Chemical Vapor Deposited Silicon Carbide Research Articles

Mechanism of Silicon Carbide Film Deposition at Room Temperature Using Monomethylsilane Gas

The mechanism of silicon carbide chemical vapor deposition on a silicon surface using a monomethylsilane gas at room temperature was studied. Because the silicon carbide film surface tended to have large hillocks at the high monomethylsilane gas concentrations, the surface chemical reaction for the silicon carbide film formation was considered to include a three-dimensional pass, even at room temperature. The composition of the obtained film was consistent with that expected from the film formation process. Because the lowest temperature of hydrogen annealing for enabling the silicon carbide film formation coincided with the lowest temperature for practically removing the native oxide film by the hydrogen annealing, the silicon dimer at the silicon surface formed by the hydrogen annealing and the cooling in ambient hydrogen was concluded to play a key role.

Demonstration of PECVD SiC–SiO$_{2}$–SiC Horizontal Slot Waveguides

We report on the first demonstration of guiding light in horizontal slot-waveguides using a plasma-enhanced chemical vapor deposition silicon carbide (SiC)-silicon oxide (SiO2)-SiC structure. Propagation losses of 23.9 ±1.2 dB/cm have been measured for the quasi-transverse-magnetic mode of the fabricated slot waveguides at 1.3 ?m .

Theoretical Study of the Pyrolysis of Methyltrichlorosilane in the Gas Phase. 3. Reaction Rate Constant Calculations

The rate constants for the gas-phase reactions in the silicon carbide chemical vapor deposition of methyltrichlorosilane (Ge, Y. B.; Gordon, M. S.; Battaglia, F.; Fox, R. O. J. Phys. Chem. A 2007, 111, 1462.) were calculated. Transition state theory was applied to the reactions with a well-defined transition state; canonical variational transition state theory was applied to the barrierless reactions by finding the generalized transition state with the maximum Gibbs free energy along the reaction path. Geometry optimizations were carried out with second-order perturbation theory (MP2) and the cc-pVDZ basis set. The partition functions were calculated within the harmonic oscillator and rigid rotor approximations. The final potential energy surfaces were obtained using the left-eigenstate coupled-cluster theory, CR-CC(2,3) with the cc-pVTZ basis set. The high-pressure approximation was applied to the unimolecular reactions. The predicted rate constants for more than 50 reactions were compared with the experimental ones at various temperatures and pressures; the deviations are generally less than 1 order of magnitude. Theory is found to be in reasonable agreement with the experiments.

A study on the thermoelectric properties of chemical vapor deposited SiC films with temperature and diluent gases variation

Chemical vapor deposited (CVD) silicon carbide (SiC) provides many advantages over other materials due to its high thermal, chemical and mechanical stability at high temperature. For these reasons, CVD SiC has replaced Si in components for semiconductor process. For application of CVD SiC to semiconductor fabrication equipment, thermoelectric properties controls are important. Therefore, we have studied the effects of different diluent gases, deposition temperatures and microstructures of deposited SiC on change of thermoelectric properties. The electrical conductivity of SiC which used N2 diluent gas was larger than SiC deposited with H2 diluent gas. Electrical resistivity varied by an order of 102 for different diluent gases at the same deposition temperature, and Seebeck coefficient also depended on the gas used. Additionally, SiC deposited with H2 showed n-type semiconductor behavior while that deposited with N2 showed p-type characteristics.

Fabrication and characteristics of a PECVD SiC evanescent wave optical sensor

This work presents a simple evanescent wave-sensing system based on plasma-enhanced chemical vapour deposition (PECVD) silicon carbide (SiC) waveguides. Thin SiC films were deposited on Si substrates with a SiO 2 film acting as a cladding layer around the carbide core. In the sensor, the evanescent tale of the light travelling in a waveguide senses an absorbant medium placed above the waveguide. By using a 1 × 2 power splitter, the sensor is calibrated using one arm as a reference. This shows that the sensitivity of such a sensor is improved by choosing SiC as waveguide material compared to silicon nitride (SiN) films.

Surface finishing of new type RS-SiC ceramics

The bending strength of a new type Reaction Sintered Silicon Carbide (RS-SiC) is about two times that of other SiC ceramics. In this research, the surface finishing of three types of SiC ceramics, RS-SiC, Pressure less Sintered Silicon Carbide (PS-SiC) and Chemical Vapour Deposition Silicon Carbide (CVD-SiC), were performed with Electrolytic In-process Dressing (ELID) mirror grinding technique. The grinding force and micro-hardness were investigated for the new type RS-SiC. It was found that the micro-hardness of the near-surface layer could increase by more than 80% under special finishing conditions. The mechanism of the 'near-surface hardening' phenomenon was discussed. In addition, a lightweight RS-SiC mirror with 250 mm in diameter was finished by ELID technique and as a result the surface roughness reached 1.5 nm Root Mean Square (RMS).

Strength measurement of a brittle coating with a trilayer structure using instrumented indentation and in situ observation techniques

A mechanical-testing method, devised to measure the strength of brittle thin coatings with a trilayer structure, was investigated. A semi-empirical relationship among radial cracking and associated parameters was derived by introducing a buffer and coating layer with an effective thickness concept, extending the established bilayer equation. Adjustable parameters of the proposed trilayer equation were determined for various ratios of coating thicknesses and moduli. The validity of the FEA-based relationship was analyzed by an experimental method utilizing a graphite/glass/substrate structure. An in situ observation of radial cracks through the transparent substrate during sphere indentation enabled the determination of the strength of the thin coating layer. Chemical vapour-deposited silicon carbide films were used to evaluate the strength and Weibull modulus using the present technique, in a case study format. The validity of the trilayer equation in terms of critical load for radial cracking and the strength of the thin brittle coating are discussed. This study can contribute to knowledge in the area of evaluating brittle thin coating systems on a compliant substrate.

PDL free plasma enhanced chemical vapor deposition SiC optical waveguides and devices

Planar silicon carbide (SiC) waveguides are proposed for fabrication on a silicon substrate with an oxide isolation layer. Using post deposition annealing it is possible to achieve low polarisation-dependent loss (PDL) within optical SiC waveguides fabricated using a low temperature deposition technique. The proposed waveguides are optically characterised and successfully used in power splitters and vibration sensors. Results before and after annealing cycles for those devices are discussed. The interesting optical characteristics of SiC waveguides as well as the first passive components presented open the way for photonic sensing in harsh environment where SiC is a very promising material.

Silicon-Carbide Microfabrication by Silicon Lost Molding for Glass-Press Molds

This paper describes two silicon carbide (SiC) microfabrication processes for SiC glass-press molds. One is silicon lost molding combined with SiC chemical-vapor deposition (CVD) and SiC reaction sintering (RS). The other is silicon lost molding combined with SiC CVD and SiC solid-state reaction bonding (SSRB). In both of these processes, an original pattern on a silicon substrate is transferred to a CVD SiC film, and then the film is backed by bulk SiC to obtain rigidity and robustness against pressing force. Finally, the silicon substrate is etched away to release a SiC mold. In the process using SiC CVD and RS, an original pattern on a silicon substrate was transferred to a SiC mold, but the surface roughness of the SiC mold was 0.05-0.08 /spl mu/m Ra, and worse than required by the glass-press mold. This was caused by the transformation of amorphous SiC to polycrystalline SiC in RS, which was confirmed by the X-ray diffraction (XRD) data of the CVD SiC film before and after RS. In the process using SiC CVD and SSRB, the surface of the SiC mold was smooth (0.004-0.008 /spl mu/m Ra) without the crystallization of the amorphous CVD SiC film. The SiC mold was pressed to Pyrex glass to demonstrate its high-temperature strength. The Pyrex glass was deformed by the SiC mold at 850 /spl deg/C without a void, and no significant deformation of the SiC mold was observed.

The Effect of Excess Carbon on the Crystallographic, Microstructural, and Mechanical Properties of CVD Silicon Carbide Fibers

ABSTRACTSilicon carbide (SiC) fibers made by chemical vapor deposition (CVD) are of interest for organic, ceramic, and metal matrix composite materials due their high strength, high elastic modulus, and retention of mechanical properties at elevated processing and operating temperatures. The properties of SCS-6™ silicon carbide fibers, which are made by a commercial process and consist largely of stoichiometric SiC, were compared with an experimental carbon-rich CVD SiC fiber, to which excess carbon was added during the CVD process. The concentration, homogeneity, and distribution of carbon were measured using energy dispersive x-ray spectroscopy (SEM/EDS). The effect of excess carbon on the tensile strength, elastic modulus, and the crystallographic and microstructural properties of CVD silicon carbide fibers was investigated using tensile testing, x-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

Thermophysical and Mechanical Properties of a Three‐Dimensional Hi–Nicalon/SiC Composite

Key thermophysical and mechanical properties of a three‐dimensional Hi‐Nicalon™/silicon carbide (SiC) composite were tested. The relationship between the thermal expansion coefficient and temperature of the composite from room temperature (RT) to 1400°C was similar to that of chemical vapor deposition SiC. The thermal diffusivity of the composite could be well fitted by a logarithmic function. The composite exhibited excellent mechanical properties at RT and high temperature in vacuum. At RT, the flexural strength and flexural modulus were 1193 MPa and 255.6 GPa, respectively. Above 1200°C, the value of the flexural strength and flexural modulus at high temperature in vacuum decreased as the temperature increased, while the fracture toughness increased as the temperature increased.

Thermodynamics, Kinetics, and Microstructure of Laser Chemical Vapor Deposition of SiC

Thermodynamic and kinetic analyses as well as extensive experimentation were used to better understand the laser chemical vapor deposition of silicon carbide (SiC). The thermodynamic calculations suggested the use of lower processing temperatures, which experimentally proved advantageous for growth of uniform SiC fibers. The apparent activation energy was 163 KJ/mol, and the order of reaction with respect to the concentration of methyltrichlorosilane (MTS) was 0.36. Characterization via scanning electron microscopy revealed the deposits to be polycrystalline. Elongated grains oriented in the growth direction had aspect ratios in the range of 4–32 with diameters of 2–50 μm, depending on the deposition temperature. Temperature had a larger effect on the deposition rate and microstructure than did the H2/MTS ratio.

Fracture Origins in Miniature Silicon Carbide Structures

Direct tension strength tests were conducted on chemical vapor deposited silicon carbide microspecimens. Three types of specimens were used: straight gage section, tapered gage section, and notched gage section. The average strengths and standards deviations were: 0.42 GPa ± 0.13 GPa; 0.47 GPa ± 0.16 GPa; and 0.68 GPa ± 0.19 GPa, respectively. The fracture origins were identified by fractographic analysis and were cracks in large grains next to surface grooves from the deep reactive ion etch (DRIE) process used to fabricate the specimens.

Characterization of Si and CVD SiC to Glass Anodic Bonding Using TEM and STEM Analysis

Anodic bonding is a common process used in microelectromechanical systems (MEMS) device fabrication and packaging. Polycrystalline chemical vapor deposited (CVD) silicon carbide (SiC) is emerging as a new MEMS device and packaging material because of its excellent material properties including high strength, hardness, and thermal conductivity. A novel process recipe, requiring a SiC RMS surface roughness of 45 nm, was developed for anodically bonding CVD SiC to bulk Pyrex and Hoya SD-2 glass substrates. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) and elemental analysis presented distinct differences in elemental depletion band(s) of bulk Pyrex and Hoya SD-2 glasses bonded to Si, and in interfacial bonding between Pyrex and CVD SiC compared to Pyrex and Si. This study indicates that magnesium in the Pyrex glass network also participates in the depletion layer process compared to previous studies where only potassium, calcium, aluminum, and sodium were identified. For the first time, this study identifies aluminum, magnesium, sodium, and zinc participating in the depletion layer process in Hoya SD-2glass.

Fracture Toughness and Flexural Strength of Chemically Vapor-Deposited Silicon Carbide As Determined Using Chevron-Notched and Surface Crack in Flexure Specimens

Two different techniques used to measure the fracture toughness of silicon carbide (SiC) produced by chemical vapor deposition (CVD) are compared, and the influence of the material growth direction on toughness and flexural strength are evaluated. Fracture toughness values for monolithic CVD SiC are found to be independent of the CVD growth direction and test temperature from ambient to 1100°C with values ranging from 2.8 to 5.5 MPa·m1/2. This isotropic nature is notably different from hot-pressed α-SiC and is likely a result of the cubic β-SiC structure produced by the CVD process and the transgranular fracture mode. The range of fracture toughness results obtained using a chevron-notched specimen (2.8–4.0 MPa·m1/2) was less than values obtained using a surface crack in flexure method (3.7–5.5 MPa·m1/2), and these differences are statistically significant. These differences can be attributed to difficulties in resolving the true precrack size for the surface crack in the flexure specimen. Flexural strength values for monolithic CVD SiC are found to be isotropic with respect to the CVD growth direction from room temperature to 1090°C, as observed for the fracture toughness values. Flexural strength values measured at 1090°C are significantly higher (69% to 10% higher) than those measured at room temperature, while the modulus measured at 1090°C is less (−25% to −10% lower) than that measured at room temperature. Since the fracture toughness values are independent of temperature between room temperature and 1090°C, the increased flexural strength at elevated temperature is difficult to explain on the basis of classical fracture mechanics and must be influenced by other factors. Surface machining flaws on flexure specimens are shown to produce a 35% to 50% decrease in the flexure strength of monolithic CVD SiC that was quantified using the fracture toughness and flaw-size data.

Plasma-enhanced chemical vapor deposited silicon carbide as an implantable dielectric coating.

Amorphous silicon carbide (a-SiC) films, deposited by plasma-enhanced chemical vapor deposition (PECVD), have been evaluated as insulating coatings for implantable microelectrodes. The a-SiC was deposited on platinum or iridium wire for measurement of electrical leakage through the coating in phosphate-buffered saline (PBS, pH 7.4). Low leakage currents of <10(-11) A were observed over a +/-5-V bias. The electronic resistivity of a-SiC was 3 x 10(13) Omega-cm. Dissolution rates of a-SiC in PBS at 37 and 90 degrees C were determined from changes in infrared absorption band intensities and compared with those of silicon nitride formed by low-pressure chemical vapor deposition (LPCVD). Dissolution rates of LPCVD silicon nitride were 2 nm/h and 0.4 nm/day at 90 and 37 degrees C, respectively, while a-SiC had a dissolution rate of 0.1 nm/h at 90 degrees C and no measurable dissolution at 37 degrees C. Biocompatibility was assessed by implanting a-SiC-coated quartz discs in the subcutaneous space of the New Zealand White rabbit. Histological evaluation showed no chronic inflammatory response and capsule thickness was comparable to silicone or uncoated quartz controls. Amorphous SiC-coated microelectrodes were implanted in the parietal cortex for periods up to 150 days and the cortical response evaluated by histological evaluation of neuronal viability at the implant site. The a-SiC was more stable in physiological saline than LPCVD Si(3)N(4) and well tolerated in the cortex.

Morgan at Semicon West

At Semicon West this year, Morgan Advanced Ceramics (MAC) focused on its Chemical Vapour Deposition Silicon Carbide (CVD SiC) and Pyrolytic Boron Nitride (PBN) material solutions. This is a short news story only. Visit www.three-fives.com for the latest advanced semiconductor industry news.

OS06W0409 Characterization of thin films for MEMS optical and electrical device packaging applications

Micromachined films are proposed as mechanical clips to clamp optic fibres and other electrical components in optical packages. This paper reports mechanical test structures used to evaluate the properties of new materials for these MEMS and MST applications. A micromechanical beam 100μm wide and 400μm long is scanned with a stylus profilometer which deflects the beam, and the mechanical properties are deduced from the deflection characteristics. For example, prototype structures in 5μm thick silicon carbide film on a silicon substrate are produced by (a) laser cutting a track in the SiC film, (b) undercutting the SiC by anisotropic silicon etching using KOH in water, and (c) trimming if necessary with the focused laser system or with a focused ion beam. This approach has the advantages of fast design turn around and proof of concept, and it is practical to apply it to a wide range of materials. From the stylus profilometer data the Youngs modulus for chemical vapour deposited silicon carbide is 360 +/-50 GPa indicating that it is a promising material for packaging applications.

Fabrication of a glass-implemented microcapillary electrophoresis device with integrated contactless conductivity detection.

Glass microdevices for capillary electrophoresis (CE) gained a lot of interest in the development of micrototal analysis systems (microTAS). The fabrication of a microTAS requires integration of sampling, chemical separation and detection systems into a microdevice. The integration of a detection system into a microchannel, however, is hampered by the lack of suitable microfabrication technology. Here, a microfabrication method for integration of insulated microelectrodes inside a leakage-free microchannel in glass is presented. A combination of newly developed technological approaches, such as low-temperature glass-to-glass anodic bonding, channel etching, fabrication of buried metal interconnects, and deposition of thin plasma-enhanced chemical vapour deposition (PECVD) silicon carbide layers, enables the fabrication of a CE microdevice with an integrated contactless conductivity detector. The fabrication method of this CE microdevice with integrated contactless conductivity detector is described in detail. Standard CE separations of three inorganic cations in concentrations down to 5 microM show the viability of the new microCE system.

Growth rate predictions of chemical vapor deposited silicon carbide epitaxial layers

Complete 3D simulations of a silicon carbide chemical vapor deposition (CVD) reactor, including inductive heating and fluid dynamics as well as gas phase and surface chemistry, have been performed. For the validation of simulated results, growth was conducted in a horizontal hot-wall CVD reactor operating at 1600°C, using SiH 4 and C 3H 8 as precursor gases. Simulations were performed for an experimental hot-wall CVD reactor, but the results are applicable to any reactor configuration since no adjustable parameters were used to fit experimental data. The simulated results obtained are in very good agreement with experimental values. It is shown that including etching and parasitic growth on all reactor walls exposed to the gas greatly improves the accuracy of the simulations.