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Vertically aligned 3D gallium nitride (GaN) nanowire arrays with sub-50 nm feature sizes were fabricated using a nanosphere lift-off lithography (NSLL) technique combined with hybrid top-down etching steps (i.e., inductively coupled plasma dry reactive ion etching (ICP-DRIE) and wet chemical etching). Owing to the well-controlled chemical surface treatment prior to the nanobead deposition and etching process, vertical GaN nanowire arrays with diameter of ~35 nm, pitch of ~350 nm, and aspect ratio of >10 could be realized using 500 nm polystyrene nanobead (PN) masks. This work has demonstrated a feasibility of using NSLL as an alternative for other sophisticated but expensive nanolithography methods to manufacture low-cost but highly ordered 3D GaN nanostructures.

Diamond and/or carbon thin films are in the center of interest due to their variability and extraordinary combination of intrinsic properties. However, some applications require fabrication of films with tailored properties. Especially, fabrication of periodic structures is highly attractive due to their increased surface area. In this contribution we point out the key technological aspects for fabrication of micro- and nano-sized carbon-based structures. Three representative structures are presented: diamond nanorods, self-assembled templates and self-standing diamond membranes. We found that the diameter of diamond nanorods can be controlled in a broad range from 10 to 200 nm by the masking material (Au vs Ni) and its initial thickness (from few to tens of nanometers). The assembly of polystyrene microspheres in mono- or multi-layer with square or hexagonal periodicities was controlled by the spin-coating parameters. The diamond porous membrane was selectively grown on Si substrate with an interdigital or mesh like geometry. Advantages of each structure as well as the fabrication limitations are discussed more in detail and finally their representative applications are pointed out. [ABSTRACT FROM AUTHOR]

Thin diamond strips on Si with the thickness of approx. 0.5 and 1 μm and two different widths (100 and 200 μm) were fabricated in two different ways: i) selective ion etching of the continuous diamond films and ii) selective area diamond growth. The stress induced in the films was measured by Raman spectroscopy. The measured values were in the range from − 0.7 to − 0.1 GPa. It was found that the stress was compressive and independent of the film thickness. In the films deposited at 950 K, more compressive stress than at 1100 K was measured. The thermal part of the stress as a consequence of heterostructure cooling from high deposition temperature down to room temperature was calculated by Finite Element Method (FEM) simulations and compared with the measurement. It was found that the calculated thermal stress of the continuous film was rather close to the stress values measured for the etched films. The qualitative distribution of the stress measured from the diamond strip center to its edge coincided very well with the FEM simulations. It was shown that relevant stress studies can be made with a relatively low spatial resolution of the Raman measurement in combination with qualitative results of FEM simulations. [ABSTRACT FROM AUTHOR]

Structured diamond films are required for several uses as photonic crystals, (bio-) sensors, biomedicine, etc. Often, these uses require fabrication of nano-sized features with the assistance of lithographic techniques. In this paper, we demonstrate the growth of diamond structures well ordered in periodic arrays. The technological process starts with ultrasonic seeding of Si substrates by ultra-dispersed detonation diamond nanoparticles. Then, a monolayer of polystyrene microspheres (PS) is deposited on seeded Si substrates by Langmuir-Blodgett method. The primary diameter of PS varies from 253 to 940 nm. The self-assembled PS are employed as a mechanical mask for reactive ion etching of the seeding layer via reducing the PS diameter down. The seeding structures remained under reduced PS were used for growing periodically ordered diamond arrays by microwave plasma-assisted chemical vapor deposition from a hydrogen rich gas mixture. Cross-section SEM images reveal that the diameter and size of the formed diamond structures increase both in vertical and lateral direction. At a certain deposition time, the structures start to coalesce into a continuous layer. [ABSTRACT FROM AUTHOR]

Diamond-on-GaN heterostructure is a promising hybrid material system with a variety of applications such as heat spreaders, high-temperature, and high-power devices. From a practical point of view, polycrystalline diamond is shown to be an attractive solution to the limited use of the expensive monocrystalline diamond substrates. Here we present selective area diamond deposition on AlGaN/GaN layers focusing on the elimination of surface and metal contact damage (Ni, NiO, Ir, and IrO2) and suppressing the spontaneous nucleation of diamond. Metal contacts are important for further applications such as diamond-coated GaN based electronic devices. The growth of diamond films was performed by microwave chemical vapor deposition in different gas mixtures with the addition of CO2 or N2 to CH4/H2. Adding CO2 resulted in polycrystalline (PCD), while adding N2 led to the formation of nanocrystalline diamond film (NCD). The diamond deposition was carried out using selective area nucleation in a three-layer sandwich structure (polymer/seeding layer/polymer), which avoided damage to the electrode and GaN surfaces from ultrasonic seeding by diamond particles. No protective layer was used on the GaN surface before diamond deposition, i.e., diamond films were grown directly on the AlGaN/GaN heterostructures. In the case of NCD deposition, no surface damaging of GaN was observed. For both NCD and PCD films, increasing methane from 1% to 2% in H2 minimized the surface damage of GaN films. [ABSTRACT FROM AUTHOR]

Abstract: A key factor in engineering integrated devices such as electro-optic switches or waveguides is the patterning of high quality crystalline thin films into specific geometries. In this contribution high vacuum chemical vapor deposition (HV-CVD) was employed to grow titanium dioxide (TiO2) patterns onto silicon. The directed nature of precursor transport – which originates from the high vacuum environment during the process – allows shading certain regions on the substrate by shadow masks and thus depositing patterned thin films. While the use of such masks is an emerging field in stencil or shadow mask lithography, their use for structuring thin films within HV-CVD has not been reported so far. The advantage of the employed technique is the precise control of lateral spacing and of the distance between shading mask and substrate surface which is achieved by manufacturing them directly on the substrate. As precursor transport takes place in the molecular flow regime, the precursor impinging rates (and therefore the film growth rates) on the surface can be simulated as function of the reactor and shading mask geometry using a comparatively simple mathematical model. In the current contribution such a mathematical model, which predicts impinging rates on plain or shadow mask structured substrates, is presented. Its validity is confirmed by TiO2-deposition on plain silicon substrates (450°C) using titanium tetra isopropoxide as precursor. Limitations of the patterning process are investigated by the deposition of TiO2 on structured substrates and subsequent shadow mask lift-off. The geometry of the deposits is according to the mathematical model. Shading effects due to the growing film enables to fabricate deposits with predetermined variations in topography and non-flat top deposits which are complicated to obtain by classical clean room processes. As a result of the enhanced residual pressure of decomposition products and titanium precursors and the corresponding surface coverage of them, growth conditions differ in proximity of the shadowed areas compared to the case of plain substrates and the obtained film thickness differs significantly from predictions. [Copyright &y& Elsevier]

Sn–Ni alloy coatings on mild steel substrates produced by selective area deposition process with layer thickness of about 14 μm were investigated with regard to the structural and corrosion properties. X-ray diffraction analysis revealed that the selective area plated Sn–Ni alloy was heterogeneous and composed of NiSn, Ni3Sn2 and Ni3Sn4 phases. Uniform surface coverage of the substrate by granular morphology was observed from SEM and AFM. The alloy composition was determined by X-ray fluorescence (XRF). The corrosion protection performance of Sn–Ni alloy on mild steel was assessed using salt-water immersion and electrochemical corrosion tests. A sharp decrease in I corr and high charge transfer resistance indicated improved corrosion resistant behavior of the selective area deposited Sn–Ni alloy. [ABSTRACT FROM AUTHOR]

In fabricating inorganic thin-film devices, the relative etch rates of materials in a given etch chemistry often limit the obtainable multilayer structures. Alternatively, in fabricating multilayer organic devices by solution processing, the ability to formulate the active organic materials in orthogonal solvent systems is limiting. The pattered-by-printing method uses the combination of selective area deposition (SAD) and atomic layer deposition (ALD) to form high-quality metal oxide thin-film devices. We print an inhibiting polymer ink that patterns the functional inorganic materials that are deposited via spatial ALD (SALD). The process is inherently orthogonal, as the polymer ink does not etch or swell the inorganic functional layers. Each functional layer is additively patterned as deposited, with device isolation and vias defined by the printed inhibitor. The combination of process orthogonality and additive patterning removes processing-related constraints on device design, and readily allows for any combination of bottom- and top-gate thin-film transistor architectures to be formed on the same substrate. The freedom of this approach is further demonstrated by both all-enhancement-mode circuits and enhancement-depletion-mode circuits. In addition, we present a new tool to tune circuit performance by local control of dielectric thickness.

We describe improvements in both yield and performance for thin-film transistors (TFTs) fabricated by spatial atomic layer deposition (SALD). These improvements are shown to be critical in forming high-quality devices using selective area deposition (SAD) as the patterning method. Selective area deposition occurs when the precursors for the deposition are prevented from reacting with some areas of the substrate surface. Controlling individual layer quality and the interfaces between layers is essential for obtaining good-quality thin-film transistors and capacitors. The integrity of the gate insulator layer is particularly critical, and we describe a method for forming a multilayer dielectric using an oxygen plasma treatment between layers that improves crossover yield. We also describe a method to achieve improved mobility at the important interface between the semiconductor and the gate insulator by, conversely, avoiding oxygen plasma treatment. Integration of the best designs results in wide design flexibility, transistors with mobility above 15 cm(2)/(V s), and good yield of circuits.