Deposition Of Metal Films Research Articles

Sub-15-nm patterning of asymmetric metal electrodes and devices by adhesion lithography.

Coplanar electrodes formed from asymmetric metals separated on the nanometre length scale are essential elements of nanoscale photonic and electronic devices. Existing fabrication methods typically involve electron-beam lithography—a technique that enables high fidelity patterning but suffers from significant limitations in terms of low throughput, poor scalability to large areas and restrictive choice of substrate and electrode materials. Here, we describe a versatile method for the rapid fabrication of asymmetric nanogap electrodes that exploits the ability of selected self-assembled monolayers to attach conformally to a prepatterned metal layer and thereby weaken adhesion to a subsequently deposited metal film. The method may be carried out under ambient conditions using simple equipment and a minimum of processing steps, enabling the rapid fabrication of nanogap electrodes and optoelectronic devices with aspect ratios in excess of 100,000.

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.

Fabrication and characterization of gridded Pt/SiO2/Si MOS structure for hydrogen and hydrogen sulphide sensing

A gridded gate Pt/SiO2/Si MOS capacitor has been fabricated for detection of Hydrogen (H2) and Hydrogen Sulphide (H2S) gases. The MOS device was fabricated on P-type Si <100> (1–6 Ω cm) wafer with thermal oxide layer of thickness about 100 Å, whereas, Platinum (Pt) gate of ∼350 Å was deposited by thermal evaporation technique. The C–V (capacitance vs voltage) and G–V (conductance vs voltage) measurements have been performed for the evaluation of gas sensing behavior of fabricated MOS capacitor structure in H2 (250–4000 ppm) and H2S (1000–6000 ppm) gases at both room and 120 °C temperatures, in a closed chamber in air atmosphere. It has been observed that the value of capacitance decreases with increase in gas concentration. The fabricated MOS capacitor sensor has shown better sensitivity towards H2 (88.6%) at room temperature (∼25 °C) as compared to (∼45%) at 120 °C. Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) studies have revealed the porous nature of the deposited metal film. The side wall diffusion, spillover of Hydrogen into oxide layer, increase in fixed oxide charge density, increase in surface area caused by gridded structure, the formation of dipole layer and change in interface state density on gas exposure, may be the mechanisms of gas sensing for improved sensitivity of the fabricated MOS device.

Adhesion and Interfacial Structure of Metal Film Electrolessly Deposited on Si Using Au Nanoparticles As Catalysts

Surface metallization of silicon (Si), that is, adhesive metal-film formation on Si is important for obtaining infallible electrical contacts in various devices, such as solar cells and power devices. Autocatalytic electroless deposition, which is a conventional method to metallize nonmetallic substrates, has several advantages including simplicity of process, uniformity of films, and the covering of complicated structures. So, the autocatalytic electroless deposition is expected to replace sputtering of back metal of power devices and screen printing of metal electrodes of solar cells. This deposition requires surface activation (catalyzation pretreatment) of nonmetallic substrates, generally using tin and palladium (1). It is difficult to obtain adhesive metal films on Si substrates with conventional catalyzation pretreatments. Heat treatments before and after the deposition improved the adhesion of electrolessly deposited metal films on Si (2, 3). We recently developed a new surface-activation process for the direct electroless deposition of adhesive metal films on silicon substrates that consists of two steps (4): Step 1) formation of metal nanoparticles by electroless displacement deposition; and Step 2) Metal-film formation on the Si surface by autocatalytic electroless deposition. In previous study, we found that gold nanoparticles have an excellent ability to bind metal films to silicon surfaces (4). In addition, the contact resistance between Si substrate and the nickel-phosphorus alloy (Ni-P) film formed by this process was approximately 0.01 Ωcm2(5). In this study, we investigated the interfacial structure of Ni-P film/Si substrate by a transmission electron microscope (TEM) analysis. At the first step of the two-step process, gold nanoparticles, 5-25 nm in diameter and ca. 1011 cm-2in particles density, were deposited on a p-Si substrate by immersing the substrate in metal salt solution containing HF. At the second step, a Ni-P film was electrolessly formed on the Si substrate by using phosphinate as a reducing agent. The adhesion of deposited metal films on Si substrates was examined by a tape test based on Japanese Industrial Standard JIS H8504 corresponding to ISO 2819. We observed the interfacial structure by a TEM (JEOL JEM-2100). An X-ray analysis was performed using a FE-TEM (HITACHI HF-2000, 2-nm nanoprobe). Figure 1 shows the percentage of the area of the electrolessly deposited Ni-P films that remained on the silicon substrates after the tape test as a function of the thickness of deposited Ni-P films. No peeling occurred for Ni-P films thinner than 1.3 μm after aging of samples at atmospheric ambient for a day. The thickness of starting point of peering increased to 1.7 μm after aging for 7 days. This shows that the adhesion of the films improves by aging under mild conditions. Figure 2 shows the typical interfacial structures of metal-nanoparticle/Si. The Ag particles were in contact barely with Si (Fig. 2a). The Au nanoparticles formed mixing structure with Si (Fig. 2b and c). The formation of amorphous layer between Ni-P film and Si substrate was observed (Fig. 2c). These images indicate that a silicon and gold metallic alloy was formed at the interface between silicon and gold even at room temperature. This alloy formation is expected to improve the adhesion of metal film on silicon. Thus, gold nanoparticles work not only as catalysts to initiate autocatalytic electroless metal deposition but also as binding-points and as electric-contacts between the deposited metal film and the silicon surface.ACKNOWLEDGEMENTSThe present work was partly supported by JSPS KAKENHI (23560875) and A-STEP from JST.REFERENCESM. Paunovic and M. Schlesinger, Fundamentals of Electrochemical Deposition, 2nd. ed., Wiley, NY (2006).V. M. Dubin, J. Electrochem. Soc., 139, 1289 (1992).S. Karmalkar and V. P. Kumar, J. Electrochem. Soc., 151, C554 (2004).S. Yae, et al., ECS Trans., 53 (6), 99 (2013).Y. Orita, et al., Abst. 225th. ECS Meeting, Symp. D2 (2014).

Electroless Deposition By Surface Limited Redox Replacement in One Cell Configuration

The deposition of thin noble metal films is an area of wide interest for many different industrial applications. These films allow for an application to take advantage of the beneficial properties of said metal of interest while minimizing cost. Thusly, thin films are currently being applied as low-cost, high-activity fuel cell catalysts, photovoltaic semiconductors, and protective coatings in circuitization of electronic devices.Surface limited redox replacement (SLRR) is a technique that has been applied to depositing ultra thin films of metals and alloys and has also shown the ability to grow epitaxial metal layers utilizing the monolayer limited nature of underpotential deposition (UPD). In SLRR an UPD monolayer of a sacrificial element is formed via a potential pulse. This layer is sequentially replaced by a more noble metal at free corrosion conditions. This sequence of events ultimately yields the deposition of one layer of the more noble metal 1. This technique can be then applied to subsequent events resulting in perfectly controlled layer by layer metal growth 2-6.During SLRR the potential pulse that is applied to form the UPD layer has conventionally been performed by an external power device (potentiostat). In this work instead of the application of external power, a corrosion pair scenario is realized in a three-electrode configuration with a Pb wire in solution serving as the “executive” electrode, a Hg/Hg2SO4 reference electrode and a Au polycrystalline disc used as working electrode. The difference in equilibrium potentials of the executive and working electrode coupled with specific aspects of the kinetics of the Pb-Au corrosion pair allow for efficient control of the potential applied to the Au substrate. More specifically, electrical contact between executive and working electrodes results in the application of a potential to the Au electrode, nearly identical to the Pb equilibrium potential. This ultimately leads to the formation of a sacrificial Pb UPD layer on the Au surface. Subsequent disconnection of the electrical contact allows for the electroless, in nature, SLRR to occur. This technique can consequentially be used to coat a substrate metal surface with another metal or alloy of interest as illustrated in Figure 1. In the present report, the proposed approach has been applied to an ideal system in the plating of Ag on Au in order to ascertain the protocol’s applicability for metal deposition. The work has also been extended to the industrially more relevant system of Pt on Au. Adopting the herein presented routine, SLRR can be simplified and prove even more cost effective with no need for external power source and little to no energy cost, ultimately improving industrial viability.

Fabrication of an ordered nanodot array by thermal dewetting on a patterned substrate

Abstract A new process to fabricate an ordered gold nanodot array by thermal dewetting on a patterned substrate is proposed in this paper. Its feasibility was demonstrated through the experiments. The process comprises three steps; fabrication of a square nano-grooves grid on a substrate by nano-plastic forming, deposition of a thin gold film on the patterned substrate, and annealing the metal coated substrate to form an ordered nanodot array. The effects of the thickness of the deposited metal film on the morphology of nanodot array are studied. It is found that a nanodot array of good uniformity and regularity is obtained by optimizing the gold film thickness. It is verified that patterning of groove grid on a substrate is effective to improve the uniformity and regularity of the nanodot array in the thermal dewetting process.

Balanced double-loop mesoscopic interferometer based on Josephson proximity nanojunctions

We report on the fabrication and characterization of a two-terminal mesoscopic interferometer based on three V/Cu/V Josephson junctions having nanoscale cross-section. The junctions have been arranged in a double-ring geometry realized by metallic thin film deposition through a suspended mask defined by electron beam lithography. Although a significant amount of asymmetry between the critical current of each junction is observed, we show that the interferometer is able to suppress the supercurrent to a level lower than 6 parts per thousand, being here limited by measurement resolution. The present nano-device is suitable for low-temperature magnetometric and gradiometric measurements over the micrometric scale.

Deposition of thin metal films in via holes of LSI by using the IBE method

The characteristics of an ablation plasma generated by using an intense, pulsed ion beam were studied experimentally by using high-speed photography and calorimetry. From the high-speed photographs, it is found that the ablation plasma were found to expand toward the substrate, and it is kept for about 20 μs after the start of the beam irradiation. The calorimetry diagnostic results should that the thermal energy carried by the ablation plasma instantly, a increased the substrate surface temperature to over 900 K. After that, thermal conduction in the substrate dominated and the temperature dropped at a rate of 108 K/s. Using the high-density ablation plasmas produced by pulsed ion beam interaction with solid targets, we successfully embedded tungsten thin films in via holes with an aspect ratio of 4.3, not only in the bottom of the silicon, but also in the side walls.

Selective Coating Deposition on High-Q Single-crystal Silicon Resonators for the Investigation of Thermal Noise Statistical Properties

Silicon resonators are widely used in a large class of applications including sensing and actuation, signal processing and energy harvesting. Very often, their application as sensors requires the deposition of metallic thin films or dielectric coatings, to set the electrical conductivity, the optical coupling, or other physical-chemical properties of the device. Invariably coatings degrade the quality factor (Q) of resonance by increasing the amount of energy dissipated during vibration. In this paper, we show a class of resonators used for the investigation of thermal noise statistical properties in non-thermodynamic equilibrium. Design strategies to preserve the silicon Q-factor are discussed.

New organometallic precursors and processes for chemical vapor deposition in the technology of nanomaterials

Processes of chemical vapor deposition (CVD) of metal and dielectric (high-k and low-k) films with the help of unconventional initial reagents (volatile complex and organoelement compounds) were developed. Complex investigation of the chemical and phase composition and structure of (HfO2)1 − x(Me2O3)x double oxides (where Me = Al, Sc), and silicon carbonitrides and oxycarbonitrides was carried out. It was shown that the resulting materials enjoy a number of unique functional properties, which makes them promising for application in micro-, nano-, and optoelectronic devices.

Laser-Induced Metal Reduction from Liquid Electrolyte Precursor

A special sort of laser methods such as direct writing of metal and thin film deposition from liquid precursors was developed for the surface processing and the localized metallization of different kinds of materials. Laser radiation initiates the chemical reaction resulted in the reduction of the metal complexes to the metals in the liquid electrolyte, followed by the metal deposition on the substrate with a high degree of the adhesion. In this study, continuous wave of Ar+ laser generated in multiwave regime with laser power from 5 to 500 mW was chosen for the Copper reduction and deposition on SiO2 substrate. In order to investigate the effect of salt precursors on the properties of the deposited structures, two kinds of electrolyte solution were prepared on the base of CuSO4 and CuCl2. It was shown that metal deposition can be initiated at the laser power of 50 mW. The width of the deposits was found to be substantially dependent on the applied laser power. Deposits were revealed as conductive layers and the resistance of the layers depends strongly on the solution temperature and the salt precursor.

Spray deposition of nanostructured metal films using hydrodynamically stabilized, high pressure microplasmas

Cu, Pd, and Ni nanoparticles and films compose of fibers, matchsticks, and dense columns were grown using a hydrodynamically stabilized, high pressure (∼Torr) microplasma jet source at low substrate temperatures. Organometallic precursors were dissociated in the microplasma jet under highly reducing conditions, creating a directed flux of active metal species for the subsequent growth of nanostructured films. The growth process can be tuned (e.g., from nanoparticles, to competitive columns, to dense films with nanoscale grain structure) by adjusting the precursor flux, plasma current, background gas atmosphere, and jet–substrate distance. Microplasma jet operation, dynamics of the growth process, and the resulting metallic films are discussed.

Self-localization of mixed organophosphonic acid and organothiol monolayers on patterned Al–Cu substrates

The aim of this work is to investigate the selective adsorption of ultra-thin organic films on model heterogeneous aluminum–copper surfaces via self-assembly from mixed monomer solutions. Patterned aluminum/copper substrates were prepared via microsphere lithography by means of sequential physical vapour deposition of the respective metal films on silicon wafers. The formation of monolayers with a methylene end group on the bi-metallic surfaces was performed from a dilute cocktail solution of two organic molecules with thiol and phosphonic acid head groups. The ordering of the monolayers was analyzed by means of Polarization Modulated-Infrared Reflection Absorption Spectroscopy (PM-IRRAS). Imaging Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) experiments were performed to analyze the lateral distribution of the two mono-functional molecules. The preferred adsorption sites of the functionalities in the cocktail solution reproduced the patterned image of the model substrate with chemical contrast. The copper regions were covered with monolayers of thiol head group and organophosophonic acid monolayer was detected on aluminum regions. This self-localization of the organofunctional molecules converted the heterogeneous surface of the patterned substrate to a surface uniformly covered with methyl terminated self-assembled monolayers (SAMs).

(Invited) Catalytic Surface Reactions during Nucleation and Growth of Atomic Layer Deposition of Noble Metals: A Case Study for Platinum

Atomic layer deposition (ALD) of noble metals has attracted much attention in recent years for the deposition of thin metal films, as well as for the synthesis of supported metallic nanoparticles. Noble metal surfaces and nanoparticles possess catalytic activity for dissociation of metalorganic precursor and O2 molecules, which has important consequences for the reaction mechanisms of ALD. In this work, a case study is presented with respect to the importance of catalytic surface reactions during the nucleation and growth of Pt ALD, which serves as a model system for the growth of other noble metals by ALD. It is illustrated that atomic level understanding of these processes is vital for the development of novel nanopatterning and nanoparticle synthesis approaches.

Volatile and Thermally Stable Mid to Late Transition Metal Complexes Containing α-Imino Alkoxide Ligands, a New Strongly Reducing Coreagent, and Thermal Atomic Layer Deposition of Ni, Co, Fe, and Cr Metal Films

Treatment of MCl2 (M = Cu, Ni, Co, Fe, Mn, Cr) with 2 equiv of α-imino alkoxide salts K(RR'COCNtBu) (R = Me, tBu; R' = iPr, tBu) afforded M(RR'COCNtBu)2 or [Mn(RR'COCNtBu)2]2 in 9-75% yields. These complexes combine volatility and high thermal stability and have useful atomic layer deposition (ALD) precursor properties. Solution reactions between Ni, Co, and Mn complexes showed that BH3(NHMe2) can reduce all to metal powders. ALD growth of Ni, Co, Fe, and Cr films is demonstrated. Mn film growth may be possible, but the films oxidize completely upon exposure to air.

Fabrication of high temperature moiré grating and its application

The fabrication technique of high temperature moiré grating has been presented, which combines thermal nanoimprint process method and high temperature transferring technique. And the quality of grating was evaluated by analyzing its configuration through the Atomic Force Microscope (AFM) images. From the analysis, it was found that the optimal depth of grating will cause different stress condition in the process of vacuum deposition, and thicker deposited metal film on the grating may enhance the oxidation resistant ability. However, with the increase of the thickness of the metal film, cracks may occur in the film, In order to avoid this mechanical failure, the optimization of the depth of grating was performed. The optimized depth was obtained by analyzing the stress intensity using Finite Element Method (FEM). In order to verify the reliability of high temperature grating, the tensile experiment of high temperature alloy (GH3030) at 650°C was carried out, and the experimental results demonstrated that fabricated high temperature grating was feasible.

Photodetection and piezoelectric response from hard and flexible sponge-like ZnO-based structures

In this work a comprehensive characterization of sponge-like nanostructured zinc oxide films is proposed, with a marked attention to the exhibited sensing properties. Sponge-like zinc oxide films were grown on different kinds of hard and flexible substrates, by a two-step process involving a room temperature sputtering deposition of metallic sponge-like zinc films, followed by a low-temperature oxidation treatment. This method allowed growing films with thickness of a few micrometers. The material presented a polycrystalline porous structure with randomly oriented grains. After the formation of top electrodes, the sensing properties of the samples were assessed. In particular, the films exhibited UV sensing capability, with photocurrents up to four orders of magnitude higher than the current values measured in dark conditions. The material also showed considerable piezoelectric response: the mechanical stimulus exerted by the impact of a water drop delivered on its surface generated intense piezoelectric output voltage peaks, thus proving material sensing capability. A maximum average output power density of 2.4nW/cm2 was calculated. Such interesting properties make sponge-like ZnO a promising smart material for sensing and energy harvesting applications.

Self-assembled Al nanoparticles on Si and fused silica, and their application for Si solar cells

This paper presents a novel method for the self-assembly of aluminum nanoparticles on Si and fused silica. Due to high reactivity with oxygen, ex-vacuo annealing of thin deposited metal films, a method used extensively with other metals, does not work with aluminum. In the present experiment this problem was overcome by annealing the samples in-vacuo in the deposition chamber. Aluminum was thermally evaporated onto substrates at elevated temperatures (200–400 ° C) and annealed for 60 min without breaking the vacuum. It is shown that at 300 and 400 ° C the average particle size can be controlled by adjusting the amount of evaporated aluminum. Particle diameters ranging from 20 to 130 nm are demonstrated. These particles support localized surface plasmon resonances, a property that can be utilized for enhancing the efficiency of thin Si solar cells. This is explored here, and an increase in external quantum efficiency of up to 15% in a thin-film Si solar cell is demonstrated.

Electroless Metallization of Silicon Using Metal Nanoparticles as Catalysts and Binding-Points

Gold nanoparticles on silicon work not only as catalysts to initiateautocatalytic electroless metal deposition but also as bindingpointsbetween the deposited metal film and the silicon surface.Conventional catalysts of autocatalytic electroless metal deposition,such as palladium and silver, require heat treatments or anchorformation to obtain practical adhesion of deposited metal films onsilicon. Gold nanoparticles can directly produce adhesive metalfilms on flat silicon surfaces without any treatments. Crosssectionaltransmission electron microscopic observation revealsthat gold nanoparticles form an alloy with silicon at the roomtemperature. This alloy is expected to improve the adhesion ofmetal film on silicon.

The Nanoporous Metallization of Polymer Membranes through Photocatalytically Initiated Electroless Deposition

We present the novel use of Photocatalytically Initiated Electroless Deposition (PIED) for the deposition of metal films with highly ordered arrays of sub-µm (hemi)spherical pores directly onto the surface of insulating organic membrane-based substrates. This is achieved by sensitisation of the target substrate with a TiO2 photocatalyst followed by the self-assembly of a hexagonally close packed polystyrene microsphere template at the substrate surface. Metallisation then occurs through PIED into the template interstices and directly onto the TiO2 sensitised membrane surface. The dimensions of the resultant pores in the deposited metal are determined by the size of the template microspheres while metal film thickness may be controlled by the deposition period. The fabrication of nanoporous metal by this novel method adds a conductive and permeable metallic structure of high surface area to an otherwise electrically insulating polymer membrane surface. Such metallised insulating membranes have potentially wide applications in membrane and separation technology, desalination and electrode / solid electrolyte composites for fuel cells.