Hot‐wire assisted atomic layer deposition (HWALD) is a novel energy‐enhancement technique. HWALD enables formation of reactive species (radicals) at low substrate temperatures, without the generation of energetic ions and UV photons as by plasma. This approach employs a hot wire (tungsten filament) that is heated up to a temperature in the range of 1300–2000 °C to dissociate precursor molecules. HWALD has the potential to overcome certain limitations of plasma‐assisted processes. This work investigates the ability of a heated tungsten filament to catalytically crack molecular hydrogen or ammonia into atomic hydrogen and nitrogen‐containing radicals. The generation of these radicals and their successful delivery to the wafer (substrate) surface are experimentally confirmed by dedicated tellurium‐etching and silicon‐nitridation experiments. It further reports on deposition of low‐resistivity oxygen‐free tungsten films by using HWALD, as well as on the effect of hot‐wire‐generated nitrogen radicals and atomic hydrogen in deposition of aluminum nitride and boron nitride films. In parallel, this work provides important illustrative examples of using in situ real‐time monitoring of deposition and etching processes, together with extracting a variety of film properties, by spectroscopic ellipsometry technique.
RAMAZAN OG UZHAN APAYDIN, BURÇ AK EBIN, and SEBAHATTIN GÜ RMENNanostructured copper-nickel (CuNi) and copper-nickel-indium (CuNiIn) alloy particles were produced from aqueous solutions of copper, nickel nitrates and indium sulfate by hydrogen reduction-assisted ultrasonic spray pyrolysis. The effects of reduction temperatures, at 973 K, 1073 K, and 1173 K (700°C, 800°C, and 900°C), on the morphology and crystalline structure of the alloy particles were investigated under the conditions of 0.1 M total precursor concentration and 0.5 L/min H 2 volumetric flow rate. X-ray diffraction studies were performed to investigate the crystalline structure. Particle size and morphology were investigated by scanning electron microscope and energy-dispersive spectroscopy was applied to determine the chemical composition of the particles. Spherical nanocrystalline binary CuNi alloy particles were prepared in the particle size range from 74 to 455 nm, while ternary CuNiIn alloy particles were obtained in the particle size range from 80 to 570 nm at different precursor solution concentrations and reduction temperatures. Theoretical and experimental chemical compositions of all the particles are nearly the same. Results reveal that the precursor solution and reduction temperature strongly influence the particle size of the produced alloy particles.
This work studies the deposition of boron/boron nitride (B/BN) composite films at low substrate temperature (275-375 °C) by alternating pulses of diborane (B 2 H 6 ) and ammonia (NH 3 ) with argon purging in between to avoid gas-phase reactions of the precursors. This process is similar to atomic layer deposition in which the dominance of surface reactions simplifies the growth mechanism. However, non-self-limiting decomposition of B 2 H 6 and incomplete nitridation lead to the incorporation of pure boron (pure-B), causing deviation from the desired 1:1 B:N stoichiometry. Using the pure-B fraction as a measure of incomplete nitridation, this article describes consecutive experiments to control this effect and ultimately understand it in the context of a surface reaction model. First, it is demonstrated that, in a purely thermal mode, the growth of the layers and their composition strongly depend on the total gas pressure. The pure-B content (not to be confused with the total boron content) could thus be varied in the range of ∼6-70 vol. %. Next, enhancement of nitridation by the dissociation of NH 3 into reactive radicals using a hot-wire was found to be insufficient to produce stoichiometric BN. Finally, plasma-assisted deposition at 310 °C resulted in nearly stoichiometric polycrystalline BN with an interplane distance matching that of hexagonal BN; the material was stable in air for at least six months. The pressure dependence in the purely thermal mode is consistent with a growth model of BN from B 2 H 6 and NH 3 via the so-called surface-adduct mechanism. The effects of the radical-enhanced methods on nitridation are explained using this model.
This work considers the possible occurrence of two distinct phases in thin films of overall composition B1−xNx (0.21 ≤ x ≤ 0.47) grown by chemical vapor deposition from sequential pulses of diborane (B2H6) and ammonia (NH3). Two distinct peaks are identified in B1s x-ray photoelectron spectroscopy (XPS), related to two populations of B atoms with different oxidation states. The data are most consistent with a model in which one population mainly bonds to B atoms, and the other population mainly bonds to N atoms, as expected for a composite of B and BN. Based on peak broadening, interfaces between the two types contribute significantly to the spectra. Furthermore, spectroscopic ellipsometry (SE) found that the samples displayed optical absorption consistent with that of pure-B. This work, thus, developed a fit model to characterize the films optically by SE. Describing the films as composites of pure-B and BN, and using optical constants of reference layers thereof, the relative fractions could be estimated in reasonable agreement with XPS. Differences between the models and data in both SE and XPS are consistent with the effects of hydrogenation and the contribution of atoms in interface states. Evidence from SE suggests that the films may consist of stacked lamellar phases, which would indeed have a large surface-to-volume ratio.
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