Use of fractals and kinetic equations to model thermally induced hillock formation and growth in thin metal films

We investigated the applicability of a model based on fractals and the Smoluchowski kinetic equations to describe hillock formation in thin metal films. We have previously used this model to analyze cluster and ultrafine particle production. We show how to extract two parameters from measured hillock size distributions which may reveal the scaling of the mobility of clusters and vacancies in films with varying hillock size. On the basis of our application of this model to certain data taken from the literature, the model shows considerable potential for being able to provide an internally consistent quantitative basis for monitoring thermally driven mass redistribution processes in metal films.     

Stress formation and relaxation in amorphous Ta–Cr films

In the present paper, measurements of the intrinsic stress of thin amorphous Ta–Cr alloy films made by magnetron sputtering have been carried out. From the curvature of the substrates and by use of the Stoney formula, the stresses were determined. The bombardment of the growing film with energetic particles is shown to control the magnitude and sign of the intrinsic stress. When changing the deposition parameters, compressive or tensile stresses can be generated in the films in a range from about −2 GPa to +1 GPa. Also the stress relaxation, the change in the stress with time, has been studied for various temperatures. The stress relaxation was measured with a cantilever beam technique using a three-terminal capacitance method to detect the beam (substrate) deflection. The stress-relaxation data have been fitted to a mathematical model for stress relaxation related to inhomogeneous flow in amorphous films. This behaviour is expected to occur in the low-temperature, high-stress regime with deformation taking place along localized shear bands.     

Effect of SiO2 passivation overlayers on hillock formation in Al thin films

Hillock formation in Al thin films with varying thicknesses of SiO₂ as a passivation layer was investigated during thermal cycling. Based on the stress measurements and the number of hillocks, 250 nm thick SiO₂ was thick enough to suppress the hillock formation and the suppression of hillock at 250 nm passivation and the lack of suppression at thinner passivation is related to the presence/absence of protection against the diffusive flow of atoms from the surrounding area to the surface due to the biaxial compressive stresses present in the film through the weak spots in the passivation layer. The stress state of Al films measured during annealing (the driving force for hillock formation) did not vary much with SiO₂ thickness. A small number of hillocks formed during the plasma enhanced chemical vapor deposition of SiO₂ overlayers at 300 °C.     

Study of the formation of chromate conversion coatings on Alclad 2024 aluminum alloy using spectroscopic ellipsometry

The influence of pH of a chromate bath on the morphological and chemical properties of a chromate conversion coating, formed on Alclad 2024-T3 aluminum alloy, has been investigated by variable angle spectroscopic ellipsometry in the visible and infra-red regions. Other techniques such as glow discharge optical emission spectroscopy, transmission and scanning electron microscopy, atomic force microscopy and Auger electron spectroscopy have been used in order to confirm and sustain the results obtained with this technique. The combination of different analytical methods showed a decrease in thickness together with changes in the morphology and chemical composition of the chromate film when the pH is increased from 1.2 to 2.4. Although the complexity of the chromate system and the pronounced roughness of commercial rolled aluminum limit the accuracy of spectroscopic ellipsometry, it is demonstrated that this technique can be usefully applied to the study of thin chromate films formed on industrially relevant aluminum products.     

Cryo-transfer TEM study of vacancy cluster formation in thin films of aluminum and copper elongated at low temperature

Kiritani et al. encountered a large number of vacancy clusters in heavily deformed thin metal films at room temperature. In the present work, thin films of aluminum and copper were loaded to fracture in liquid nitrogen and transferred directly to the TEM without warming up (Cryo-transfer TEM). In thin films of Al and Cu deformed at 78 K, many defect clusters were observed at 120 K. In thin Al films, small defect clusters disappeared by the 120 keV electron irradiation. Upon isochronal annealing, some of the dislocation loops grew in their size, which is much larger than those observed at 120 K. However, in regions that were not exposed to electron irradiation at 120 K, only a large number of stacking fault tetrahedra were observed after room temperature annealing. In copper, the 200 keV electron beam did not significantly change the defect clusters observed at 120 K.     

Phase diagram study of the formation and crystallization of Ge-metal amorphous alloy films

The Ge-Au and Ge-Ag alloy films were deposited in vacuum at room temperature and then systematically observed in the TEM. The maximum metallic concentrations in the alloy films,C _max, which form the stable amorphous alloy phases of germanium with gold and silver, were obtained. The annealed crystallization temperatureT _c, which falls with increasing metallic content in these films was also found. The structures of these films and their annealed specimens were also studied. There are various factors which influence the formation of amorphous alloy films deposited in vacuum for Ge-metal systems. A new formula forC _max has been derived. The annealed crystallization character has been explained by means of the variation of the free energy and the activation energy of crystallization. The activation energy of crystallization,E _a, can be obtained from the data values ofT _c. For Ge-Au films,E _a (Au)=E _a ^o /(–18.66C _Au ² +16.83C _Au+1)±3.3 (kcal mol^–1); for Ge-Ag films,E _a (Ag)=E _a ^o /(–2.754C _Ag ² +3.815C _Ag+ 1)±2.6 (kcal mol^–1). In order to explain all these results, two kinds of phase diagram for the alloy films have been introduced. One is the three-dimensional relationship diagrams of phase formation in semiconductor-metallic alloy films; it was introduced to explain the influencing factors. The other is the three-dimensional phase diagrams of annealed semiconductor-metallic films systems. From this diagram all the phase transitions can be found.     

Comparative study of direct and indirect forging processes for rheological material of A356 aluminium alloy

Abstract

Using a vacuum electromagnetic stirring system, a high quality rheological material is developed in order to fabricate the engineering components without defects like internal porosities, which are caused by the entrapment of external air into the melt and impurities arising from the penetration of surface oxides by vacuum electromagnetic stirring. For practical application in vehicle industry, forming of the knuckle component that is used in automobiles was demonstrated by both direct and indirect type rheoforging processes. Here, insufficient filling behaviour occurred during direct forging processes, whereas indirect rheoforging of material with a solid fraction of 30–40% produced a completely formed knuckle component; thus, an indirect forging process may be suitable for forming the knuckle part. Through microstructural investigations and tensile tests before and after T6 heat treatment of the material, mechanical properties were characterised. By obtaining data about the rheoforging process and material properties of the rheoforged product associated with microstructural features, feasibility for future practical application was investigated. Moreover, the die structure for direct and indirect rheological forging processes was comparatively studied.     

一种新的铝合金晶界检测算法及应用

晶粒度检测是金相检验中的一个重要问题，在应用图像处理方法时体现为边缘检测，原有的边缘检测算法的各向同性的特点导致边缘提取的效果不理想，本文通过对图像边缘的分析，提出一种新的边缘检测算法，设计出一种各向异性，权重合理的边缘检测算子。与传统的边缘检测算法实验结果的比较显示了其优良的性能，在铝合金的晶界检测中取得了较好的效果。     

Atomic layer deposition of tantalum nitride based thin films from cyclopentadienyl type precursor

Tantalum nitride based thin films have been deposited on p-Si (100) and SiO₂/Si by thermal Atomic Layer Deposition (ALD) using either the Ta(= N^tBu)(NEt₂)₃ or a derivative, in which one dialkylamido ligand is substituted by a η⁵-cyclopentadienyl (η⁵-Cp), as metal organic precursors with ammonia as reducing agent. TaN_xC_y self-limiting temperature dependent ALD growth was achieved for the TaCp(= N^tBu)(NEt₂)₂/NH₃ process with a growth rate of 0.51-0.91 Å cycle⁻¹ in the 400-425 °C temperature range while between 240 and 280 °C, the growth of TaN based films from the Ta(= N^tBu)(NEt₂)₃ was accompanied by a partial decomposition of the precursor. The η⁵-cyclopentadienyl type compound allows lower nitrogen content in the precursor and thereafter in the deposited film. Although N/Ta ratio is close to one at temperatures of 390 and 400 °C, as analyzed by Rutherford Back Scattering and Nuclear Reaction Analysis, films were amorphous independently of the deposition temperature. Since Ta-C bonds are present in the Cp derivative, the TaCp(= N^tBu)(NEt₂)₂ tends more likely to form tantalum carbide compared to Ta(= N^tBu)(NEt₂)₃, which leads to lower thin film resistivity. For both precursors, employed in their respective ALD window, films were smooth with a root-mean-square roughness close to 1 nm.     

A study on the parametric optimization of drawing metal stamping process for aluminum alloy tailgate parts using response surface methodology

The tailgate-extension in a vehicle is a part that connects the upper and lower parts of the tailgate. Since this part does not require high strength, aluminum must be used in order to reduce the weight of the vehicle. However, when choosing aluminum, it is difficult to satisfy the shape quality with the existing manufacturing process. Therefore, this study was conducted for the purpose of optimizing the draw metal stamping process for the development of tailgate extensions for vehicles using aluminum. The response surface methodology was utilized to optimize the draw metal stamping process. The process design parameters were established as blank holding force, coefficient of friction and die speed. Finally, the reliability of the optimization process and finite element analysis was secured by conducting field experiments to review the derived optimal process conditions.     

A computational study of kinetic phase diagrams for CoPt alloy films during epitaxial growth

We have studied the kinetic processes of the epitaxial growth for CoPt alloy films using the master equation method. The kinetic phase diagrams of CoPt alloy films which show the phase formation conditions during the epitaxial growth are determined. From the kinetic phase diagrams, we find that the [001] ordered structure is much easy to be grown at high temperature while the [100] ordered structure is easy to be grown at low temperature although both the [001] and [100] ordering could be the equilibrium ground states. The atomic deposition, ordering and surface segregation lead to a rich variety of phases in epitaxial growth. The surface segregation is found to enhance the [001] ordering and leads to the formation of the [001] ordered phase at high temperature.     

Influence of constitutional liquation on corrosion behaviour of aluminium alloy 2017A

The purpose of this work was to investigate microstructural aspects of constitutional liquation in the aluminium alloy 2017A and to determine its effect on corrosion behaviour of this alloy. Non-equilibrium melting of the alloy in the naturally aged condition was provoked by rapid heating above the eutectic temperature and immediate cooling in air. Corrosion testing was performed by exposure to a marine onshore atmosphere. The microstructure examinations were carried out using light microscopy, scanning electron microscopy, X-ray energy dispersion and X-ray diffraction analysis. It was found that, due to rapid heating rate, coarse θ (Al₂Cu) particles were melted by constitutional liquation and this way introduced strong susceptibility of 2017A alloy to intergranular corrosion.     

Electrical stability of polyimide siloxane films for interlayer dielectrics in multilevel interconnections

Electrical stability of a polyimide siloxane (PSI) film for ultra-large scale integrated circuit (ULSI) multilevel interconnections is studied. The PSI films, modified by p-aminophenyltrimethoxysilane (APTMS), are designed to have three-dimensional polymer structures through Si–O bonds. It has been revealed that the PSI films are more stable in electrical properties at higher temperatures than 150°C, as compared to the conventional polyimide (PI) films. The electrical conduction mechanism study for the PSI films has revealed that Schottky emission is dominant. Barrier height φ_B obtained from the electrical property for the PSI film was 0.460 eV in the temperatures ranging from 25–250°C. On the other hand, barrier height of 0.422 eV at lower temperatures than 150°C and activation energy of 1.09 eV at higher temperatures than 150°C were obtained for the conventional PI film. The difference in polymer structure is very sensitive to the electrical conduction at high temperature, due to sodium ion migration. The ideal band diagrams of metal-insulator-semiconductor (MIS) structures were also discussed. The optical band gaps for PSI and conventional PI films were 3.320 eV and 3.228 eV, respectively. This result suggests that the band gap of PI films can be enlarged by modification with Si–O components. The differential barrier height between the PSI and conventional PI films is 0.038 eV, and is close to the difference in half of optical band gaps (0.046 eV).     

Influence of heat treatments and anodization on fatigue life of 2017A alloy

In order to investigate the coupled effects of heat treatments and anodizing processes on fatigue life of aluminium alloy 2017A, a series of fatigue tests were conducted at 25 Hz. The effect of different tempers, naturally and artificially ageing (T4 and T6) and overageing (T7) conditions before sulphuric anodization were studied. Additionally, information on the microstructure of the anodic films was acquired by Scanning Electron Microscopy (SEM) analyses. The image analysis yielded qualitative information on the evolution of the surface morphology as a function of the substrate microstructure. Hence measured mechanical properties were directly related to the corresponding microstructure, the result of fatigue tests showed a decrease in fatigue life of anodized specimens as compared to untreated ones. This phenomenon became more pronounced in the T6 and T7 states. The decrease in the fatigue life could mainly be attributed to the brittle nature of oxide layer and to the heterogeneous microstructure of the film.     

铁磁形状记忆合金Ni-Mn-Ga薄膜制备工艺研究

铁磁形状记忆合金（FSMA）是种新型智能材料，Ni—Mn—Ga合金是这种材料的典型代表。本文使用ECR磁控溅射方法在NaCl晶片上制备出了Ni—Mn—Ga薄膜，并对其制备溅射功率进行了探讨。通过对薄膜成分和表面性质的分析，知22．5W为其制备的最佳功率。对沉积在玻璃片上的薄膜进行衍射分析各其为有序化程度不高的晶态。     

Surface morphology, composition and thermal behavior of tungsten-containing anodic spark coatings on aluminium alloy

Anodic spark coatings on aluminium alloy were prepared in aqueous electrolytes with sodium tungstate. The influence of boric acid addition in the electrolyte on the surface morphology, elemental and phase composition of the coatings was investigated. In both cases the coatings contained O, Al and W. The coatings obtained in electrolyte with boric acid and sodium tungstate contain also B at approximately 1 at.%. Scanning electron microscopy indicated that the coatings had three layers: the grey underlayer of anodic alumina, the second black layer of crystalline or amorphous aluminium tungstate agglomerated into fibers and the outer green layer of WO₃. It was proposed that isopoly- and heteropolyanions in the electrolyte used take part in the coating growth.     

Some metallurgical aspects of chip formation in cutting Ti-6wt.%Al-4wt.%V alloy

Adiabatic shear banding is a phenomenon observed in machining titanium and some other metals and alloys as well. The shear localized chips are important in the chip disposal process, machined surface integrity and the automation of machining operations. It is therefore necessary to understand the mechanisms of metal cutting such as the formation of shear banding in the produced chips. In this paper, the behaviour of the chip formation is investigated using various metallurgical analysis techniques. It was found, in cutting Ti-6wt.%Al-4wt.%V titanium alloy, that some non-diffusional phase transformation took place in the shear localized chips. The process of chip formation with shear banding and the effects of cutting conditions on shear banding frequency were also studied. The results of these tests are presented in this paper.     

溅射钽靶材用高纯钽粉工艺研究

分析了高纯钽粉生产的技术特点,介绍了一种改进的钽靶材用高纯钽粉的生产方法。采用高温脱氢(900~950℃)和低温脱氧(700~800℃)分步进行的工艺,有利于钽粉氧、氢、镁含量及粒度的控制,所得样品兼具低氧和小粒度的特点。采用真空热处理(700~800℃)工艺可以有效除去脱氧后残余的金属镁、酸洗带入的H、F等杂质,确保颗粒不长大,同时使杂质含量得到了很好的控制。     

Synthesis of anodic films in the presence of aniline and TiO2 nanoparticles on AA2024-T3 aluminium alloy

Coatings, comprising an inner porous anodic alumina film and an outer polyaniline/TiO₂ nanoparticle layer, were electrochemically synthesised on an AA2024-T3 aluminium alloy by single-step, anodic polarisation in an oxalic acid-based electrolyte. The morphology and composition of the coatings were examined by TEM, SEM and XPS, with the size and zeta-potential of the TiO₂ nanoparticles in the oxalic acid solution also measured. Observation of the growth of the coating during of anodic polarisation revealed that a distinct, two-layered coating is formed from the early stages of polarisation, with the anodic film forming at a constant rate and the outer layer developing at a rate that decreases markedly with times beyond about 30 min. Nanoparticles, agglomerated in the electrolyte, migrate to the anode due to the negative zeta-potential and form the nanoparticle-containing layer at the surface of anodic film. Such particles are not incorporated in the pores due to agglomeration and disordered film porosity at the outer layer of the anodic film.     

Tantalum pentoxide (Ta2O5) thin films for advanced dielectric applications

This paper reviews the present knowledge on tantalum pentoxide (Ta₂O₅) thin films and their applications in the field of microelectronics and integrated microtechnologies. Different methods used to produce tantalum oxide layers are described, emphazing elaboration mechanisms and key parameters for each technique. We also review recent advances in the deposition of Ta₂O₅ in the particular field of microelectronics where high quality layers are required from the structural and electrical points of view. The physical, structural, optical, chemical and electrical properties of tantalum oxide thin films on semiconductors are then presented and essential film parameters, such as optical index, film density or dielectric permittivity, are discussed. After a reminder of the basic mechanisms that control the bulk electrical conduction in insulating films, we carefully examine the origin of leakage currents in Ta₂O₅ and present the state-of-the-art concerning the insulating behaviour of tantalum oxide layers. Finally, applications of tantalum oxide thin films are presented in the last part of this paper. We show how Ta₂O₅ has been employed as an antireflection coating, insulating layer, gate oxide, corrosion resistant material, and sensitive layer in a wide variety of components, circuits and sensors.