Dynamic Ellipsometric Porosimetry Investigation of Permeation Pathways in Moisture Barrier Layers on Polymers

The quality assessment of moisture permeation barrier layers needs to include both water permeation pathways, namely through bulk nanoporosity and local macroscale defects. Ellipsometric porosimetry (EP) has been already demonstrated a valuable tool for the identification of nanoporosity in inorganic thin film barriers, but the intrinsic lack of sensitivity toward the detection of macroscale defects prevents the overall barrier characterization. In this contribution, dynamic EP measurements are reported and shown to be sensitive to the detection of macroscale defects in SiO₂ layers on polyethylene naphthalate substrate. In detail, the infiltration of probe molecules, leading to changes in optical properties of the polymeric substrate, is followed in time and related to permeation through macroscale defects

First-Principles Investigation of C–H Bond Scission and Formation Reactions in Ethane, Ethene, and Ethyne Adsorbed on Ru(0001)

We have studied all possible elementary reactions (including isomerization reactions) involved in the interaction of CH₄ (methane), CH₃CH₃ (ethane), CH₂CH₂ (ethene), and CHCH (ethyne) with the Ru(0001) surface using density functional theory based first-principles calculations. Site preference and adsorption energies for all the reaction intermediates and activation energies for the elementary reactions are calculated. From the calculated adsorption and activation energies, we find that dehydrogenation of the adsorbates is thermodynamically favored in agreement with experiments. Dehydrogenation of CH (methylidyne) is the most difficult in the dehydrogenation of CH₄ (methane). CH₃CH₃ (ethane), CH₂CH₂ (ethene), and CHCH (ethyne) dehydrogenate through the CH₃C (ethylidyne) intermediate. Of the five possible pathways for the production of CH₃C (ethylidyne), the CH₂CH (ethenyl)–CH₂C (ethenylidene) pathway is the most dominant. In the case of ethene, the ethynyl–ethenylidene pathway is also the dominant pathway on Pt(111). Comparison of α and β-C–H bond scission reactions, important for the Fischer–Tropsch process, shows that alkenes should be the major products compared to the formation of alkynes. Dehydrogenation becomes slightly favorable at lower coverages of the hydrocarbon fragments while hydrogenation becomes slightly unfavorable. In addition to resolving the dominant pathways during decomposition of the above hydrocarbons, the activation energies calculated in this paper can also be used in the modeling of processes that involve the considered elementary reactions at longer length and time scales

Atomic Layer Deposition of Silicon Nitride from Bis(tertiary-butyl-amino)silane and N₂ Plasma Studied by <i>in Situ</i> Gas Phase and Surface Infrared Spectroscopy

The atomic layer deposition process (ALD) of silicon nitride (SiN_<i>x</i>), employing bis­(tertiary-butyl-amino)­silane (SiH₂(NH^<i>t</i>Bu)₂, BTBAS) and N₂ plasma, was investigated by means of Fourier transform infrared (FT-IR) spectroscopy. <i>In situ</i> gas phase, film, and surface infrared measurements have been performed during different stages of the ALD process. From gas phase IR measurements it can be concluded that <i>tert</i>-butylamine is the main reaction product released during precursor exposure. Infrared measurements performed on the deposited SiN_<i>x</i> films revealed the incorporation of C in the form of CN and SiC, where more C is incorporated at a deposition temperature of 85 °C compared to 155 or 275 °C. Surface IR measurements, employing a four-axes sample manipulator, showed the formation of SiH- and NH-groups on the surface and revealed that most of the H is incorporated during the precursor exposure step. Furthermore, after the N₂ plasma step a vibrational mode around 2090 cm^–1 was observed. This mode could be attributed to the formation of Si-NCH complexes and are likely to be formed by the so-called redeposition effect. For higher deposition temperatures, these Si-NCH complexes are removed again during the following precursor exposure step. At 85 °C, some of the complexes remain at the surface. Overall, from the gained knowledge about the surface chemistry, a reaction mechanism of the SiN_<i>x</i> ALD process has been proposed

Supported Core/Shell Bimetallic Nanoparticles Synthesis by Atomic Layer Deposition

A continuing goal in catalysis research is to engineer the composition and structure of noble metal nanomaterials in order to precisely tune their catalytic activity. Herein, we present proof-of-concept results on the synthesis of supported bimetallic core/shell nanoparticles entirely by atomic layer deposition (ALD). ALD is a novel and scalable method, which can be used to prepare noble-metal catalysts on high surface area support materials. Two properties of ALD of noble metals, namely the Volmer–Weber growth and surface-selectivity, are exploited to decouple primary island growth from subsequent selective shell growth. This concept is applied to synthesize highly dispersed Pd/Pt and Pt/Pd nanoparticles. In-depth characterization of the nanoparticles provides evidence for the core/shell morphology and for the narrow size distribution. The self-limiting nature of the ALD process allows for independent control of the core and shell dimensions, opening up unique possibilities for precise engineering of metallic nanoparticle properties

Influence of Oxygen Exposure on the Nucleation of Platinum Atomic Layer Deposition: Consequences for Film Growth, Nanopatterning, and Nanoparticle Synthesis

Control of the nucleation behavior during atomic layer deposition (ALD) of metals is of great importance for the deposition of metallic thin films and nanoparticles, and for nanopatterning applications. In this work it is established for Pt ALD, that the exposure to O₂ during the O₂ pulse of the ALD process is the key parameter controlling the nucleation behavior. The O₂ dependence of the Pt nucleation is explained by the enhanced diffusion of Pt species in the presence of oxygen, and the resulting faster aggregation of Pt atoms in metal clusters that catalyze the surface reactions of ALD growth. Moreover, it is demonstrated that the O₂ exposure can be used as the parameter to tune the nucleation to enable (i) deposition of ultrathin films with minimal nucleation delay, (ii) preparation of single element or core/shell nanoparticles, and (iii) nanopatterning of metallic structures based on area-selective deposition

Atomic Layer Deposition of High-Purity Palladium Films from Pd(hfac)₂ and H₂ and O₂ Plasmas

A plasma-assisted atomic layer deposition (ALD) process has been developed that allows for low temperature (100 °C) synthesis of virtually 100% pure palladium thin films with low resistivity of 24 ± 3 μΩ cm on oxide substrates. This process is based on Pd­(hfac)₂ (hfac = hexafluoroacetylacetonate) precursor dosing followed by sequential H₂ plasma and O₂ plasma steps in a so-called ABC-type ALD process. Gas-phase infrared spectroscopy studies revealed that the O₂ plasma pulse is required to remove carbon contaminants from the Pd surface that remain after the H₂ plasma reduction step. Omitting the O₂ plasma step, that is, Pd ALD from Pd­(hfac)₂ and H₂ plasma in a typical AB-like ALD process, leads to a carbon contamination of >10% and significantly higher resistivity values. From transmission electron microscopy, it has also been observed that the ABC-type process leads to a faster nucleation of the Pd nanoparticles formed during the initial stage of film growth. As this novel process allows for the deposition of high-purity Pd at low temperatures, it opens prospects for various applications of Pd thin films and nanoparticles

Atomic Layer Deposition of Silicon Nitride from Bis(<i>tert</i>-butylamino)silane and N₂ Plasma

Atomic layer deposition (ALD) of silicon nitride (SiN_<i>x</i>) is deemed essential for a variety of applications in nanoelectronics, such as gate spacer layers in transistors. In this work an ALD process using bis­(<i>tert</i>-butylamino)­silane (BTBAS) and N₂ plasma was developed and studied. The process exhibited a wide temperature window starting from room temperature up to 500 °C. The material properties and wet-etch rates were investigated as a function of plasma exposure time, plasma pressure, and substrate table temperature. Table temperatures of 300–500 °C yielded a high material quality and a composition close to Si₃N₄ was obtained at 500 °C (N/Si = 1.4 ± 0.1, mass density = 2.9 ± 0.1 g/cm³, refractive index = 1.96 ± 0.03). Low wet-etch rates of ∼1 nm/min were obtained for films deposited at table temperatures of 400 °C and higher, similar to that achieved in the literature using low-pressure chemical vapor deposition of SiN_<i>x</i> at >700 °C. For novel applications requiring significantly lower temperatures, the temperature window from room temperature to 200 °C can be a solution, where relatively high material quality was obtained when operating at low plasma pressures or long plasma exposure times

Atomic Layer Deposition of In₂O₃:H from InCp and H₂O/O₂: Microstructure and Isotope Labeling Studies

The atomic layer deposition (ALD) process of hydrogen-doped indium oxide (In₂O₃:H) using indium cyclopentadienyl (InCp) and both O₂ and H₂O as precursors is highly promising for the preparation of transparent conductive oxides. It yields a high growth per cycle (>0.1 nm), is viable at temperatures as low as 100 °C, and provides a record optoelectronic quality after postdeposition crystallization of the films (ACS Appl. Mat. Interfaces, 2015, 7, 16723−16729, DOI: 10.1021/acsami.5b04420). Since both the dopant incorporation and the film microstructure play a key role in determining the optoelectronic properties, both the crystal growth and the incorporation of the hydrogen dopant during this ALD process are studied in this work. This has been done using transmission electron microscopy (TEM) and atom probe tomography (APT) in combination with deuterium isotope labeling. TEM studies show that an amorphous-to-crystalline phase transition occurs in the low-temperature regime (100–150 °C), which is accompanied by a strong decrease in carrier density and an increase in carrier mobility. At higher deposition temperatures (>200 °C), enhanced nucleation of crystals and the incorporation of carbon impurities lead to a reduced grain size and even an amorphous phase, respectively, resulting in a strong reduction in carrier mobility. APT studies on films grown with deuterated water show that the incorporated hydrogen mainly originates from the coreactant and not from the InCp precursor. In addition, it was established that the incorporation of hydrogen decreased from ∼4 atom % for amorphous growth to ∼2 atom % after the transition to crystalline film growth

Atomic Layer Deposition of Wet-Etch Resistant Silicon Nitride Using Di(<i>sec</i>-butylamino)­silane and N₂ Plasma on Planar and 3D Substrate Topographies

The advent of three-dimensional (3D) finFET transistors and emergence of novel memory technologies place stringent requirements on the processing of silicon nitride (SiN_<i>x</i>) films used for a variety of applications in device manufacturing. In many cases, a low temperature (<400 °C) deposition process is desired that yields high quality SiN_<i>x</i> films that are etch resistant and also conformal when grown on 3D substrate topographies. In this work, we developed a novel plasma-enhanced atomic layer deposition (PEALD) process for SiN_<i>x</i> using a mono-amino­silane precursor, di­(<i>sec</i>-butylamino)­silane (DSBAS, SiH₃N­(^sBu)₂), and N₂ plasma. Material properties have been analyzed over a wide stage temperature range (100–500 °C) and compared with those obtained in our previous work for SiN_<i>x</i> deposited using a bis-aminosilane precursor, bis­(<i>tert</i>-butylamino)­silane (BTBAS, SiH₂(NH^tBu)₂), and N₂ plasma. Dense films (∼3.1 g/cm³) with low C, O, and H contents at low substrate temperatures (<400 °C) were obtained on planar substrates for this process when compared to other processes reported in the literature. The developed process was also used for depositing SiN_<i>x</i> films on high aspect ratio (4.5:1) 3D trench nanostructures to investigate film conformality and wet-etch resistance (in dilute hydrofluoric acid, HF/H₂O = 1:100) relevant for state-of-the-art device architectures. Film conformality was below the desired levels of >95% and attributed to the combined role played by nitrogen plasma soft saturation, radical species recombination, and ion directionality during SiN_<i>x</i> deposition on 3D substrates. Yet, very low wet-etch rates (WER ≤ 2 nm/min) were observed at the top, sidewall, and bottom trench regions of the most conformal film deposited at low substrate temperature (<400 °C), which confirmed that the process is applicable for depositing high quality SiN_<i>x</i> films on both planar and 3D substrate topographies

Area-Selective Atomic Layer Deposition of Metal Oxides on Noble Metals through Catalytic Oxygen Activation

Area-selective atomic layer deposition (ALD) is envisioned to play a key role in next-generation semiconductor processing and can also provide new opportunities in the field of catalysis. In this work, we developed an approach for the area-selective deposition of metal oxides on noble metals. Using O₂ gas as co-reactant, area-selective ALD has been achieved by relying on the catalytic dissociation of the oxygen molecules on the noble metal surface, while no deposition takes place on inert surfaces that do not dissociate oxygen (i.e., SiO₂, Al₂O₃, Au). The process is demonstrated for selective deposition of iron oxide and nickel oxide on platinum and iridium substrates. Characterization by <i>in situ</i> spectroscopic ellipsometry, transmission electron microscopy, scanning Auger electron spectroscopy, and X-ray photoelectron spectroscopy confirms a very high degree of selectivity, with a constant ALD growth rate on the catalytic metal substrates and no deposition on inert substrates, even after 300 ALD cycles. We demonstrate the area-selective ALD approach on planar and patterned substrates and use it to prepare Pt/Fe₂O₃ core/shell nanoparticles. Finally, the approach is proposed to be extendable beyond the materials presented here, specifically to other metal oxide ALD processes for which the precursor requires a strong oxidizing agent for growth