Hot-wall CVD Reactor Research Articles

Surface morphology of 3C–SiC layers grown on 4H–SiC substrates using TCS as silicon precursor

The hetero-epitaxial growth of 3C–SiC layers on on-axis 4H–SiC substrates has been demonstrated in a hot-wall CVD reactor using trichlorosilane and ethylene as precursors. The additional chlorine is supplied by hydrogen chloride for variation of Cl/Si ratio. The influence of temperature, C/Si ratio and Cl/Si ratio process parameters on the morphology is studied. Double-position-boundaries free 3C–SiC epitaxial layers have been successfully grown at the optimized condition, which is at a temperature of 1340 °C, with C/Si = 0.6 and Cl/Si = 6 using a carbon-rich pretreatment. Low temperature near bandgap photoluminescence shows a good optical property of the obtained 3C–SiC epitaxial layers. Compared to the standard chemistry, a higher growth rate of 12 μm/h could be achieved by utilizing the chlorinated precursors. This study provides a feasible way to grow double-position-boundaries free 3C–SiC epitaxial layers using TCS as silicon precursor.

Insights into the effect of susceptor rotational speed in CVD reactor on the quality of 4H-SiC epitaxial layer on homogeneous substrates

In this work, 4H-SiC homoepitaxial layers were grown on 4°off-axis substrates at different susceptor rotation speeds by using a hot-wall horizontal CVD reactor. The effect of different susceptor rotation speed on the quality of 4H-SiC epitaxial layers in terms of thickness, thickness uniformity, crystallinity, surface morphology and morphological defects was investigated via Fourier transform infrared spectroscopy (FTIR), high-resolution X-ray diffraction (XRD), atomic force microscopy (AFM), confocal differential interference contrast microscopy (CDIC), ultra-violet photo-luminescence spectroscopy (UV-PL), scanning electron microscopy (SEM), and micro-Raman spectroscopy, respectively. A flow field simulation was performed to explain the impact of susceptor rotation speed on the film deposition. The FTIR results suggested that the susceptor rotation speed could be an important factor to adjust thickness uniformity and deposition rate. The XRD patterns showed that crystallinity was independent of the susceptor rotation speed. The surface morphology can be improved by changing the susceptor rotation speed. According to CDIC scans, the down-fall related defects were reduced through the increase in the susceptor rotation speed. The origin of down-fall related defects was interpreted by Raman spectroscopy and speculative models. To sum up, the susceptor rotation speed is a crucial factor in increasing growth rate and improving uniformity. Also, the faster susceptor rotation speed helps reduce the number of down-fall related defects in the hot-wall CVD reactor.

MT-CVD Ti(C,N,O) coatings controlled by CO: Microstructure evolution and its effect on the hardness

Incorporation of oxygen into Ti(C,N) coating by CO doping during moderate temperature chemical vapor deposition (MT-CVD) process is a promising strategy for enhancing the performance of cutting tools. In this work, Ti(C,N,O) coatings were prepared by MT-CVD in a hot-wall industrial-scale CVD reactor with increased CO volume fraction from 0 % to 8.0 % in the feed gas mixture. Microstructure evolution is revealed by high-resolution scanning electron microscopy, electron backscatter diffraction detector, and high-resolution transmission electron microscopy. Its effect on the hardness is investigated. The results show that as the CO fraction increases, the microstructure changes from columnar and large faceted grains to equilateral and nanoscale grains. An increasing density of plane defects including twins, especially Σ3 twin boundaries and stacking faults are identified in Ti(C,N,O) coatings with increasing CO fraction. The hardness of Ti(C,N,O) coatings increase from 26 GPa at 0 % CO to 34 GPa at 8.0 % CO, due to the grain refinement, solution strengthening, increased stacking faults, twins and {111} texture. A considerably lower rate of hardness increase is observed at CO fractions above 4.0 %, which is hypothesized to be related to grain boundary sliding, residual chlorine and excessive density stacking faults.

The Optimizing Effect of Nitrogen Flow Ratio on the Homoepitaxial Growth of 4H-SiC Layers

In this study, a 4H-SiC homoepitaxial layer was grown on a 150 mm 4° off-axis substrate using a horizontal hot-wall CVD reactor. The research aimed to investigate the impact of varying the C/Si ratio and temperature while also changing the N2 flow rate and N2 flow ratio on the growth rate (thickness), doping, surface roughness, and uniformity of the large-size 4H-SiC epitaxial layer. The results indicate that the growth rate and thickness uniformity of the film increases with an increase in the C/Si ratio. Additionally, adjusting the N2 flow rate in a timely manner based on the change in the C/Si ratio is crucial to achieving the best epitaxial layer doping concentration and uniformity. The study found that, as the temperature increases, the film thickness and thickness uniformity also increase. The maximum thickness recorded was 6.2 μm, while the minimum thickness uniformity was 1.44% at 1570 °C. Additionally, the surface roughness reached its lowest point at 0.81 nm at 1570 °C. To compensate for the difference in thickness and doping concentration caused by temperature distribution and uneven airflow, the N2 flow ratio was altered. In particular, at a growth temperature of 1570 °C, a N2 flow ratio of 1.78 can improve the uniformity of doping by 4.12%.

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

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

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

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

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

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

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

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

High Quality 4H-SiC Epitaxial Layer by Tuning CVD Process

In this work many steps concerning the epitaxial layer growth on 4H-SiC are studied, evaluated and optimized to obtain high quality 4H-SiC epitaxy. The processes evaluated have been studied on a Hot Wall CVD reactor. The first step related to the substrate surface etching has been tuned by choosing the H2 flow, temperature and process time at which most of defects (mainly stacking faults) are not propagated. Then, the buffer layer step has been optimized by increasing the thickness at which an effective reduction of defect density and an improved electrical performance of power devices have been detected. Also, during the buffer layer growth a strong dependence between basal plane dislocations propagation and the growth rate has been observed. A crucial step carefully studied has been the drift layer growth. It was optimized by increasing the growth rate (13&lt;GR&lt;15µm/h) that results in a lower defectiveness, good thickness and doping uniformity. Final stage concerning the cooling of the process has been strongly revisited. A significant decreasing of the morphological defects (carrots, pits) and stacking faults has been observed by slowing the cool down process (~ 25 °C/min).

New SiC Epitaxial Growth Process with up to 100% BPD to TED Defect Conversion on 150mm Hot-Wall CVD Reactor

The future challenges for SiC device technology are cost reduction and increased reliability. A key point to achieve that is the increase of yield during epitaxial layer growth through the reduction of structural defects (such as basal plane dislocations and triangle defects), an increased thickness and doping uniformity, and a high growth rate. Despite significant advancements in SiC epitaxial growth technology, it still constitutes a big challenge to find the optimum working point at which all those requirements are fulfilled. By implementing a new epitaxial layer growth process, we are able to grow basal plane dislocation free epitaxial layers, while the density of other structural defects remains low. Additionally, intra-wafer thickness and doping uniformities of the epitaxial layers are further improved.

Homoepitaxial Growth on Si-Face (0001) On-Axis 4H-SiC Substrates

Homoepitaxial growths of 4H-SiC were performed on Si-face (0001) on-axis substrates in a SiH4-C2H4-H2-HCl system by using our home-made vertical hot wall CVD reactor. The influence mechanism of the growth temperature and C/Si ratio on the morphology and growth rate was studied. It is found that the steps in the epilayer become more clear with the increasing temperatures. The result indicates that the C/Si ratio window of on-axis epitaxial growth is very narrow. Only when the C/Si ratio was 1.2, a slightly improved surface morphology can be achieved. The results indicate that 4H-SiC epitaxial layers were obtained on on-axis substrates and the films were highly-oriented 4H-SiC.

Volatile zirconium complexes with sterically hindered β-diketonates: Structure and thermal properties

The structure and thermal properties of a novel zirconium(IV) complex with a methoxy substituted β-diketonate ligand tetrakis-(2-methoxy-2,6,6-trimethylheptane-3,5-dionato)zirconium are described. The complex sublimes without decomposition under low pressure (10–2 Torr) at 200 °C. The crystal structure of the complex is molecular and is composed of two structural Zr(zis)4 isomers in a 1:1 ratio. The crystallographic data are as follows: C88H152F24O24Zr2, P-1, a = 12.1350(7) A, b = 19.7733(10) A, c = 21.0526(12) A, α = 83.338(2)°, β = 89.571(2)°, γ = 73.515(2)°, V = 4809.5(5) A3, Z = 2, d = 1.227 g/cm3. The coordination environment of the zirconium atom consists of eight oxygen atoms from four β-diketonate ligands; the coordination polyhedron is a square antiprism. The Zr–O distances are in a range 2.127-2.202 A. The thermal properties of the complex are studied by TG–DTA. The effect of the crystal structure (molecular packing) on the volatility and thermal properties is compared for the new complex and two other analogous zirconium complexes with β-diketonate ligands containing bulky terminal substituents. The results of the mass spectrometric study of thermal behavior of the complexes on programmed heating of vapor under the conditions similar to those in a hot wall CVD reactor under low pressure, including the decomposition in the presence of oxygen, are discussed.

Preparation and characterization of an oxide-oxide continuous fiber reinforced ceramic matrix composite with a zinc oxide interphase

In this study, metal organic chemical vapor deposition (MOCVD) was used to deposit zinc oxide (ZnO) for use as a ceramic matrix composite (CMC) interphase. ZnO coatings (400–500nm) were deposited on 3M Nextel™ 610 fabric by thermal decomposition of zinc acetate dihydrate in a low pressure hot wall CVD reactor. An α-alumina matrix was applied to the 8 ply fabric lay up for a total CMC porosity of 30% with 32% fiber volume. The morphology, structure and strength of the resulting continuous fiber CMC were characterized in conjunction with a control CMC with no interphase. The results show that when a zinc acetate dihydrate precursor is used, a functional interphase can be obtained. Flexural strength of the Oxide-Oxide CMC could be increased up to 30% upon addition of this oxide interphase with corresponding toughening mechanisms.

A germanium(II) aminopyridinato compound and its potential as a CVD precursor

A germanium(II) aminopyridinato compound has been synthesized and characterized by 1H and 13C NMR spectroscopy, elemental analysis and X-ray diffraction. It was easily obtained in high yield through a salt-elimination reaction by mixing the corresponding lithium salt and the GeCl2-dioxane adduct. Thermal properties, including stability, volatility, transport behavior and vapor pressure, were evaluated by thermogravimetric analysis (TGA) to confirm that it is suitable for the CVD procedure. Deposition was accomplished in a hot-wall CVD reactor system, which verified its ability as a CVD precursor for the fabrication of germanium containing films.

150mm Silicon Carbide Selective Embedded Epitaxial Growth Technology by CVD

In this work, we have developed a selective embedded epitaxial growth process on 150-mm-diameter wafer by vertical type hot wall CVD reactor with the aim to realize the all-epitaxial 4H-SiC MOSFETs [1, 2, 3, 4, 5]. We found that at elevated temperature and adding HCl, the epitaxial growth rate at the bottom of trench is greatly enhanced compare to growth on the mesa top. And we obtain high growth rate 7.6μm/h at trench bottom on 150mm-diameter-wafer uniformly with high speed rotation (1000rpm).

A family of 1,1,1,2,2,2-hexa(-primary-)amino-disilanes as potential CVD precursors: Tuning thermal properties by small variation of the substituent

A family of 1,1,1,2,2,2-hexaamino-disilanes with the formula (RHN)3Si-Si(NHR)3 (R=nPr, iPr, nBu, iBu, sBu, Cy) as precursors for the CVD growth of silicon-based films has been synthesized and characterized by 1H NMR, 13C NMR, 29Si NMR, EI-HRMS, elemental analysis and X-ray diffraction where necessary. Thermal properties, including stability, volatility, transport behavior and vapor pressure were evaluated by thermogravimetric analysis (TGA) to verify that thermal properties of the precursors can be tuned by small variation of the substituents form secondary amino to primary amino units and to confirm their suitability for the CVD procedure. Finally, deposition was accomplished in a hot wall CVD reactor, which preliminarily verified the ability of these compounds as CVD precursors.

Early stages of growth and crystal structure evolution of boron nitride thin films

A study of the nucleation and crystal structure evolution at the early stages of the growth of sp2-BN thin films on 6H-SiC and α-Al2O3 substrates is presented. The growth is performed at low pressure and high temperature in a hot wall CVD reactor, using ammonia and triethylboron as precursors, and H2 as carrier gas. From high-resolution transmission electron microscopy and X-ray thin film diffraction measurements we observe that polytype pure rhombohedral BN (r-BN) is obtained on 6H-SiC substrates. On α-Al2O3 an AlN buffer obtained by nitridation is needed to promote the growth of hexagonal BN (h-BN) to a thickness of around 4 nm followed by a transition to r-BN growth. In addition, when r-BN is obtained, triangular features show up in plan-view scanning electron microscopy which are not seen on thin h-BN layers. The formation of BN after already one minute of growth is confirmed by X-ray photoelectron spectroscopy.

Low Pressure Homoepitaxial Growth of 4H-SiC on 4°off-Axis Substrates

Step-bunching and triangular defects are significant problems in achieving higher growth rate 4H-SiC epilayers in a horizontal hot wall CVD reactor using a standard non-chlorinated chemistry of silane-propane-hydrogen on 4°off-axis substrates. In this work, the impact of growth pressure on generation of step-bunching and triangular defects and the correlations between the surface roughness and the formation of defects were investigated. It has been found that the impact of growth pressure on concentration of the triangle defects and surface roughness is obviously different. An overall reduction of defects was observed with decreasing growth pressure while the surface roughness increased. The increased adatom surface mobility in low pressure range and minimization of surface free energy are the main reasons for the phenomenon above. High Resolution X-Ray Diffraction (HRXRD) indicated that the structural quality of 4H-SiC epilayers performed at low pressure was higher than that obtained at high pressure.

Assessment of H-intercalated graphene for microwave FETs through material characterization and electron transport studies

Epitaxial graphene is grown on semi-insulating (SI) 4H-SiC in a hot wall CVD reactor by graphitization and in-situ intercalation with (H)ydrogen. A holistic material characterization is performed in order to ascertain the number of layers, layer uniformity, and electron transport properties of the epi-layers via electronic test structures and Raman spectroscopy. Bilayer graphene field effect transistors (GFETs) are fabricated using a full electron beam lithography (EBL) process which is optimized for low contact resistances of rc<0.2Ωmm. Mobilities of order 2500cm2/Vs are achieved on bilayer samples after fabrication. The devices demonstrate high transconductance gm=400mS/mm and high current density Ids=1.8A/mm. The output conductance at the bias of maximum transconductance is gds=300mS/mm. The GFETs demonstrate an extrinsic ftext and fmaxext of 20 and 13GHz, respectively and show 6dB power gain at 1GHz in a 50Ω system, which is the highest reported to date.

The influence of pressure on growth of 3C-SiC heteroepitaxial layers on silicon substrates

3C-SiC epitaxial layers were grown on on-axis (100)- and (110)-oriented silicon substrates in a RF heated horizontal hot-wall CVD reactor. We focused on the relationship between the pressure used during carbonization growth and the crystalline quality of obtained layers. A comprehensive analysis of the surface morphology of the 3C-SiC carbonization layer was performed, after which two pressure values guaranteeing top crystalline quality were determined. The carbonization layer with the lowest surface roughness was obtained at around 20mbar, while for 30mbar, the surface roughness was slightly worse but more homogenous. To sum up, we successfully grew 1.5µm thick 3C-SiC layers on silicon substrates with both orientations using the said pressure conditions.