycling compares well in nature with that of the concurrent variation in film stress, indicating that large strain hardening effects contribute toward the film flow stress.

Metallurgical factors influencing the corrosion of aluminum, Al-Cu, and Al-Si alloy thin films in dilute hydrofluoric solution

The corrosion behavior of sputter-deposited Al, Al-Cu, and Al-Si alloy thin films in dilute hydrofluoric (HF) acid solution was investigated. These materials maintain a thin aluminum oxide film in dilute HF solutions and, consequently, are susceptible to localized corrosion. Pit densities increase for the alloys with Cu and, to a lesser extent, Si additions. Open circuit potentials (OCP) are more positive for such alloys relative to the OCP of pure Al. Metastable pits in Al-Cu alloys are formed in Cu-depleted zones at grain boundaries which are galvanically coupled to adjacent θ-Al2Cu precipitates. Metastable pits in Al-Si alloys are formed in the Al matrix which is galvanically coupled to adjacent elemental Si nodules. θ-Al2Cu has different electrochemical characteristics than Al, even though both maintain a thin Al oxide in dilute HF solutions. θ-Al2Cu has a more positive OCP than pure Al and facilitates cathodic reactions at enhanced rates relative to pure Al. Hence, its presence raises the potential of the adjacent pure Al grain boundary to potentials which increase the probability of metastable pitting. Evidence is also presented which suggests that metastable pit growth may be cathode limited. A new hypothesis describing one mechanism by which θ-Al2Cu supports cathodic electron transfer re-actions is discussed.

Abnormal grain growth in aluminum alloy thin films

Abnormal grain growth in 0.75-μm-thick aluminum alloy thin films has been studied using x-ray diffractometry, plan-view and cross-sectional transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray analysis. Transmission electron microscopy was used with preannealed samples as well as with samples annealed in situ. By varying the deposition temperatures, compositions, and annealing conditions, we have determined the roles of alloying elements in the formation of second-phase precipitates and in promoting abnormal grain growth.

Ultramicrohardness of aluminum and aluminum alloy thin films

The ultramicrohardness (UMH) of vapor-deposited aluminum and aluminum alloy thin films was determined at room temperature by indentation experiments at small indenter forces. For pure aluminum films both the dependence of the measured hardness upon film thickness and the hardness-microstructure relationship are described. The increase in UMH of aluminum by alloying was studied for alloy films prepared by simultaneous vapor deposition of aluminum with the metals silver, copper, titanium or vanadium. The hardness of the pure aluminum films hardly changes upon annealing. The as-deposited aluminum alloy films are single-phase alloys, which are highly supersaturated. Consequently, their hardness values are rather high. Alloy softening was observed after an anneal treatment at relatively high temperature. The importance of the various hardening mechanisms will be discussed.

Pitting of Sputtered Aluminum Alloy Thin Films

not Available.

Effects of composition and structure on electromigration kinetics in aluminum-alloy thin films

Variations in time to failure data for electromigration processes have shown the importance to conductor design of factors that include composition, grain size, and passivation thickness. Traditionally, these variables have been studied separately. An understanding of the combined effects of these variables is necessary to design reliable conductors. Temperature-ramp resistance analysis to characterize electromigration (TRACE) has been applied to sample groups in which composition, passivation thickness, and grain size were varied. The results of these experiments provide the kinetic parameters for electromigration, and from these values, a calculation is proposed that allows an estimate of the conductors’ resistance to electromigration. The results suggest that the predominant factor controlling electromigration rates is the passivation thickness.

Grain growth in Al alloy conductors as a result of rapid annealing

Aluminum and aluminum alloy thin films were rapidly annealed using high intensity visible light. Under suitable conditions, substantial grain growth was achieved in the Al-Cu and Al-Si-Cu conductors and this grain growth had a beneficial effect on electromigration. Unfortunately, this growth did not occur uniformily across the wafer. A second phenomenon, which resulted from thermal cycling, was the solid phase reduction of SiO2 by the overlying Al film.