Chemical Vapor Deposition Process Research Articles

Water-Assisted Catalytic VACNT Growth Optimization for Speed and Height

The super-growth approach for carbon nanotubes synthesis is frequently used to boost the growth rate, catalyst lifespan, and height of vertically aligned carbon nanotubes. The elimination of amorphous carbon from catalyst particles, commonly made of iron, by injecting water vapor into a chemical vapor deposition process can enhance the purity, alignment, and height of carbon nanotubes and prevent the partial oxidation of the metallic catalyst. We present the development of a modified growth-optimized water-assisted super-growth vertically aligned carbon nanotube process by optimizing the catalyst layer structure and water vapor concentration for a carbon nanotube growth process for 4” diameter Si wafers. A significant finding is that under optimized water-assisted growth conditions over 4 mm, highly uniform tall, vertically aligned carbon nanotube structures can be grown with a minimum top crust layer of about ~5–10 μm thickness. This was achieved with a catalyst film comprising a >400 mm thermal SiO2 layer on top of a 4” diameter Si wafer that was overcoated with an e-beam batch process run that first deposited a 20 nm SiO2 layer, a 10 nm Al2O3 layer, and a 1.1 nm Fe layer, in a 4-h growth process step.

The Advantages of Double Catalytic Layers for Carbon Nanotube Growth at Low Temperatures (<400 °C) in 3D Stacking and Power Applications

A double catalytic layer scheme is proposed and investigated for the low temperature growth of carbon nanotubes (CNTs) over Co (Cobalt), Al (Aluminum), and Ti (Titanium) catalysts on a silicon substrate. In this work, we demonstrate the growth of CNTs by a thermal chemical vapor deposition (TCVD) process at both 350 °C and 400 °C. Based on scanning electron microscopy (SEM) and Raman spectroscopy analyses, the good quality of the CNTs is demonstrated. This study contributes to the on-going research on integrating semiconductors into packaging and power-related applications, as demonstrated with the low resistance (~128 Ω) and high thermal conductivity (~29.8 Wm−1 K−1) of our developed CNTs.

Tio2 and Nickel Coatings on Resistance Welding Electodrs to exetended Life Using Chemical Vapour Desposition Process

TiO2/Ni coating has been deposited onto the electrodes by chemical vapour deposition to improve electrode life during resistance welding of Zn- coated steels. However, welding results revealed that molten Zn penetrates into coating through the cracks and then reacts with substrate copper alloy to form brasses. In the present work, laser treatment was performed on the TiO2/Ni coated electrodes to eliminate cracks formed in the as-deposited TiO2/Ni coating. In addition, a chemical vapour deposition of Ni, TiO2/Ni and Ni has also been carried out to improve coating quality. On the other hand, a Ti coating was also investigated. Those coatings were characterized by electro-microscopy, energy- dispersive X-ray analysis, X-ray diffraction and micro-hardness tests. The results showed that cracks within the as-deposited TiO2/Ni coating could be eliminated with the use of laser treatment and chemical vapour deposition process. However, softening of copper substrate after laser treatment was a problem that restricted welding performance. Welding tests showed that the multi-layer TiO2/Ni coating acted as a better barrier to decrease alloying between the copper alloy and molten Zn as well as pitting (erosion) of electrode. The TiO2 coating demonstrates its potential application on the electrode to further improve the electrode’s life Key Word: Electrode; Molecular; Titanium; Nanotechnology; Nickel.

Dielectric-on-Dielectric Achieved on SiO2 in Preference to W by Water-free Chemical Vapor Depositions with Aniline Passivation.

Selective and smooth dielectric-on-dielectric was achieved by water-free single-precursor chemical vapor deposition (CVD) processes with the help of aniline passivation. Aniline selective passivation was demonstrated on W surfaces in preference to SiO2 at 250, 300, and 330 °C. After aniline passivation, selective HfO2, Al2O3, and TiO2 were deposited only on the HF-cleaned SiO2 surface by water-free single-precursor CVD using hafnium tert-butoxide Hf(OtBu)4, aluminum-tri-sec-butoxide (ATSB), and titanium isopropoxide Ti(OiPr)4 as the precursor reactants, respectively. Hf(OtBu)4 and Ti(OiPr)4 single-precursor CVD was carried out at 300 °C, while the ATSB CVD process was conducted at 330 °C. HfO2 and Al2O3 nanoselectivity tests were performed on W/SiO2 patterned samples. Transmission electron microscopy images of the W/SiO2 patterned samples after deposition demonstrated nanoselectivity and low surface roughness of HfO2 and Al2O3 deposition on the SiO2 regions only.

Performance Enhancement of Polymer Electrolyte Membrane Fuel Cells with Cerium Oxide Interlayers Prepared by Aerosol-Assisted Chemical Vapor Deposition

In this study, the performance and durability of a Pt/CeOx catalyst membrane electrode assembly (MEA) fabricated by chemical vapor deposition and sputtering using aerosols were investigated for use in a polymer electrolyte membrane fuel cell (PEMFC). The cost burden of Pt-based catalysts and the degradation of performance and durability owing to corrosion of the carbon support under certain conditions limit the commercialization of PEMFCs. To solve these problems, the development of Pt alloy catalysts (Pt–Co, Pt–Ni, and Pt–Fe), Pt-based core–shell catalysts (Pt–TiO2 and Pt–CeO2), Pt bimetallic catalysts (Pt–Pd, Pt–Ru, and Pt–Sn), and Pt-based nanocomposites (Pt/graphene and Pt/carbon nanotubes) is being actively researched. Inserting a CeOx interlayer between Pt and carbon has three advantages: (i) oxygen supply to Pt due to CeOx interlayer’s ability to store oxygen improves catalyst utilization, (ii) improves the dispersibility of Pt, and (iii) solves the problem of performance and durability degradation by preventing the formation of reactive intermediates. For the deposition of ceria, the aerosol-assisted chemical vapor deposition process, which is performed at atmospheric pressure and can be uniformly deposited over a wide area with spray-based precursor delivery characteristics, was applied. The performance and electrochemical surface area of the Pt/CeOx MEA were determined using I–V measurements and cyclic voltammetry, and the durability of the Pt/CeOx MEA was analyzed using electrochemical impedance spectroscopy and an accelerated degradation test. As a result, when the Pt/CeOx on the gas diffusion layer (GDL) MEA was used, the performance improved by 46% compared to that of Pt on the GDL.

Evaluation of different carbon-modified zeolite derivatives preparation methods as a filler in mixed matrix membrane on their gas separation performance

Carbon-modified zeolite from different preparation methods, including impregnation and chemical vapor deposition (CVD), was investigated and applied as fillers in polysulfone (PSF) membranes in order to improve gas separation performance. Using the impregnation method and CVD, carbon structures were added into the zeolite template. These fillers are zeolite composite carbons (ZCC). After removing the template, zeolite-templated carbons (ZTC) were obtained and analyzed with XRD, SEM, and the N2 adsorption-desorption isotherm. In addition, further investigations were carried out in MMMs embedded by these fillers with XRD, FTIR, TGA, DSC, and gas permeation tests. PSF/ZTC synthesized using CVD demonstrated favorable improvement, which enhanced the gas permeances and CO2/CH4, O2/N2, H2/CH4, and CO2/N2 selectivity up to 107.66%, 24.79%, 140.56%, and 18.55%, respectively. The improvement in gas selectivity was contributed by the high microporosity of the filler. Moreover, the proposed gas diffusion mechanism in MMMs was elucidated, which was dominated by Knudsen and surface diffusion. It was interesting to note that the use of a very small percentage of ZTC-C loading was sufficiently considered to provide a high enhancement compared to those for a high percentage of loading with different fillers. Therefore, the CVD process is more promising for preparing zeolite-carbon fillers to boost gas separation performance and opens up possibilities for further development of advanced membranes.

Hydrogenated amorphous carbon films deposited using plasma enhanced chemical vapor deposition processes

Hydrogenated amorphous carbon films deposited using plasma enhanced chemical vapor deposition processes

Adsorption on 3C-SiC surfaces in chemical vapor deposition process of CH3SiCl3–H2 system: a first-principles study

SiC has become increasingly important in high-energy semiconductor device materials and structural composite materials in recent years. Many systematic experimental studies have been conducted on the preparation of cubic silicon carbide (3C-SiC) by the chemical vapor deposition (CVD) process. Despite this, the microscopic mechanism of the SiC deposition process has not been fully elucidated due to the limitations of the experimental methods. Based on these problems, the structural parameters, adsorption energies, charge populations, transition states, and electronic densities of states of Si-Cl-C-H at different sites were simulated by a first-principles method, and the micro-mechanism of the surface deposition reaction was analyzed. The calculated results provide a theoretical and experimental basis for the study of 3C-SiC preparation by CVD.

Equation-based and data-driven modeling strategies for industrial coating processes

Computational Fluid Dynamics (CFD) and Machine Learning (ML) approaches are implemented and compared in an industrial Chemical Vapor Deposition process for the production of cutting tools. In this work, the aim is to analyze the pros and cons of each method and propose a blend of the two approaches that is suitable in industrial applications, where the process is too complicated to address with first-principles models and the data do not allow the implementation of data-hungry methods. Both approaches accurately predict the coating thickness (Mean Absolute Percentage Error (MAPE) of 6.0% and 4.4% for CFD and ML respectively for the test case reactor). CFD, despite its increased computational cost, both in terms of developing and also calibrating for the application at hand, provides meaningful insight and illuminates the process. On the other hand, ML can provide predictions in a time-efficient manner, and is thus appropriate for inline and concurrent predictions. However, it is limited by the available data and has low extrapolation ability. Equation-based and data-driven methods are combined by exploiting a handful of CFD results for efficient interpolation in a reduced space defined by the principal components of the dataset, by implementing Gappy POD. This allows for the accurate reconstruction of the full state-space with limited data.

Stabilization of the Nano-Sized 1T Phase through Rhenium Doping in the Metal-Organic CVD MoS2 Films.

Heterogeneous nanostructures composed of metastable tetragonal 1T-MoS2 and stable hexagonal 2H-MoS2 phases are highly promising for a wide range of applications, including catalysis and ion batteries, due to the high electrical conductivity and catalytic activity of the 1T phase. However, a controllable synthesis of stabilized 1T-MoS2 films over the wafer-scale area is challenging. In this work, a metal-organic chemical vapor deposition process allowing us to obtain ultrathin MoS2 films containing both 1T and 2H phases and control their ratio through rhenium doping was suggested. As a result, Mo1-xRexS2 films with a 1T-MoS2 fraction up to ≈30% were obtained, which were relatively stable under normal conditions for a long time. X-ray photoelectron spectroscopy and Raman spectroscopy also indicated that the 1T-MoS2 phase fraction increased with rhenium concentration increase saturating at Re concentrations above 5 at. %. Also, its concentration was found to significantly affect the film resistivity. Thus, the resistivity of the film containing approximately 30% of the 1T phase was about 130 times lower than that of the film without the 1T phase.

Effective Variational-Autoencoder-Based Generative Models for Highly Imbalanced Fault Detection Data in Semiconductor Manufacturing

In current semiconductor manufacturing, limited raw trace data pertaining to defective wafers make fault detection (FD) assignments extremely difficult due to the data imbalance in wafer classification. To mitigate, this paper proposes using a variational autoencoder (VAE) as a data augmentation strategy for resolving data imbalance of temporal raw trace data. A VAE with few defective samples is first trained. By means of extracting the latent variables that characterize the distribution of the defective samples, we make use of the statistical randomness of the latent variables to generate synthesized defective samples via the decoder scheme in the trained VAE. Two data representations and VAE modeling strategies, concatenation of multiple and individual raw trace data as the input of the VAE during the training stage, are investigated. A real-data plasma enhanced chemical vapor deposition (PECVD) process having only few defective samples is used to illustrate the performance enhancement to wafer classification arising from the proposed data augmentation framework. Based on the computational comparisons between noted classification models, the proposed generative VAE model via the individual strategy enables the adaptive boosting (AdaBoost) classifier to achieve perfect performances in every metrics if the 80% and 100% over-sampling ratios are adopted.

Role of Hydrogen in Ethylene-Based Synthesis of Single-Walled Carbon Nanotubes.

We examined the effect of hydrogen on the growth of single-walled carbon nanotubes in the aerosol (a specific case of the floating catalyst) chemical vapor deposition process using ethylene as a carbon source and ferrocene as a precursor for a Fe-based catalyst. With a comprehensive set of physical methods (UV-vis-NIR and Raman spectroscopies, transmission electron microscopy, scanning electron microscopy, differential mobility analysis, and four-probe sheet resistance measurements), we showed hydrogen to inhibit ethylene pyrolysis extending the window of synthesis parameters. Moreover, the detailed study at different temperatures allowed us to distinguish three different regimes for the hydrogen effect: pyrolysis suppression at low concentrations (I) followed by surface cleaning/activation promotion (II), and surface blockage/nanotube etching (III) at the highest concentrations. We believe that such a detailed study will help to reveal the complex role of hydrogen and contribute toward the synthesis of single-walled carbon nanotubes with detailed characteristics.

Superconformal silicon carbide coatings via precursor pulsed chemical vapor deposition

In this work, silicon carbide (SiC) coatings were successfully grown by pulsed chemical vapor deposition (CVD). The precursors silicon tetrachloride (SiCl4) and ethylene (C2H4) were not supplied in a continuous flow but were pulsed alternately into the growth chamber with H2 as a carrier and a purge gas. A typical pulsed CVD cycle was SiCl4 pulse—H2 purge—C2H4 pulse—H2 purge. This led to growth of superconformal SiC coatings, which could not be obtained under similar process conditions using a constant flow CVD process. We propose a two-step framework for SiC growth via pulsed CVD. During the SiCl4 pulse, a layer of Si is deposited. In the following C2H4 pulse, this Si layer is carburized, and SiC is formed. The high chlorine surface coverage after the SiCl4 pulse is believed to enable superconformal growth via a growth inhibition effect.

Controllable Al2O3 coating makes TiO2 photocatalysts active under visible light by pulsed chemical vapor deposition

TiO2 catalysts, modified by coating Al2O3, presented high visible-light photocatalytic activity. Al2O3 nano-films were successfully deposited onto TiO2 particles using AlCl3 as a precursor via the pulsed chemical vapor deposition process. And, the alumina was anchored onto TiO2 surface via Ti–O–Al bonds. The morphology, constitution, photocatalytic activity and photoelectrochemical performance of the Al2O3-coated TiO2 were characterized. Controllable Al2O3 coating increased the oxygen vacancies and hydroxyl groups, and induced the formation of surface disordered TiO2 layer, which enhanced light absorption, increased charge carrier separation and transfer efficiency, and surface redox efficiency. Therefore, the TiO2/Al2O3 catalyst obtained via the pulsed chemical vapor deposition technique may break through the limitation of the band gap, and the pulsed chemical vapor deposition provided an effective strategy for the TiO2 production with active defective sites.

Sulfur-Passivated InSb Nanowires for Infrared Photodetectors

Sulfur-passivated InSb nanowires (S-InSb NWs) with a single-crystalline structure were synthesized via a chemical vapor deposition process, where S plays the role of a growth catalyst as well as a surface passivator. Studies revealed that the prepared S-InSb NWs displayed typical n-type semiconductor behavior with a maximum field-effect mobility of 823.62 cm2 V–1 s–1 at room temperature. The S-InSb NW-based photodetector was characterized as possessing stable negative photoresponse properties toward incident infrared light, and the corresponding responsivity and external quantum efficiency were calculated to be 123.46 A/W and 14,400%, respectively, for 1.06 μm light and 120.99 A/W and 9680%, respectively, for 1.55 μm light. These values are higher than those for other reported photodetectors based on InSb nanosheets. Through the analysis of excited electron states in the band structure during light irradiation, the negative photoresponse was identified as stemming from the photogating effect of the Sb–S layer on the S-InSb NW surface. These outstanding transport and optoelectronic performances empower S-InSb NWs with technological potential to be used in next-generation infrared quantum devices.

Grain Size Engineering of CVD-Grown Large-Area Graphene Films.

Graphene, a single atomic layer of graphitic carbon, has attracted much attention because of its outstanding properties hold great promise for a wide range of technological applications. Large-area graphene films (GFs) grown by chemical vapor deposition (CVD) are highly desirable for both investigating their intrinsic properties and realizing their practical applications. However, the presence of grain boundaries (GBs) has significant impacts on their properties and related applications. According to the different grain sizes, GFs can be divided into polycrystalline, single-crystal, and nanocrystalline films. In the past decade, considerable progress has been made in engineering the grain sizes of GFs by modifying the CVD processes or developing some new growth approaches. The key strategies involve controlling the nucleation density, growth rate, and grain orientation. This review aims to provide a comprehensive description of grain size engineering research of GFs. The main strategies and underlying growth mechanisms of CVD-grown large-area GFs with nanocrystalline, polycrystalline, and single-crystal structures are summarized, in which the advantages and limitations are highlighted. In addition, the scaling law of physical properties in electricity, mechanics, and thermology as a function of grain sizes are briefly discussed. Finally, the perspectives for challenges and future development in this area are also presented.

窒化物半導体の化学気相成長における表面科学の進展

Data-driven materials development using first-principles calculations (materials informatics, MI) is widely known. Process informatics (PI), which explores crystal growth processes, is expected to be pioneered as the next research target in materials development. However, simulation techniques for the chemical vapor deposition (CVD) process, which is the core of PI, have not been developed. This paper describes recent progress in simulation technology for CVD processes, with a particular focus on surface modeling.

特集「結晶成長ダイナミクスの展望 ―平衡過程と非平衡過程の協奏―」企画趣旨

In recent years, crystal growth processes have attracted great interest because of the importance in semiconductor devices as well as organic devices. In the present articles, experimental innovations to observe crystal growth processes using various microscopic methods are reviewed. Correspondingly, novel approaches in the theoretical investigation of crystal growth processes are also reviewed. Step dynamics including macrostep formation and step bunching, pattern formation, high-quality crystallization, chemical vapor deposition (CVD) process, and various crystal growth environments not only in vacuum but also in liquid and in space are focused.

Well-Dispersed Fe Nanoclusters for Effectively Increasing the Initial Coulombic Efficiency of the SiO Anode.

An efficient surface modification strategy is proposed to significantly increase the initial Coulombic efficiency (ICE) of SiO anode material. The SiO@Fe material with the Fe nanocluster homogeneously decorating on the SiO surface is successfully prepared by a chemical vapor deposition process. The well-dispersed Fe nanoclusters realize an Ohmic contact with lithium silicates, the commonly regarded irreversible lithiation product, which effectively lowers the electron conduction barriers and promotes the concomitant lithium-ion release of the lithium silicates upon the delithiation process, increasing the ICE of the SiO anode. The prepared SiO@Fe exhibits a much higher ICE of 87.2% compared to 64.4% of pristine SiO, with the largest increment (23%) never reported, except for the prelithiation, and delivers significantly enhanced cycling and rate performance. These findings provide an effective way to convert the "inert" phase to "active" which essentially increases the ICE of the electrode.

Mn atomic clusters and Fe nanoparticles in-situ confined nitrogen carbon nanotubes for efficient and durable ORR electrocatalysts in both alkaline and acidic media

Developing robust and durable nonprecious metal ORR electrocatalysts for use in both alkaline and acidic media is still challenging. Herein, highly dispersed Mn atomic clusters and standalone Fe nanoparticles dual-sites in-situ confined nitrogen doped carbon nanotubes (Mn-Fe@NCNTs) were fabricated via a facile one-step process of high-temperature calcination and simultaneous chemical vapor deposition. The resultant Mn-Fe@NCNTs catalysts exhibited excellent ORR catalytic activity and durability in both alkaline and acidic media due to the special constitute and structure, which not only provided abundant active sites and defects, good electronic conductivity and effective electron transfer, but also enhanced the corrosion resistance and decreased the Fenton reactivity of the catalyst. In 0.1 M KOH solution, the half-wave potential of Mn-Fe@NCNTs is 0.872 V, more positive than that of the commercial Pt/C catalyst (E1/2 = 0.835 V) and many other previously reported NCNTs based non-precious metal ORR electrocatalysts. While in 0.1 M HClO4 solution, Mn-Fe@NCNTs exhibits a half-wave potential of 0.760 V, only 60 mV negative shift compared to the Pt/C catalyst. Furthermore, the as-prepared catalysts exhibit much higher stability, with much lower current attenuation and smaller shift of the ORR polarization curves after continuous chronoamperometric testing for 29,000 s and continuous CV test for 5,000 cycles, than those of Pt/C in both alkaline and acidic solutions. When applied in Zn-air batteries for testing, the Mn-Fe@NCNTs electrocatalysts are obviously outperforming the commercial Pt/C with higher specific capacity of 774.0 mAh g−1Zn and power density of 139.2 mW cm−2. This study offers a facile and instructive protocol for developing low-cost and high-efficiency electrocatalysts to be applied in fuel cells, metal-air cells and many other clean electrochemical storage devices.