High‐speed heteroepitaxial growth of 3C‐SiC (111) thick films on Si (110) by laser chemical vapor deposition

3C‐SiC (111) thick films were grown on Si (110) substrate via laser chemical vapor deposition (laser CVD) using hexamethyldisilane (HMDS) as precursor and argon (Ar) as dilution gas. The 3C‐SiC (111) polycrystalline films were prepared at deposition temperature (T_dep) of 1423‐1523 K, whereas the 3C‐SiC (111) epitaxial films were obtained at 1573‐1648 K with the thickness of 5.40 to 9.32 μm. The in‐plane relationship was 3C‐SiC [‐1‐12]//Si [001] and 3C‐SiC [‐110]//Si [‐110]. The deposition rates (R_dep) were 16.2‐28.0 μm/h, which are 2 to 100 times higher than that of 3C‐SiC (111) epi‐grown on Si (111) by conventional CVD. The growth mechanism of 3C‐SiC (111) epitaxial films has also been proposed.     

Infra-red characterization of carbonization of Si surfaces by gas source molecular beam epitaxy

The carbonization and epitaxial growth of cubic SiC films on Si(100) substrates using C₂H₂ and solid Si sources has been investigated by means of infra-red Fourier transform spectroscopy. The carbonization of the Si surface is performed under continuous C₂H₂ flux in two steps: an ordinary process, plus an increase of the substrate temperature to its final value. Subsequent epitaxial films were grown under simultaneous supply of elemental Si and C₂H₂ gas beam. Infra-red reflectivity spectra of samples under different conditions are reported and permit the direct verification for the presence of SiC in carbonized layers, measure the thickness of the films and evaluate their quality.     

Low surface temperature synthesis and characterization of diamond thin films

Polycrystalline diamond films are deposited on p-type Si(100) and n-type SiC(6H) substrates at low surface deposition temperatures of 370–530 °C using a microwave plasma enhanced chemical vapor deposition (MPECVD) system. The surface temperature during deposition is monitored by an IR pyrometer capable of measuring temperature between 250 and 600 °C in a microwave environment. The lower deposition temperature is achieved by using an especially designed cooling stage. The influence of the deposition conditions on the growth rate and structure of the diamond film is investigated. A very high growth rate up to 1.3 μm/h on SiC substrate at 530 °C surface temperature is attributed to an optimized Ar-rich Ar/H₂/CH₄ gas composition, deposition pressure, and microwave power. The structure and microstructure of the films are characterized by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. A detailed stress analysis of the deposited diamond films of grain sizes between 2 and 7 μm showed a net tensile residual stress and predominantly sp³-bonded carbon in the deposited films.     

碳化硅超细粉末形核生长过程的研究

用热化学气相合成法制备的超细SiC粉末的组织结构,保留了许多与形核生长过程直接有关的许多特点,为用高分辨电子显微术研究其形核生长过程提供了有利条件。据此,本文讨论了SiC超细粉末形成的主要机制——均相形核生长过程。它可分为5个主要方面:非晶相核的形成;SiC旋涡状生长及受阻;亚稳的SiC旋涡的析晶;聚结;表面非晶SiC的形成。另外,也分析了固态Si上的SiC的异相成核、外延以及固态Si的碳化过程。     

Fast preparation of (111)‐oriented β‐SiC films without carbon formation by laser chemical vapor deposition from hexamethyldisilane without H2

(111)‐oriented β‐SiC films were prepared by laser chemical vapor deposition using a diode laser (wavelength: 808 nm) from a single liquid precursor of hexamethyldisilane (Si(CH₃)₃–Si(CH₃)₃, HMDS) without H₂. The effects of laser power (P_L), total pressure (P_tot) and deposition temperature (T_dep) on the microstructure, carbon formation and deposition rate (R_dep) were investigated. β‐SiC films with carbon formation and graphite films were prepared at P_L ≥ 170 W and P_to ≥ 1000 Pa, respectively. Carbon formation strongly inhibited the film growth. β‐SiC films without carbon formation were obtained at P_tot = 400‐800 Pa and P_L = 130‐170 W. The maximum R_dep was about 50 μm·h^?1 at P_L = 170 W, P_tot = 600 Pa and T_dep = 1510 K. The investigation of growth mechanism shows that the photolytic of laser played an important role during the depositions.     

Structural study of β‐SiC(001) films on Si(001) by laser chemical vapor deposition

β‐SiC thin films have been epitaxially grown on Si(001) substrates by laser chemical vapor deposition. The epitaxial relationship was β‐SiC(001){111}//Si(001){111}, and multiple twins {111} planes were identified. The maximum deposition rate was 23.6 μm/h, which is 5‐200 times higher than that of conventional chemical vapor deposition methods. The density of twins increased with increasing β‐SiC thickness. The cross section of the films exhibited a columnar structure, containing twins at {111} planes that were tilted 15.8° to the surface of substrate. The growth mechanism of the films was discussed.     

Model of morphology evolution in the growth of polycrystalline β-SiC films

The growth of β-SiC films via chemical vapor deposition (CVD) has been under intensive investigation because this is viewed to be an enabling material for a variety of new semiconductor devices in areas where silicon cannot effectively compete. However, the difficulty in achieving single-crystal or highly textured surface morphology in films with low bulk defect density has limited the use of β-SiC films in electronic devices. Although several researchers have reported results relating the morphology of β-SiC films to deposition parameters, including substrate temperature and gas composition, detailed knowledge of the effects of deposition parameters on film morphology and crystallographic texture is still lacking. If these relationships between deposition parameters and film morphology can be quantified, then it may be possible to obtain optimal β-SiC film morphologies via CVD for specific applications such as high-power electronic devices.The purpose of this study is to predict the dependence of the surface morphology of β-SiC films grown by CVD on substrate temperature and inlet atom ratio of Si:C, and to model the morphological evolution of the growing polycrystalline film. The Si:C ratio is determined by the composition of the reactant gases, propane (C₃H₈) and silane (SiH₄). A two-dimensional numerical model based on growth rate parameters has been developed to predict the evolution of the surface morphology. The model calculates the texture, surface roughness, and grain size of continuous polycrystalline β-SiC films resulting from growth competition between nucleated seed crystals of known orientation. Crystals with the fastest growth direction perpendicular to the substrate surface are allowed to overgrow all other crystal orientations. When a continuous polycrystalline film is formed, the facet orientations of crystals are represented on the surface. In the model, the growth parameter α_2D, the ratio of the growth rates of the {10} and {11} faces, determines the crystal shapes and, thus, the facet orientations of crystals. The growth rate parameter α_2D used in the model has been derived empirically from the textures of continuous β-SiC films reported in the literature.     

Remote hydrogen microwave plasma chemical vapor deposition of silicon carbonitride films from a (dimethylamino)dimethylsilane precursor: Characterization of the process,chemical structure,and surface morphology of the films

Amorphous hydrogenated silicon carbonitride (a-Si:C:N:H) films were produced by remote microwave hydrogen plasma CVD (RP-CVD) using (dimethylamino)dimethylsilane as single-source precursor. The effect of the substrate temperature (T_S) on the rate and yield of the RP-CVD process, chemical composition, chemical structure, and surface morphology of resulting film is reported. The temperature dependencies of the mass- and thickness-based growth rate and growth yield of the film imply that for low substrate temperature range (T_S = 30–100 °C) film growth is limited by desorption of film-forming precursors, whereas in high substrate temperature range (T_S = 100–400 °C) film growth is independent of the temperature and RP-CVD is mass-transport limited process. The increase of the substrate temperature from 30 to 400 °C causes the elimination of organic moieties from the film and the formation of Si–N and Si–C network structures. The films were found to be morphologically homogeneous materials exhibiting very small surface roughness, which vary in a narrow range of values.     

Epitaxial growth of 3C–SiC on Si(111) and (001) by laser CVD

Epitaxial 3C–SiC films have been deposited on Si(111) and Si(001) substrates via laser CVD with deposition rate of 12.32 and 15.56 μm/h, respectively. The activation energy of 3C–SiC on Si(111) and Si(001) was 80 and 160 kJ/mol, and the root mean square (RMS) roughness (w) as a function of the film thickness (h) follows power laws of w~h^0.31 and w~h^0.06, respectively. The growth mechanisms of epitaxial 3C–SiC films on Si(111) and Si(001) was investigated based on the structural analysis and roughness evolution.     

Role of oxygen in surface kinetics of SiO2 growth on single crystal SiC at elevated temperatures

Understanding surface kinetics of SiO₂ growth on single crystal SiC at elevated temperatures is crucial to fabricate high-performance SiC-based devices. However, the role of oxygen in the evolution mechanism of SiC surface at atomic scale has not been comprehensively elaborated. Here, we reveal the manipulation effect of oxygen on the competitive growth of thermal oxidation SiO₂ (TO-SiO₂) and thermal chemical vapor deposition SiO₂ (TCVD-SiO₂) on the 4H-SiC substrate at 1500 °C. TO-SiO₂ is formed by the thermal oxidation of SiC, in which the substrate undergoes layer-by-layer oxidation, resulting in an atomically flat SiC/TO-SiO₂ interface. TCVD-SiO₂ growth includes the sublimation of Si atoms, the reaction between sublimated Si atoms and reactive oxygen, and the adsorption of gaseous Si_xO_y species. A relatively high sublimation rate of Si atoms at SiC atomic steps causes the transverse evolution of the nucleation sites, leading to the formation of nonuniform micron-sized pits at the SiC/TCVD-SiO₂ interface. The low oxygen concentration favors TCVD-SiO₂ growth, whose crystal quality is much better than that of TO-SiO₂ due to the high surface mobility in the thermal CVD process. We further achieve the epitaxial growth of graphene on 4H-SiC in an almost oxygen-free reaction atmosphere. Additionally, ReaxFF reactive molecular dynamic simulation results illustrate that the decrease in oxygen concentration can promote the growth kinetics of SiO₂ on single crystal SiC from being dominated by thermal oxidation to being dominated by thermal CVD.     

The Effect of Si Substitution for SiC on SHS in the Ti–Si–C System

Investigated was the effect of Si substitution for SiC on SHS in the Ti–Si–C system. Starting powders were intermixed to obtain 3Ti–SiC–C and 3Ti–Si–2C green mixtures and then green compacts by uniaxial pressing. The influence of heating rate, reactor temperature, and replacement of SiC by Si was studied by XRD, SEM, and TEM. In combustion products obtained in optimized conditions, Ti₃SiC₂ was found to be predominant. In comparison with conventional methods, our products obtained in a one-step low-temperature process contained minimal amounts of undesired impurities and required no finishing processes such as chemical purification.     

Mechanical and field emission properties of CGed Si(C,N) films synthesized by PECVD from HMDS precursor

Compositionally graded (CGed) Si(C,N) films were prepared by Ar/H₂/N₂ plasma enhanced chemical vapor deposition from liquid injected hexamethyldisiloxane precursor. The films were characterized by scanning/transmission electron microscopy (SEM/TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Monolithic crystalline SiC and amorphous SiN_x films were produced from Ar/H₂ and Ar/H₂/N₂ thermal plasma, respectively. The CGed SiC–SiN_x film was obtained by changing N₂ flow rate from 2 L/min to zero in Ar/H₂/N₂ during the deposition process, and it was composed of an uppermost crystalline SiC layer, a thin intermediate layer containing nanocomposite c-SiC/a-SiN_x and an innermost layer of amorphous SiN_x. The CGed SiN_x–SiC film, in which SiN_x acts as a top layer with a SiC layer underneath, was fabricated by an inverse change of the plasma gas supply from initial Ar/H₂ to Ar/H₂/N₂. Microhardness increase and promising field emission properties were obtained from these CGed films in comparison with monolithic SiC and SiN_x films.     

Comparison of the efficiency of various substrates in growing vertically aligned carbon nanotube carpets

Vertically aligned multi-walled carbon nanotube (VACNT) carpets have been synthesized on metal and isolating thin films without the use of a pre-deposited catalyst. We used ferrocene as precursor powder catalyst and acetylene as a carbon source to grow VACNT carpets using three-temperature-zone chemical vapor deposition (TTZ-CVD). Tuning the carrier gas Ar flow rate and the sublimation time of ferrocene in the TTZ-CVD extended the lifetime of the catalyst, increasing the efficiency of growth. Increasing the number of ferrocene loads increased the growth height of VACNT carpets on metal and isolating thin films. The effective growth rates of VACNT carpets were 10.4, 7.13, 4.8, 3, 2, 9.55, 7.6, 13.3, and 32.32 μm/min, respectively, on Cu, Ti, Au, Pt, Mo, Cr, Ag, Ni, and Si. VACNT carpets such as SiO₂ and Al₂O₃ also grew on the isolating thin films with growth rates of 37.28 and 23.8 μm/min, respectively. By controlling the growth parameters, the growth of VACNT carpets on selective substrates can be controlled.     

Strain modification in epitaxial 2H-AlN layers on 3C-SiC/Si(111) pseudo-substrates

Optical measurements are used to investigate the crystalline quality and the stress in thin AlN layers; these thin films are grown on cubic silicon carbide layers which are in turn grown on silicon (111) substrates. Different Ge amounts were deposited at the silicon substrate in order to reduce the lattice parameters mismatch between Si and SiC grown layers. The residual stress of the hexagonal AlN layers is derived from the phonon frequency shifts of the E₁(TO) phonon mode. The crystalline quality of AlN films is investigated by considering the intensity of E₁(TO) mode of the 2H-AlN and its full width of the half maximum (FWHM). Ge deposition at low temperature 325 °C, before the carbonization process leads to an improved crystalline quality and a reduced residual stress in the AlN/SiC/Si heterostructures. The best crystalline quality and the lowest stress value are found in the case where 1ML Ge amount was predeposited. The E₁(TO) mode, phonon frequency shifts-down by 3 cm^? 1/GPa with respect to an unstrained layer. The obtained values for the phonon deformation are in reasonable agreement with theoretical calculations.     

Optimization of the ceramization process for the production of three-dimensional biomorphic porous SiC ceramics by chemical vapor infiltration (CVI)

The ceramization process for the preparation of three-dimensional (3D) biomorphic porous SiC ceramics by chemical vapor infiltration (CVI) with methyltrichlorosilane/hydrogen mixture has been optimized in this work. As a first step, two alternative ceramization routes have been compared with each other with regard to composition, morphology and bending strength of the resulting ceramics using flat samples. Optimal ceramization route was found to be a three-step process including carbonization of the paper preforms, followed by chemical vapor infiltration with stoichiometric SiC layers and a final oxidation step, in which the residual carbon from the template (C_b) is burnt out of the ceramics. Based on these results 3D honeycomb structures have been ceramized. Prior to these experiments, a computational fluid dynamics simulation of the gas flow in the reactor and through the honeycomb structure has been performed with the software STAR-CD. As a result, homogeneously infiltrated three-dimensional structured SiC ceramics could be produced.     

Preparation strategy for low-stress and uniform SiC-on-diamond wafer: A silicon nitride dielectric layer

Reducing the self-heating of SiC- and GaN/SiC-based high-powered devices by integrating diamond films offers promising performance enhancement of these devices. However, such a reduction strategy faces serious problems, such as diamond nucleation on SiC and stress accumulation greater than 10 GPa. In this work, a SiN_x dielectric layer (～50 nm) was coated onto the C polar face of a 4H–SiC wafer using microwave plasma chemical vapor deposition (MPCVD) to improve direct dense diamond nucleation and growth, significantly reduce the stress, and build Si–C(SiC)?Si?C(diamond) bond bridges. This SiN_x thin layer, prepared by activating Si ions under Ar/N plasma during magnetron sputtering, gave rise to local Si₃N₄ crystal features and a low effective work function (EWF) for promoting surface dipoles with electronegative carbon-containing groups. In the H plasma environment during diamond growth, the local Si₃N₄ crystal was amorphized, and the N atoms escaped as a result of atomic H and the high temperature. At the same time, C atoms diffused into the SiN_x and formed C–Si bonds (49.7% of the total C bonds) by replacing N–Si and Si–Si, thus increasing the direct nucleation density of the diamond grains. The diamond thin film grew rapidly and uniformly, with a grain size of approximately 2 μm in mixed orientation, and the stress of the 2-inch SiC-on-diamond wafer was extremely low (to ～0.1–0.2 GPa). In comparison, partially connected diamond grains (>10 μm) on the bare SiC in the preferential (110) orientation resulted in a film with twin-grain features and significant stress, which was associated with the hexagonal lattice interface of 4H–SiC. These results are considered the material and surface/interface bases for actively controlling wafer fabrication and enhancing the heat dissipation of SiC and GaN/SiC electronics.     

Influence of nitrogen gas over microstructural,vibrational and mechanical properties of CVD Titanium nitride (TiN) thin film coating

In this experimental investigation, the influence of different N₂ gas flow rates on different properties (e.g. morphological, mechanical, etc.) of chemical vapor deposited (CVD) Titanium nitride (TiN) coatings has been discussed. The TiN coatings had been grown on Si (100) substrate at elevated temperature (1000 °C) using Titanium dioxide (TiO₂) powder. SEM images reveal a dense uniform microstructure with an irregular surface pattern. The surface roughness of the coatings was found to be increased from 12.42 to 28.56 nm with an increase in flow rate. XRD results indicate a B1 NaCl crystal structure of the film with reduced crystallite size with the increasing N₂ flow rate. Through the corrosion test, it has been observed that due to the variation of N₂ flow rate the corrosion resistance of the films decreases with increasing N₂ flow rate. The mismatch of thermal expansion co-efficient in between Si substrate and TiN thin film reduces with higher N₂ flow rate. The acoustic and optic phonon mode of TiN coatings have been shifted to higher intensities with higher N₂ flow rate. The mechanical properties of the film reveal that the maximum value of hardness (H) and Young's modulus (E) are 30.14 and 471.85 GPa respectively.     

Structural characteristics and ablative behavior of C/C–ZrC–SiC composites reinforced with “Z-pins like” Zr–Si–B–C multiphase ceramic rods

In order to improve the ablation and oxidation resistance of C/C–ZrC–SiC composites in wide temperature domain, “Z-pins like” Zr–Si–B–C multiphase ceramic rods are prepared in the matrix. The influence of different sintering temperatures on the microstructure of ceramic rods and the ablative behavior of heterogeneous composites are studied. The results showed that the ZrB₂ and SiC phases are formed in the sintered matrix, and the increase of sintering temperature is beneficial to improve the density of the ceramic rods. The ablation properties of samples have been greatly improved. The mass and linear ablation rate are 0.8 mg/s and 3.85 μm/s, respectively, at an ablation temperature of 3000 °C and an ablation time of 60 s. After ablation, the matrix surface is covered with SiO₂ and ZrO₂ mixed oxide films. This is due to the preferential oxidation of “Z-pins like” Zr–Si–B–C multiphase ceramic rods in the ablation process, and B₂O₃ melt, SiO₂ melt, borosilicate glass, ZrSiO₄ melt and ZrO₂ oxide film can be generated successively from the low-temperature segment to the ultra-high temperature segment. These oxidation products can be used as compensation oxide melts for the healing of cracks and holes on the matrix surface in different temperature ranges and effectively prevent the external heat from spreading into the matrix. Therefore, C/C–ZrC–SiC composites with “Z-pins like” Zr–Si–B–C multiphase ceramic rods achieve ablation resistance in wide temperature domain.     

Thermodynamic approach to the vaporization and growth phenomena of SiC ceramics. I. SiC and SiC-SiO2 mixtures under neutral conditions

Matter transport by vaporization and condensation processes during sintering or consolidation of SiC components at high temperature is analysed using thermodynamics of the binary Si-C and ternary Si-C-O systems. The erosion flows due to vaporization and the potential growth flow of SiC are calculated in order to determine the conditions prevailing at the surface of SiC powder grains. Pure SiC vaporization leads to rapid precipitation of carbon at the SiC surface. Vaporization of SiC-SiO₂ mixtures under neutral atmospheric conditions or absolute vacuum contributes to the rapid departure of any Si or C impurities first of all, and then silica according to congruent vaporization in the SiC-SiO₂ pseudo-binary system. The calculated SiC growth rate by vapour transport is always less than the erosion rate and further subsequent growth of pure SiC cannot be obtained as long as silica co-exists with SiC.     

Effects of CCl4 concentration on nanocrystalline diamond film deposition in a hot-filament chemical vapor deposition reactor

The effect of CCl₄ concentration on the nanocrystalline diamond (NCD) films deposition has been investigated in a hot-filament chemical vapor deposition (HFCVD) reactor. NCD films with a thickness of few-hundred nanometers have been synthesized on Si substrates from 2.0% and 2.5% CCl₄/H₂ at a substrate temperature of 610 °C. Polycrystalline diamond films and nanowall-like films with higher formation rates than those of the NCD films were deposited from lower and higher CCl₄ concentrations, respectively. The grain sizes of the diamond film grown using 2.0% CCl₄ increased with film thickness while a diamond film with uniform nanocrystalline structure all over a thickness of 1 μm can be deposited in the case of 2.5% CCl₄. We suggest that both the primary nucleation and the secondary nucleation processes are crucial for the growth of the NCD films on Si substrates.