TaCx Thin Films Prepared by Atomic Layer Deposition as Diffusion Barriers for Cu Metallization

TaC_x films were deposited by atomic layer deposition (ALD) using tris (neopentyl) tantalum dichloride, (Ta[CH₂C(CH₃)₃]₃Cl₂) and H₂ plasma as the precursor and reactant, respectively, at substrate temperatures ranging from 200°C to 400°C. The ALD–TaC_x films with the formation of nanocrystalline structures and a rock‐salt phase were confirmed by X‐ray and electron diffraction. The ALD temperature window was found to be 225°C–300°C with a growth rate of ~0.11 nm per cycle. The resistivity of the ALD–TaC_x films was dependent on the microstructural features, such as the grain size and crystallinity, as well as their composition (C/Ta ratio), and the presence of impurities in the films, which could be controlled by varying the deposition parameters, such as the deposition temperature and reactant pulse conditions. With increasing deposition temperature and reactant pulse time, Ta‐rich films with a low Cl impurity concentration and larger grain size were obtained. The film with a resistivity less than 400 μΩ cm was obtained at 300°C, which was within the ALD temperature window, by optimizing the H₂ plasma pulse time. The step coverage of the film deposited at 300°C was approximately 100% over the trench structure (top opening width of 25 nm) with an aspect ratio of ~4.5. The performance of the ALD–TaC_x films deposited under the optimized conditions was evaluated as a diffusion barrier for the Cu interconnects. The structure of Cu (100 nm)/ALD–TaC_x (5 nm)/ Si was stable without the formation of copper silicide after annealing at 600°C for 30 min.     

Significant Enhancement of the Dielectric Constant through the Doping of CeO2 into HfO2 by Atomic Layer Deposition

Films of CeO₂ were deposited by atomic layer deposition (ALD) using a Ce(mmp)₄ [mmp = 1‐methoxy‐2‐methyl‐2‐propanolate] precursor and H₂O reactant. The growth characteristics and film properties of ALD CeO₂ were investigated. The ALD CeO₂ process produced highly pure, stoichiometric films with polycrystalline cubic phases. Using the ALD CeO₂ process, the effects of Ce doping into an HfO₂ gate dielectric were systematically investigated. Regardless of Ce/(Ce + Hf) composition, all ALD Ce_xHf_1?xO₂ films exhibited constant growth rates of approximately 1.3 Å/cycle, which is essentially identical to the ALD HfO₂ growth rates. After high‐temperature vacuum annealing at 900°C, it was verified, based on X‐ray diffraction and high‐resolution cross‐sectional transmission electron microscopy results, that all samples with various Ce/(Ce + Hf) compositions were transformed from nanocrystalline to stabilized cubic or tetragonal HfO₂ phases. In addition, the dielectric constant of the Ce_xHf_1?xO₂ films significantly increased, depending on the Ce doping content. The maximum dielectric constant value was found to be nearly 39 for the Ce/(Ce + Hf) concentration of ~11%.     

Photocatalytic WO3 and TiO2 Films on Brass

This paper reports on the structure, mechanical, and photocatalytic properties of titanium dioxide (TiO₂) and tungsten oxide (WO₃) films on a brass substrate. TiO₂ and WO₃ films have been successfully deposited on brass by a simple sol‐gel dip‐coating method and it has been shown that, while both films possess photocatalytic properties, WO₃ films were superior to TiO₂. Higher surface area and rod‐like morphology of WO₃ films might have contributed to their higher photocatalytic activity. Nanoindentation results have shown that both films attach well to the substrate and possess good mechanical properties.     

Sol-gel derived WOx and WOx/Pt films for direct methanol fuel cell catalyst applications

WO_x was synthesised from W(OC₂H₅)₆ by two different methods using the sol-gel (SG) approach, Type 1 using ethanol as the solvent, while Type 2 was water-based. Films and powders made from these sols were subjected to analysis by cyclic voltammetry (CV), powder X-ray diffraction (XRD), and scanning electron microscopy (SEM). Sweep rate experiments revealed that compared to Type 1 films, Type 2 films have a significantly greater number of electroactive WO_x sites, and that a smaller proportion of the total active sites are surface sites, indicative of a higher film porosity (consistent with the SEM results). XRD analysis showed that both Type 1 and Type 2 WO_x were poorly crystallised. However, the patterns for the two WO_x types were distinctly different, with Type 2 WO_x giving a more well-defined pattern. WO_x sols were also successfully combined with a pre-formed Pt sol. Unlike Pt-only catalysts, methanol oxidation currents on Type 2 WO_x/Pt films did not decay rapidly with potential cycling, indicating the occurrence of co-catalytic behaviour, while Type 1 films were not very active, overall. The low resistance exhibited by the WO_x component makes it suitable as an ionically and electronically conducting support for direct methanol fuel cell electrocatalysts.     

Phase-gradient atomic layer deposition of TiO2 thin films by plasma-induced local crystallization

Atomic layer deposition (ALD) is a thin-film fabrication method that can be used to deposit films with precise thickness controllability and uniformity. The low deposition temperature of ALD, however, often interrupts the facile crystallization of films, resulting in inferior optical and electrical properties. In this study, the extremely localized crystallization of TiO₂ thin films was demonstrated by per-cycle plasma treatment during the plasma-enhanced ALD process. By layering crystalline and amorphous films, a phase-gradient TiO₂ film with precisely modulated optical and electrical properties was fabricated. Moreover, the ratio between the amorphous and crystalline layer thicknesses for a high dielectric constant and low leakage current density was optimized.     

Atomic layer deposition of TiO2 from tetrakis-dimethylamido-titanium and ozone

Ozone (O₃) was employed as an oxygen source for the atomic layer deposition (ALD) of titanium dioxide (TiO₂) based on tetrakis-dimethyl-amido titanium (TDMAT). The effects of deposition temperature and O₃ feeding time on the film growth kinetics and physical/chemical properties of the TiO₂ films were investigated. Film growth was possible at as low as 75 °C, and the growth rate (thickness/cycles) of TiO₂ was minimally affected by varying the temperatures at 150–225 °C. Moreover, saturated growth behavior on the O₃ feeding time was observed at longer than 0.5 s. Higher temperatures tend to provide films with lower levels of carbon impurities. The film thickness increased linearly as the number of cycles increased. With thicker films and at higher deposition temperatures, surface roughening tended to increase. The as-deposited films were amorphous regardless of the substrate temperatures and there was no change of crystal phase even after annealing at temperatures of 400–600 °C. The films deposited in 0.5 mm holes with an aspect ratio of 3: 1 showed an excellent conformality.     

Effects of oxygen sources on properties of atomic-layer-deposited ferroelectric hafnium zirconium oxide thin films

Orthorhombic Hf_xZr_1-xO₂ (HZO) is a promising ferroelectric material for realizing ferroelectric devices in the modern semiconductor industry because of its excellent CMOS compatibility and scalability. Atomic layer deposition (ALD) facilitates the growth of robust ferroelectric HZO films that can be used in nanoelectronic devices. Herein, we provide a comprehensive understanding of the effects of the oxygen source, either H₂O or O₃, on the properties of ALD-grown HZO films. Although the growth per cycle promoted by ALD does not change with the type of oxygen source, the impurity content of the HZO film grown with H₂O are higher than that with O₃. The low impurity content of the HZO film grown with O₃ results in low leakage current. The ALD process with O₃ further suppresses the emergence of the nonferroelectric monoclinic phase in the ferroelectric orthorhombic HZO matrix. Consequently, the HZO film grown with O₃ exhibits a small coercive field for ferroelectric domain switching and high electrical reliability. This study demonstrates that O₃ is more favorable for growing high-quality HZO films via ALD by using metal precursors comprising tetrakis(ethylmethylamino) ligands.     

Electrochemical characterization of TiO2/WOx nanotubes for photocatalytic application

TiO₂/WO_x nanotubes have unique photo-energy retention properties that have gathered scientific interest. Herein, we report the synthesis, morphological characterization, and the electrochemical characterization of TiO₂/WO_x nanotubes compared with pure TiO₂ nanotubes, prepared by anodization technique. Significant structural differences were not observed in TiO₂/WO_x nanotubes as observed by using scanning electron microscopy and transmission electron microscopy. The charge transfer resistance of TiO₂/WO_x before and after photo irradiation determined by using electrochemical impedance spectroscopy proves the inherent energy retention property which was not observed in pure TiO₂ nanotubes.     

Multi-Directional Growth of Aligned Carbon Nanotubes Over Catalyst Film Prepared by Atomic Layer Deposition

The structure of vertically aligned carbon nanotubes (CNTs) severely depends on the properties of pre-prepared catalyst films. Aiming for the preparation of precisely controlled catalyst film, atomic layer deposition (ALD) was employed to deposit uniform Fe₂O₃ film for the growth of CNT arrays on planar substrate surfaces as well as the curved ones. Iron acetylacetonate and ozone were introduced into the reactor alternately as precursors to realize the formation of catalyst films. By varying the deposition cycles, uniform and smooth Fe₂O₃ catalyst films with different thicknesses were obtained on Si/SiO₂ substrate, which supported the growth of highly oriented few-walled CNT arrays. Utilizing the advantage of ALD process in coating non-planar surfaces, uniform catalyst films can also be successfully deposited onto quartz fibers. Aligned few-walled CNTs can be grafted on the quartz fibers, and they self-organized into a leaf-shaped structure due to the curved surface morphology. The growth of aligned CNTs on non-planar surfaces holds promise in constructing hierarchical CNT architectures in future.     

Fabrication of a new type of organic-inorganic hybrid superlattice films combined with titanium oxide and polydiacetylene

We fabricated a new organic-inorganic hybrid superlattice film using molecular layer deposition [MLD] combined with atomic layer deposition [ALD]. In the molecular layer deposition process, polydiacetylene [PDA] layers were grown by repeated sequential adsorption of titanium tetrachloride and 2,4-hexadiyne-1,6-diol with ultraviolet polymerization under a substrate temperature of 100°C. Titanium oxide [TiO₂] inorganic layers were deposited at the same temperatures with alternating surface-saturating reactions of titanium tetrachloride and water. Ellipsometry analysis showed a self-limiting surface reaction process and linear growth of the nanohybrid films. The transmission electron microscopy analysis of the titanium oxide cross-linked polydiacetylene [TiOPDA]-TiO₂ thin films confirmed the MLD growth rate and showed that the films are amorphous superlattices. Composition and polymerization of the films were confirmed by infrared spectroscopy. The TiOPDA-TiO₂ nanohybrid superlattice films exhibited good thermal and mechanical stabilities.     

Tungsten oxide in polymer electrolyte fuel cell electrodes—A thin-film model electrode study

Thin films of WO_x and Pt on WO_x were evaporated onto the microporous layer of a gas diffusion layer (GDL) and served as model electrodes in the polymer electrolyte fuel cell (PEFC) as well as in liquid electrolyte measurements. In order to study the effects of introducing WO_x in PEFC electrodes, precise amounts of WO_x (films ranging from 0 to 40 nm) with or without a top layer of Pt (3 nm) were prepared. The structure of the thin-film model electrodes was characterized by scanning electron microscopy and X-ray photoelectron spectroscopy prior to the electrochemical investigations. The electrodes were analyzed by cyclic voltammetry and the electrocatalytic activity for hydrogen oxidation reaction (HOR) and CO oxidation was examined. The impact of Nafion in the electrode structure was examined by comparing samples with and without Nafion solution sprayed onto the electrode. Fuel cell measurements showed an increased amount of hydrogen tungsten bronzes formed for increasing WO_x thicknesses and that Pt affected the intercalation/deintercalation process, but not the total amount of bronzes. The oxidation of pre-adsorbed CO was shifted to lower potentials for WO_x containing electrodes, suggesting that Pt-WO_x is a more CO-tolerant catalyst than Pt. For the HOR, Pt on thicker films of WO_x showed an increased limiting current, most likely originating from the increased electrochemically active surface area due to proton conductivity and hydrogen permeability in the WO_x film. From measurements in liquid electrolyte it was seen that the system behaved very differently compared to the fuel cell measurements. This exemplifies the large differences between the liquid electrolyte and fuel cell systems. The thin-film model electrodes are shown to be a very useful tool to study the effects of introducing new materials in the PEFC catalysts. The fact that a variety of different measurements can be performed with the same electrode structure is a particular strength.     

Conformal coating of titanium suboxide on carbon nanotube networks by atomic layer deposition for inverted organic photovoltaic cells

We propose a new strategy for improving the charge selectivity of carbon nanotubes (CNTs) for organic photovoltaic cells (OPVCs). The strategy involves the coating of an ultrathin layer of titanium suboxide (TiO_x) on CNTs by atomic layer deposition (ALD). ALD can facilitate that conformal and uniform coating of TiO_x on CNT networks while preserving their nanoporous structure. We used the TiO_x-coated CNT networks as an electron transport layer in inverted OPVCs. TiO_x-coated CNTs can provide electrons with an extremely fast conductive path through CNTs and selectively block the holes by means of the hole-barrier property of the TiO_x in OPVCs. The nanoporous structure of TiO_x-coated CNT networks can improve the device performance of OPVCs due to synergetic effects of the electron selective transport property of TiO_x and the high conductivity of CNTs. In addition, further improvement of device performance can be achieved by adding a hole transport layer (MoO₃) between the active layer and the Au electrode.     

Combustion synthesis and EIS characterization of TiO2–SnO2 system

TiO₂ is an insulator, but using specific dopants, can modify sharply its electronic structure towards semiconducting behavior. This type of response is widely applied in many electrochemical and electrocatalytical devices, namely chlorine production, hydrocarbon oxidation, CO and CO₂ hydrogenation and as electroactive substrata for biological cell growth.Combustion synthesis is a very simple, rapid and clean method for material preparation, which will be used in the preparation of the (1 − x)TiO₂–xSnO₂, x = 0.05–0.3. Tin oxalate and titanium isopropoxide are used as precursors for the synthesis. The as-prepared powders are fine and homogeneous, the average particle size is in the range of 5–10 nm, powders and ceramic compact bodies are characterized by DRX, SEM–TEM–EDX, DTA–TG and EIS. The impedance spectroscopy of the sample 10 mol% of SnO₂ indicates the presence of several phases which promote a matrix composite based in an electrical TiO₂ insulator compatible with an electronic conducting phase tin rich. This could be attributed to the spinodal decomposition effect observed in TiO₂–SnO₂ system.     

Microstructure development of hydrothermally grown TiO2 thin films with vertically aligned nanorods

TiO₂ (rutile) thin films were deposited via a hydrothermal process by adjusting the amount of ethanol, deposition time, and temperature. Especially, various amounts of ethanol generated different degrees of supersaturation in precursor solution. It allowed us to systematically change the width, lengths, and crystallinity of a vertically aligned 1‐D nanorod structure of TiO₂ films. The oriented attachment, confirmed by scanning electron microscopy and transmission electron microscopy, was shown to be responsible for their lateral growth of TiO₂ nanorods bundled by numerous well‐oriented nanowires and their vertical growth. TiO₂ nanorod thin films were also characterized via X‐ray diffraction and UV‐Vis‐NIR spectrophotometer to find a correlation between the process conditions and nanostructural evolution. Dye sensitized solar cells were assembled to relate the nanostructures of TiO₂ films with the effectiveness of its role as a photoelectrode.     

Enhanced NO2 sensing properties of Pt/WO3 films grown by glancing angle deposition

In this work, WO₃ films were synthesized by glancing angle deposition (GLAD) and conventional planar deposition respectively. By depositing Pt on WO₃ by GLAD, the NO₂ sensitivity of WO₃ films were significantly improved. The structural characteristics and NO₂ sensing properties of the films were investigated in order to establish the enhancement mechanism. The results show WO₃ films prepared by GLAD have porous nanorod-like structure, and isolated Pt clusters are distributed on WO₃. The nanostructured Pt/WO₃ films show high sensitivity to NO₂ at 150 °C, detecting as low as 80 ppb NO₂ with a response of 1.23. Meanwhile, the films also exhibit high NO₂ selectivity against NH₃, CO, acetone and ethanol. The excellent NO₂ sensing properties of the Pt/WO₃ films can be explained due to large specific surface area of nanorod-like WO₃, catalysis of Pt and Schottky barriers at interfaces. The reliable Pt/WO₃ nanostructure prepared by GLAD could be potentially applied in low-temperature, highly sensitive NO₂ sensor for micro-electro-mechanical system (MEMS).     

Electrochemically Assisted Photocatalysis of Hybrid WO3/TiO2 Films: Effect of the WO3 Structures on Charge Separation Behavior

In this study, the photocatalysis of hybrid WO₃/TiO₂ films with different loadings of WO₃ were investigated with and without potential bias. It was clearly indicated that hybrid WO₃/TiO₂ films show less photo-reactivity under only UV-irradiation, while more effective photocatalysis under potential bias than either TiO₂ or WO₃ by themselves, their photocatalytic performance depending on the loadings of WO₃. In particular, a hybrid WO₃/TiO₂ film involving an amorphous-like WO₃ phase plays a significant role in an enhancement of the electrochemically assisted photocatalysis.     

Atomic layer deposition of TiO2 films on particles in a fluidized bed reactor

Atomic layer deposition (ALD) of controlled-thickness TiO₂ films was carried out on particle substrates in a fluidized bed reactor for the first time. Films were deposited on 550 nm SiO₂ spheres and 65 nm ZnO nanoparticles for enhanced optical properties. Nanoparticles were fluidized with the assistance of a magnetically-coupled stirring unit. The metalorganic precursor titanium tetraisopropoxide was used here followed by either H₂O or H₂O₂ to deposit TiO₂ at various substrate temperatures. Growth rates of 0.01 nm/cycle and 0.04 nm/cycle were achieved when using H₂O and H₂O₂ as the oxidizer, respectively. These conformal TiO₂ films were verified using HRTEM, ICP-AES, XPS and UV absorbance measurements. The specific surface area changed appropriately after the particle size increased by the deposition of films with a given density, which showed that primary particles were not agglomerated together due to the coating process. In situ mass spectrometry was used to monitor reaction progress throughout each ALD reaction cycle. Bulk quantities of powder were successfully functionalized by TiO₂ nanofilms without wasting excess precursor.     

Uniform color coating of multilayered TiO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> films by atomic layer deposition

Thin film optics, based on light interference characteristics, are attracting increasing interest because of their ability to enable a functional color coating for various applications in optical, electronic, and solar industries. Here, we report on the dependence of coloring characteristics on single-layer TiO₂ thicknesses and alternating TiO₂/Al₂O₃ multilayer structures prepared by atomic layer deposition (ALD) at a low growth temperature. The ALD TiO₂ and Al₂O₃ thin films were studied at a low growth temperature of 80°C. Then, the coloring features in the single-layer TiO₂ and alternating TiO₂/Al₂O₃ multilayers using both the ALD processes were experimentally examined on a TiN/cut stainless steel sheet. The Essential Macleod software was used to estimate and compare the color coating results. The simulation results revealed that five different colors of the single TiO₂ layers were shown experimentally, depending on the film thickness. For the purpose of highly uniform pink color coating, the film structures of TiO₂/Al₂O₃ multilayers were designed in advance. It was experimentally demonstrated that the evaluated colors corresponded well with the simulated color spectrum results, exhibiting a uniform pink color with wide incident angles ranging from 0° to 75°. This article advances practical applications requiring highly uniform color coatings of surfaces in a variety of optical coating areas with complex topographical structures.     

TiO2‐Modified Flower‐Like Bi2WO6 Nanostructures with Enhanced UV‐Vis Photocatalytic Activity

Anatase TiO₂‐modified flower‐like Bi₂WO₆ nanostructures were prepared by a simple hydrothermal reaction followed by layer‐by‐layer deposition and calcination. The photocatalytic activity was evaluated using Brilliant Red X3B, an anionic azo dye, as the target organic pollutant under UV‐Vis light irradiation. The experiment results showed that the photocatalytic activity of the hybrid increases first and then decreases with increasing loading amount of TiO₂. The hybrid coated with four layers of TiO₂ (containing 20 wt‐% TiO₂) showed the highest photocatalytic activity, which is 10.45 and 3.20 times higher than that of pure Bi₂WO₆ and TiO₂, respectively. The improved photocatalytic performance of TiO₂‐modified Bi₂WO₆ nanostructures could be ascribed to the improved light‐harvesting ability, efficient photo‐generated electron‐hole separation, and enhanced adsorption of the dye. This work may shed light on the design of complex architectures and the exploitation of their potential applications.     

Nanostructured Solids from Freeze‐Dried Precursors: Multigram Scale Synthesis of TiO2‐Based Powders

Nanocrystalline TiO₂ and Ti_1?xV_xO₂ (x = 0.01) powders have been prepared by thermal decomposition, in air, of amorphous precursors resulting from the freeze‐drying of appropriate solutions. In addition, TiO_2?xN_y (anatase and rutile) and TiO_xN_y (rock‐salt) have been prepared by thermal treatment in ammonia of a crystalline precursor (TiO₂ obtained at 673 K). TEM and SEM images, as well as the analysis of the X‐ray diffraction (XRD) patterns, show the nanoparticulated character of those solids obtained at low temperatures, with typical particle sizes in the 10–20 nm range when prepared at 673 K. The UV–Vis results indicate both the insertion of V in the anatase lattice and the feasibility of nitridation at low temperatures. The photocatalytic properties of these materials (as prepared and after their incorporation to mortar samples) in the degradation of nitrogen oxides have been preliminary evaluated. Although N‐doping enhances the photocatalytic activity of the TiO₂ matrix, V‐doping worsens it.