Deposition Of Metal Layers Research Articles

Atomic Layer Deposition of Noble Metals and Their Oxides

Atomic layer deposition (ALD) is an attractive method to deposit thin films for advanced technological applications such as microelectronics and nanotechnology. One material group in ALD that has matured in 10 years and proven to be of wide technological importance is noble metals. In this paper, thermal ALD of noble metals and their oxides is reviewed. Noble metal films are mostly grown using O2 as the nonmetal precursor in a combustion-type chemistry. Alternatively, lower growth temperatures can be reached via noble metal oxide growth with consecutive reactions with ozone and H2. The use of true reducing chemistry (i.e., H2) is typical only for ALD of palladium at low temperatures. On the other hand, ALD of noble metal oxides has been limited with reactants such as ozone and O2 gas. In this review, reaction mechanisms in various types of processes are discussed and issues in nucleation are addressed. Deposition temperatures, film growth rates, and purities as well as evaporation temperatures used for noble metal precursors are tabulated for comparison.

Catalytic Surface Reactions during Nucleation and Growth of Atomic Layer Deposition of Noble Metals: a Case Study for Platinum

not Available.

LEGO-like assembly of peelable, deformable components for integrated devices

The development of various technologies has led to the advent of a variety of deformable devices. Despite significant technological advancement in this area, it is still challenging to integrate different devices due to limitations such as substrate issues and differences among growth and deposition conditions. Creating an interconnection between two different devices currently requires the use of metallic wires/lines to build electrical connections. Here, we demonstrate a LEGO-like assembly of the free-standing film of individually operable components encapsulated in a polymer overcoat layer, leading to the production of an integrated architecture without additional electrical connections. The free-standing components are produced by the peeling-off process. The sticky nature of the polymer layer enables the construction of supercapacitor arrays and simple RLC circuits by interlocking the individual components. We expect that this approach will enable the fabrication of a variety of custom-built devices using a LEGO-like assembly method. We demonstrate a LEGO-like assembly of free-standing film of individually operable components encapsulated in a polymer overcoat layer, leading to the integrated architecture without additional electrical connection. The free-standing components are produced by the peeling-off process. The sticky nature of polymer layer enables the construction of supercapacitor arrays and simple RLC circuits through interlocking the individual components. In a collaboration between South Korea and the United States, John Rogers, Ungyu Paik and co-workers have developed a simple process to fabricate flexible circuits by assembling the separate components in the manner of Lego blocks. The researchers first prepared each part — for example a resistor, inductor or capacitor — by depositing metal layers on a common substrate comprising a silicon dioxide wafer. Next, they grew carbon nanotubes at locations determined to be electrodes and subsequently added a gel electrolyte layer. On drying, this gel converts to a sticky polymer that incorporates the required component and can be peeled away from the substrate. The resulting film is flexible and resistant to repeated bending, folding and stretching. Lastly, these free-standing components were simply interlocked into an integrated circuit without the need for further electrical connections. Poly(vinyl alcohol), the polymer used in the study, can also be functionalized, enabling the creation of more complex devices.

Cavity‐first approach for microelectromechanical system–CMOS monolithic integration

Presented is a cavity-first approach for producing released microelectromechanical system (MEMS) structures from the front side of a silicon on insulator (SOI) wafer. This approach shows excellent process compatibilities to CMOS and is significantly valuable to MEMS–CMOS monolithic integration. In this approach, prior to metal layer deposition and other components fabrication, which are easily damaged by vapour-phase hydrofluoric (HF) acid, release holes with a diameter of a few micrometres were created in the active silicon layer, and the cavities were formed after removing the underneath SiO2 box layer by vapour-phase HF etching. An amorphous fluoropolymer thin film was then successfully introduced to refill those release holes without entering into the cavities, after which the wafer can be fabricated by standard process with negligible surface fluctuation. Finally, MEMS structures were released from the front side of the wafer by inductively coupled plasma reactive ion etching (ICP-RIE). This approach enables monolithic integration of MEMS with CMOS circuits on SOI wafers with easy-package capability, eliminates the requirements on device release by wet chemical etching or ICP-RIE from the backside of the wafer and reduces the risk of device damage by vapour-phase HF etching. This approach also excels others in simplicity and high yields with better thickness uniformity and less residual stress in a MEMS structure.

ChemInform Abstract: Atomic Layer Deposition of Noble Metals ‐ New Developments in Nanostructured Catalysts

AbstractReview: 60 refs.

(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.

Fabrication of piezoelectric P(VDF-TrFE) microcantilevers by wafer-level surface micromachining

A wafer-level microfabrication process using standard cleanroom facilities was established and implemented to batch produce free-standing poly(vinylidine fluoride-trifluoroethylene) (P(VDF-TrFE)) piezoelectric microelectromechanical systems cantilevers via surface micromachining. Furthermore, the fabrication of a prototype of double-level cantilevers was demonstrated. The fabrication of working piezoelectric polymer cantilever structures required the deposition and patterning of multiple polymer and metal layers including the pattering and removal of the sacrificial layer, which posed many challenging limitations on the chemicals and processing conditions. Dedicatedly selected chemicals and materials were used in our fabrication, including water soluble PVA with an appropriate molecular weight and degree of hydrolysis as the sacrificial layer for releasing the cantilever structure. The temperature in the whole process was kept low with controlled durations, due to the sensitivity of the polymers to thermal impacts. The P(VDF-TrFE) active layers, after going through the fabrication, exhibited ferroelectric and piezoelectric properties comparable to the intact films. Furthermore, the free-standing P(VDF-TrFE) cantilevers exhibited piezoelectric vibrations under electrical excitation. This low temperature fabrication method, which only involves mild chemicals, also has the potential to be integrated with CMOS processes.

Fabrication of CuO nanotubes by electrospinning, metallisation and annealing

A straightforward combined technology of electrostatic spinning and metallisation was developed to produce novel metallic nanotubes and nanofibres. The metals were deposited onto electrospun poly(vinyl alcohol) (PVA) nanofibres as a template by metallisation method. After removal of the nanofibre template by heat treatment at 400°C for 24 h, the fibrous morphologies were satisfactorily conserved, suggesting the successful deposition of metal layer on the surface of nanofibre template. Wide-angle X-ray diffraction data confirmed that the PVA nanofibres metallised with the copper layer of 200 nm clearly showed typical copper crystalline peaks, whereas after calcination of the nanofibre templates, interestingly, new crystalline peaks were observed at 2θ = 32.5°, 35.5°, 38.7°, 48.7°, 53.4° and 58.4°, corresponding to the (1 1 0), (0 0 2), (1 1 1), ( 0 2), (0 2 0) and (2 0 2) reflections, respectively. The resulting metallic nanotubes and nanofibres were found to show a typical CuO crystalline structure.

Optical Properties of Silver and Gold Tetrahedral Nanopyramid Arrays Prepared by Nanosphere Lithography

Tetrahedral nanopyramids made of silver and gold over ITO/glass surfaces are fabricated. Our protocol is based on nanosphere lithography (NSL) with the deposition of thicker metal layers. After removing the microspheres used in the NSL process, an array of metallic tetrahedral nanostructures of ∼350–400 nm height is formed. The reported procedure avoids the use of any stabilizing surfactant molecules that are generally necessary to segregate the individual particles onto surfaces. We focus here on the optical and the physical properties of these plasmonic surfaces using near-field spectroscopy in conjunction with finite difference time domain (FDTD) modeling of the electric field. Remarkably, FDTD shows that the localized surface plasmon resonance is confined in the plane formed by the edges of two facing pyramids that is parallel to the polarization of the impinging excitation laser. The variable gap between the edges of two adjacent pyramids shows a broader localized surface plasmon and a larger specifi...

Evaluation of Properties of FIB Deposited Metal Layer and Application to Temperature Sensing

In this paper, the properties of Focused-Ion-Beam (FIB) deposited platinum layer are investigated using the MEMS processes. First, the electrical properties are examined with three parallel metal lines and the measurement result shows over one hundred times larger resistivity than that of the conventional platinum layer. This feature is due to the additional materials like carbon compound and the gallium ion. The thermal properties are also investigated about the temperature coefficient of resistivity (TCR). The measured TCR values are -0.0015~-0.0020 K-1 which are different from the positive TCR in conventional platinum layer. The carbon compound has negative TCR and changes the properties of FIB metal layer. Although some non-uniform properties are observed, the properties of FIB deposited platinum layer are sufficient for the temperature sensing applications at small area.

Influence of Oxygen Exposure on the Nucleation of Platinum Atomic Layer Deposition: Consequences for Film Growth, Nanopatterning, and Nanoparticle Synthesis

Control of the nucleation behavior during atomic layer deposition (ALD) of metals is of great importance for the deposition of metallic thin films and nanoparticles, and for nanopatterning applications. In this work it is established for Pt ALD, that the exposure to O2 during the O2 pulse of the ALD process is the key parameter controlling the nucleation behavior. The O2 dependence of the Pt nucleation is explained by the enhanced diffusion of Pt species in the presence of oxygen, and the resulting faster aggregation of Pt atoms in metal clusters that catalyze the surface reactions of ALD growth. Moreover, it is demonstrated that the O2 exposure can be used as the parameter to tune the nucleation to enable (i) deposition of ultrathin films with minimal nucleation delay, (ii) preparation of single element or core/shell nanoparticles, and (iii) nanopatterning of metallic structures based on area-selective deposition.

Six-port-based compact and low-cost near-field 35 GHz microscopy platform for non-destructive evaluation

A complete millimeter-wave solution with features such as low cost, low-power consumption, compactness, robustness and easy-to-use is proposed to address the need of non-destructive methods with sub-wavelength resolution for operation outside a laboratory environment. The measurement system is based on the association of a low-cost 35GHz six-port reflectometer and an inexpensive and easy-to-build microstrip evanescent probe with an apex size of 10μm. The instrumentation can find applications for example in the microelectronic industry where the fast diagnosis of metal layer deposition is of great interest. For demonstration purposes, the technique is applied to the near-field mapping of thin metal layers with a spatial resolution of a few microns. In particular, one-dimensional scanning of rectangular inclusions and imaging of a microsized metallic pattern processed into silicon are experimentally demonstrated to validate the technique. The usefulness and versatility of the method make it also suited for a wide range of applications.

Low temperature atomic layer deposition of noble metals using ozone and molecular hydrogen as reactants

Atomic layer deposition (ALD) of noble metals by thermal processes has relied mostly on the use of molecular oxygen as a reactant at temperatures of 200°C and above. In this study, the concept of using consecutive ozone and molecular hydrogen pulses with noble metal precursors in ALD is introduced for palladium, rhodium, and platinum metals. This approach facilitates the growth of noble metal thin films below 200°C. Also the ALD of palladium oxide thin films is demonstrated by the ozone-based chemistry. The growth rates, resistivities, crystallinities, surface roughnesses, impurity contents, and adhesion of the films to the underlying Al2O3 starting surface are reported and the results are compared with the most common noble metal ALD processes.

Identification of nickel silicide phases on a silicon surface from Raman spectra

We have demonstrated the effectiveness of Raman spectroscopy for monitoring nickel silicide formation processes on the surface of silicon wafers, with deposition of a composite metal layer (nickel, platinum, and vanadium) under industrial process conditions in microelectronics. The observed shift of all the NiSi lines toward lower energies is associated with formation of the metastable silicide phase Ni1−x Pt x Si, which leads to the presence of stresses in the lattice as a result of the increase in the distances between atoms.

Effects of process conditions on nano-dot array formation by thermal dewetting

In this paper, three kinds of self-organization processes for metal nano-dot array fabrication are compared; one is the conventional thermal dewetting, another is thermal dewetting of a grid patterned deposited metal layer, the other is thermal dewetting of a metal layer deposited on a patterned substrate. In these processes, nano plastic forming technique is utilized for patterning of groove grid. Effects of process conditions on nano-dot formation, such as substrate material, deposited metal, thickness of deposited layer, annealing condition, are experimentally studied. Also, effect of grid patterning on improvement of nano-dot array formation is studied. It is shown that grid patterning on a deposited metal layer is effective to improve alignment and configuration of nano-dot array.

Design and testing of ultrahigh vacuum microtribometer

In this paper, we present the design of a novel microtribometer operating in ultrahigh vacuum. The force sensor of the tribometer is based on the double leaf cantilever design. To remove noise and mechanical deformation due to temperature oscillation from measured signals, we employ a double laser interferometer and a passive noise reduction system. Depending on the spring constant of the cantilever used, the detection limit of lateral force measurements ranges from a few micronewtons to 1 mN. The tribometer chamber is equipped with an e-beam evaporator for deposition of metallic thin layers. The instrument is also connected to an X-ray photoelectron spectroscopy system. In the remainder of this paper, we present an experiment conducted on thin silver films that involves all of the components mentioned above.

Discoloration mechanism of UV-curable polymer/metal hybrid coating

The purpose of this study is to conduct an in-depth analysis of the discoloration mechanism of UV-curable polymer/metal hybrid coating. A variety of technical approaches, including microscopic, spectroscopic, and chromatographic analysis techniques, were used to investigate the nature of discoloration and the root cause. The hybrid coating has a typical multilayered structure consisting of a base coat, a vacuum deposited metal layer, and a top coat. The results obtained by microscopic and spectroscopic analyses demonstrated that the discoloration of the hybrid coating stemmed from yellowing of the top coat. Deterioration or degradation of the metal component in the vacuum deposited metal layer was not confirmed. The results of an analysis of additives in the discolored top coat showed that there is a small quantity of unreacted photoinitiators remaining in the top coat. From the results of solvent extraction and gel content measurement, it is believed that an excessive amount of photoinitiators was used in the resin of the top coat and one of the residual unreacted photoinitiators caused yellowing of the top coat.

Structure of solid-supported lipid membrane probed by noble metal nanoparticle deposition

Direct deposition of a noble metal layer onto a solid-supported membrane was proposed as an indirect microscopy tool to visually observe different lipid phases that may develop in the lipid membrane. The method relied on the different permeability of the lipid membrane towards the incident atoms during deposition. Liquid state or structural defects such as phase boundaries, step ledges in a multi-lamellar stack, and pores permitted the metal atoms to penetrate and nucleate inside the membrane whereas rigid gel state was relatively impermeable to the incident atoms, thus enabling visualization of liquid phase or structural defects inside the gel state. Based on the proposed method, we demonstrated the phase states resulting from thermotropic transitions of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), dioleoylphosphatidylethanolamine (DOPE)/DPPC mixture, and 1,2-dioleoyl-3-trimethylammonium propane (DOTAP). Although the proposed method does not allow in-situ observation of equilibrium states, the method should be an excellent complementary tool for visualizing the lipid phases as the method can resolve fine structural details (up to tens of nanometer scale) as seen in the DPPC membrane while providing macroscopic images (up to several micrometers).

VO2, a Metal-Insulator Transition Material for Nanoelectronic Applications

An overview is given of exploratory Metal-Insulator Transition material based nanoelectronics research at imec and UGent. The VO2 thin film growth techniques used are elaborated. This considers thermal oxidation of vanadium metal and Atomic Layer Deposition (ALD). Fundamental device properties such as voltage driven switching and tunnel junction properties are discussed. Device concepts making use of MIT materials or VO2 are elaborated.

Atom Probe Tomography Characterization of Thin Copper Layers on Aluminum Deposited by Galvanic Displacement

″Ultrathin″ metallization layers on the order of nanometers in thickness are increasingly used in semiconductor interconnects and other nanostructures. Aqueous deposition methods are attractive methods to produce such layers due to their low cost, but formation of ultrathin layers has proven challenging, particularly on oxide-coated substrates. This work focused on the formation of thin copper layers on aluminum, by galvanic displacement from alkaline aqueous solutions. Analysis by atom probe tomography (APT) showed that continuous copper films of approximately 1 nm thickness were formed, apparently the first demonstration of deposition of ultrathin metal layers on oxidized substrates from aqueous solutions. The APT reconstructions indicate that deposited copper replaced a portion of the surface oxide film on aluminum. The results are consistent with mechanisms in which surface hydride species on aluminum mediate deposition, either by directly reducing cupric ions or by inducing electronic conduction in the oxide, thus enabling cupric ion reduction by Al metal.