Hot-wall Chemical Vapor Deposition Reactor Research Articles

1,4-Bis(trimethylsilyl)piperazine—Thermal Properties and Application as CVD Precursor

We report an investigation into 1,4-Bis-N,N-(trimethylsilyl)piperazine (BTMSP) as a novel precursor for the synthesis of silicon carbonitride films by chemical vapor deposition (CVD). The thermal stability, temperature dependence of vapor pressure and thermodynamic constants of the evaporation process of BTMSP were determined by static tensimetry with a glass membrane zero manometer. The transformation of the compound in low-power (25 W) plasma conditions was investigated by optical emission spectroscopy. It was shown that BTMSP undergoes destruction, accompanied by H and CH elimination and CN formation. SiCN(H) films were deposited in a hot-wall plasma-enhanced CVD reactor. The optical properties of the films were studied by spectral ellipsometry (refractive index: 1.5–2.2; absorption coefficient: 0–0.12) and UV–Vis spectroscopy (transmittance: up to 95%; optical bandgap: 1.6–4.9 eV). Information on the aging behavior of the films is also provided. The transformation of the films occurred through water adsorption and the formation of Si–O bonds with the degradation of Si–H, N–H and Si–CHx–Si bonds.

Impact of Doping on Cross-Sectional Stress Assessment of 3C-SiC/Si Heteroepitaxy.

In this paper, we used micro-Raman spectroscopy in cross-section to investigate the effect of different doping on the distribution of stress in the silicon substrate and the grown 3C-SiC film. The 3C-SiC films with a thickness up to 10 μm were grown on Si (100) substrates in a horizontal hot-wall chemical vapor deposition (CVD) reactor. To quantify the influence of doping on the stress distribution, samples were non-intentionally doped (NID, dopant incorporation below 1016 cm-3), strongly n-type doped ([N] > 1019 cm-3), or strongly p-type doped ([Al] > 1019 cm-3). Sample NID was also grown on Si (111). In silicon (100), we observed that the stress at the interface is always compressive. In 3C-SiC, instead, we observed that the stress at the interface is always tensile and remains so in the first 4 µm. In the remaining 6 µm, the type of stress varies according to the doping. In particular, for 10 μm thick samples, the presence of an n-doped layer at the interface maximizes the stress in the silicon (~700 MPa) and in the 3C-SiC film (~250 MPa). In the presence of films grown on Si(111), 3C-SiC shows a compressive stress at the interface and then immediately becomes tensile following an oscillating trend with an average value of 412 MPa.

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.

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.

Effect of Nitrogen and Aluminum Doping on 3C-SiC Heteroepitaxial Layers Grown on 4° Off-Axis Si (100).

This work provides a comprehensive investigation of nitrogen and aluminum doping and its consequences for the physical properties of 3C-SiC. Free-standing 3C-SiC heteroepitaxial layers, intentionally doped with nitrogen or aluminum, were grown on Si (100) substrate with different 4° off-axis in a horizontal hot-wall chemical vapor deposition (CVD) reactor. The Si substrate was melted inside the CVD chamber, followed by the growth process. Micro-Raman, photoluminescence (PL) and stacking fault evaluation through molten KOH etching were performed on different doped samples. Then, the role of the doping and of the cut angle on the quality, density and length distribution of the stacking faults was studied, in order to estimate the influence of N and Al incorporation on the morphological and optical properties of the material. In particular, for both types of doping, it was observed that as the dopant concentration increased, the average length of the stacking faults (SFs) increased and their density decreased.

Characterization of 4H- and 6H-Like Stacking Faults in Cross Section of 3C-SiC Epitaxial Layer by Room-Temperature μ-Photoluminescence and μ-Raman Analysis.

We report a comprehensive investigation on stacking faults (SFs) in the 3C-SiC cross-section epilayer. 3C-SiC growth was performed in a horizontal hot-wall chemical vapour deposition (CVD) reactor. After the growth (85 microns thick), the silicon substrate was completely melted inside the CVD chamber, obtaining free-standing 4 inch wafers. A structural characterization and distribution of SFs was performed by μ-Raman spectroscopy and room-temperature μ-photoluminescence. Two kinds of SFs, 4H-like and 6H-like, were identified near the removed silicon interface. Each kind of SFs shows a characteristic photoluminescence emission of the 4H-SiC and 6H-SiC located at 393 and 425 nm, respectively. 4H-like and 6H-like SFs show different distribution along film thickness. The reported results were discussed in relation with the experimental data and theoretical models present in the literature.

Application of a Novel CVD TiN Coating on a Biomedical Co-Cr Alloy: An Evaluation of Coating Layer and Substrate Characteristics.

Titanium nitride (TiN) was deposited on the surface of a cobalt–chromium (Co–Cr) alloy by a hot-wall type chemical vapor deposition (CVD) reactor at 850 °C, and the coating characteristics were compared with those of a physical vapor deposition (PVD) TiN coating deposited on the same alloy at 450 °C. Neither coating showed any reactions at the interface. The face-centered cubic (fcc) structure of the alloy was changed into a hexagonal close-packed (hcp) phase, and recrystallization occurred over at 10 μm of depth from the surface after CVD coating. Characteristic precipitates were also generated incrementally depending on the depth, unlike the precipitates in the matrix of the as-cast alloy. On the other hand, the microstructure and phase of the PVD-coated alloy did not change. Depth-dependent nano-hardness measurements showed a greater increase in hardness in the recrystallization zone of the CVD-coated alloy than in the bulk center of the alloy. The CVD coating showed superior adhesion to the PVD coating in the progressive scratch test. The as-cast, PVD-coated, and CVD-coated alloys all showed negative cytotoxicity. Within the limitations of this study, CVD TiN coating to biomedical Co–Cr alloy may be considered a promising alternative to PVD technique.

Influence of Triangle Structure Defect on the Carrier Lifetime of the 4H-SiC Ultra-Thick Epilayer**Supported by the National Key Research and Development Program of China under Grant No 2016YFB0400500.

Effect of triangle structure defects in a 180-μm-thick as-grown n-type 4H-SiC homoepitaxial layer on the carrier lifetime is quantitatively analyzed, which is grown by a horizontal hot-wall chemical vapor deposition reactor. By microwave photoconductivity decay lifetime measurements and photoluminescence measurements, the results show that the average carrier lifetime of as-grown epilayer across the whole wafer is 2.59 μs, while it is no more than 1.34 μs near a triangle defect (TD). The scanning transmission electron microscope results show that the triangle structure defects have originated from 3C-SiC polytype and various types of as-grown stacking faults. Compared with the as-grown stacking faults, the 3C-SiC polytype has a great impact on the lifetime. The reduction of TD is essential to increasing the carrier lifetime of the as-grown thick epilayer.

Reduced order modelling for efficient numerical optimisation of a hot-wall chemical vapour deposition reactor

PurposeThe purpose of this paper is to present a reduced order computational strategy for a multi-physics simulation involving a fluid flow, electromagnetism and heat transfer in a hot-wall chemical vapour deposition reactor. The main goal is to produce a multi-parametric solution for fast exploration of the design space to perform numerical prototyping and process optimisation.Design/methodology/approachDifferent reduced order techniques are applied. In particular, proper generalized decomposition is used to solve the parameterised heat transfer equation in a five-dimensional space.FindingsThe solution of the state problem is provided in a compact separated-variable format allowing a fast evaluation of the process-specific quantities of interest that are involved in the optimisation algorithm. This is completely decoupled from the solution of the underlying state problem. Therefore, once the whole parameterised solution is known, the evaluation of the objective function is done on-the-fly.Originality/valueReduced order modelling is applied to solve a multi-parametric multi-physics problem and generate a fast estimator needed for preliminary process optimisation. Different order reduction techniques are combined to treat the flow, heat transfer and electromagnetism problems in the framework of separated-variable representations.

Hydrogen Etching Influence on 4H-SiC Homo-Epitaxial Layer for High Power Device

The surface preparation of 4H-SiC substrate plays a crucial role for the epitaxial growth. In the present work, the Hydrogen etching influence on 4H-SiC surface of substrate before the growth process was studied. The epi-layer was grown .with a commercial low-pressure, hot-wall Chemical Vapor Deposition (CVD) reactor by Tokyo Electron Limited. The etching time of the surface was increased until three time (x3) respect with the normal value usually adopted for the growth. Photoluminescence and optical inspection analyses show a clear relationship between the etching time and the defectivity. Atomic Force Microscope (AFM) measurements also show an increase of step bunching with the etching time.

Low thermal resistance of a GaN-on-SiC transistor structure with improved structural properties at the interface

The crystalline quality of AlGaN/GaN heterostructures was improved by optimization of surface pretreatment of the SiC substrate in a hot-wall metal-organic chemical vapor deposition reactor. X-ray photoelectron spectroscopy measurements revealed that oxygen- and carbon-related contaminants were still present on the SiC surface treated at 1200°C in H2 ambience, which hinders growth of thin AlN nucleation layers with high crystalline quality. As the H2 pretreatment temperature increased to 1240°C, the crystalline quality of the 105nm thick AlN nucleation layers in the studied series reached an optimal value in terms of full width at half-maximum of the rocking curves of the (002) and (105) peaks of 64 and 447arcsec, respectively. The improvement of the AlN growth also consequently facilitated a growth of the GaN buffer layers with high crystalline quality. The rocking curves of the GaN (002) and (102) peaks were thus improved from 209 and 276arcsec to 149 and 194arcsec, respectively. In addition to a correlation between the thermal resistance and the structural quality of an AlN nucleation layer, we found that the microstructural disorder of the SiC surface and the morphological defects of the AlN nucleation layers to be responsible for a substantial thermal resistance. Moreover, in order to decrease the thermal resistance in the GaN/SiC interfacial region, the thickness of the AlN nucleation layer was then reduced to 35nm, which was shown sufficient to grow AlGaN/GaN heterostructures with high crystalline quality. Finally, with the 35nm thick high-quality AlN nucleation layer a record low thermal boundary resistance of 1.3×10−8m2K/W, measured at an elevated temperature of 160°C, in a GaN-on-SiC transistor structure was achieved.

Synthesis, Characterization, and Thermal Properties of Chlorine‐Containing 1,1,2,2‐Tetraaminodisilanes and Their Potential as Chemical Vapor Deposition Precursors for Silicon Nitride Films

Three chlorine-containing aminodisilanes of the type Cl(RR′N)2Si–Si(NRR′)2Cl (with R = alkyl and R′ = H or R) as potential chemical vapor deposition (CVD) precursors for silicon nitride (SiNx) films have been synthesized and characterized by X-ray diffraction; 1H, 13C, and 29Si NMR spectroscopy; and elemental analysis. They were obtained in high yields by the reactions of hexachlorodisilane (Si2Cl6) with excess liquid amines in diethyl ether through a general single-step procedure. Their thermal properties including stability, volatility, transport behavior, and vapor pressure were evaluated by thermogravimetric analysis (TGA) to confirm that they are suitable for the CVD procedure. The deposition of SiNx films was accomplished with a hot-wall CVD reactor system, which preliminarily verified the suitability of these compounds as CVD precursors.

Investigation of Aluminum Incorporation in 4H-SiC Epitaxial Layers

In the present contribution, the trends in voluntary incorporation of aluminum in 4H-SiC homoepitaxial films are investigated. The films were grown on Si-and C-face 4H-SiC 8°off substrates by chemical vapor deposition (CVD) in a horizontal, hot wall CVD reactor. Secondary Ion Mass Spectrometry (SIMS) and capacitance-voltage (C-V) measurements were used to determine the Al incorporation in the samples. The influence of Trimethylaluminum (TMA) flow rate, growth temperature, growth pressure and C/Si ratio on the dopant incorporation was studied.

Quasi-free-standing monolayer and bilayer graphene growth on homoepitaxial on-axis 4H-SiC(0 0 0 1) layers

Quasi-free-standing monolayer and bilayer graphene is grown on homoepitaxial layers of 4H-SiC. The SiC epilayers themselves are grown on the Si-face of nominally on-axis semi-insulating substrates using a conventional SiC hot-wall chemical vapor deposition reactor. The epilayers were confirmed to consist entirely of the 4H polytype by low temperature photoluminescence. The doping of the SiC epilayers may be modified allowing for graphene to be grown on a conducing substrate. Graphene growth was performed via thermal decomposition of the surface of the SiC epilayers under Si background pressure in order to achieve control on thickness uniformity over large area. Monolayer and bilayer samples were prepared through the conversion of a carbon buffer layer and monolayer graphene respectively using hydrogen intercalation process. Micro-Raman and reflectance mappings confirmed predominantly quasi-free-standing monolayer and bilayer graphene on samples grown under optimized growth conditions. Measurements of the Hall properties of Van der Pauw structures fabricated on these layers show high charge carrier mobility (>2000cm2/Vs) and low carrier density (<0.9×1013cm−2) in quasi-free-standing bilayer samples relative to monolayer samples. Also, bilayers on homoepitaxial layers are found to be superior in quality compared to bilayers grown directly on SI substrates.

Boron nitride: A new photonic material

Rhombohedral boron nitride (r-BN) layers were grown on sapphire substrate in a hot-wall chemical vapor deposition reactor. Characterization of these layers is reported in details. X-ray diffraction (XRD) is used as a routine characterization tool to investigate the crystalline quality of the films and the identification of the phases is revealed using detailed pole figure measurements. Transmission electron microscopy reveals stacking of more than 40 atomic layers. Results from Fourier Transform InfraRed (FTIR) spectroscopy measurements are compared with XRD data showing that FTIR is not phase sensitive when various phases of sp2-BN are investigated. XRD measurements show a significant improvement of the crystalline quality when adding silicon to the gas mixture during the growth; this is further confirmed by cathodoluminescence which shows a decrease of the defects related luminescence intensity.

3C-SiC on Si Hetero-Epitaxial Growth for Electronic and Biomedical Applications

The growth of cubic silicon carbide on silicon, namely 3C-SiC/Si, has been extensively studied at the University of South Florida over the past decade and numerous electronic and biomedical applications explored using this material system. The key step to 3C-SiC devices is the growth of high-quality epitaxial layers of 3C-SiC. In order to improve the manufacturability of future 3CSiC devices, a simplified 3C-SiC growth process on 50 and 100 mm Si (100) substrates has been developed in a low-pressure horizontal hot-wall chemical vapor deposition (CVD) reactor. A simplified growth process consists of a single thermal ramp to the growth temperature followed by the 3C-SiC growth. The 3C-SiC epitaxial layers were characterized via optical microscopy, secondary electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and secondary ion mass spectrometry (SIMS). Examples of biomedical devices realized with this material system are also introduced, including neural probes and in-vitro recording devices, as well as myoglobin and glucose biosensors.

The influence of growth conditions on carrier lifetime in 4H–SiC epilayers

4H–SiC homoepitaxial layers have been grown in a horizontal hot-wall CVD (chemical vapor deposition) reactor and the measured carrier lifetimes have been correlated to the CVD growth conditions. Two different generations of reactors were compared, resulting in measured carrier lifetimes in two different orders of magnitude, from a few hundreds of ns to a few µs. The variations in measured carrier lifetime were correlated to deep level concentrations of the Z1/2 center and the D1 center, seen by photoluminescence. Decreasing the growth temperature clearly prolonged the carrier lifetime and showed lower Z1/2 concentrations, whereas lowering the growth rate only showed a small improvement of the carrier lifetime and no obvious tendency in Z1/2 defect concentrations, indicating that Z1/2 is not the only defect limiting the carrier lifetime. Increasing the C/Si ratio resulted in decreasing Z1/2 concentrations, indicating the carbon vacancy nature of the defect. However, carrier lifetime measurements showed maximum values for a C/Si ratio of 1 but otherwise an increasing tendency for increasing C/Si ratios. The reactor giving higher carrier lifetimes, correspondingly also showed lower Z1/2 concentrations indicating the lifetime limiting property of Z1/2. Furthermore, the D1 defect intensity increased with growth temperature and decreased with increasing C/Si ratio, similar to the Z1/2 concentration.

Process stability and morphology optimization of very thick 4H–SiC epitaxial layers grown by chloride-based CVD

The development of a chemical vapor deposition (CVD) process for very thick silicon carbide (SiC) epitaxial layers suitable for high power devices is demonstrated by epitaxial growth of 200µm thick, low doped 4H–SiC layers with excellent morphology at growth rates exceeding 100µm/h. The process development was done in a hot wall CVD reactor without rotation using both SiCl4 and SiH4+HCl precursor approaches to chloride based growth chemistry. A C/Si ratio <1 and an optimized in-situ etch are shown to be the key parameters to achieve 200µm thick, low doped epitaxial layers with excellent morphology.

Impact of residual carbon on two-dimensional electron gas properties in AlxGa1−xN/GaN heterostructure

High tuneability of residual carbon doping is developed in a hot-wall metalorganic chemical vapor deposition reactor. Two orders of temperature-tuned carbon concentration, from ∼2 × 1018 cm−3 down to ∼1 × 1016 cm−3, can be effectively controlled in the growth of the GaN buffer layer. Excellent uniformity of two-dimensional electron gas (2DEG) properties in AlxGa1−xN/AlN/GaN heterostructure with very high average carrier density and mobility, 1.1 × 1013 cm−2 and 2035 cm2/V·s, respectively, over 3" semi-insulating SiC substrate is realized with the temperature-tuned carbon doping scheme. Reduction of carbon concentration is evidenced as a key to achieve high 2DEG carrier density and mobility.

SiC coatings grown by liquid injection chemical vapor deposition using single source metal-organic precursors

SiC coatings have been grown by direct liquid injection of organosilanes in a hot-wall chemical vapor deposition reactor (DLICVD). 1,3-disilabutane (DSB) and polysilaethylene (PSE) were used as single-source precursors. Amorphous and stoichiometric SiC coatings were deposited under low pressure on various substrates in the temperature range of 923–1073K. Thickness gradients due to the temperature profiles and the precursor depletion were observed along the reactor axis but the thickness uniformity could be improved as a function of the deposition conditions. Growth rates as high as 90μm·h−1 were obtained using pure precursors. The injection of PSE solutions in toluene significantly reduces the deposition rate due to the decrease of the PSE mole fraction but allows a better control of the growth rates and the microstructure of coatings. They exhibit a smooth surface morphology and a very dense structure. The films grown using pure precursors exhibit an Si:C atomic ratio equal to 1:1 while those using toluene solutions are slightly C-rich (54at.% C). The presence of solvent vapor in the CVD reactor becomes a source of carbon contamination at deposition temperatures equal to or higher than 1073K. The influence of the growth conditions is discussed, in particular the presence of toluene vapor.