CVD Reactor Research Articles

Ambient Pressure Chemical Vapor Deposition of Flat and Vertically Aligned MoS2 Nanosheets

Molybdenum disulfide (MoS2) got tremendous attention due to its atomically thin body, rich physics, and high carrier mobility. The controlled synthesis of large area and high crystalline monolayer MoS2 nanosheets on diverse substrates remains a challenge for potential practical applications. Synthesizing different structured MoS2 nanosheets with horizontal and vertical orientations with respect to the substrate surface would bring a configurational versatility with benefit for numerous applications, including nanoelectronics, optoelectronics, and energy technologies. Among the proposed methods, ambient pressure chemical vapor deposition (AP-CVD) is a promising way for developing large-scale MoS2 nanosheets because of its high flexibility and facile approach. Here, we show an effective way for synthesizing large-scale horizontally and vertically aligned MoS2 on different substrates such as flat SiO2/Si, pre-patterned SiO2 and conductive substrates (TaN) benefit various direct TMDs production. In particular, we show precise control of CVD optimization for yielding high-quality MoS2 layers by changing growth zone configuration and the process steps. We demonstrated that the influence of configuration variability by local changes of the S to MoO3 precursor positions in the growth zones inside the CVD reactor is a key factor that results in differently oriented MoS2 formation. Finally, we show the layer quality and physical properties of as-grown MoS2 by means of different characterizations: Raman spectroscopy, scanning electron microscopy (SEM), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). These experimental findings provide a strong pathway for conformally recasting AP-CVD grown MoS2 in many different configurations (i.e., substrate variability) or motifs (i.e., vertical or planar alignment) with potential for flexible electronics, optoelectronics, memories to energy storage devices.

CFD modeling and optimal design of SiC deposition on the fuel combustion nozzle in a commercial CVD reactor

This work presents a new CFD model developed to investigate the SiC film growth over a fuel combustion nozzle in the commercial hot-wall CVD reactor. A detailed 3D model consisting of the compressive transport models and the reaction mechanism to account for the chemistry of the gas-phase and surface reactions are developed. The velocity, temperature, and concentration profiles inside the reactor are predicted numerically. The multispecies transport and its interplay with the gas and surface reactions are understood to operate the reactor effectively. The natural convection and hydrodynamics stability of the flow is investigated using various dimensionless groups (Re, Pr. Pe, and Gr/Re2). It has been observed that the buoyancy-driven flow is dominant at a large Reynolds number (Re) and Gr/Re2 ratio. This results in flow recirculation, which ultimately deteriorates the film uniformity. A sensitivity analysis is performed to identify how critical parameters affect the deposition process. Besides, the optimisation of the CVD reactor is also served by combining the support vector machine, a versatile supervised machine learning method, and the Nelder-Mead algorithm to improve the film quality. Our results demonstrate that the present methodology effectively obtains optimal process conditions, significantly enhancing the film performance.

Optimisation of processing conditions during CVD growth of 2D WS2 films from a chloride precursor

Monolayer tungsten disulphide (WS2) is a direct band gap semiconductor which holds promise for a wide range of optoelectronic applications. The large-area growth of WS2 has previously been successfully achieved using a W(CO)6 precursor, however, this is flammable and a potent source of carbon monoxide (CO) upon decomposition. To address this issue, we have developed a process for the wafer-scale growth of monolayer WS2 from a tungsten hexachloride (WCl6) precursor in a commercial cold-wall CVD reactor. In comparison to W(CO)6, WCl6 is less toxic and less reactive and so lends itself better to the large-scale CVD growth of 2D layers. We demonstrate that a post-growth H2S anneal can lead to a dramatic improvement in the optical quality of our films as confirmed by photoluminescence (PL) and Raman measurements. Optimised films exhibit PL exciton emission peaks with full width at half maximum of 51 ± 2 meV, comparable to other state-of-the-art methods. We demonstrate that our WS2 films can be readily transferred from the sapphire growth substrate to a Si/SiO2 target substrate with no detectable degradation in quality using a polystyrene support layer. Our approach represents a promising step towards the industrial-scale fabrication of p-n junctions, photodetectors and transistors based on monolayer WS2.

Investigation of transport processes in a commercial hot wall CVD reactor with multi-substrates for high-quality pyrocarbon deposition

A 3D CFD model is developed to illustrate the complex reacting flow in the commercial hot-wall CVD reactor using detailed gas and surface chemistry. This helps to understand multi-species transport and their interplay with the gas and surface reactions for pyrocarbon (PyC) deposition. The detailed transport phenomena models with temperature-dependent physical properties are incorporated into the model to improve accuracy. Valuable information such as microscopic local variations in gas velocity, temperature, and species distributions is obtained, which otherwise difficult to acquire experimentally. A sensitivity analysis is also performed to realize how the operating conditions affect the distributions of intermediate species and, ultimately, the growth rate of PyC. The understanding gained in this study is further used to optimize the CVD reactor to obtain high-quality PyC. The response surface methodology is employed to examine the interactions among various operating parameters that influence film performance.

Experimental Study of the Effect of Precursor Composition on the Microstructure of Gallium Nitride Thin Films Grown by the MOCVD Process

Abstract Chemical vapor deposition (CVD) is a widely used manufacturing process for obtaining thin films of materials like silicon, silicon carbide, graphene, and gallium nitride that are employed in the fabrication of electronic and optical devices. Gallium nitride (GaN) thin films are attractive materials for manufacturing optoelectronic device applications due to their wide band gap and superb optoelectronic performance. The reliability and durability of the devices depend on the quality of the thin films. The metal-organic chemical vapor deposition (MOCVD) process, which uses compounds that contain metals and organic ligands as precursors in a CVD reactor, is a common technique used to fabricate high-quality GaN thin films. The deposition rate and uniformity of thin films are critical to a successful and useful process. These are determined by the thermal transport processes and chemical reactions occurring in the reactor, and are manipulated by controlling the operating conditions and the reactor geometrical configuration. In this study, the epitaxial growth of GaN thin films on sapphire (Al2O3) substrates is carried out in two commercial MOCVD systems: a vertical rotating disk MOCVD reactor and a close-coupled showerhead MOCVD reactor. The surface morphology and crystal quality of GaN thin films have been examined using atomic force microscopy (AFM) and scanning electron microscope (SEM). This paper focuses on the composition of the precursor and the carrier gases since earlier studies have shown the importance of precursor composition. The results show that the flow rate of trimethylgallium (TMG), which is the main ingredient in the process, has a significant effect on the deposition rate and uniformity of the films. Also, the carrier gas plays an important role in deposition rate and uniformity. Using hydrogen as a carrier gas enhances the quality of the thin film but a lower deposition rate occurs on the wafer surface. On the other hand, a high flow rate of pure nitrogen gas improves the growth rate of the film. However, it decreases the uniformity of the film and promotes carbon contamination on the wafer surface. Thus, the use of an appropriate mixture of hydrogen and nitrogen as the carrier gas can improve the deposition rate and quality of GaN thin films.

Replacement of Waveguides by a Resonant Cavity in a Microwave CVD Reactor

There are several configurations of a microwave chemical vapor deposition (MWCVD) reactor. The common characteristic of this reactor is the presence of waveguides. We describe a method that replaces the waveguide, responsible for conducting electromagnetic waves, with a resonant cavity (RC) coupled to a low-pressure chamber. Using RCs over waveguides can help produce dense plasma, which can be used in dissociation processes as the reagents are forced to move within a cavity until they reach the reaction chamber. Based on the excellent performance of the system, it was possible to deposit silicon oxide (SiO2), with the aid of the argon gas mixture, oxygen, and tetraethylorthosilicate (TEOS), on a silicon substrate at room temperature. The film formed was analyzed using an interferometer and FTIR, concluding on the satisfactory quality of the film.

Effect of pyrrolic-N defects on the capacitance and magnetization of nitrogen-doped multiwalled carbon nanotubes

Heteroatoms in multiwalled carbon nanotubes modify their chemical reactivity and electronic properties. Nitrogen as a doping element changes the morphology by boosting the surface area, the density of defects, electronic states, and chemically actives sites that improve the electrocatalytic activity and other properties. Nitrogen defects create mainly the pyridinic, pyrrolic, and quaternary-N configurations presenting different localized electronic configurations. This work outlined and studied the distribution and physicochemical properties of N-doped multiwalled carbon nanotubes as a function of the temperature profile along a CVD reactor. X-ray photoelectron spectroscopy demonstrated that the nitrogen content is maximal in the second furnace high-temperature zone, and the pyrrolic-N doping predominate. The ID/IG ratio from Raman spectroscopy increases in this zone, revealing a defective graphitic material. The cyclic voltammetry showed that the specific capacitance increases for pyrrolic-N from the last three-quarters of the reactor due to the augment of active carbon atoms associated with pyrrolic-N defects and the chemical decomposition of nitrogen precursor alongside the reactor. Theoretical calculation on the electronic properties and potential electrostatic surface of carbon nanotubes suggests the surface metallicity when pyridinic-N and quaternary-N are dominant and active sites for possible hydrogen or oxygen binding when pyrrolic-N are prevalent.

Large-scale CMOS-compatible process for silicon nanowires growth and BC8 phase formation

A novel, low temperature process for the formation of Si-BC8 phase is obtained while growing Silicon nanowires. The nanowires growth is performed in a CVD reactor under exposure of the substrate to microwaves, employing Sn nanospheres as catalyst and a flux of SiH4 as precursor, respectively. Microwaves allow for selective heating of the metal catalyst while keeping the substrate at low temperature. At the end of the process, silicon nanowires with the metal sphere on top are obtained, together with the (unexpected) transition of a portion of silicon substrate from the diamond to the Si-BC8 crystallographic phase. Silicon atoms in Si-BC8 phase are arranged in body-centered-cubic unit cells resulting into a different energy-wavevector diagram compared to the silicon diamond cubic phase. Indeed, Si-BC8 possesses a direct band gap as low as 30 meV at room temperature. These features may be employed in a large variety of applications, requiring CMOS-compatible manufacturing.Systematic structural analysis and a phenomenological model for Si-BC8 phase formation are discussed.

Growth of carbon nanotubes inside porous anodic alumina membranes: Simulation and experiment

Porous anodic alumina (PAA) membranes represent a widely used and extensively studied template for production of carbon nanotubes (CNT). The PAA–CNT membranes possess a number of unique properties, such as controllable nanotube geometry, size– and chemically–based selectivity as well as high water permeability. In this work, we first propose a combination of gas phase and surface reaction models to quantitatively describe the growth of carbon nanotubes in PAA membranes in a commercial CVD reactor. A complimentary experimental study of CNT formation from ethanol precursor with argon as a carrier gas is performed. A new method for characterizing carbon nanotubes geometry by SEM and TEM image processing of membrane cross–sections is proposed. The simulations show that the carbon growth rate (in nm/min) averaged over the membrane remains constant during the deposition process until the pore diameter becomes relatively small, and rapidly falls to zero after that. The carbon nanotube thickness near the membrane surface is slightly higher than that in the membrane center. The carbon growth rate increases with synthesis temperature and pressure, while it decreases with the argon flow rate. The dependence of carbon growth rate on the ethanol/water flow rate reaches maximum at some intermediate value. These results are supported by the experimental data obtained from SEM/TEM image processing. It is found that the SEM data provide overestimated values of nanotube diameter and thickness in comparison with the TEM data. The obtained results provide new insights into the CNT growth kinetics in nanoporous media, and develop quantitative guidelines for synthesis of CNT–PAA membranes with precisely controlled nanopore geometry. It also validates the combined homogenous / heterogeneous reaction model by comparison with carbon deposition kinetics on a nanometer scale.

Influence and Suppression of Harmful Effects Due to By-Product in CVD Reactor for 4H-SiC Epitaxy

Suppression of harmful effect due to by-product on homo-epitaxial growth of 4H-SiC films using a high speed wafer rotation vertical CVD method was demonstrated. Influence of by-product, such as 3C-SiC deposit on a hot-wall and Si deposit on gas nozzles, formed during the epitaxial growth was investigated in two comparative studies. The analysis of triangular defects with 3C-SiC down-falls on the films revealed that the most of the down-falls which were peeled from the hot-wall adhered to the wafers before the epitaxial growth. By increasing the wafer rotation speed to 300 rpm just after wafer loading into the reactor, the down-falls dropped towards the wafer surface were effectively eliminated, and the maintenance period of the reactor could be increased more than 4 times compared to the case of maintaining the wafer rotation speed of 50 rpm until just before epitaxial growth step. Additionally, the relationship between Si deposit formed on the gas nozzles in the gas inlet and fluctuation of thickness and doping concentration of the films suggested that Si deposit formed on the gas nozzles acts as a trap site of Si source gas. By suppression of the Si deposit using optimizing gas flow condition, no significant fluctuation of thickness and doping concentration of the films were observed and the maintenance period of the gas nozzles could be increased more than 3 times compared to the epitaxial growth using the nozzles on which Si deposit was formed.

Characterization of Reversed Arc Hydrocarbon Plasma in Material Processing

A comprehensive study of the reversed arc plasma enhanced CVD (RACVD) reactor utilizing an Ar + H2 + CH4 plasma-creating mixture in the pressure range 1–100 Torr with a plasma flow direction opposite to the direction of the arc current was carried out. The reversed arc discharge has rising current–voltage characteristics showing voltage increasing with pressure and hydrogen concentration. The spectrum of the Ar-H2-CH4 plasma column includes CH, C2, and H2 molecular bands, in addition to Hα, Hβ, Hγ, and Hδ lines. The dissociation degree of H2 was estimated from the intensity ratio IHα/IArI of the Hα and ArI 750 nm lines using the optical actinometry method, yielding an average dissociation degree of hydrogen in the arc plasma of 15–20%. The average vibrational and rotational temperatures of CH radicals are Tv = Tr = 3000 K ± 300 K. The dissociation degree of hydrogen in the reversed arc discharge was calculated by the advection–diffusion-reaction model and showed reasonably good agreement both with experimental findings and with LTE calculations. The high concentration of nascent hydrogen and hydrocarbon radicals in the reversed arc plasma and its uniform distribution across the arc column makes it suitable for diamond coatings. The results obtained on the interaction of reversed arc plasma with substrates suspended within the current-carrier arc plasma column were applied to the description of a dusty reversed arc plasma in fluidized bed reactors. It was found that the energy effectiveness of the treatment of nanoparticles in the RACVD fluidized bed reactor exceeds 90%.

Detailed gas-phase kinetics and reduced reaction mechanism for methane pyrolysis involved in CVD/CVI processes

A detailed gas-phase kinetic model consisting of 37 species and 318 reactions is developed for methane pyrolysis involved in the chemical vapour deposition/infiltration (CVD/CVI) processes. The model was used to perform the simulations of CH4 pyrolysis in a hot-wall CVD reactor over a wide range of operating conditions and validated against the experimental data. The overall trend of the concentration profiles of notable species is in good agreement with experimental results. The sensitivity analysis and reaction path flux diagram revealed that CH4 pyrolysis directly proceeds without any induction period. C2 species are the primary intermediates for the formation of acetylene, ethylene, and benzene. Besides, the accuracy of the present model is better than the models available in the literature. The detailed kinetic model was then systematically reduced to a small mechanism comprising 13 species and 29 reactions. The predictions of reduced mechanism also agreed well with the detailed mechanism at low inlet partial pressure (<10 kPa). Although the error in the mole fraction of light species was minimal, the relatively large error for C6H6 species was observed at high inlet partial pressure of CH4.

Анализ эпитаксии карбида кремния из газовой фазы как базового процесса в техно-логии силовой электроники. Обзор

Currently, chemical gas deposition is the main method for producing high-quality and reproducible epitaxial layers for commercial silicon carbide (SiC) power devices. Based on the experience of ETU «LETI» in the synthesis of monocrystalline SiC, an analysis of the current state of silicon carbide gas phase epitaxy (CVD) technology was carried out. It has been shown that modern CVD reactors allow to implement the growth processes of SiC epitaxial structures of high quality with the following parameters: substrates diameter up to 200 mm; thicknesses of epitaxial layers from 0.1 to 250 μm; layers of n - and p -types conductivity with ranges of doping levels 10-10 cm and 10-10 cm, respectively. At the same time, setting up the technology of the reproducible high-quality growth of epitaxial layers is an individual task for a specific type of reactor. It requires a detailed consideration of the technological factors presented in this paper, which at the end determine the achievable parameters of SiC-epitaxial products

Creation of Localized Ensembles of NV Centers in a Diamond Grown in a Microwave CVD Reactor and Study of Their Properties

Creation of Localized Ensembles of NV Centers in a Diamond Grown in a Microwave CVD Reactor and Study of Their Properties

ZrO2-Sm2O3 Layer Growth Using the MOCVD Method at Low Temperatures and Under Reduced Pressure

This work presents the results of structure, microstructure, and chemical composition investigations performed on ZrO2-Sm2O3 layers synthesized by MOCVD (metal-organic chemical vapor deposition) using Zr(tmhd)4 and Sm(tmhd)3 as reactants on quartz glass substrate. The molar percentage of Sm(tmhd)3 used to obtain the layers at both 500 and 550 °C was 14% and 22.75%, respectively. Synthesis parameters were selected so that the value of the extended criterion Grx/Rex2 (Gr—Grashof number, Re—Reynolds number, x—the distance from the gas inflow point to the CVD (MOCVD) reactor) could be maintained below 0.01. It was determined from XRD (X-ray diffraction) analyses that the layers deposited at 500 °C contained small amounts of a crystalline phase and the layers obtained at 550 °C contained greater amounts of the crystalline phase (solid solution). SEM (scanning electron microscope) observations have also shown that the crystalline phase is present in the layers synthesized at 500 °C, as well as at 550 °C. EDS (energy dispersive spectroscopy) studies have indicated that molar content of Sm2O3 in the crystalline phase is lower in comparison to the amount present in the respective amorphous phase. The larger the Sm2O3 content in the layer, the higher the growth rate.

Elimination of Silicon Droplets Formation during 4H-SiC Epitaxial Growth by Chloride-Based CVD in a Vertical Hot-Wall Reactor

The growth pits formed during 5-10 μm 4H-SiC epitaxial growth by a home-built vertical hot-wall CVD reactor are investigated and their formation mechanisms are discussed. The origin of the growth pits is believed to be the silicon droplets related to the unoptimized growth condition. The growth pits are successfully removed by adding more HCl to the in-situ etching stage and the after-growth cooling stage.

Process Optimization and Modeling of the Silicon Growth in Trichlorosilane-Hydrogen Gas Mixture in a Planetary CVD Reactor

In this study, the effect of operating conditions of the chemical vapor deposition process on the silicon growth rate in a trichlorosilane-hydrogen (TCS-H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) system was evaluated. The influence of five parameters, including wafer rotation, TCS fraction, pressure, temperature, and mass flow rate was investigated. Response surface methodology (RSM) based on three-dimensional CFD simulations were used to analyze the coupled effect of the process parameters. A second-order polynomial model was used to predict the response. Analysis of variance showed that the model is statistically significant and only 1.22% of the total variations are not explained by the regression model. According to the RSM results, the growth rate increases as a function of the TCS fraction, pressure, and temperature. Additionally, the coupled effect of the TCS fraction and pressure has a significant effect on the growth rate while the coupled effect of wafer rotation speed and mass flow rate had the lowest effect. Finally, four confirmation tests were executed for a random combination of factors to verify the accuracy of the regression model. The maximum deviation between the CFD and regression model values of the silicon growth rate was found to be 4.4 %.

3D Modeling and optimization of SiC deposition from CH3SiCl3/H2 in a commercial hot wall reactor

In this paper, the 3D modeling and optimization of a commercial hot wall vertical reactor for SiC coating is presented to investigate the effect of various process parameters on the hydrodynamic stability of the CVD reactor. The correlation between experimental and simulated results was established by tuning the kinetic parameters for the surface reaction. Besides, the incorporation of various dimensional numbers such as Reynolds number (Re), Péclet number (Pe), and Grashof number (Gr) enabled the systematic investigation of the effect of the natural convection phenomena on film growth performance. It was found that the buoyancy-driven flow can occur inside the reactor at a high Reynolds number and Gr/Re2 ratio. The process optimization was performed using response surface methodology (RSM) to obtain the desired film quality. The CFD-RSM collaborative approach allowed a significant reduction in the number of experiments and simulations required to optimize the CVD process.

Scrolled Production of Large-Scale Continuous Graphene on Copper Foils*Supported by the Beijing Natural Science Foundation (Grant No. JQ19004), the Key R&D Program of Guangdong Province (Grant Nos. 2019B010931001, 2020B010189001, 2018B010109009 and 2018B030327001), Bureau of Industry and Information Technology of Shenzhen (Graphene platform 201901161512), the National Natural Science Foundation of China (Grant Nos. 51991340, 51991342 and 51522201), the National Key R&D

We report an efficient and economical way for mass production of large-scale graphene films with high quality and uniformity. By using the designed scrolled copper-graphite structure, a continuous graphene film with typical area of 200 × 39 cm2 could be obtained in 15 min, and the production rate of the graphene film and space utilization rate of the CVD reactor can reach 520 cm2⋅min−1 and 0.38 cm−1⋅min−1, respectively. Our method provides a guidance for the industrial production of graphene films, and may also accelerate its large-scale applications.

Catalytic Performance of Calcium Titanate for Catalytic Decomposition of Waste Polypropylene to Carbon Nanotubes in a Single-Stage CVD Reactor

Calcium titanate mixed metal oxides with different contents were used as supports for NiMo catalyst prepared by the sol–gel method. The activities of these catalysts were tested in the catalytic decomposition of waste polypropylene (PP) for the synthesis of carbon nanotubes (CNTs) using a single-stage chemical vapor deposition technique. The physico-chemical properties of the catalysts and deposited carbon over the catalysts were checked by X-ray diffraction (XRD), scanning electron microscopy (SEM), temperature-programmed reduction (TPR), N2 physisorption, transmission electron microscopy (TEM), Raman spectroscopy, and thermogravimetric analysis (TGA). The TEM and XRD results presented a high dispersion of the active metal species on the surface of the support materials. The result showed that increasing the support content led to an increased crystallite size of the catalysts and a resultant reduction in CNTs yield from 44% to 35%. NiMo-supported CaTiO3 catalyst displayed good catalytic activity and stability toward CNTs growth. Furthermore, the effect of calcination temperature on the morphology, yield, and quality of CNTs was also studied, and it was observed that thermal treatment up to 700 °C could produce well graphitized, high-quality, and high-yield CNTs from the waste PP.