Growth of TiO2 with thermal and plasma enhanced atomic layer deposition

We show a comparative study of the TiO2 ALD with TTIP and either O2 or O2-plasma on Si/SiO2 substrates. In particular we compare the surface morphology and crystalline phase by means of Atomic Force Microscopy (AFM), X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) for different O2-plasma procedures upon changing the time between cycles and the N2-purging pressure. The AFM images show that already these parameters may induce structural changes in the TiO2 films grown by ALD, with the formation of crystallites with average lateral width varying between 15 and 80 nm. By means of XAS we also found that the crystallites have mixed anatase and rutile crystalline phases and that smaller crystallites have a greater rutile component than the larger ones.     

Electrical properties of quaternary HfAlTiO thin films grown by atomic layer deposition

Quaternary alloyed HfAlTiO thin (~ 4-5 nm) films in the wide range of Ti content have been grown on Si substrates by Atomic Layer Deposition technique, and the effect of both the film composition and the interfacial reactions on the electrical properties of HfAlTiO films is investigated. It is shown that depending on the Ti content, the permittivity and the leakage current density I_leak in HfAlTiO films vary in the range k = 18 ÷ 28 and 0.01-2.4 A cm^− 2, respectively. The incorporation of ultra thin SiN interlayer in Al/HfAlTiO/SiN/Si stack gives rise to the sharp (× 10³) decrease of the I_leak ~ 6 · 10^− 5 A/cm² at the expense of the rather low capacitance equivalent thickness ~ 0.9 nm.     

Thermal and Electrical Conduction in Ultrathin Metallic Films: 7 nm down to Sub‐Nanometer Thickness

For ultrathin metallic films (e.g., less than 5 nm), no knowledge is yet available on how electron scattering at surface and grain boundaries reduces the electrical and thermal transport. The thermal and electrical conduction of metallic films is characterized down to 0.6 nm average thickness. The electrical and thermal conductivities of 0.6 nm Ir film are reduced by 82% and 50% from the respective bulk values. The Lorenz number is measured as 7.08 × 10^?8 W Ω K^?2, almost a twofold increase of the bulk value. The Mayadas‐Shatzkes model is used to interpret the experimental results and reveals very strong electron reflection (>90%) at grain boundaries.     

Electrical resistivity of Ti-Zn mixed oxide thin films deposited by atomic layer deposition

Ti-Zn mixed oxide thin films, with thickness less than 50 nm, were grown with atomic layer deposition (ALD) technique at low temperature (90 °C) varying the composition. ALD is a powerful chemical technique to deposit thin films with thickness of few atomic layers. ALD oxide material growth is achieved by dosing sequentially the metal precursor and the oxidizing agent. Thanks to ALD nature of layer by layer growth it was possible to realize mixed metal, Ti and Zn, oxide thin films with controlled composition, simply by changing the number of cycles of each metal oxide layer. Structural and electrical properties of the prepared thin films were studied as a function of their composition. Synchrotron radiation X-ray diffraction technique was used to follow thin film crystallization during sample annealing, performed in situ. It was observed that the onset temperature of crystallization raises with Ti content, and sample structure was Zn₂TiO4 phase. Electrical resistivity measurements were performed on crystalline samples, annealed at 600 °C, revealing an increase in resistivity with Ti content.     

Applications of atomic layer deposition to nanofabrication and emerging nanodevices

Recently, with scaling down of semiconductor devices, need for nanotechnology has increased enormously. For nanoscale devices especially, each of the layers should be as thin and as perfect as possible. Thus, the application of atomic layer deposition (ALD) to nanofabrication strategies and emerging nanodevices has sparked a good deal of interest due to its inherent benefits compared to other thin film deposition techniques. Since the ALD process is intrinsically atomic in nature and results in the controlled deposition of films at the atomic scale, ALD produces layers with nanometer scale thickness control and excellent conformality. In this report, we review current research trends in ALD processes, focusing on the application of ALD to emerging nanodevices utilizing fabrication through nanotechnology.     

Hybrid nanomaterials through molecular and atomic layer deposition: Top down,bottom up,and in-between approaches to new materials

The ability to produce or alter materials to obtain drastically different or improved properties has been the driving goal of materials science since its inception. Combining multiple elements, compounds, or materials while maintaining the beneficial aspects of each constituent is a complex problem often involving highly interdisciplinary research. Hybrid materials, i.e. materials that incorporate organic and inorganic parts, have become popular in a variety of fields. Though not entirely new, the modern embodiment of hybrid materials has led to a large variety of new materials and techniques to produce them. One of the most recent being combination of atomic layer deposition (ALD), which produces inorganic materials, and molecular layer deposition (MLD), which produces organic materials. Furthermore, a variation on these techniques, commonly referred to as infiltration, has allowed for the modification of a variety of natural and synthetic polymers with surprising results related to their bulk mechanical properties. In this review three approaches are taken. First, hybrid materials through bottom-up combinations of ALD and MLD are reviewed, focusing on the process and properties of the resulting materials. Second, the modification of biomaterials through coating is discussed, and finally the relatively new concept of vapor phase infiltration is considered as a new and unique method to produce hybrid materials from a top down perspective.     

Electrical conduction in 10-20 nm thick polycrystalline tin oxide thin films deposited by chemical vapor deposition

Electrical properties were studied for chemical vapor deposited fluorine doped tin oxide films that were less than 20 nm thick. The electrical properties of the coatings were found to be affected by the type of additive alcohol used in the deposition process. Conductivity was superior for ethanol or isopropyl alcohol (IPA) compared to methanol. Hall effect measurements showed that mobility and carrier concentration were best for IPA, less for ethanol, and least for methanol. Influence of carrier scattering factors to electrical properties was speculated. Potential barrier for carrier scattering at grain boundaries was estimated to be lower in an IPA-added film compared to methanol-added films. Experimental results suggested electrical properties were influenced by size and density of tin oxide micro-grains. It was concluded that interconnections between the micro-grains increased mobility and carrier concentration of very thin films.     

Influence of thickness and growth temperature on the properties of zirconium oxide films grown by atomic layer deposition on silicon

ZrO₂ films of thicknesses varied in the range of 3–30 nm were atomic layer deposited from ZrI₄ and H₂O–H₂O₂ on p-Si(100) substrates. The effects of film thickness and deposition temperature on the structure and dielectric properties of ZrO₂ were investigated. At 272 and 325 °C, the growth of ZrO₂ started with the formation of the cubic polymorph and continued with the formation of the tetragonal polymorph. The ratio between the lattice parameters increased with the film thickness and growth temperature. The effective permittivity, determined from the accumulation capacitance of Hg/ZrO₂/Si capacitors, increased with the film thickness, reaching 15–17 in 25-nm-thick films. The permittivity decreased with the increasing growth temperature. The hysteresis of the capacitance–voltage curves was the narrowest for the films deposited at 325 °C, and increased towards both lower and higher deposition temperatures.     

Using fence post designs to speed the atomic layer deposition of optical thin films

Atomic layer deposition (ALD) at this time is much slower than conventional optical thin-film deposition techniques. A more rapid ALD process for SiO(2) has been developed than for other ALD materials. A fence post design for optical thin films has thin layers of high-index posts standing above a broad low-index ground. If a design for ALD can be predominantly composed of SiO(2) layers with thin high-index layers, the deposition times can be correspondingly shortened, and it is shown that the required performance can still be nearly that of more conventional designs with high- and low-index layers of equal thickness. This combination makes the ALD benefits of conformal coating and precise thickness control more practical for optical thin-film applications.     

Controlled dielectrophoretic nanowire self-assembly using atomic layer deposition and suspended microfabricated electrodes

Effects of design and materials on the dielectrophoretic self-assembly of individual gallium nitride nanowires (GaN NWs) onto microfabricated electrodes have been experimentally investigated. The use of TiO(2) surface coating generated by atomic layer deposition (ALD) improves dielectrophoretic assembly yield of individual GaN nanowires on microfabricated structures by as much as 67%. With a titanium dioxide coating, individual nanowires were placed across suspended electrode pairs in 46% of tests (147 out of 320 total), versus 28% of tests (88 out of 320 total tests) that used uncoated GaN NWs. An additional result from these tests was that suspending the electrodes 2.75 μm above the substrate corresponded with up to 15.8% improvement in overall assembly yield over that of electrodes fabricated directly on the substrate.     

Rayleigh-instability-induced metal nanoparticle chains encapsulated in nanotubes produced by atomic layer deposition

Cu nanoparticle chains encapsulated in Al2O3 nanotubes were successfully generated in a controlled manner by reduction of CuO nanowires embedded in Al2O3 at a sufficiently high temperature. The Al2O3 coating was deposited by atomic layer deposition (ALD). The particles mainly show a rodlike shape and are regularly distributed. The particle diameters and chain lengths corresponding to the inner diameters and lengths of the tubes, respectively, are controlled by the size of the CuO nanowire templates. Rayleigh instability, assisted by the uniform volume shrinkage created by the reduction of oxide to metal, is proposed to induce the formation of the nanochains. This method may potentially be extended to the synthesis of nanochains of other metals by reducing corresponding oxide nanowires embedded in ALD shells.     

Surface engineering of synthetic nanopores by atomic layer deposition and their applications

In the past decade, nanopores have been developed extensively for various potential applications, and their performance greatly depends on the surface properties of the nanopores. Atomic layer deposition （ALD） is a new technology for depositing thin films, which has been rapidly developed from a niche technology to an established method. ALD films can cover the surface in confined regions even in nanoscale conformally, thus it is proved to be a powerful tool to modify the surface of the synthetic nanopores and also to fabricate complex nanopores. This review gives a brief introduction on nanopore synthesis and ALD fundamental knowledge, and then focuses on the various aspects of synthetic nanopores processing by ALD and their applications, including single-molecule sensing, nanofiuidic devices, nanostructure fabrication and other applications.     

Controlling spatial density and size of nanocrystals by two-step atomic layer deposition

Two-step atomic layer deposition (ALD) is proposed in order to control both the spatial density and size of nanocrystals (NCs) via modulation of the nucleation rate during deposition. In this process, two different deposition conditions are sequentially used: a high nucleation rate condition for the formation of high density NCs and a low nucleation rate condition with a slow growth rate for the subsequent growth of pre-formed NCs. To control the nucleation rate of Ru during ALD, pulsing time and carrier flow rate of the Ru precursor are varied. By controlling those factors, both the film growth rate and a nucleation rate of Ru are decreased considerably. Two-step ALD of Ru NCs using the surface-saturated condition followed by the reduced condition allows for variation of the spatial density from 7.9 × 10(11) to 3.2 × 10(12) cm(-2) and variation of the average diameter from 1.9 to 3.3 nm.     

TiCp*(OMe)3 versus Ti(OMe)4 in atomic layer deposition of TiO2 with water--ab initio modelling of atomic layer deposition surface reactions

It is a common finding that titanocene-derived precursors do not yield TiO2 films in ALD with water. For instance, ALD with Ti(OMe)4 and water gives 0.5 A/cycle, while TiCp*(OMe)3 does not show any growth (Me=CH3, Cp* = C5(CH3)5). This is apparently in contradiction with the computed reactivity of the ligands: the energetics of hydrolysis of the gas-phase precursor indicate that TiCp*(OMe)3 is more reactive to ligand elimination than Ti(OMe)4. However such a model of precursor reactivity neglects surface reactions such as adsorption, diffusion and desorption, all of which can have an important effect on ALD growth rate. A more accurate model of the surface reaction is needed to find the reason for the different behaviours of Ti(OMe)4 and TiCp*(OMe)3 in the ALD process. The more realistic surface model is a TiO2 slab that is periodic in three dimensions. These calculations reveal that TiCp*(OMe)3 does not chemisorb in the usual way because of extreme crowding of the Ti centre by Cp* and that this prevents ALD growth.     

Stable p-type ZnO films grown by atomic layer deposition on GaAs substrates and treated by post-deposition rapid thermal annealing

Long-term stable p-type ZnO films were grown by atomic layer deposition on semi-insulating GaAs substrates and followed by rapid thermal annealing (RTA) in oxygen ambient. Significant decrease in the electron concentration and increase in the hole concentration, together with the intensity enhancement of acceptor-related A^oX spectral peak and the shift of bound exciton peak from D^oX to A^oX in the low-temperature photoluminescence spectra, were observed as the RTA temperature increased. Conversion of conductivity from intrinsic n-type to extrinsic p-type ZnO occurred at the RTA temperature of 600 °C. The p-type ZnO film with a hole concentration as high as 3.44 × 10²⁰ cm^− 3 and long-term stability up to 180 days was obtained as the RTA treatment was carried out at 700 °C. The results were attributed to the diffusion of arsenic atoms from GaAs into ZnO as well as the activation of As-related acceptors by the post-RTA treatment.     

Structure and morphology of aluminium doped Zinc-oxide layers prepared by atomic layer deposition

The aim of this work is to study the effects of deposition temperature and aluminium incorporation on the crystalline properties, orientation and grain size of atomic layer deposited ZnO layers. X-ray diffraction analysis revealed a change in the dominant crystallite orientation with increasing substrate temperature. The most perfect crystal structure and largest grain size was found at 2 at.% aluminium content. Accumulation of compressive strain developed a monotonous increase with the growth temperature. Electric resistivity showed no anisotropy despite the change in the orientation, therefore the dominant conduction mechanism is not grain boundary related.     

Influence of AlN buffer layer thickness and deposition methods on GaN epitaxial growth

A gallium nitride (GaN) epitaxial layer was grown by metal-organic chemical vapor deposition (MOCVD) on Si (111) substrates with aluminum nitride (AlN) buffer layers at various thicknesses. The AlN buffer layers were deposited by two methods: radio frequency (RF) magnetron sputtering and MOCVD. The effect of the AlN deposition method and layer thickness on the morphological, structural and optical properties of the GaN layers was investigated. Field emission scanning electron microscopy showed that GaN did not coalesce on the sputtered AlN buffer layer. On the other hand, it coalesced with a single domain on the MOCVD-grown AlN buffer layer. Structural and optical analyses indicated that GaN on the MOCVD-grown AlN buffer layer had fewer defects and a better aligned lattice to the a- and c-axes than GaN on the sputtered AlN buffer layer.