Deposition Of Thin Metal Films Research Articles

Jigsaw electrode design for electrowetting devices

A new type of electrode design (jigsaw in shape) is presented for actuating inner electrodes in electrowetting-on-dielectric devices containing large two-dimensional array of electrodes. Electrodes are diagonally connected with one external pin to the voltage supply. Each electrode-pad is made by carving (or cutting) out two triangular sections from the sides and adding two triangular sections on the top and bottom of the traditional square electrode. This modification in electrode shape creates an imbalance of electromechanical force at the three-phase contact line on applying the supply voltage to the actuating electrode. Droplet moves towards either horizontal or vertical directions depending on the direction of the dominant force. The scheme requires a single layer of metal thin film deposition for device fabrication and also reduces the number of external pin connections to the power supply.

Density Functional Theory Study of the Surface Adsorption and Dissociation of Copper(I) Acetamidinates on Cu(110) Surfaces

Metal amidinates are common compounds with many applications, and are of particular value as precursors for the chemical deposition of thin metal films on solid surfaces. In order to better underst...

Functionalized gold electroless-plated optical fiber gratings for reliable surface biosensing

In the context of plasmonic sensing using optical fibers, the controlled deposition of thin metal films remains a challenge, especially because of their cylindrical shape. In this work, we study the gold electroless plating (ELP), which is a direct and cost-effective technique to improve the quality and reproducibility of the metal deposition. In this paper, we use optical fibers to monitor the deposition process in real time. Our analysis is conducted on gratings photo-imprinted in the fiber core. Using polarized light, we show how the comb-like amplitude spectra of tilted fiber Bragg gratings (TFBGs) evolve depending on the ELP duration. This spectral evolution linked to a thorough study of the metal surface allows us to define the optimized process for improved surface refractometry. We experimentally show that this happens for a particular arrangement of gold nanoparticles yielding spectral features comparable to those obtained for localized surface plasmon resonance (LSPR) excitation. Biosensing experiments were performed and a LOD of 1 ng/mL (14 pM) is reported. This comes along with an enhanced specificity, contrasting with a poor sensitivity to bulk refractive index. All this is paving the way to a fast online coating procedure for nano-scaled and label-free biosensing using optical fibers.

Influence of the crystalline structure of metal films on the performance of plasmonic biosensors

The development of plasmonic biosensors requires careful consideration of various factors associated with the deposition of thin metal films. The quality of metal films is mostly determined by their polycrystalline structure, where smaller crystallite sizes produce higher optical losses. In present work we obtained the dependence of optical losses in thin gold and copper films on their thicknesses. These experimental results are used for the analysis of the performance of plasmonic biosensors, which demonstrate an increase in the limit of detection of up to 50% and 35% for gold and copper films, respectively.

Fabricação de uma evaporadora de metais como forma de agregar valor aos serviços do microempreendedor individual

Existe um mercado promissor de deposição de filmes finos metálicos para aplicações de alta tecnologia no Brasil. Esse mercado não tem sido explorado pelos microempreendedores por falta de um estudo de viabilidade básico da construção de equipamentos que possam evaporar metais com qualidade e controle. Neste trabalho, foi feito um estudo de viabilidade da construção de uma evaporadora de metais que foi construída para uma primeira avaliação prática. Os resultados sugerem que com investimentos da ordem de R$ 4.000,00 a R$ 15.000,00, é possível fabricar evaporadoras de filmes finos com qualidade industrial. Uma atenção especial deve ser dada ao circuito de vácuo para controle da qualidade do filme depositado. O mercado pode ser facilmente explorado no desenvolvimento e fabricação de placas de energia solar, deposição de camadas metálicas em vidros instalados em automóveis, antenas de satélites e até na fabricação de joias e bijuterias.

Coupling Additive Manufacturing and Wet Metallization for Advanced Microfabrication

Nano and microfabrication are general terms to indicate a broad selection of techniques suitable to produce functional structures at the nano or microscale. This ability is at the base of many advanced applications in the main fields of engineering. However, many techniques typically used in microfabrication, like lithography or thin film deposition, are characterized by a limited tridimensionality of the final product. These manufacturing methods are commonly said to operate in 2.5 dimensions, due to the limited envelope achievable in the vertical direction. To overcome said limitations, 3D printing techniques able to work at the microscale have been introduced in the last few years. The application of such techniques, based on direct writing of the different layers that compose the object by mean of a laser beam, to microfabrication gave origin to a new concept of production: additive microfabrication [1]. The main disadvantage of methodologies like stereolithography (SLA) or two photons lithography (2PL) is the material used for printing: a mixture of photocurable polymers. The need to use resins implies significant limitations on the final properties of the object: relatively low mechanical properties and total or partial lack of conductivity. A possible approach to impart metallic properties to SLA or 2PL printed parts is the deposition of metal thin films on the surface of the 3D printed part. In the present work, a possible hybrid production route that combines SLA and wet metallization is described in general and applied to real microfabrication. Electroless deposition on SLA resins has already been attempted in the past [2], as well as deposition of multilayers. Starting from these propaedeutic work, the hybrid SLA/wet metallization approach is here applied to the micromanufacturing of two prototypical devices belonging to two distinct classes: MEMS and magnetically steerable microdevices. These two selected applications demonstrate the applicability of the manufacturing methodology but does not limit the range of possible uses, which span from bioengineering to microelectronics or to microfluidics. [1] Misawa, Hiroaki, ed. (2006). 3D Laser Microfabrication: Principles and Applications, Germany: Wiley [2] R. Bernasconi, C. Credi, M. Tironi, M. Levi, L. Magagnin, Electroless Metallization of Stereolithographic Photocurable Resins for 3D Printing of Functional Microdevices. J. Electrochem. Soc. 164, B3059–B3066 (2017)

(Invited) Precursor Innovations Directed Toward the Area Selective, Thermal Atomic Layer Deposition of Electropositive Metal Thin Films

Our laboratory is developing new chemical precursors for the growth of electropositive metal and element thin films by atomic layer deposition (ALD). We are also interested in processes that exhibit area selective growth. ALD has many current applications in copper metallization, diffusion barriers, liners, and transistor fabrication. Thermal ALD is often preferred because plasmas can afford low conformal coverage due to radical recombination on the walls of deep and narrow features. There has been extensive progress in the thermal ALD of copper and noble metal films in recent years, because the positive electrochemical potentials allow relatively easy reduction of precursor ions to the metals. Thermal ALD approaches to most other metals and elements in the periodic table are not well developed, due to the negative electrochemical potentials of the ions and a current lack of ALD co-reagents that can convert the ions to the metals or elements. Herein, we will describe the thermal ALD growth of electropositive metals such as nickel, cobalt, aluminium, and others. The ALD of nickel and cobalt metal films has been achieved using precursors containing diazadienyl ligands (precursors 1 and 2). These precursors enable the deposition of cobalt and nickel metal films at temperatures below 200 °C and use alkylamines as benign co-reagents. Growth rates are high (0.60 Å/cycle for nickel, 0.98 Å/cycle for cobalt), high purity, low resistivity metal films are obtained, and the films have low rms roughnesses. The processes exhibit inherent selective growth on metal substrates such as platinum, ruthenium, and copper. By contrast, no growth is observed on insulating substrates. We will also overview a new thermal ALD process for the growth of aluminum metal films. This process entails treatment of surface-bound AlCl3 with a thermally stable, volatile aluminium hydride co-reagent. The growth rate for the aluminium metal ALD process is high, and high purity, low resistivity aluminium metal films are obtained. Prospects for the area selective growth of aluminum metal films will be presented. These examples demonstrate that ALD processes can be enabled for electropositive metals through careful design of precursors and chemistry. Moreover, many of the metal ALD processes exhibit area selective growth. Figure 1

Nanoporous Ag Films Prepared by Cluster‐Source Sputtering as Substrates for Surface‐Enhanced Raman Scattering

By mounting a cluster source on a conventional sputtering system, a new sputtering system is devised for the deposition of nanoporous metal thin films at room temperature. First, the diameter of the nozzle is fixed while the pressure inside the cluster source is kept at several hundreds of mTorr. By adjusting the length of the cluster source, nanoporous films of different thickness can be formed at room temperature. The Raman response characteristics according to the process conditions are then analyzed, and the applicability of the sputtered thin film as a substrate for surface‐enhanced Raman scattering (SERS) is examined. The results show that the Raman intensity increases with increasing film thickness and reaches a saturated value at a thickness of 2 µm. Therefore, the proposed system takes advantage of an existing sputtering process, and it is possible to form a nanoporous metal film with thickness of several micrometers or more that can be used as a Raman substrate.

Electrodeposition Though Polyelectrolyte Layers: Control of Interfacial Reaction, Deposition Rate, and Morphology of Deposited Thin Films

Demand for the development of deposition strategies of well-defined metal thin films with good chemical and physical characteristics has been rapidly growing in the field of various electronics applications. For example, copper electro- or electroless deposition has been widely utilized and investigated in microelectronics industry due to its low electrical resistivity and high electromigration resistance, as compared with aluminum. The conventional plating bath for electro- or electrolless copper deposition involves various chemical reagents such as deposition promoter (or inhibiter), brightening and smoothing agent, etc. These additives, typically organic molecules, sometimes cause mechanical problems due to inclusion of such additives during deposition process, and the discharge from the deposition bath can be a serious environmental issue. Therefore, the development of a facile process that enables additive-free deposition of metallic thin films as well as low environmental toxicity is an important challenge for the fabrication of microelectronic elements. In order to sustain the demand for generating multichip packaging systems for future electronic devices, it would be exceedingly useful to develop novel electrochemical deposition strategy with high-throughput capability that would allow stability of electrochemical reaction at higher deposition rate from plating bath without organic additives. In this context, direct metal deposition processes though ion conducting films have been investigated, such as the fabrication of metallic patterns on polymer substrates using ion-doped precursor films. A variety of direct deposition techniques have been introduced by several groups, including ours,1,2) based on photoinduced chemistry, thermal treatment, and selective chemical reduction for polyimide and other functional polymers. We have also reported a chemical metallization strategy that utilizes electrochemical constructive lithography with post lift-off process, which enables the fabrication of metal patterns on the polyimide substrate.3) The use of ion-doped precursors has triggered the development of new concept for electrochemical deposition. Herein we report for the first time that metallic thin films can be deposited through polyelectrolyte thin layers placed on the cathode electrode by the diffusion of metallic ions from the interior of polyelectrolyte, which is essentially different to conventional solution-phase electrodeposition processes (Fig. 1). By taking advantage of the cation-exchangeable nature of polyelectrolyte layers used for creation of solid interface, we demonstrate in this study how it is possible to merge the electrochemical deposition at cathode-polyelectrolyte interface and diffusion of cations through polyelectrolytes for development of novel solid electrodeposition (SED) process. As a proof of concept study, we herein present the successful electrochemical deposition of copper and nickel thin films at the interface between an electrode and ion-doped polyelectrolyte layers from the baths containing only metal salts (without any additives). The effect of cation concentration, temperature, and electrochemical deposition conditions on the deposition rate, growth process and morphology of the films has been investigated. Several electrochemical, microscopic and quantitative analysis revealed that the metallic films have been successfully deposited at the cathode-polyelectrolyte interface through ion exchange reaction in the polyelectrolyte layers, the deposition rate of which are determined by ion exchange rate of cations. This strategy offers an opportunity to translate solution-phase electrochemical deposition into a high-throughput, cost-effective, environmentally-friendly process for the fabrication of metal thin films on substrates. 1) Matsumura, Y. Enomoto, T. Tsuruoka, K. Akamatsu, H. Nawafune, Langmuir, 26, 12448-12454 (2010). 2) S. Ikeda, H. Yanagimoto, K. Akamatsu, H. Nawafune, Adv. Funct. Mater., 17, 889-897 (2007). 3) K. Akamatsu, Y. Fukumoto, T. Taniyama, T. Tsuruoka, H. Yanagimoto, H. Nawafune, Langmuir, 27, 11761-11766 (2011). Figure 1

Impurity-controlled film growth and elastic properties of CoCrCuFeNi thin films

The growth mode during physical vapor deposition of metallic thin films is very sensitive to the presence of impurity species. These impurities can originate from the residual ambient gases present in the vacuum chamber and usually impede continued crystal growth by inducing renucleation. During magnetron sputtering at intermediary base pressures (~10−4Pa), the effect of these impurities can be estimated from the ratio of the impurity flux to the metallic flux. In this study, the influence of the ambient impurity flux on the growth mode of CoCrCuFeNi High-Entropy Alloy (HEA) thin films is investigated. It is shown that the impurity-to-metal flux ratio effectively controls the texture, grain size, porosity, and elastic properties of the nanocrystalline CoCrCuFeNi thin films. A less clear (111) fiber texture is observed at higher impurity-to-metal flux ratio. With increasing impurity-to-metal flux ratio the grain size decreases while the porosity increases. The elastic constants, and Young's modulus for CoCrCuFeNi is reported to be the highest for the 〈111〉 direction. Hence, the change in film texture also affects the elastic constants and Young's modulus which tend to become lower as more grains with different orientation are observed at higher flux ratios. This study demonstrates that an exact knowledge of the impurity-to-metal flux ratio, or otherwise stated, of the base pressure and deposition rate during sputter deposition is imperative for the synthesis of HEA films with reproducible properties.

Efficient Process for Direct Atomic Layer Deposition of Metallic Cu Thin Films Based on an Organic Reductant

We report a promising approach to use an organic reductant for in situ atomic layer deposition (ALD) of metallic copper films. The process is based on sequentially pulsed precursors copper acetyl acetonate (acac), water, and hydroquinone (HQ) and yields crystalline copper films at temperatures as low as <200 °C with an appreciably high deposition rate of ∼2 A/cycle. Deposition parameters are explored for the process m × [n × (Cu(acac)2–H2O)–HQ] with several values of m and n, keeping m × n fixed to 500. The films are found crystalline with metallic copper as the main phase, but different trace amounts of Cu2O are observed when the HQ pulse frequency decreases below 1/5. The as-deposited copper films are shiny and specularly reflecting and show metallic-type electrical conductivity. The absolute resistivity of the films estimated at room temperature is in the order of 2–5 μΩ cm, having a sizable contribution, with 0.5 μΩ cm from residual resistivity as a result of impurities and/or imperfections. We believ...

Metallic Copper Thin Films Grown by Plasma‐Enhanced Atomic Layer Deposition of Air Stable Precursors

The authors, report here on the deposition of metallic copper thin films by plasma‐assisted atomic layer deposition (ALD) with an air stable and volatile precursor − [Cu((Py)CHCOCF3)2]2 (Py = pyridine) − that stands out due to its facile synthesis and easy handling under ambient conditions. Copper thin films are obtained by decomposing [Cu((Py)CHCOCF3)2]2 in hydrogen plasma in a concomitant deposition and recrystallization process. The thermal stability of the precursor prevents thermally induced decomposition, which allows precise control over thickness and film homogeneity. Electrical measurements of the as‐deposited samples show clear interdependence of sheet resistance on the substrates surface roughness, thereby, films with higher roughness show higher resistance. Combined X‐Ray photoelectron spectroscopy of Cu 2p peak and Cu LMM peak, as well as resistivity values of 58 Ω □−1 confirm the high quality of copper films without the need of further annealing steps under reducing atmosphere.

Deposition of metallic molybdenum thin films on 304L steel substrate by SUT-PF

Abstract The present research work aims to employ plasma focus in order to deposit molybdenum (Mo) on the 304 stainless steel substrate. The processing parameters were shot numbers as well as the distance of substrate from the anode tip. Stereo, atom force microscopy (AFM) and field emission-scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectroscopy (EDS) were used to study the deposited coatings. Microhardness measurements were also performed on the coatings. Results indicated that the plasma focus can be successfully applied to deposit Mo anode on the stainless steel substrate. The coatings contained discrete pores with sizes varying by processing parameters. The thickness of coatings decreased as the distance of substrate from the anode tip increased. Furthermore, the Mo content decreased in the deposited coating as the thickness of coating increased.

XPS study of thermal and electron-induced decomposition of Ni and Co acetylacetonate thin films for metal deposition

Optimizing thin metal film deposition techniques from metal-organic precursors such as atomic layer deposition, chemical vapor deposition (CVD), or electron beam-induced deposition (EBID) with the help of surface science analysis tools in ultrahigh vacuum requires a contamination-free precursor delivery technique, especially in the case of the less volatile precursors. For this purpose, the preparation of layers of undecomposed Ni(acac)2 and Co(acac)2 was tried via pulsed spray evaporation of a liquid solution of the precursors in ethanol into a flow of nitrogen on a CVD reactor. Solvent-free layers of intact precursor molecules were obtained when the substrate was held at a temperature of 115 °C. A qualitative comparison of thermally initiated and electron-induced precursor decomposition and metal center reduction was carried out. All deposited films were analyzed with respect to chemical composition quasi in situ by x-ray photoelectron spectroscopy. Thermally initiated decomposition yielded higher metal-to-metal oxide ratios in the deposit than the electron-induced process for which ratios of 60:40 and 20:80 were achieved for Ni and Co, resp. Compared to continuous EBID processes, all deposits showed low levels of carbon impurities of ∼10 at. %. Therefore, postdeposition irradiation of metal acetylacetonate layers by a focused electron beam and subsequent removal of intact precursor by dissolution in ethanol or by heating is proposed as electron beam lithography technique on the laboratory scale for the production of the metal nanostructures.

Fabrication of Disordered Subwavelength Structures on Curved Surfaces by Using a Thermal Dewetting Process

We present disordered moth eye structures on curved surfaces fabricated by dry etching of thermally dewetted metal nanoparticles. This lithography-free fabrication allows the formation of subwavelength scale nanostructures on the strongly inclined surfaces such as ball lens as well as on the microlens arrays with low curvature. In particular, we found that the size and average distance of nanostructures are closely related to the inclined angle of the surface. Experimental results on oblique angle deposition of metal thin films followed by thermal dewetting also support these effects.

Observation and Origin of Extraordinary Atomic Mobility at Metal-Semiconductor Interfaces at Low Temperatures.

Extraordinarily high mobility of Si and Ge atoms at semiconductor (Si, Ge)-metal (Al) interfaces is observed at temperatures as low as 80K during thin metal film deposition. Insitu x-ray photoemission spectroscopic valence-band measurements reveal a changed chemical bonding nature of the semiconductor atoms, from localized covalentlike to delocalized metalliclike, at the interface with the Al metal. The resulting delocalized bonding nature of the interfacial semiconductor atoms brings about the observed extreme enhancement of their mobility. The finding opens avenues for tailoring reaction kinetics and phase transformations in nanostructured materials, as functional thin-film systems, at ultralow temperatures by dedicated interfacial design.

Bio-Inspired Chemical Fabrication of Stretchable Transparent Electrodes.

Stretchable and transparent electrodes are fabricated by chemical deposition of metal thin films on natural veins of leaves at ambient conditions. These vein-based transparent electrodes show excellent electro-optical property (0.9 Ω sq(-1) at 83% T) even at 50% tensile strains, ideal for flexible and stretchable optoelectronic devices.

Equipment for deposition of thin metallic films bombarded by fast argon atoms

Deposition of thin metallic films on dielectric substrates using a source of metal atom flow combined with a flow fast argon atoms has been investigated and the investigation results are presented. The fast atoms are produced due to charge-exchange collisions in a vacuum chamber of argon ions, which are accelerated by potential difference between the hollow-cathode glow-discharge plasma and an emissive grid and enter the chamber through the grid. The metal atoms produced due to ion sputtering of a metallic foil placed on the inner surface of the hollow cathode enter the chamber through the same grid. Substrate pretreatment and pulse-periodic bombardment of the growing film by ∼1-keV argon atoms both ensure adhesion of copper to glass up to 2 × 107 Pa. The use of a hollow substrate holder, whose inner surface is also covered with the same foil, makes it possible to exclude losses of the depositing metal and allows recommendation of the equipment for beam-assisted deposition of precious metal films.

Biosynthesis of large area (30×30 cm2) silver thin films

For the first time, biosynthesis of large area (30×30cm2) silver thin films onto glass substrates using chemical successive ionic layer adsorption and reaction (SILAR) method is reported. The SILAR deposition method is relatively inexpensive and convenient for large area deposition of metal thin films. Silver nanostructurals are deposited using AgNO3 solution and guava leaves extract. The characteristics of silver thin films are studied using UV–visible spectrophotometer, scanning electron microscopy (SEM), X-ray diffraction (XRD), atomic force microscopy (AFM), contact angle and photoluminescence (PL) techniques. The UV–visible spectrophotometer confirmed the formation of silver thin film. Also, the absorbance spectra confirmed that the silver thin films exhibit absorption maximum at 435nm, which is a characteristic feature of surface plasmon resonance (SPR) peak for silver nanoparticles. The scanning electron microscopy (SEM) images showed the formation of aggregated silver nanoparticle with increasing thicknesses. The AFM study showed that the silver nanoparticles are nonuniform on the substrate surface. The XRD analyses confirmed the nanocrystalline phase of silver thin film with face center cubic (FCC) crystal structure. Contact angle measurement suggested that the film is hydrophilic in nature. The silver thin films are found to be photoluminescent with a characteristic peak at 479nm. The present study demonstrates an easy method for biosynthesis of large area silver thin films using green and ecofriendly SILAR method. Finally, as an application these films are used effectively in antibacterial activity study.

Polymer activation by reducing agent absorption as a flexible tool for the creation of metal films and nanostructures by electroless plating

The ability to modify the activity of polymer substrates for subsequent electroless plating is of fundamental importance for both the homogeneous metallization of macroscopic work pieces and the fabrication of advanced nanomaterials. In this study, we demonstrate the high flexibility of a polymer activation technique based on the absorption of reducing agents, followed by metal nanoparticle precipitation in the presence of metal salt solutions. We show that the process can be applied to polymers with very different chemical properties, namely polycarbonate, poly(ethylene terephthalate), acrylonitrile butadiene styrene and polyvinyl alcohol. Furthermore, the effects of important reaction parameters (type of reducing agent, metal precursor, concentration of the sensitization and activation solutions) on the seeding properties (particle size, shape and density) are evaluated extensively. Based on these results, synthetic guidelines are provided on how the substrate activity can be tailored for the successful fabrication of free-standing metal nanotubes in ion-track etched polycarbonate templates. In addition, we demonstrate that the process can be applied to prepare polymeric films and three-dimensional structures for the electroless deposition of metal thin films.