Chemical Vapor Deposition Reactor Research Articles

Design and simulation of a novel MPCVD reactor with three-cylinder cavity

A novel microwave plasma chemical vapor deposition (MPCVD) reactor with three-cylinder cavity and outstanding tuning capability was proposed. The electric field and plasma in the reactor were simulated, and four geometric parameters were optimized. After optimization, the electric field intensity above the substrate exceeded 5×103V/m (input power of 1 W), which was 1.6 times that of the similar cylindrical reactors. Only one strong plasma formed above the substrate surface with an input power of 5 kW once the gas pressure exceeds 8 kPa. But the plasma coverage area was decreased with the increase of the gas pressure. The plasma coverage area could be restored by adjusting the height difference between the adjusting mechanism 1 and 2. The frequency detuning caused by the microwave frequency changes also could be returned by adjusting the adjusting mechanisms. The subsequent experimental results showed that uniform and high-quality diamond films could be deposited under the simulation condition (5 kW and 12 kPa). It could verify the accuracy of the simulation and the excellent performance of the new MPCVD reactor.

Trench filling with phosphorus-doped monocrystalline and polycrystalline silicon

Optimized epitaxial processes for the filling of deep trenches are mandatory for the fabrication of advanced devices in the microelectronic industry. The use of Selective Epitaxial Growth (SEG) in deep cavities faces multiple issues such as inhomogeneities along the growth direction or defect formation. In this work, the main objective was to develop void-free processes to fill 1:6 up to 1:16 aspect ratio trenches with monocrystalline and polycrystalline Si:P respectively, in a Reduced Pressure – Chemical Vapour Deposition (RP-CVD) reactor. Previous studies suggested the use of a SiH2Cl2 (DCS) + PH3 + HCl chemistry, with an optimization of the DCS/HCl mass-flow ratio (MFR) to conformally fill large and high aspect ratio trenches with monocrystalline Si:P (c-Si:P) while preventing overgrowth at the trench entrance and voids at the bottom. Current studies were first of all conducted on blanket wafers at T = 950 °C and P = 10 Torr, in order to choose the best strategy for varying DCS/HCl MFRs. The P+ ions concentration was quantified and two trends were highlighted depending on the PH3 partial pressure (P(PH3)). For P(PH3) lower than 10-5 Torr, the dopant concentration (in the 1017 - 1018 cm-3 range) increased solely with the phosphine flow and did not depend on the HCl flow. Meanwhile, for PH3 partial pressures higher than 10-5 Torr and thus higher doping levels (between 3x1018 and 2x1019 cm-3), the P+ ions concentration increased with the PH3 flow and decreased as the HCl flow increased. The filling of 1:6 aspect ratio trenches by monocrystalline Si:P was then achieved thanks to a three steps process with various DCS/HCl MFRs. Characterizations showed good crystalline quality together with a steady doping level of 1.3x1018 at cm-3. Further optimizations will however be required to completely suppress voids. Meanwhile, the filling of 1:16 aspect ratio trenches or needles by poly-Si:P was successfully achieved at 10 Torr with a SiH4 + PH3 chemistry, provided that the deposition temperature, 750°C, was low enough to avoid the formation of large poly-Si:P grains, notably at the entrance of such cavities.

Gas‐phase kinetic of boron carbide chemical vapor deposition using BCl3+CH4+H2 mixture

AbstractA detailed chemical kinetic mechanism consisting of 472 reactions and 61 species for the gas‐phase thermal decomposition of BCl3+CH4+H2 mixtures is used to model the chemical vapor deposition (CVD) of boron carbide. The mechanism is constructed using a reaction mechanism generator (RMG), which is automatic and requires no or less human intervention. New functionality, considerable thermodynamic and kinetic data have been added to RMG to account for boron chemistry. The model considers all necessary reactions in the reaction pathways and reasonably predicts the experimental data available from the literature. The sensitivity analysis identifies crucial species responsible for boron carbide formation. Besides, a reduced mechanism (15 species and 26 reactions) is derived from a detailed mechanism, which could be used to expedite an effective CVD reactor design through numerical simulations. The performance of the reduced model is also evaluated concerning the complete mechanism, which shows that the reduced model can predict the reactor behavior reasonably well.

Microwave plasma modelling in clamshell chemical vapour deposition diamond reactors

A microwave plasma model of a chemical vapour deposition (CVD) reactor is presented for understanding spatial heteroepitaxial growth of polycrystalline diamond on Si. This work is based on the TM0(n>1) clamshell style reactor (Seki Diamond/ASTEX SDS 6K, Carat CTS6U, ARDIS-100 style) whereby a simplified H2 plasma model is used to show the radial variation in growth rate over small samples with different sample holders. The model uses several steps: an electromagnetic (EM) eigenfrequency solution, a frequency-transient EM/plasma fluid solution and a transient heat transfer solution at low and high microwave power densities. Experimental growths provide model validation with characterisation using Raman spectroscopy and scanning electron microscopy. This work demonstrates that shallow holders result in non-uniform diamond films, with a radial variation akin to the electron density, atomic H density and temperature distribution at the wafer surface. For the same process conditions, greater homogeneity is observed for taller holders, however, if the height is too extreme, the diamond quality reduces. From a modelling perspective, EM solutions are limited but useful for examining electric field focusing at the sample edges, resulting in accelerated diamond growth. For better accuracy, plasma fluid and heat transfer solutions are imperative for modelling spatial growth variation.

Microstructural Analysis of Copper Foil Etched and Annealed in ECR Plasma Reactor

Microstructural analysis of commercially available cold-rolled polycrystalline copper foil, etched and annealed in an in-house developed Electron Cyclotron Resonance (ECR) Plasma Enhanced Chemical Vapour Deposition (PE-CVD) reactor, have been carried out using x-ray diffraction (XRD) studies. The annealing experiments were carried out under a vacuum environment, keeping the working pressure of the reactor at 50×10-3 mbar, for three different time spans of 30 mins, 45 mins and 1 hour at 823 K (550 °C) and 923 K (650 °C) respectively in presence of hydrogen plasma. The XRD studies reveal the significance of annealing time at two different temperatures for the determination of physical and microstructural parameters such as the average grain size and micro-strain in copper lattice by Williamson-Hall (W-H) method.

Catalytic pyrolysis of low density polyethylene and polypropylene wastes to fuel oils by N-clay

Abstract Dealing effectively with plastic wastes has been a major global challenge. Different methods have been previously employed to proffer solution to plastic wastes problem however, all showed their energetic, economic and environmental implications. In this research, catalytic pyrolysis of low density polyethylene and polypropylene wastes was carried out to proffer solution to the problem. The plastic materials were collected and appropriately prepared after which ultimate and proximate analysis was carried out on them. The clay was collected from Naka, Gwer West Local Government Area of Benue State, Nigeria, thereafter, referred to as N-clay and was appropriately prepared, then analyzed by a BET analyzer for the following properties: the surface area, which was found to be 85.418 m2/g, pore size 2.100 nm and pore volume of 0.042 cc/g. Also, the XRF determination of the chemical composition of the N-clay was done and the SiO2/Al2O3 ratio was found to be 70.81/29.19. The N-clay and the plastics were then pyrolyzed in a chemical vapor deposition (CVD) reactor in the ratio 1:3 respectively, at 500 oC with residence time of 30 min using nitrogen as purge gas. The polypropylene yielded 70.34 % liquid oil, 6.43 % char and 23.23 % gas. The liquid was analyzed for functional groups, using Raman spectrometer. Physicochemical analysis was also done on the oil and it was determined that the oil had properties consistent with commercial-grade gasoline. The low density polyethylene yielded wax, instead of liquid, char and gas. Finally, it was concluded that the N-clay was suitable as catalyst for the pyrolysis of plastics and the fuel oil obtained from polypropylene pyrolysis is comparable to gasoline fuel.

Electrochemical properties of silver nanoparticle decorated on vertical graphene nanosheets

Vertical Graphene Nanosheets (VGNs) can be described as graphite sheet nanostructures with edges that are composed of stacks of planar graphene sheets standing almost vertically on the substrate which has attracted much attention for energy storage application due to their unique properties such as large surface area, high electrical conductivity, and open 3D network structures. The present study reports VGNs synthesized on the nickel substrate under 5 mTorr gas pressure and CH4/Ar plasma in an Electron Cyclotron Resonance – Chemical Vapor Deposition (ECR-CVD) reactor. Further, a homogenous dispersion of Ag nanoparticles is coated over VGNs by the electrochemical deposition method. In this work, the electrochemical performance of VGNs/Ni and Ag-VGNs/Ni are investigated. The results for Ag-VGNs/Ni composites exhibit the higher specific capacitance of 318μF/cm2 compared to that of VGNs/Ni (70μF/cm2) at a scan rate of 20 mV/s. This enhanced capacitance can be a result of highly conductive 3D network of VGNs and also Ag nanoparticles conduction which can provide faster electron and ion transport. Scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray diffraction (XRD) and Raman spectroscopy are also used to study the morphology and structure properties of the surfaces.

Defect reduction in SiC epilayers by different substrate cleaning methods

Low defect epitaxial layers are of highest importance for the fabrication of high power SiC devices using large chip area. To minimize the impact of defects and particles on the substrates, the influence of different automated cleaning procedures on defects of epitaxial layers subsequently grown on 150 mm 4H–SiC substrates was investigated. Therefore, 12 μm thick n-type epitaxial layers were grown on commercially available 150 mm 4H–SiC Si-face substrates with lowest micropipe density using a warm-wall chemical vapor deposition reactor. The defects of all samples were characterized utilizing surface microscopy as well as ultra-violet photoluminescence techniques. With these methods, a qualitative, as well as quantitative, characterization of surface defects and crystallographic defects from the as-received substrate to the finished epitaxy was carried out and is discussed. Yield prediction maps for high voltage metal-oxide-semiconductor field-effect-transistors were generated and the reduction of critical defects, which results in a predicted die yield increase, as well as an outlook on future investigations, is discussed.

Strain engineering in III-V photonic components through structuration of SiNx films

We describe work to quantify the effects of structured dielectric thin films, such as SiNx, at the surface of III-V semiconductors, in terms of strain engineering with applications to photonic components such as waveguides and lasers. We show that the strain in the semiconductor can be engineered by controlling the stress in the dielectric thin film by tuning its deposition process. In the first part of this study, we describe how we can control the amount of this built-in mechanical stress, in the case of SiNx, over a large range, from highly tensile (300 MPa) to highly compressive (−800 MPa), using two different kinds of plasma-enhanced chemical vapor deposition reactors: a standard capacitively coupled reactor with radiofrequency excitation and an electron cyclotron resonance reactor with microwave excitation. We focused on characterizing and understanding these thin films' optical and chemical bonding properties through spectroscopic ellipsometry and Fourier transform infrared spectroscopy. We have also studied their mechanical properties experimentally using the wafer curvature measurement technique, microstructure fabrication, and nanoindentation measurements. In the second part, we show accurate measurements of the strain distribution induced within GaAs wafers when such thin films are structured in the shape of elongated stripes of variable width, using standard optical lithography and plasma etching. For this, we map the anisotropic deformation, measuring the degree of polarization of the spectrally integrated photoluminescence (PL) generated within GaAs by excitation with a red laser. PL from the bulk cubic semiconductors such as GaAs and InP is unpolarized, whereas anisotropic strain produces some degree of polarization. These maps were measured either from the semiconductor surface or from cleaved cross sections. They provide a detailed and complete image of the crystal deformation in the vicinity of the structured stressor film. Finally, we have performed some finite element simulations trying to reproduce the experimental maps. This investigation covering the different steps, including control of the built-in stress within the SiNx thin films, mapping of the anisotropic deformation field generated within the semiconductor beneath the structured films, and numerical simulation of these effects, allows us to propose a set of recipes that can be employed for strain engineering of III-V photonic components. Our simulation scheme is helpful for the design of the photonic components, e.g., to predict the local changes in the refractive index due to the photoelastic effect.

Optimal design of CH4 pyrolysis in a commercial CVD reactor using support vector machines and Nelder-Mead algorithm

Chemical vapour deposition (CVD) of pyrocarbon (PyC) effectively fabricates advanced carbon materials. Controlling the nanotexture of PyC is critical for the desired application. Reactor operating conditions, including temperature, pressure, inlet flow rate, reactant concentration, govern thickness, and film uniformity. The optimal film performance can be obtained by selecting appropriate process conditions. However, the optimisation of the CVD reactor is challenging due to the highly nonlinear and multi-variable nature of the process. In this study, the support vector machine, a robust supervised learning algorithm and Nelder-Mead algorithm are coupled to optimise the CH4 pyrolysis in a commercial CVD reactor. To this end, a comprehensive CFD model for CH4 pyrolysis in a commercial CVD reactor is first constructed. The model accuracy is improved by considering temperature-dependent transport properties of gas mixture and incorporating the detailed gas and surface chemistry (14 species and 32 reactions). The deposition rate and film uniformity are then obtained using a parametric study. Subsequently, the support vector machine (SVM) is employed to deduce the correlation between the PyC growth rate/film uniformity and operating variables. It has been found that the accuracy of SVM is better than the linear regression model. Finally, SVM coupled with the Nelder-Mead algorithm is proposed to optimise the CVD process parameters to maximise the PyC film quality.

Growth of Pseudomorphic GeSn at Low Pressure with Sn Composition of 16.7.

Group-IV alloy GeSn holds great promise for the high-performance optoelectronic devices that can be monolithically integrated on Si for near- and mid-infrared applications. Growth of GeSn using chemical vapor deposition technique with various Sn and Ge precursors has been investigated worldwide. To achieve relatively high Sn incorporation, the use of higher pressure and/or higher order Ge hydrides precursors were reported. In this work, we successfully demonstrated the growth of high-quality GeSn with Sn composition of 16.7% at low pressure of 12 Torr. The alloy was grown using the commercially available GeH4 and SnCl4 precursors via a chemical vapor deposition reactor. Material and optical characterizations were performed to confirm the Sn incorporation and to study the optical properties. The demonstrated growth results reveal a low-pressure growth window to achieve high-quality and high Sn alloys for future device applications.

Hierarchical Carbon Nanofibers@Nickel Phosphide Nanoparticles for High‐Performance Supercapacitors

The design and synthesis of novel active materials as the capacitor electrodes is of great significance to fabricate high‐performance supercapacitors, namely those with large and stable capacitances as well as high power and energy densities. Herein, binder‐free and hierarchical carbon nanofibers@nickel phosphide nanoparticles are grown in a chemical vapor deposition reactor, where Ni5TiO7 nanowires and a TiO2 outer layer are in situ converted into interconnected nickel phosphide nanoparticles and a TiC layer, respectively. The initially formed hierarchical nickel phosphide nanoparticles boost the catalytic growth of CNFs, leading to the generation of a 3D interconnected texture, which features a high specific surface area and excellent conductivity. The combination of this nanocomposite as a capacitor electrode with redox electrolyte of 0.05 m Fe(CN)63−/4− generates a specific capacitance of 59.3 mF cm−2 at a current density of 5 mA cm−2. This capacitor electrode exhibits 95% of its initial capacitance even after 10 000 charging/discharging cycles. The as‐fabricated supercapacitor device offers an energy density of as high as 27.4 Wh kg−1 accompanied with a power density of 7.25 kW kg−1. The proposed method thus provides an approach to produce binder‐/current‐collector‐free capacitor electrodes, which can be utilized to fabricate high‐performance supercapacitors.

Fabrication of silicon PIN diode with SiGe junction for soft x-ray detector using low-temperature technology

In this paper, a low-temperature technology was introduced for the fabrication of PIN photodiode. A double dielectric oxide layers were prepared by nitric acid oxidation and PECVD, respectively. The selective epitaxial growth of SiGe thin layers, which were in-situ doped in a reactive thermal chemical vapor deposition system, were applied for the preparation of PN junction and high-low junction. A SiNx passivation layer combined with a post-annealing was adopted to lower the reverse current. The temperature was controlled below 450 °C for the whole fabrication process. Finally, the reverse current of 0.7 nA was achieved at room temperature for our 5 mm-diameter PIN detector and the energy resolution of 240 eV was obtained at 5.9 keV, −60 °C. The results indicated that the low-temperature technology is suitable for the fabrication of high quality PIN detector, and the cost can be reduced effectively.

Preparation of single-crystal diamond for Small Angle X-ray Scattering in situ loading test

A 2.45 GHz/6 kW cylindrical cavity type microwave plasma chemical vapor deposition reactor was used for the growth of high optical quality single-crystal diamonds. The effects of growth temperature on the surface morphology and crystal quality and the optical properties of the synthesized diamond were studied using optical microscopy, XRD rocking curve, Raman spectroscopy, photoluminescence spectroscopy, Small Angle X-ray Scattering and X-ray topography. Diamond single crystal of the size of Φ7 × 0.5 mm3 were obtained at 1000 °C in a pocket holder with the average growth rate of 7.5 um/h. X-ray rocking curve of the sample was 32 arcsec, while the X-ray transmittance was over 80%. There were no evident NV defects peak in PL. After high pressure blasting test, the diamond windows prepared at 1000 °C can also withstand the pressure of 27 MPa. All these performances were suitable for the windows which was applied on Small Angle X-ray Scattering in situ loading test. Design of a device for Small Angle X-ray Scattering in situ loading test was demonstrated. The device was convenient for the research of material structural changes under high pressure.

Quasistatic Equilibrium Chemical Vapor Deposition of Graphene

AbstractThis study reviews the majorly used chemical vapor deposition (CVD) with a focus on confined reaction configurations in which quasistatic equilibrium conditions are obtained for the fabrication of graphene with large size and high quality through controlled nucleation density, feedstock flux, and growth rates. The confinement configurations can also be used to tune the thickness, domain size and shape, and stacking order of the synthetic graphene. The confined CVD reaction configurations discussed include enclosure systems, inner‐tube setups, sandwiched substrates, as well as other types of configurations. The advantages and limitations of the different confinement configurations are presented, along ways to optimize the operational parameters for them.

Selective Growth and Robust Valley Polarization of Bilayer 3R-MoS2.

Noncentrosymmetric transition-metal dichalcogenides, particularly their 3R polymorphs, provide a robust setting for valleytronics. Here, we report on the selective growth of monolayers and bilayers of MoS2, which were acquired from two closely but differently oriented substrates in a chemical vapor deposition reactor. It turns out that as-grown bilayers are predominantly 3R-type, not more common 2H-type, as verified by microscopic and spectroscopic characterization. As expected, the 3R bilayer showed a significantly higher valley polarization compared with the centrosymmetric 2H bilayer, which undergoes efficient interlayer scattering across contrasting valleys because of their vertical alignment of the K and K' points in momentum space. Interestingly, the 3R bilayer showed even higher valley polarization compared with the monolayer counterpart. Moreover, the 3R bilayer reasonably maintained its valley efficiency over a very wide range of excitation power density from ∼0.16 kW/cm2 to ∼0.16 MW/cm2 at both low and room temperatures. These observations are rather surprising because valley dephasing could be more efficient in the bilayer via both interlayer and intralayer scatterings, whereas only intralayer scattering is allowed in the monolayer. The improved valley polarization of the 3R bilayer can be attributed to its indirect-gap nature, where valley-polarized excitons can relax into the valley-insensitive band edge, which otherwise scatter into the contrasting valley to effectively cancel out the initial valley polarization. Our results provide a facile route for the growth of 3R-MoS2 bilayers that could be utilized as a platform for advancing valleytronics.

Silica Microspheres for Economical Advanced Solar Applications

Solar cells made of silicon nanowires (Si-NWs) have several potential benefits over conventional bulk Si ones or thin-film devices related primarily to light absorption and cost reduction. Controlling the position of Si-NWs without lithography using silica microspheres is indeed an economical approach. Moreover, replacing the glass sheets with polycarbonates is an added advantage. This study employed the Nanoscale Chemical Templating (NCT) technique in growing Si-NWs seeded with Al. The growth was undertaken at the Chemical Vapor Deposition (CVD) reactor via the original growth process of vapor–liquid–solid (VLS). The bottom-up grown nanowires were doped with aluminum (Al) throughout the growth process, and then the p–n junctions were formed with descent efficiency. Further work is required to optimize the growth of Si-NWs between the spun microspheres based on the growth parameters including etching time, which should lead to more efficient PV cells.

High-rate growth of single crystal diamond in AC glow discharge plasma

The detailed experimental behavior of an AC abnormal glow discharge plasma assisted chemical vapor deposition reactor for single crystal diamond (SCD) synthesis operating within the wide-range (20–250 Torr) pressure regime was presented. Within the discharge operating window absorbed power densities of 250–9000 W/cm3 were achieved and high quality SCD synthesis with growth rate up to 80 μm/h was demonstrated. At the power densities over 2500 W/cm3 the diamond substrates were located directly on water-cooled substrate holder without any intermediate molybdenum holder. The influence of several input experimental variables including pressure, N2 and Ar concentration, CH4 percentage, and discharge current on SCD deposition was explored. The quality of synthesized crystals approved competitive purity level of glow discharge CVD process.

One-Step Cost-Effective Growth of High-Quality Epitaxial Ge Films on Si (100) Using a Simplified PECVD Reactor

Heteroepitaxial growth of Ge films on Si is necessary for the progress of integrated Si photonics technology. In this work, an in-house assembled plasma enhanced chemical vapor deposition reactor was used to grow high quality epitaxial Ge films on Si (100) substrates. Low economic and thermal budget were accomplished by the avoidance of ultra-high vacuum conditions or high temperature substrate pre-deposition bake for the process. Films were deposited with and without plasma assistance using germane (GeH4) precursor in a single step at process temperatures of 350–385 °C and chamber pressures of 1–10 Torr at various precursor flow rates. Film growth was realized at high ambient chamber pressures (>10−6 Torr) by utilizing a rigorous ex situ substrate cleaning process, closely controlling substrate loading times, chamber pumping and the dead-time prior to the initiation of film growth. Plasma allowed for higher film deposition rates at lower processing temperatures. An epitaxial growth was confirmed by X-Ray diffraction studies, while crystalline quality of the films was verified by X-ray rocking curve, Raman spectroscopy, transmission electron microscopy and infra-red spectroscopy.

Room Temperature Growth of Silica Nanowires on Top of Ultrathin Si Nanowires Synthesized with Sn‐Cu Bimetallic Seeds

Si nanowires (NWs) are grown by the vapor–liquid–solid method using Cu–Sn bimetallic catalysts in a plasma‐enhanced chemical vapor deposition (PECVD) reactor. The microstructure of the NWs is analyzed by transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. An amorphous SiO2 region, much larger than the native oxide, is present on top of each crystalline SiNW: in SiNWs with diameter below 10 nm, it takes the form of a silica NW of up to 50 nm in length. The new NW separates the initial catalyst particle into one that stays in contact with the SiNW and one or more that lies at the top of the new NW. The former is made of Cu and Cu3Si and contains no Sn, whereas the latter keeps amounts of both elements. The observed microstructure appears to be the result of a mechanism of Si oxidation catalyzed by Cu3Si. The deposit after SiNW growth, in the PECVD reactor, of a protecting 2 nm thick layer of hydrogenated amorphous Si, completely suppresses this mechanism. Reference for future applications based on Cu–Sn‐catalyzed quantum‐sized SiNWs is provided.