Chemical Vapor Deposition Reactor Research Articles

Manufacturing of Gallium Nitride Thin Films in a Multi-Wafer MOCVD Reactor

Abstract Gallium nitride (GaN) thin films have attracted considerable attention for manufacturing optical and electronic devices. They have wide bandgap and superb performance in these applications. The reliability and durability of optoelectronic devices depend on the quality of the GaN thin films. The metal-organic chemical vapor deposition (MOCVD) process is a common manufacturing technique for fabricating high-quality thin films. By manipulating the operating conditions and the reactor design, one can control the deposition rate and the uniformity of the thin film. In this paper, the manufacturing process for GaN thin films in a multi-wafer MOCVD reactor is simulated based on the three-dimensional computational model of an experimental system which provides data for validation as well as realistic design parameters. The reactor pressure and the flow rate of the precursor, trimethyl-gallium (TMG), significantly affect the deposition rate and film uniformity. The incursion of impurities in the deposition can be reduced by increasing the volumetric ratio of NH3 to TMG (V/III) and reducing the reactor pressure. The deposition rate and quality of the thin film are enhanced using an appropriate mixture of H2 and N2 as the carrier gas. The design of the inlet can also be varied to improve the utilization of metal-organic precursors and increase the deposition rate. This paper presents and discusses results on these aspects for this important manufacturing process. Thus, it leads to a better understanding of the basic mechanisms involved and provides guidelines for obtaining high deposition rates with high film quality in practical chemical vapor deposition reactors.

CFD simulation of CVD reactors in the CH3SiCl3(MTS)/H2 system using a two-step MTS decomposition and one-step SiC growth models

In this study, we report on a computational fluid dynamics (CFD) simulation of the chemical vapor deposition reactor of silicon carbide (SiC) in the methyltrichlorosilane (MTS, CH3SiCl3)/H2 system. The formation of SiC thin film is controlled by various process parameters, such as temperature and pressure. In this study, we propose a reaction mechanism of MTS decomposition to SiC growth on a substrate surface for CVD reactors in the CH3SiCl3(MTS)/H2 system. The reaction mechanism has two gas-phase pyrolysis reactions and one SiC film formation reaction. However, we individually build and validate MTS decomposition and SiC growth models to reduce uncertainty. An in-house version of reactingFoam, a reactive flow solver within OpenFOAM v2006, was used as the simulation tool. Our model accurately reproduced MTS decomposition for T = 1100–1350 K and [H2]/[MTS] = 2.65–14 at p = 101,325 Pa. Then, the MTS decomposition model was coupled with the SiC growth model, and the coupled model was applied to the SiC deposition data. The model could reproduce multiple datasets through validation studies.

Investigation of the cap layer for improved GeSn multiple quantum well laser performance.

The study of all-group-IV SiGeSn lasers has opened a new avenue to Si-based light sources. SiGeSn heterostructure and quantum well lasers have been successfully demonstrated in the past few years. It has been reported that, for multiple quantum well lasers, the optical confinement factor plays an important role in the net modal gain. In previous studies, adding a cap layer was proposed to increase the optical mode overlap with the active region and thereby improve the optical confinement factor of Fabry-Perot cavity lasers. In this work, SiGeSn/GeSn multiple quantum well (4-well) devices with various cap layer thicknesses, i.e., 0 (no cap), 190, 250, and 290 nm, are grown using a chemical vapor deposition reactor and characterized via optical pumping. While no-cap and thinner-cap devices only show spontaneous emission, the two thicker-cap devices exhibit lasing up to 77 K, with an emission peak at 2440 nm and a threshold of 214 kW/cm2 (250 nm cap device). The clear trend in device performance disclosed in this work provides guidance in device design for electrically injected SiGeSn quantum well lasers.

The influence of droplet-based seeding of nanodiamond particles on the morphological, optical, and mechanical properties of diamond coatings on glass

This work investigates four different methods for the seeding of nanodiamond (ND) particles towards applying nanocrystalline diamond coatings on glass. The standard spin coating and dip coating are investigated together with two droplet-based techniques, ink-jet printing and ultrasonic spray coating (USSC). The application of these last two techniques for diamond coatings on glass is novel and is specifically designed for patterning and large area deposition, respectively. Comparing the seeding processes, their impact on the chemical vapor deposited nanocrystalline diamond (NCD) layers is unclear. Here, particularly the impact on the morphological, optical, and mechanical properties, are studied. In this work, borosilicate glass substrates were seeded, after which diamond layers were grown in a linear antenna microwave plasma-enhanced chemical vapor deposition reactor to thicknesses of 45, 100, and 500 nm. The coatings showed a roughness that is 2 to 3 times higher for the droplet-based seeding techniques compared to spin coating. It was found that the optical absorption coefficient for 100 nm thick samples prepared using USSC was 2400 cm−1 at the wavelength of 550 nm, compared to 1500 cm- 1 using spin and dip seeding techniques. The stress in the film was compressive as determined by curvature measurements. Sand-trickling tests on samples coated with 100 nm thick diamond films showed similar resistance against damaging for all seeding techniques without delamination. Therefore, the different techniques achieve mechanically competitive performance. On top USSC and ink-jet printing have the opportunity to fully cover substrates on large-scale flat and even 3D surfaces, or pattern fine structures, which is not possible for standard spin and dip coating. It can be concluded that diamond coatings on large glass plates for scratch resistance, and sensing due their somewhat higher roughness, are within reach using these innovative droplet-based seeding technologies.

Numerical Simulation of Graphene Growth by Chemical Vapor Deposition Based on Tesla Valve Structure

Chemical vapor deposition (CVD) has become an important method for growing graphene on copper substrates in order to obtain graphene samples of high quality and density. This paper mainly focuses on the fluid flow and transmission phenomenon in the reactor under different process operating conditions and reactor structures. Two macroscopic physical parameters that are established as important for CVD growth are temperature and pressure. Based on the special structure of a miniature T45-R Tesla valve acting as a CVD reactor structure, this study uses numerical simulation to determine the effect of the pressure field inside a Tesla valve on graphene synthesis and temperature variation on the graphene surface deposition rate. This macroscopic numerical modeling was compared to the existing straight tube model and found to improve the graphene surface deposition rate by two orders of magnitude when the 1290–1310 K reaction temperature range inside the Tesla valve was maintained and verified through the experiment. This study provides a reference basis for optimizing the reactor geometry design and the effects of changing the operating parameters on carbon deposition rates during a CVD reaction, and will furthermore benefit future research on the preparation of high-quality, large-area, and high-density graphene by CVD.

Growth behavior of CVD Ti(C,N,O) coating on cemented carbide controlled by CO and the mechanism

In α-Al2O3-based chemical vapor deposition (CVD) coatings, Ti(C,N)- or Ti(C,N,O)-based layer exerts a significant influence on the crystal growth of α-Al2O3 and the performance of the coated cemented carbide cutting tools. To explore the reinforcement measures and the related mechanism of α-Al2O3-based coating, the effect of CO volume fraction from 0 to 8% on the growth behavior of Ti(C,N,O) on cemented carbide is systematically investigated. Both multilayer and monolayer Ti(C,N,O) coatings and Ti(C,O) intermediate were deposited at 830 °C in an industrial-scaled hot-wall CVD reactor. Experimental results show that CO reacts with TiCl4 in the H2 atmosphere, resulting in the formation of nanocrystalline Ti(C0.5,O0.5) with a slow growth rate. Thermodynamic calculation reveals that with the increase of CO fraction, the equilibrium partial pressure of HCN increases, which is a vital gas-phase for the formation of Ti(C,N,O). As a result, grain refinement and increase in the growth rate and oxygen content of Ti(C,N,O) coating are achieved by increasing the CO fraction and hence the amount of Ti(C0.5,O0.5) with strong reactivity. The growth mechanism of Ti(C,N,O) concerning the codeposition and their in situ reaction of Ti(C,N) and Ti(C,O) is proposed, and the related phenomena of preferential growth transformation and Cl residue in Ti(C,N,O) coating are discussed.

Inherent selective pulsed chemical vapor deposition of aluminum oxide in nm scale

Inherent selective pulsed chemical vapor deposition (CVD) of aluminum oxide on Si and SiO2 in preference to SiCOH has been studied. SiCOH is alkyl (-CxHy) terminated SiO2, which was used as a non-reactive surface. For aluminum oxide deposition, pulsed CVD processes using aluminum tri sec-butoxide (ATSB) and trimethylaluminum (TMA) were tested. ATSB alone can induce a pulsed thermal CVD reaction to selectively deposit aluminum oxide at 300 °C sample temperature; ∼4 nm of aluminum oxide were selectively deposited on Si and SiO2 in preference to SiCOH. By adding a periodical pulse of TMA during ATSB pulses, higher selectivity was achieved with ∼12 nm and ∼14 nm of aluminum oxide on Si and SiO2 with around 0.4–0.5 nm root mean square (RMS) roughness at 330 °C. The high selectivity persisted on the nanoscale: STEM showed that ∼10 nm of aluminum oxide could be selectively deposited on nanoscale patterned features. The selectively deposited AlOx films showed low k (∼4) dielectric performance with low leakage (around 10−6 A/cm2 at ± 2 V for a 15 nm thick film). This selective aluminum oxide pulsed CVD process has the potential to be applicable in nanoscale fabrication, such as low k spacer and etch stop layer.

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.