Uniform Film Growth Research Articles

From nucleation to coalescence of Cu2O islands during in situ oxidation of Cu(001)

The nucleation, growth, and coalescence of Cu2O islands due to oxidation of Cu(001) films were visualized by in situ ultrahigh-vacuum transmission electron microscopy. We have previously demonstrated that the nucleation and initial growth of copper oxides is dominated by oxygen surface diffusion. These surface models have been extended to quantitatively represent the coalescence behavior of copper oxidation in the framework of the Johnson–Mehl–Avrami–Kolmogorov theory. An excellent agreement exists between the experimental data of nucleation to coalescence with the surface model. The implication could be an alternate paradigm for passivation and oxidation, since classic theories assume uniform film growth.

Applications of atomic layer chemical vapor deposition for the processing of nanolaminate structures

Atomic layer chemical vapor deposition (ALCVD) is a variant of a CVD process that involves surface deposition for the controlled growth of nano-thickness films. ALCVD is based on the self-limiting surface reaction with less than a monolayer chemisorption of chemical precursors. Advantages of the ALCVD process are uniform film growth on large area substrate, easy control of composition in atomic level, low growth temperature, multi-layer thin film growth with various composition, and wide process window. Since initially developed by Suntola in 1977, ALCVD has been used for the growth of various materials, including oxides, nitrides, metals, elements, and compound semiconductors. This article reviews the basic principle, mechanism, characteristics, and applications of ALCVD.

A metal-organic chemical vapor deposition approach to double-sided Tl2Ba2Ca1Cu2O8superconducting films on LaAlO3(100) substrates

Double-sided Tl2Ba2CaCu2O8 (Tl-2212) films for device applications have been fabricated through thallium vapor diffusion into BaCaCuOF matrices deposited by a novel metal-organic chemical vapor deposition (MOCVD) process onto 10 × 10 mm2 LaAlO3 (100) substrates. The present approach uses a multimetal molten single source in a monocomponent hot-wall MOCVD reactor whose geometry allows simultaneous and uniform film growth on both sides of the substrate. Both sides are epitaxially coated by homogeneous and monophasic Tl-2212 films, which, even more importantly, have comparable superconducting and transport properties.

A review: Thermal processing in fast ramp furnaces

The capabilities and advantages of advanced batch furnaces in meeting semiconductor process requirements (up to a minimum of 100 nm technology node) are reviewed. Hot wall batch furnaces continue to provide accurate temperature control, low cost of ownership, and process advantages as compared to single-wafer tools. Recent advances by various furnace vendors have addressed the hot-walled furnace shortcomings of thermal response, process times, and automation overload, resulting in improved manufacturing economics. The inherent benefits such as large load size, isothermal processing, uniform film growth, high reliability, and low capital cost have ensured a substantial cost of ownership advantage over single-wafer processes. Accurate temperature modulation at high temperatures during both heating and cooling cycles has allowed synthesis of ultra thin gate oxides for devices below sub-200 nm design rule.

Study on the lateral growth of silicon films from metal solutions with temperature gradient

The growth of Si film from Cu–Si solution with temperature gradient was conducted experimentally and examined by a simplified diffusion-controlled growth model calculation. It was found that the relation between the grown film thickness distribution along the temperature gradient direction and the cooling rate could be explained by the model calculation, and values for binary diffusion coefficient in the Cu–Si solution was estimated. The experimental results showed that a uniform film growth at the cooling rate as high as 0.1°C/s was possible.

Cluster deposition study by molecular dynamics simulation: Al and Cu cluster

The ionized cluster beam deposition of Al and Cu clusters has been investigated with a classical molecular dynamics simulation and the Metropolis Monte–Carlo simulation. The spreading of the cluster has been studied as functions of cluster size and initial cluster energy. When the local area reached the local melting spot on the surface around the impact point of an energetic cluster, during a few ps, intermixing was easily achieved and a good epitaxial film with optimum bulk density was formed. For uniform film growth using a cluster impact, it is necessary to make the local area temperature higher than melting temperature on the surface around the impact point of an energetic cluster.

Design and fabrication of zeolite-based microreactors and membrane microseparators

This paper demonstrates that zeolites (i.e., Sil-1, ZSM-5 and TS-1) can be employed as catalysts, membrane or structural materials in miniature chemical devices. Traditional semiconductor fabrication technology was employed in micromachining the device architecture. The fabricated miniature zeolite-based structures find applications as catalytic microreactors and membrane microseparators. Four strategies for the manufacture of zeolite catalytic microreactors were discussed: zeolite powder coating, uniform zeolite film growth, localized zeolite growth, and etching of zeolite–silicon composite film. These zeolites were deposited either as film or discrete islands with controlled particle size, crystal morphology, layer thickness (3–16 μm) and film orientation (e.g., highly oriented (1 0 1) and (2 0 0) films). Crystal intergrowth was also manipulated through the use of growth inhibitors. Silicalite-1 was also prepared as free-standing membrane for zeolite membrane microseparators.

Chemical Bath Deposition of Zinc Sulfide from Acidic Solutions

ABSTRACTAt present, the soft processing of materials attracts considerable interest. Chemical bath deposition (CBD) effects film formation by means of a controlled chemical reaction. Adherent, uniform and reproducible films of zinc sulfide (ZnS) have been deposited, upon low iron-content microscope slides, under acidic conditions, from a solution containing zinc chloride, urea and thioacetamide. Scanning electron micrographs of the deposited layers suggest that, as the reaction proceeds, uniform film growth is associated with increasing particle size, rather than continuous nucleation and deposition of new primary particles. Energy Dispersive Analysis by X-Rays (EDAX) spectra are typical of CBD-deposited films of ZnS; signals attributable to elements within the glass substrate are also detected, an observation consistent with the thin nature of the films. Grain size distributions have been investigated using computational image analysis, and an average increase in the diameter of the deposited particles of 33.7 nanometres per hour has been calculated.

Simulation Study of Copper Cluster Deposition

ABSTRACTThe ionized cluster beam deposition of Al and Cu clusters has been investigated with a classical molecular dynamics simulation and the Metropolis Monte Carlo simulation. The spreading of the cluster has been studied as functions of cluster size and initial cluster energy. When the local area reached local melting spot on the surface, around the impact point of an energetic cluster, during a few ps, intermixing was easily achieved and a good epitaxial film with optimum bulk density was formed. For uniform film growth using cluster impact, it is necessary to make the local area temperature higher than melting temperature on the surface around the impact point of an energetic cluster.

Chemical vapor deposition of alpha aluminum oxide for high-temperature aerospace sensors

Thin-film thermocouples and strain gages are being developed for high-temperature application on aerospace propulsion hardware for both development test purposes and as active control sensors. The critical technology necessary in the fabrication of the sensor is an adherent, dense, and homogeneous dielectric to provide electrical isolation at engine operating temperatures. Techniques are being developed to create a crystalline aluminum oxide dielectric formed by a combination of a thermally grown oxide (TGO) from a NiCoCrAlY hardcoating, which is then enhanced with the addition of a chemical vapor deposited (CVD) crystalline aluminum oxide layer. This article will focus on the process development used to deposit the α alumina layer on the TGO using CVD in a coldwall reactor at 1100 °C. The chemistry employed in this process is the pyrolitic decomposition of aluminum tri-isopropoxide. The hexagonal (HCP) α phase is achieved at deposition temperatures of 1000–1100 °C, as confirmed by x-ray diffraction analysis. By eliminating gas phase and hot wall decomposition, this approach minimizes precursor depletion effects, yielding a more dense and uniform film morphology. Conformal coatings up to 10 μm thick with high resistivity and good adhesion and hardness have been observed on complex airfoil geometries. Growth rates up to 10 μm/h are possible, although low growth rates lead to more desirable film properties. The kinetics of the deposition indicate that the reaction proceeds by a mass transport limited mechanism. Uniform temperature control over highly complex geometry is desirable, but not essential for uniform film growth. Results indicate that the gas flow uniformity and the precursor transport rate are the critical variables.

Optimal Design of Reactors for Metalorganic Vapor Phase Epitaxy of Group III Nitrides

AbstractMetalorganic Vapor Phase Epitaxy (MOVPE) has emerged as the technique of choice for growing thin films and structures of group III-nitrides. The objective of this work is to address the optimal design of vertical rotating disk and stagnation flow MOVPE reactors in order to achieve film thickness uniformity over large area substrates. Gas inlets that preserve the axial symmetry and enable alternating feeding of the precursors through coaxial rings were studied. The growth of GaN films from trimethyl-gallium and ammonia was used as a typical example. A fundamental reaction-transport model of the MOVPE process including gas-phase reactions and gas-surface interactions has been developed. The model was validated through comparison with growth rate data obtained from both research-scale and industrial-scale reactors. Performance diagrams for industrial-scale stagnation flow and rotating disk reactors were developed by varying the reactor geometry and operating conditions to identify regions of uniform film growth.

Behaviour of copper and generation of oxygen during anodizing of Nb-Cu alloys

The anodic oxidation behaviour of two compositions of Nb–Cu alloy is examined with particular reference to the oxidation of copper at the alloy/film interface and the generation of oxygen within the anodic film. Anodizing of an Nb–3 at.% Cu alloy results in a uniform, niobia-based anodic film, with copper species, which migrate faster than Nb5+ ions, distributed throughout the film. The oxidation of copper proceeds without significant enrichment of copper in the alloy. Further, the film is free of bubbles of oxygen, which is not generated in significant amounts during film growth to relatively high voltages. In contrast, copious amounts of oxygen are generated during anodizing of an Nb–30 at.% Cu alloy, with the consequential development of a highly flawed anodic film of non-uniform thickness. The oxygen is present mainly in numerous bubbles located within the niobia-based film material. Bursting of the bubbles, with release of trapped oxygen, leads to a highly damaged film. The continuous generation of oxygen consumes much of the current and limits the anodizing voltage to a low value. The large-scale generation of oxygen for the more concentrated alloy is suggested to be associated with the distribution of copper in the alloy, with copper having a tendency to form copper-rich clusters, which are enhanced in size by an initial brief period of uniform film growth. Oxygen is then generated, probably following oxidation of such clusters. Copyright © 2000 John Wiley & Sons, Ltd.

Coordinate Covalent Cobalt-Diisocyanide Multilayer Thin Films Grown One Molecular Layer at a Time

Multilayer thin films consisting of alternating layers of cobalt and 1,4-diisocyano-benzene (DiCNB) synthesized layer by layer on an amine functionalized silicon substrate were first reported in 1996. This paper describes further work in characterizing these films using X-ray photoelectron spectroscopy (XPS), ellipsometry, attenuated total reflectance−infrared spectroscopy (ATR−IR), and reflection−absorption infrared spectroscopy (RAIRS). Ellipsometry shows the films grow uniformly, suggesting sequential binding of metal and diisocyanide components. Control experiments confirm that both components are necessary for film growth and that 1-isocyano-2-phenylethane, a mono-functional isocyanide, caps the film and terminates further growth. Although the ellipsometry data suggests uniform film growth consistent with DiCNB molecules oriented perpendicular to the plane of the substrate, in accord with a simple model of these films, a more complex picture of the resulting film constituents is seen with further analysis. FTIR and XPS results indicate the presence of significant amounts of oligomeric isocyanide species in the films. We also report the growth of uniform multilayers of cobalt and 1,6-diisocyanohexane.

Effect of initial plasma geometry and temperature on dynamic plume expansion in dual-laser ablation

Recent experiments have revealed the capability of large-area, uniform film growth using dual-laser ablation. The mechanism of this dynamic plume expansion is investigated in this letter. We report the critical role played by the initial geometry and temperature of the plasma in the subsequent expansion under dual-laser ablation. Initial plasma dimensions in the dual-laser ablation of ZnO are quantified by gated intensified charge-coupled detector-array imaging and combined with a hydrodynamic theoretical expansion model to yield radial thickness profiles for the deposited films. Comparisons with ellipsometric film thickness profiles indicate that the primary factors responsible for increased expansion of the dual-laser ablated plume are an extension of the initial plasma dimension in the axial direction as well as enhanced plasma temperature.

Formation and accommodation of gold atom clusters and oxygen bubbles during amorphous anodic alumina growth

The growth of anodic oxide films on metals and alloys is of both theoretical value, in particular with relation to the mechanism of ionic transport in amorphous materials, and practical interest, especially in the surface treatment of metals and alloys and the use of anodic films in electronics applications. Most previous work has focused on uniform film growth, with formation of either an essentially single–layered or a duplex oxide. The present work, employing transmission electron microscopy and Rutherford backscattering spectroscopy, addresses the generation of metallic and gaseous phases in association with the usual film growth, and reveals the ability of the labile amorphous film to accommodate these non–oxide phases. Thus, anodizing of a thin Al–0.47 at.% Au alloy, deposited upon an electropolished aluminium substrate, is shown to result in formation of gold atom clusters of ca . 1–5 nm size and fine oxygen bubbles, at high pressures, which are contained by the growing amorphous alumina film. The generation of the phases originates from enrichment of gold in a thin layer of the alloy, probably containing gold–rich precursor clusters, during the oxidation of the alloy layer and the subsequent enforced incorporation of gold atom clusters into the anodic film by the electropolishing film on the aluminium. The final clusters are essentially immobile following incorporation into the growing anodic film. At the time of, and briefly after, the incorporation of clusters into the film, oxygen gas is produced by oxidation of O2- ions from the alumina, which occurs at the cluster–alumina interface prior to electrical isolation of the cluster due to undermining by further film growth. The resultant oxygen bubbles generated within the alumina expand as the film grows, driven by the high gas pressure and assisted by the effective plasticity of the labile amorphous alumina under the electric field.

The Role of Gas‐Phase Reactions during Chemical Vapor Deposition of Copper from (hfac)Cu(tmvs)

The chemistry of copper chemical vapor deposition (Cu‐CVD) from the precursor (hfac)Cu(tmvs), where hfac = 1,1,1,5,5,5‐hexafluoroacetylacetonate and tmvs = trimethylvinylsilane, on sputtered titanium nitride (TiN) films was investigated using a hot‐wall tube reactor. We found that gas‐phase reactions contribute to Cu deposition and there is negligible contribution of direct surface decomposition of source precursors. The weak Cu‐(tmvs) bond is cleaved by heating via gas‐phase reactions and the intermediate Cu(hfac) is the real film precursor. Film deposition in a macrocavity confirmed the presence of gas‐phase reactions, because film growth rates increased with increasing volume/surface ratio of the macrocavity. Above 180°C, gas‐phase reactions for producing the intermediate species is the rate‐limiting step and limits the growth rate. Below 145°C, the surface reaction of intermediates limits the growth rate. The rate constants of the gas‐phase and surface reactions are [1/s] and [m/s], respectively, where and T equals; temperature in kelvin. The growth rate profiles agree very well with those predicted using the reaction mechanism and rate constants obtained in this study. This reaction model and kinetic information can be used to optimize reactor design for uniform film growth.

Ultrathin Molybdenum Polyoxometalate−Polyelectrolyte Multilayer Films

Ultrathin multilayer films of a novel molybdenum(VI) polyoxometalate cluster ((NH4)21[H3Mo57V6(NO)6O183(H2O)18]) (Mo57) and poly(allylamine hydrochloride) (PAH) have been prepared by the consecutive stepwise adsorption of Mo57 and PAH from dilute aqueous solution. The Mo57/PAH multilayer films have been characterized by optical spectroscopy and small-angle X-ray reflectivity (XR) methods. UV−vis measurements reveal regular film growth with each Mo57 adsorption. The average Mo57 surface density was found to be (1.4 ± 0.4) × 1013 clusters per cm2, corresponding to an average surface coverage of 56 ± 12%. XR experiments confirm uniform film growth, with the film thickness increasing with each Mo57 adsorption step. The average thickness for the Mo57/PAH layer pair was determined to be 0.8 ± 0.1 nm. The Mo57 density in the film can be readily controlled by varying the polyelectrolyte interlayer separation between each Mo57 layer, and the total film thickness can be controlled by altering the number of adsorption cycles.

Interactions of alloying elements during anodizing of dilute Al-Au-Cu and Al-W-Zn alloys and consequences for film growth

The anodizing behaviour of sputter-deposited Al-4 at.% Au-1 at.% Cu and Al-1.6 at.% W-0.6 at.% Zn alloys has been examined by Rutherford backscattering spectroscopy and transmission electron microscopy. Initially, a uniform, amorphous alumina film, free of copper and gold species, is formed on the Al-Au-Cu alloy; at the same time, a thin alloy layer, beneath the anodic film, is enriched in copper and gold. The uniform film growth is eventually terminated by generation of oxygen at gold-rich particles at, or near, the alloy/film interface, leading to bubble formation, subsequent rupture of the film and release of oxygen. Film growth on the Al-W-Zn alloy causes mainly enrichment of tungsten in the alloy, with the limited enrichment of zinc contrasting with the behaviour of Al-Zn alloys. Uniform film growth proceeds to high voltages with incorporation of mobile tungsten and zinc species into the film.

Growth of diamond films on SiC, WC and cubic BN substrates

The growth morphology of diamond films grown on single crystals of SiC and on sintered WC and cubic BN (CBN) substrates by hot filament assisted chemical vapour deposition was examined using transmission electron microscopy and scanning electron microscopy. Diamond was found to have the form of particles on the substrates of SiC and WC in the initial stage of film growth. Both an amorphous layer and a directly bonded area were seen at the interface. Several orientation relationships, different from the cube/cube relation, were observed in these systems. On the other hand, in the case of diamond films on CBN substrates, the growth morphology of diamond was affected by the surface condition of the substrates. When CBN substrates were polished with a diamond paste before deposition, diamond grew in the form of particles. The growth morphology was changed by ion sputtering of the surface of the substrate from particle growth to uniform film growth. These results are discussed on the basis of lattice mismatch at the interface.

Crystallographic and electronic structure of Cu/Cr/Cu(001) sandwiches

Thin Cu layers have been evaporated at room temperature on Cr films (~ 10 monolayers) deposited on a Cu(001) single crystal. The Crystallographic structure of these sandwiches is analysed by means of low-energy electron diffraction (LEED), angle-resolved ultra-violet photoemission spectroscopy (ARUPS) and X-ray photoemission spectroscopy. The data show that the attenuation of the Cr signal versus Cu deposition is much lower than expected for a uniform film growth. Moreover, the LEED pattern characteristic of the Cr film (made of Cr(110) domains with four different orientations) is visible for Cu coverages as high as 23 ML. This indicates a strong diffusion of the Cu atoms on the Cr film surface and the formation of Cu three-dimensional islands which present, according to ARUPS and X-ray photoelectron diffraction measurements, a highly disordered fcc Crystallographic structure. However the low reactivity of the sandwiches towards oxygen suggests that the whole Cr surface is wetted by at least 1 ML of Cu.