Chemical Vapor Deposition Reactor Research Articles

Ultrahigh Incorporation of Tin in SiSn Nanowires Grown via In-Plane Solid-Liquid-Solid Mechanism

We report on the growth of sn-catalyzed in-plane silicon nanowires (SiNWs) using the solid–liquid-solid (SLS) mechanism and their application to nano-electronics. The in-plane SLS growth process allows us to obtain very high tin concentrations ∼ 10 at.% (more than 1000 times the expected concentration from the phase diagram). The growth is achieved in a plasma-enhanced chemical vapor deposition reactor, in a single pump-down process. Atom probe tomography (APT) and transmission electron microscopy (TEM) are used to assess the composition of these SiSn NWs. The atomic-scale investigation shows that Sn atoms are similarly distributed in crystalline SiSn NWs grown at 300 °C and 400 °C, with different sn-enrichments along structural defects. A NW-based field-effect transistor (FET) is fabricated in which a SiSn NW is implemented as the channel for charge transport, reaching a field effect hole mobility of 80 cm2/V.s.

Microstructural Characteristics of ECR Plasma Etched and Heat Treated Commercial Copper Foil

AbstractThe structural quality of the catalytic transition metal substrate plays a critical role in pristine graphene synthesis by chemical vapor deposition. In this work, the microstructural parameters of commercial copper foils are investigated in lieu of conventional laboratory grade crystalline copper foils. Initially, the commercial copper foils are simultaneously plasma etched and heat treated for a period of 30, 45 min, and 1 h respectively at two elevated temperature levels of 823 and 923 K under the exposure of hydrogen plasma. The experiments are carried out in a 2.45 GHz Electron Cyclotron Resonance (ECR) Plasma Enhanced Chemical Vapor Deposition (PE‐CVD) reactor, at an operating pressure of 5 × 10−2 mbar. X‐ray diffraction (XRD) results are plotted and analyzed by Williamson–Hall (W–H) method to determine microstructural parameters, e.g., micro‐strain, stress, average domain size, and energy density associated to the processed copper foils.

Nucleation and coalescence of tungsten disulfide layers grown by metalorganic chemical vapor deposition

The nucleation of tungsten disulfide WS2 crystallites and coalescence behaviour of monolayer WS2 films grown on C-plane sapphire have been studied in a commercial AIXTRON close coupled showerhead metalorganic chemical vapor deposition (MOCVD) reactor using tungsten hexacarbonyl and di-tert-butyl sulfide as precursors. The influence of sapphire substrates offcut (both orientation and angle), as well as the substrate annealing conditions and growth temperature, on the nucleation and size of the WS2 domains has been investigated. A higher nucleation temperature combined with increased substrate annealing temperatures was found to promote an increase in the WS2 domain size. The dependence of surface coverage and coalescence behaviour of the WS2 domains on the growth duration has also been determined, allowing monolayer WS2 films with < 10 % bilayer to be obtained. Crystalline quality of the coalesced WS2 films has been assessed by grazing incidence XRD and misorientation mapping using 4D-scanning transmission electron microscopy, showing a slight in-plane misorientation of the crystallites in the WS2 monolayer. The electrical performance of the coalesced WS2 films was assessed using backgated TLM structures demonstrating mobility values of up to 5 cm2/Vs and a high Ion/Ioff ratio greater than 108.

Growth Conditions and Substrate Misorientation Angle Dependences of Silicon Incorporation in Chemical Vapor Deposition Diamond

The results of a study of the incorporation of silicon in diamond depending on the growth conditions of epitaxial layers in a chemical vapor deposition (CVD) reactor in a gas mixture of hydrogen, methane, and silane are presented. A detailed study of the effect of methane and silane flows, substrate temperature, gas mixture pressure, and substrate misorientation angle has been carried out. The influence of the surface misorientation angle on the formation of silicon‐vacancy (SiV) centers in diamond has been studied. It has been found that the carbon content in the gas mixture has a significant effect on the incorporation of silicon into diamond. Studies of the CVD growth of silicon‐doped diamond are carried out simultaneously with studies of the optical spectra of plasma emission in the reactor. The content of silicon in plasma is compared with content of silicon incorporated into diamond during CVD synthesis. The most efficient formation of SiV centers is observed for substrate misorientation angles from 2° to 4°.

Boron-Silicon Thin Film Formation Using a Slim Vertical Chemical Vapor Deposition Reactor

A boron-silicon film was formed from boron trichloride gas and dichlorosilane gas at about 900℃ in ambient hydrogen at atmospheric pressure utilizing a slim vertical cold wall chemical vapor deposition reactor designed for the Minimal Fab system. The gas flow rates were 80, 20 and 0.1 - 20 sccm for the hydrogen, dichlorosilane and boron trichloride gases, respectively. The gas transport condition in the reactor was shown to quickly become stable when evaluated by quartz crystal microbalances at the inlet and outlet. The boron-silicon thin film was formed by achieving the various boron concentrations of 0.16% - 80%, the depth profile of which was flat. By observing the cross-sectional TEM image, the obtained film was dense. The boron trichloride gas is expected to be useful for the quick fabrication of various materials containing boron at significantly low and high concentrations.

In situ minority carrier lifetime via fast modulated photoluminescence

Modulated photoluminescence (MPL) is a powerful technique for determining the effective minority carrier lifetime (τeff) of semiconductor materials and devices. MPL is based on the measurement of phase shifts between two sinusoidal waves (minimal amplitude excitation; and PL signal). In particular, in situ τeff has been proven to be an effective measurement at showing changes within a plasma-enhanced chemical vapor deposition reactor during fabrication of c-Si solar cells. However, the required time for a single measurement, using the previous method, was 40 s. In this paper a new input signal is proposed, called Dolphin's Wave, providing a method for decreasing the required measurement period to under 2 s, using superposition, frequency sweeps, and wavelets.

Event-triggered adaptive NN practical finite-time control with its application to MPCVD reactors

The practical finite-time control problem of uncertain nonlinear systems is investigated in this paper. To address the uncertain nonlinearities of the system, neural networks are introduced to approximate the lumped nonlinearities containing the system unknown functions. On the other hand, to alleviate the signal transmission pressure of the system, an improved event-triggered mechanism is presented to reduce the controller update frequency without degrading the control performance of the system. By using practical finite-time stability, it is obtained that the system tracking errors are practical finite-time stable without Zeno behavior. Finally, the effectiveness of the proposed method is verified by the simulation results of its application to a microwave plasma chemical vapor deposition (MPCVD) reactor system.

Influence of Temperature and Flow Ratio on the Morphology and Uniformity of 4H-SiC Epitaxial Layers Growth on 150 mm 4° Off-Axis Substrates

The homoepitaxial growth of 4H-SiC films was conducted on 4H-SiC 150 mm 4° off-axis substrates by using a home-made hot-wall chemical vapor deposition (CVD) reactor. Special attention was paid to the influence of the growth temperature on the surface morphology, growth rate, doping efficiency, and structural uniformity of the films. Among the above factors, growth temperature and flow ratio were shown to be the essential parameters to produce high-quality homoepitaxial layers. Furthermore, a two-side flow tunnel was introduced to control the growth temperature nonuniformity in the reactor. The influence of flow ratio on the epitaxial layer uniformity was also studied. It was found that the surface roughness increased with the increasing temperature, achieving its minimum value of 0.183 nm at 1610 °C. Besides that, the film growth rate decreased with the increase in growth temperature, whereas the degrees of thickness non-uniformity, N2 doping non-uniformity, and doping efficiency increased. Meanwhile, both the thickness and doping uniformity can be improved by adjusting H2 and N2 flow ratios, respectively. In particular, the use of the H2 ratio of 1.63 and N2 ratio of 0.92 enabled one to increase the degree of uniformity of thickness and doping by 0.79% (standard deviation/mean value) and 3.56% (standard deviation/mean value), respectively, at the growth temperature of 1630 °C.

Chlorine-Assisted Growth of Epitaxial InGaN and AlGaN Crystals at Low Temperatures Using Plasma-Enhanced Chemical Vapor Deposition

The chlorine-assisted growth of epitaxial indium gallium nitride (InGaN) and aluminum gallium nitride (AlGaN) crystals was achieved with high reproducibility at the low temperature of 600 °C in the plasma-enhanced chemical vapor deposition (PECVD) reactor via the reaction between the metal trichlorides with high vapor pressures and nitrogen plasma. After adding hydrogen gas to the growth processes of InGaN and AlGaN, the problems for the etching of chlorine plasma on the as-grown InGaN crystals and the appearance of crystal planes different from (002), derived from the worse and the better bonding abilities of materials, respectively, were solved effectively. Inside AlGaN crystals, the phase separation of gallium nitride (GaN) and aluminum nitride (AlN) can be avoided by controlling the amount of precursor aluminum. The epitaxial InGaN and AlGaN crystals have the same (002) crystal plane as the GaN(002) bottom layers and exhibit the same ⟨0001⟩ crystallographic growth direction along the axial direction of GaN microrods, representing the consistent growth orientation of the epitaxial crystals. The process temperatures of InGaN and AlGaN can be greatly decreased using chlorine gas and plasma so that the related applications of low-temperature growth may be expanded drastically in the future.

Investigation on Strain Sensitivity and Temperature Behaviour of Nitrogen Doped 3C-SiC Thin Films

Electrical resistance-strain behaviour of nitrogen doped 3C-SiC thin films was investigated to determine whether they could be used as strain gauges. Using a hot wall vertical low pressure chemical vapour deposition (LPCVD) reactor, these films were deposited on thermally oxidised Si (100) and alumina substrates at 2.5 mbar pressure and 1040°C temperature from methyltrichlorosilane (MTS) precursor. The nitrogen doping gas utilised was ammonia (NH3). Using four-point bending method, the gauge factor (GF) was determined for all thin films (0, 9, 17, and 30 atomic % nitrogen doped). Systematic annealing of films in a vacuum atmosphere was used to determine the TCR of nitrogen doped 3C-SiC (111). Film sheet resistance was evaluated using a four-probe approach, and it was observed to decrease as the temperature rises from 40 to 550°C. The resistivity, average TCR, and strain sensitivity of film doped with 17 atomic % nitrogen concentration were 0.14 cm, -103 ppm/°C, and -9.6, respectively, indicating that it can be employed as a strain gauge material in high temperature applications. However, film doped with 30 atomic % of nitrogen concentration showed an increase in the resistivity, TCR and strain sensitivity.

Heterometallic Porphyrin Conjugated Polymer Thin Films—A Gas‐Phase Approach for the Engineering of New Fused Porphyrin Systems

AbstractFor the first time, the simultaneous synthesis and deposition of heterometallic porphyrin conjugated polymer thin films from a simple and scalable gas‐phase approach are reported. The oxidative chemical vapor deposition (oCVD) reaction of 5,15‐(diaryl) porphyrins chelated with different metal cations (M = Co(II), Ni(II), Zn(II), Cu(II), Pd(II)) readily yields the formation of new hetero‐metalated fused porphyrin tapes, such as evidenced by in‐depth high‐resolution mass spectrometry studies. The impact of the coreactants on the regioselectivity of the intermolecular dehydrogenative coupling reaction and the formation of double or triple bonds between the porphyrin units is demonstrated. The oCVD reaction of multiple porphyrins brings the possibility to easily engineer the chemical features and the electronic and optoelectronic properties of these highly conjugated porphyrin polymers. Particularly, it is demonstrated that porphyrin conjugated polymers having different chelated metal cations can achieve higher electrical conductivities and promote narrower bandgaps. The gas‐phase approach presented herein overcomes the main limitations of the conventional solution‐based approaches and opens the path to the engineering of a novel class donor–acceptor heterometallic polymers with high interest in several fields including multimetallic electrocatalysis, photocatalysis, sensing, and nonlinear optics applications.

The simultaneous synthesis of carbon dots and carbon spheres with tunable sizes using a vertical chemical vapour deposition method

Herein we report on the direct synthesis of solid hydrophobic carbon dots (CDs) and simultaneously carbon spheres (CSs), using a vertical chemical vapour deposition (CVD) reactor. The HRTEM data indicated that the CDs and CSs originated from different carbon building blocks indicated that the CDs and CSs originated from different carbon building blocks. The CDs were obtained by reacting acetylene (C2H2) and Ar mixtures at high flow rates (&gt;500 sccm) and high temperatures (800-1000 °C). TEM studies indicated that the CDs produced were graphene-like quantum dots that increased in size from c. 3 nm to 8 nm as the Ar flow rate (constant C2H2 flow rate) was decreased, while small solid CSs (c. 100 nm) were also synthesised in the process. The CSs had a typical spherical layered structure with no graphitic core. A mechanism to rationalise the observation that the CDs and CSs grew simultaneously by different pathways with no formation of intermediate-sized particles is given.

Synthesis, characterization, and thermal properties of a 2-isopropyl-aminopyridine adduct of cobalt(II) chloride and its potential as a CVD precursor for cobalt-based films

• The detailed study on synthesis, characterization, and thermal properties of an alkyl-aminopyridine adduct of cobalt(II) chloride. • By adding alkyl-aminopyridine to cobalt(II) chloride, the obtained compound exhibits high stability, sufficient volatility, and suitable thermal stability, which is benefit for industrial application. • A promising CVD precursor for preparation of cobalt-based films. In this study, a 2-isopropyl-aminopyridine adduct of cobalt(II) chloride [Co(2- i PrNH-C 5 H 4 N) 2 Cl 2 ] was synthesized and used as a precursor for preparing cobalt-based films through chemical vapor deposition (CVD). This compound was synthesized through a simple coordination reaction and characterized through 1 H NMR, elemental analysis, and single-crystal diffraction. The thermal properties (including volatility, vapor pressure, and thermal stability) of the compound were investigated through thermogravimetric analysis (TGA) to determine its feasibility for use in CVD. Moreover, a film deposition experiment was conducted in a low-pressure CVD reactor system, and a Co 3 O 4 film was obtained. This result verified the reported compound’s applicability as a CVD precursor for fabricating cobalt-based films.

Structural, chemical network and optoelectronic properties of Ag catalyzed CVD grown gallium nitride nanowires in reduced atmosphere

Silver catalyst-mediated Gallium Nitride Nanowires (Ag-GNNWs) were synthesized on Si (100) substrate taking Ga2O3 powder, N2 and H2 gas as raw material using a chemical vapor deposition (CVD) reactor. The structural, chemical network and optoelectronic environment of Ag-GNNWs were investigated by employing AFM, FTIR, Raman, XRD, Photoluminescence (PL), and XPS characterization with the variation of H2 flow rate. The AFM and XRD results confirmed that the diameters and crystallite size, D of Ag-GNNWs varied from 50 to 250 nm and 15.06 nm respectively. The microstrain of Ag-GNNWs varied from 0.00174 to 0.01183 with an increase of H2 gas reduced atmosphere. The FTIR signatures at 463, 514, 567, 610, 667 and 739 cm−1 correspond to H-Ga-O, N-Ga-N, N-Ga-O, O-Ga-O(GaOO), O-Ga = O(O-Ga = O) and A1(LO) phonon respectively indicated Oxygen present as contamination. The increase in FWHM of Raman spectra signified decreased phonon lifetime of the transverse optic (A1 & E1), surface optic (A & E), E2(High) and defect-induced phonon with increasing H2 gas flow rate. The ISO(A) / ISO(E) and its respective FWHM ratio increased from 1.22 to 1.49 and 1.09 to 1.30 cm−1, indicating decreasing structural anisotropy and crystalline quality with the variation of H2 flow rate. The prominent PL peak centered at around 2.97 eV implied nitrogen-vacancy (VN) in the Ag-GNNWs. The XPS spectrum confirmed the presence of Ga, Ag, N2 and O are present in Ag-GNNWs. Moreover, semiempirical deconvolution predicts possible chemical networks in the Ag-GNNWs.

Solar-thermal cold-wall chemical vapor deposition reactor design and characterization for graphene synthesis

Manufacturing processes are often highly energy-intensive, even when the energy is primarily used for direct heating processes. The required energy tends to derive from local utilities, which currently employ a blend of sources ranging from fossil fuels to renewable wind and solar photovoltaics, among others, when the end manufacturing need is thermal energy. Direct solar-thermal capture provides a compelling alternative that utilizes renewable energy to reduce greenhouse gas emissions from industrial processes, but one that has rarely been employed to date. In this study, a 10 kWe custom-built high flux solar simulator (HFSS) that closely approximates the solar spectrum produces a heat flux distribution with an adjustable peak between 1.5 and 4.5 MW/m2. The HFSS system is coupled to a cold-wall chemical vapor deposition (CVD) system that is equipped to automate graphene synthesis while providing safe operation, precise control, and real-time monitoring of process parameters. A numerical heat transfer model of a thin copper substrate is derived and validated to compute the substrate’s temperature profile prior to the synthesis process. The peak substrate temperature is correlated to the HFSS supply current and vacuum pressure, as it serves as a critical design parameter during graphene synthesis. We report the synthesis of high-quality graphene films on copper substrates with an average Raman peak intensity ratio ID/IG of 0.17. Backscattered electron microscopy reveals a characteristic grain size of 120 μm, with an area ratio of 16 when compared to that of low-quality graphene on copper. The reported solar-thermal CVD system demonstrates the ability to produce a high-value product, namely, graphene on copper, directly from a renewable energy resource with process control and automation that enables synthesis under a variety of conditions.

Pressure Dependence of Rate Coefficients of Unimolecular and Chemical Activation Reactions Connected to the Potential Energy Wells of Si2H2Cl4, Si2Cl6, and Si2Cl4 via Rice-Ramsperger-Kassel-Marcus Calculations.

Rate coefficients for elementary reactions connected to the potential energy wells of Si2H2Cl4, Si2Cl6, and Si2Cl4, which are important Si2 species in chemical vapor deposition (CVD) processes that use chlorosilanes as silicon source gases, were determined through the Rice-Ramsperger-Kassel-Marcus theory under various conditions of temperature and pressure. The optimized structures and vibrational frequencies of the reactants, products, and transition state were obtained using (U)B3LYP/6-31+G(d,p), and the single-point energies of the optimized structures were recalculated using the coupled cluster method with single and double excitations plus triple perturbation (U)CCSD(T) with complete basis set extrapolation. Many of the unimolecular decomposition channels and chemical activation reactions investigated in this work were found to be in the fall-off regime under subatmospheric to moderately high-pressure conditions so that it is expected that accurate modeling of the gas phase in the chlorosilane CVD reactor requires careful determination of the rate coefficients as functions of temperature and pressure for the conditions of interest, instead of using high-pressure limit rate coefficients. The rate coefficients determined here were expressed through Chebyshev coefficients and also modified Arrhenius parameters to be used in simulations of systems under a wide range of temperature and pressure conditions.

Combining density functional theory and CFD-PBM model to predict TiO2 nanoparticle evolution during chemical vapor deposition

Preparation of TiO2 nanoparticles by TiCl4 hydrolysis during chemical vapor deposition (CVD) is one of the effective techniques for producing TiO2 nanoparticles, while the mechanisms of TiO2 nanoparticle evolution are not well understood. This paper uses computational fluid dynamics (CFD) population balance model (PBM) to predict particle size distribution during CVD, and density functional theory (DFT) calculations to explore reaction mechanisms. DFT calculations reveal that the gas phase hydrolysis reaction can be simplified into two processes, the hydrolysis of TiCl4 to form TiO(OH)2 and the decomposition of TiO(OH)2 to TiO2. During the surface reactions, the energy barriers of TiO(OH)2 decomposition reactions on the surfaces of (TiO2)n nanoclusters (n = 1–8) are generally lower than those in the gas phase reactions, and the largest energy barrier of the surface reaction occurs on the surface of (TiO2)6 nanoclusters. Simulations using a perfect stirred reaction model indicate that Ti(OH)4 is the dominant hydrolysis products when the temperature is lower than 548 K, while TiO2 production starts at ∼610 K, indicating reaction temperature is a crucial factor that governs the products of TiCl4 hydrolysis. CFD-PBM model predict the evolution of Particle Size Distribution (PSD) of nanoparticles in a CVD reactor, which is agreed with experimental measurements in the literature. Increasing the reaction temperature results in an increase of the peak of the PSD of nanoparticles in the reactor. This study provides atomic insights into the nanoparticle evolution and a practical model to predict the nanoparticle evolution during the CVD process.

A wide-angle X-ray scattering laboratory setup for tracking phase changes of thin films in a chemical vapor deposition chamber.

The few-layer transition metal dichalcogenides (TMD) are an attractive class of materials due to their unique and tunable electronic, optical, and chemical properties, controlled by the layer number, crystal orientation, grain size, and morphology. One of the most commonly used methods for synthesizing the few-layer TMD materials is the chemical vapor deposition (CVD) technique. Therefore, it is crucial to develop in situ inspection techniques to observe the growth of the few-layer TMD materials directly in the CVD chamber environment. We demonstrate such an in situ observation on the growth of the vertically aligned few-layer MoS2 in a one-zone CVD chamber using a laboratory table-top grazing-incidence wide-angle X-ray scattering (GIWAXS) setup. The advantages of using a microfocus X-ray source with focusing Montel optics and a single-photon counting 2D X-ray detector are discussed. Due to the position-sensitive 2D X-ray detector, the orientation of MoS2 layers can be easily distinguished. The performance of the GIWAXS setup is further improved by suppressing the background scattering using a guarding slit, an appropriately placed beamstop, and He gas in the CVD reactor. The layer growth can be monitored by tracking the width of the MoS2 diffraction peak in real time. The temporal evolution of the crystallization kinetics can be satisfactorily described by the Avrami model, employing the normalized diffraction peak area. In this way, the activation energy of the particular chemical reaction occurring in the CVD chamber can be determined.

Pressure Sensor Devices Featuring a Chemical Passivation Made of a Locally Synthesized Diamond Layer

The rear side of a pressure sensor diaphragm is prepared with an additional diamond layer as protective coating against harsh media. The preparation sequence for the diamond coating is developed as a simple backend process, combining only two additional steps in the standard process. These are the local seeding of nanodiamond layer and the low‐temperature diamond growth at &lt;300 °C in a linear antenna microwave plasma‐enhanced chemical vapor deposition reactor, where only at the nanodiamond seeded sites, a high‐quality diamond film was synthesized. The seeding resolution in the setup used was limited to ≈80 μm, but can be further reduced. In an industry‐typical assembly sequence the diamond coated pressure sensor devices are further equipped with a support wafer and mounted to a TO‐8 socket. Tests of such sensor systems indicate that the diamond layer does not hamper the stability of the device. This proofed method of postprocessing an only‐local and low‐temperature synthesis of a diamond layer on the wafer‐level opens‐ up possibilities for many other applications, since this approach is scalable and in general cost effective.

Large Area Growth and Phase Selectivity of MoTe2 Nanosheets through Simulation‐Guided CVD Tellurization

AbstractAmong transition metal dichalcogenides, molybdenum ditelluride (MoTe2) holds significant attention due to its polymorphic nature including semiconducting, metallic, and topological semimetal phases. Considerable efforts are devoted to synthesizing MoTe2 nanosheets to make them suitable for device integration in nanotechnologies and for fundamental investigations. In this respect, chemical vapor deposition (CVD) via tellurization of a pre‐deposited Mo thin film is an easy and flexible way for synthesizing large scale MoTe2 nanosheets. Here, the study report on the CVD of large‐area (up to 4 cm × 1 cm) MoTe2 nanosheets with pure 1T’ and 2H phase selection by design. Within the tellurization scheme, the vapor‐solid reaction between the pre‐deposited molybdenum film and tellurium vapor is studied thus optimizing the scalability and quality of the MoTe2 nanosheets grown on SiO2/Si substrates. It is demonstrated that the MoTe2 structure and morphology are kinetically dictated by the tellurium concentration gradient on the reaction site with varying geometric configurations inside the CVD reactor. This study provides a pivot scheme for enabling scalable 1T’ and 2H‐MoTe2 integration in applications for novel micro‐ and nano‐electronics, spintronics, photonics, and thermoelectric devices.