Commercial Chemical Vapor Deposition Research Articles

Development of GeSn epitaxial films with strong direct bandgap luminescence in the mid-wave infrared region using a commercial chemical vapor deposition reactor

Germanium tin (GeSn) is a material of interest for electronic and photonic device applications, but its development and commercialization have been limited by material quality issues and lack of availability from epitaxy suppliers. In this paper, we report initial studies in optimizing GeSn films deposited on a Ge buffer layer grown on 200-mm diameter silicon (Si) substrates with an ASM Epsilon 2000 chemical vapor deposition reactor designed for commercial production. Using a single-step growth process, a Sn content up to 22% near the surface of a GeSn film was achieved due to the increase in Sn incorporation via strain relaxation. A two-step growth process resulted in a bilayer structure with a nearly 100% relaxation on the first layer, followed by a higher quality GeSn layer with 18% Sn as evident by a high photoluminescence intensity emitting in the mid-wave infrared region at 3.2 μm at 20 K.

Sustainable preparation of aminosilane monomers, oligomers, and polymers through Si-N dehydrocoupling catalysis.

This article covers historical and recent efforts to catalyse the dehydrocoupling of amines and silanes, a direct method for Si-N bond formation that offers hydrogen as a byproduct. In some applications, this transformation can be used as a sustainable replacement for traditional aminosilane synthesis, which demands corrosive chlorosilanes while generating one equivalent of ammonium salt waste for each Si-N bond that is formed. These advantages have driven the development of Si-N dehydrocoupling catalysts that span the periodic table, affording mechanistic insight that has led to advances in efficiency and selectivity. Given the divergence in precursors being used, characterization methods being relied on, and applications being targeted, this article highlights the formation of monomeric aminosilanes separately from oligomeric and polymeric aminosilanes. A recent study that allowed for the manganese catalysed synthesis of perhydropolysilazane and commercial chemical vapor deposition precursors is featured, and key opportunities for advancing the field of Si-N dehydrocoupling catalysis are discussed.

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.

Modelling of ethanol pyrolysis in a commercial CVD reactor for growing carbon layers on alumina substrates

Chemical vapour deposition (CVD) is widely used for preparation of pyrolytic carbons from various precursors. The prediction of deposition kinetics requires deep understanding of all transport phenomena involved. In this work, we perform the computational modelling of ethanol pyrolysis in a commercial CVD reactor (a tube furnace). The reactor is employed for growing carbon layers on alumina substrates. The inlet gas flow is produced by evaporating azeotrope ethanol/water mixture and mixing it with inert gas (argon). The modelling is performed in 3D and 2D statements using Marinov mechanism with 57 species participating in 383 reactions. The heat and species transport is taken into account with temperature dependent physical properties. It is shown that the inlet gas velocity in the 2D statement should be corrected for a meaningful comparison with the 3D case. A good agreement is found between species mole fractions at the substrate position for 3D and 2D statements at low volume flow rates, while at high flow rates some deviations are observed. The temperature at the substrate position is found to be lower than at the reactor wall due to inflow of a colder gas. The main pyrolysis products at moderate temperatures (around 900 °C) are water, ethylene, hydrogen, carbon monoxide, and methane. With increasing temperature, the mole fractions of hydrogen, acetylene, and carbon monoxide increase, while those of water and methane become smaller. With increasing ethanol/water volume flow rate, the mole fractions of ethanol and pyrolysis products saturate at some constant values due to incomplete thermal decomposition of ethanol in the reactor volume. The rise of argon flow rate leads to the decrease of pyrolysis products mole fractions due to decrease of residence time. The obtained results can be employed for simulating and analyzing pyrolysis processes in realistic CVD reactors with complex geometry as well as for the development of coupled gas phase and surface reaction model of carbon layer deposition on nanoporous substrates.

Homoepitaxial growth of multiple 4H-SiC wafers assembled in a simple holder via conventional chemical vapor deposition

Although homoepitaxial growth of multiple 4H-SiC wafers in one run can be realized in commercial specialized chemical vapor deposition equipment, wafers must be loaded onto a rotatable large susceptor and overspread on it, which leads to the diameter of the susceptor increases as the number or the total area of the epitaxial wafer increases. in this work, we demonstrated a facile method for growth of multiple 4H-SiC wafers assembled in a simple holder via a home-made single-wafer conventional chemical vapor deposition equipment without a large susceptor. The structural properties of the obtained 4H-SiC films on each wafer were investigated by means of optical microscope, AFM, SEM and Raman. Results showed that high quality of homogeneous 4H-SiC film was epitaxially grown on the inner region of each wafer, while on the outer region, influenced by the mechanical parts of the simple holder, the quality was degraded. At last we draw a prospective on homoepitaxial growth of whole wafer through further reducing the adverse outer region via advanced holder and wafer assembly, which could greatly improve production efficiency and reduce energy consumption.

Upgrade of the compact neutron spectrometer for high flux environments

In this paper new version of the 6Li-based neutron spectrometer for high flux environments is described. The new spectrometer was built with commercial single crystal Chemical Vapour Deposition diamonds of electronic grade. These crystals feature better charge collection as well as higher radiation hardness. New metal contacts approaching ohmic conditions were deposited on the diamonds suppressing build-up of space charge observed in the previous prototypes. New passive preamplification of the signal at detector side was implemented to improve its resolution. This preamplification is based on the RF transformer not sensitive to high neutron flux. The compact mechanical design allowed to reduce detector size to a tube of 1 cm diameter and 13 cm long. The spectrometer was tested in the thermal column of TRIGA reactor and at the DD neutron generator. The test results indicate an energy resolution of 300 keV (FWHM), reduced to 72 keV (RMS) excluding energy loss, and coincidence timing resolution of 160 ps (FWHM). The measured data are in agreement with Geant4 simulations except for larger energy loss tail presumably related to imperfections of metal contacts and glue expansion.

Fabrication of submillimeter-sized single-crystalline graphene arrays by a commercial printing-assisted CVD method

Submillimeter-sized single-crystalline graphene arrays have been successfully prepared by a commercial printing-assisted chemical vapor deposition method.

A Facile Method for Heteroepitaxial Growth of Homogeneous 3C-SiC Thin Films on Both Surfaces of Suspended Si Wafer by Conventional Chemical Vapor Deposition

Although epitaxial growth of Si films on both surfaces of silicon wafer (epi-Si/Si-wafer/epi-Si) can be realized in foundry by means of mounting certain amounts of silicon wafers in a boat in commercial specialized chemical vapor deposition equipment (s-CVD), for its counterpart epi-SiC/Si-wafer/epi-SiC, neither is it readily realized in s-CVD, nor is it easily achieved in conventional chemical vapor deposition equipment (c-CVD) which is generally used for growth of 3C-SiC on single surface of silicon wafer (epi-SiC/Si-wafer). Since the growth of epi-SiC/Si-wafer/epi-SiC in one run is more efficient, and is anticipated, in this work, we demonstrated a facile method for growth of epi-SiC/Si-wafer/epi-SiC in c-CVD. The Si wafer was double-side polished and mounted in a suspension mode on the susceptor in the c-CVD chamber. It was found that homogeneous 3C-SiC(100) films were heteroepitaxially grown on both surfaces of the suspended Si(100) wafer simultaneously. The structural and electrical properties of the obtained 3C-SiC films on both surfaces were investigated by means of SEM, XRD, Raman and J-V measurements. Results showed that each film was uniform and continuous, with same trend of slight degradation from the inner to the outer region of the wafer. This indicated a possible way of making mass production of high quality 3C-SiC films on Si wafers in one run in c-CVD for the potential applications such as sensors, with working principle based on voltage drop difference of two back-to-back diodes on epi-SiC/Si-wafer/epi-SiC, or graphene growth from epi-SiC/Si-wafer/epi-SiC templates.

A combined CFD modeling and experimental study of pyrolytic carbon deposition

Understanding the chemical reaction mechanism and deposition kinetics is of great importance to guide the production of pyrolytic carbon (PC). A practical approach to mimic the commercial chemical vapor deposition (CVD) process and eventually predict the PC deposition rate is highly desired. In this work, a simplified two-step reaction mechanism was proposed for the CVD of PC, with the first step in the gas phase and the second step on the substrate surface. The kinetic parameters were determined by trial and error using a computational fluid dynamics simulation. The velocity, temperature, and concentration profiles in a cold-wall, forced-flow reactor were modeled based on the geometry and experimentally determined boundary conditions. The computed PC deposition rates for substrate temperatures between 700 and 3000°C were in good accordance with experimental results. Rate limiting steps were observed for both the deposition experiments and simulations. Mass-transport-limited and reaction-limited regimes were identified in wide temperature and flow rate ranges. A higher deposition rate was found in a cold-wall reactor compared with those in an insulated reactor or a hot-wall reactor. Finally, the PC microstructure was characterized using optical microscopy, scanning electron microscopy, Raman spectroscopy, and X-ray diffraction, demonstrating progressive development of graphitization with increasing deposition temperature.

Reduced-Pressure Chemical Vapor Deposition Growth of Isolated Ge Crystals and Suspended Layers on Micrometric Si Pillars.

In this work, we demonstrate the growth of Ge crystals and suspended continuous layers on Si(001) substrates deeply patterned in high aspect-ratio pillars. The material deposition was carried out in a commercial reduced-pressure chemical vapor deposition reactor, thus extending the "vertical-heteroepitaxy" technique developed by using the peculiar low-energy plasma-enhanced chemical vapor deposition reactor, to widely available epitaxial tools. The growth process was thoroughly analyzed, from the formation of small initial seeds to the final coalescence into a continuous suspended layer, by means of scanning and transmission electron microscopy, X-ray diffraction, and μ-Raman spectroscopy. The preoxidation of the Si pillar sidewalls and the addition of hydrochloric gas in the reactants proved to be key to achieve highly selective Ge growth on the pillars top only, which, in turn, is needed to promote the formation of a continuous Ge layer. Thanks to continuum growth models, we were able to single out the different roles played by thermodynamics and kinetics in the deposition dynamics. We believe that our findings will open the way to the low-cost realization of tens of micrometers thick heteroepitaxial layer (e.g., Ge, SiC, and GaAs) on Si having high crystal quality.

Efficient tracing and stability analysis of multiple stationary and periodic states with exploitation of commercial CFD software

A computational approach is presented that enables commercial Computational Fluid Dynamics (CFD) codes to detect Hopf bifurcations and with necessary adjustments, compute the frequency and amplitude of the periodic orbits that arise from the Hopf point. The proposed computational framework, which combines a homemade Matlab code with Ansys/Fluent, is an extension of a previously presented methodology for the efficient tracing of solution branches that contain turning points. The need for the special attention to periodic orbits springs from recently published results that indicate that time-periodic states occur in industrial-scale Chemical Vapor Deposition (CVD) reactors. Nevertheless the method presented here is not limited to deposition processes; in fact it treats the CFD process model as a “black box” and requires no alteration of the commercial software. To prove the effectiveness of the computational framework, it is implemented here on the benchmark case of laminar flow around a cylinder, where Hopf bifurcations have been identified via eigenvalue analysis. Once the method is validated, it is implemented on a rotating-disk commercial CVD reactor model in the region of parameter space where Hopf points are observed. In both the benchmark and the industrial-scale CVD cases, stable and unstable, stationary and periodic states are computed for the same parameter values.

Tetrasilane and digermane for the ultra-high vacuum chemical vapor deposition of SiGe alloys

Tetrasilane and digermane were used to grow epitaxial silicon germanium layers on silicon substrates in a commercial ultra-high vacuum chemical vapor deposition tool. Films with concentrations up to 19% germanium were grown at temperatures from 400°C to 550°C. For all alloy compositions, the growth rates were much higher compared to using mono-silane and mono-germane. The quality of the material was assessed using X-ray diffraction, atomic force microscopy, and spectroscopic ellipsometry; all indicating high quality epitaxial films with low surface roughness suitable for commercial applications. Studies of the decomposition kinetics with regard to temperature were performed, revealing an unusual growth rate maximum between the high and low temperature deposition regimes.

Structural Tuning Using a Novel Membrane Reactor for Carbon Nanotube Synthesis

ABSTRACTCarbon nanotubes come in many varieties, with chemical, mechanical, and electrical properties depending on carbon nanotube (CNT) structural morphology. In order to provide a platform for CNT structural tuning, a membrane reactor was designed and constructed. This reactor provided more intimate gas-catalyst contact by decoupling the carbon feedstock gas from carrier gas in a chemical vapour deposition (CVD) environment using an asymmetric membrane and a macroporous membrane. Growth using this membrane reactor demonstrated normalized yield improvements of ∼300% and ∼1000% for the asymmetric and macroporous membrane cases, respectively, over standard CVD methods. To illustrate the possibility for control, growth variation with time was successfully demonstrated by growing vertically aligned multi-walled CNTs to heights of 0.71 mm, 1.36 mm, and 1.84 mm after growth for 15, 30, and 60 minutes in a commercial thermal CVD reactor. To demonstrate CNT diameter control via catalyst particle size, dip coating and spray coating methods were explored using ferrofluid and Fe(NO3)3 systems. CNT diameter was demonstrated to increase with increasing particle size, yielding CNT like growth with diameters ranging from 15 -150 nm. Demonstration of these dimensions of control coupled with the dramatic efficiency increases over growth in a commercialized CVD reactor establish this new reactor technology as a starting point for further research into CNT structural tuning.

Growth and Characterization of Epitaxial Ge1-XSnx Alloys and Heterostructures Using a Commercial CVD System

Fully strained and relaxed epitaxial Ge1-xSnx alloys with Sn contents up to 12 at. % have been grown on Ge buffered Si using an Epsilon® 2000 Plus commercial chemical vapor deposition system. Using a specialized growth approach intrinsic, p-type, and n-type alloys have been demonstrated. Material and optical characterization of these alloys indicate that the alloys are of high crystal quality in which the Sn is fully substitutional. Heterostructures of doped Ge/Ge1-xSnx/Ge have also grown to demonstrate their application in light emitting and detecting devices. Phosphorus doped Ge1-xSnx photoluminescence has also been observed at wavelengths up to 2.4 μm. Growth, materials and optical properties of these materials will be discussed.

Growth and Characterization of Epitaxial Ge1-XSnx Alloys and Heterostructures Using a Commercial CVD System

Group IV alloys incorporating Sn have several possible applications ranging from optoelectronics to stress engineering in FinFET based CMOS designs. From an optoelectronics perspective the benefits of incorporating Sn into Ge is realized in the reduction of the difference between the direct and indirect band gap transitions resulting in more efficient luminescence/ absorption. Furthermore, alloys of Ge1-xSnx are theoretically expected to become a direct band gap material for Sn contents of approximately 10 at. % [1]. With regards to logic applications of Sn containing alloys the possibilities include the passive function as a common strain relieved buffer (SRB) for both NMOS and PMOS applications as well as PMOS S/D stressor for an active GeSn channel FinFET devices [2]. Given these potential application one of the key issues lies in the lack of viable growth process on a commercial deposition system.The Ge1-xSnx alloys and Ge buffer layers presented here were grown in an ASM Epsilon® 2000 Plus chemical vapor deposition (CVD) system This system is ideally suited for the low deposition temperatures required to form these metastable alloys. A specialized growth approach has been adopted to grow the Ge1-xSnx layers at temperatures of less than 450°C.Material and optical characterization of these alloys indicate that the materials are of high crystal quality. Figure 1 shows a series symmetrical (004) 2θ-ω XRD scans for Ge1-xSnx alloys with Sn contents ranging from 0.5 to 10 at. % in which the perpendicular lattice constant increases with Sn content. Rutherford Backscattering Spectroscopy (RBS) in combination with ion channeling was used to verify the thickness and composition of the alloys as well as to determine substitutionality of the Sn within the Ge lattice (Fig.1). The thickness and composition of these alloys was in close agreement with those obtained from SIMS. Further structural characterization of the Ge1-xSnx alloys was obtained by cross-sectional Transmission Electron Microscopy (XTEM) analysis. Figure 3 shows a bright field XTEM image of a Ge0.93Sn0.07/Ge/Si heterostructure in which no threading defects are observed propagating through the GeSn epilayer. Room temperature photoluminescence studies of the as-deposited alloys show a strong well-defined peak which shifts to lower energy with increasing Sn contents. Growth of heterostructures with different alloy compositions have also been demonstrated in which abrupt compositional transitions are observed. Optical devices based on these alloys have been fabricated.

Material Characterization of Ge1−x Sn x Alloys Grown by a Commercial CVD System for Optoelectronic Device Applications

High-quality compressive-strained Ge1−xSnx/Ge films have been deposited on Si(001) substrate using a mainstream commercial chemical vapor deposition reactor. The growth temperature was kept below 450°C to be compatible with Si complementary metal–oxide–semiconductor processes. Germanium tin (Ge1−xSnx) layers were grown with different Sn composition ranging from 0.9% to 7%. Material characterizations, such as secondary-ion mass spectrometry, Rutherford backscattering spectrometry, and x-ray diffraction analysis, show stable Sn incorporation in the Ge lattice. Comparison of the Sn mole fractions obtained using these methods shows that the bowing factor of 0.166 nm (in Vegard’s law) is in close agreement with other experimental data. High-resolution transmission electron microscopy and atomic force microscopy results show that the films have started to relax through the formation of misfit and threading dislocations. Raman spectroscopy, ellipsometry, and photoluminescence (PL) techniques are used to study the structural and optical properties of the films. Room-temperature PL of the films shows that 7% Sn incorporation in the Ge lattice results in a decrease in the direct bandgap of Ge from 0.8 eV to 0.56 eV.

Morphology evolution of MOCVD grown GaN epitaxial layers on nanoPSS

AbstractNanoscale patterned sapphire substrates (NPSS) were fabricated through nanoimprint lithography (NIL) technology and etching treatment. With optimized growth conditions, high‐quality GaN epilayers were epitaxially grown by commercial metal organic chemical vapor deposition (MOCVD) system. Structural and optical properties were studied. Better imprint stamp as well as faster transition between different growth modes during lateral epitaxial growth were found to be two important factors that improve the crystal quality and reduce the density of the defects. A new kind of irregular circular mesas was observed with random distribution, which may come from accelerated growth by template imperfection. Considering the evolution of pattern size and density, possible origin of such structure has been proposed. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Etch‐pit formation mechanism induced on HPHT and CVD diamond single crystals by H2/O2 plasma etching treatment

AbstractH2/O2 plasma treatments offer advantages over other etching processes of diamond as a technique to prepare the substrate surface prior to chemical vapor deposition (CVD) diamond growth. It allows removing defects induced on the surface by polishing, thus leading to an improved morphology and limiting the stress within the grown crystal. Moreover, they present the advantage to be performed in situ just before the CVD diamond growth. In this work, H2/O2 plasma treatments were performed so that threading dislocations and other defects are etched preferentially, thus leaving typical etch‐pits. The defect densities in several high pressure high temperature (HPHT) and CVD diamond crystals were then quantified and compared; in particular defects originating from polishing could be distinguished from extended defects inside the crystal. Furthermore, the defect density was found to be of the order of 105/cm2 for HPHT crystals, which was approximately one order of magnitude lower than that measured in low cost commercial CVD monocrystals. The use of laser microscopy also allowed observing the morphology, size and depth of different etch‐pits of 〈001〉‐oriented and misoriented crystals and their evolution with etching time in order to get a better understanding of defect density and formation during CVD growth.

Raman analysis of epitaxial graphene grown on 4H—SiC (0001) substrate under low pressure condition

In this paper, we report a feasible route of growing epitaxial graphene on 4H—SiC (0001) substrate in a low pressure of 4 mbar (1 bar=105 Pa) with an argon flux of 2 standard liters per minute at 1200, 1300, 1400, and 1500 °C in a commercial chemical vapour deposition SiC reactor. Using Raman spectroscopy and scanning electron microscopy, we confirm that epitaxial graphene evidently forms on SiC surface above 1300 °C with a size of several microns. By fitting the 2D band of Raman data with two-Lorentzian function, and comparing with the published reports, we conclude that epitaxial graphene grown at 1300 °C is four-layer graphene.

Merging Standard CVD Techniques for GaAs and Si Epitaxial Growth

A commercial Chemical Vapor Deposition (CVD) system, the ASMI Epsilon 2000 designed for Si and SiGe epitaxy, has, for the first time, been equipped for the growth of GaAs compounds in a manner that does not exclude the use of the system also for Si-based depositions. With the new system, intrinsic, Si-doped and Ge-doped GaAs epitaxial layers with excellent quality have been grown on GaAs substrate wafers by the decomposition of trimethylgallium (TMGa) and AsH3 in the reactor at reduced pressure and at temperatures in the 600-700°C range. A low AsH3 concentration, 0.7 % in H2, is used as one of the precursors, which has the added advantage that the severe safety precautions always associated with MOCVD systems need not be implemented.