Deposited Silicon Carbide Research Articles

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).

Thermodynamic Analysis of Synthetic Potentialities of the nSiC + SiO<sub>2</sub> Starting System: SiC Gas-Phase Transport via Si(g) and CO(g)

The major objective of our studies was the thermodynamic analysis of the nSiС+SiO2 system and revealing potentialities for the implementation of the SiC gas-phase transport conditions. As a result of thermodynamic scanning of the chemical activity of nSiС+SiO2 system the conditions for implementing the SiC gas-phase transport were found out within a wide temperature range. It was found out that the basic process in the gas-phase transport of silicon carbide is: SiCs + SiOg→ 2Sig + СОg SiC evaporation at T2 2Sig + СОg → SiCnanowhiskers + SiOg SiC deposition at T1 Sequential evaporation and deposition of silicon carbide result in the growth of SiC crystals from a gas phase. The processes of SiC gas-phase transport and deposition were experimentally realized. Synthesized were SiC nanocrystals over 300 μm long, ~ 300 nm in diameter that forms a three-dimensional subskeleton inside the carbon skeleton.

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.

Electrophoretic Deposition of Green Parts for LPS SiC-Based Ceramics

Electrophoretic deposition of silicon carbide in ethanol suspensions was studied with the aim to fabricate liquid-phase sintered (LPS) SiC-based ceramics densified at temperatures below 1500°C. The effect of suspensions composition (solids content, pH, sintering additives) on the deposition rate and the properties of the deposits was analysed. The consistency of deposits and their solids loading was found to be significantly dependent on composition of the starting suspension: the highest solids loading (54.5 vol. %) for pure SiC was obtained with the addition of citric acid, while for the suspension containing aluminum phosphate the deposition was more successful from alkaline suspensions.

Single-Source Chemical Vapor Deposition of SiC Films in a Large-Scale Low-Pressure CVD Growth, Chemical, and Mechanical Characterization Reactor

The development and characterization of a silicon carbide deposition process from a single source precursor, 1,3-disilabutane, in a large-scale reactor is described. Deposition was performed simultaneously on fifteen, Si wafers in a 4 or wafer-capable horizontal low-pressure chemical vapor deposition reactor. Amorphous is obtained at temperatures of and below, while some polycrystallinity is obtained at temperatures of and above. Highly uniform and relatively smooth films are realized using a closed wafer boat. A maximum growth rate of is attained at . Residual stress in the film is characterized and found to be greater than (tensile) across a wide range of deposition temperatures. Stress profiling is performed to investigate the stress distribution throughout the films. Microfabrication on the wafer level using as a structural layer is also demonstrated.

Detecting free radicals during the hot wire chemical vapor deposition of amorphous silicon carbide films using single-source precursors

A vacuum ultraviolet single photon ionization technique has been used to probe gas-phase species important in the hot wire chemical vapor deposition (HW-CVD) of amorphous silicon carbide(a-SiC:H) films using different single-source precursors. This study focuses on monomethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, and 1,1-dimethyl-1-silacyclobutane, and the reactions of these precursors on tungsten and rhenium filaments between 1000 and 1950°C. Silane is also considered for comparison. Si radicals are found to be major products of hot wire decomposition for all the organosilicon precursors; CH3 is also observed. C and H radicals are expected to be produced as well but are not detected at the ionization energy used in these experiments. Within the series of methylsilanes, the reaction rate on the filament is found to decrease with increasing number of methyl groups on the precursor. We propose a model in which Si–H bonds are cleaved with lower activation barriers than Si–CH3 bonds as the molecule adsorbs onto the hot metal surface. 1,1-dimethyl-1-silacyclobutane produces Si with a lower apparent activation energy than the other molecules. Coverage-dependent reaction pathways are proposed to play a role in the temperature profile of CH3 generation. Infrared spectra of films deposited by HW-CVD show that the film composition and growth rate for the different precursors correlate with the hot wire chemistry studied by single photon ionization.

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.

Horizontal hot wall reactor design for epi‐SiC growth

AbstractThe model adopted for the simulation of a new industrial size type of horizontal cold wall reactor for epitaxial silicon carbide deposition is reviewed. The attention is focalized on the chemical mechanism adopted and on the comparison with some growth rate data and temperature profiles for the system ethylene, silane, hydrogen and the deposition of undoped silicon carbide. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Thin film stress measurement by fiber optic strain gage

In this work, we present a new optical Fiber Bragg Grating (FBG) strain sensor which can be utilized to measure in situ the induced substrate strain caused by the film stress. The fiber optical sensor is interfaced to an analyzer to determine the wavelength shift of the reflected signal due to strain and temperature effects. The technique was used during the deposition of silicon dioxide and silicon carbide (SiC) thin films by RF magnetron sputtering, onto thin (38 μm) stainless steel substrates. The direct measurement of the wavelength shift Δ λ provides the strain value ε which can be used to find the residual stress σ present in the film/substrate interface. The preliminary results for SiC are in agreement with other works reported in the literature. The uncertainty provided by the measuring system is about 1 μm/m. Research is under way to improve the accuracy and study the possibility to develop a more compact device.

Nanoindentating Mechanical Responses and Interfacial Adhesion Strength of Electrochemically Deposited Copper Film

The nanomechanical responses and interface adhesion of electrochemically plated copper (Cu) film have been investigated for the evaluation of interconnect reliability. The hardness and elastic modulus of the Cu film were measured by nanoindentation test as about 2.1 and , respectively. A dislocation burst phenomenon was observed and revealed the initiation of plastic deformation of the Cu film. The converted true stress-strain curve provided a stress criterion of for the plastic yielding of the Cu film. Besides, the creep behavior was also analyzed under nanoindentation test and showed a power law expression with a creep stress exponent of about 22. Moreover, the interfacial adhesion strength and delamination behavior between the Cu film and silicon carbide (SiC) etch stop layer have been studied using a four-point bending test. During delamination, cracks irregularly propagated along the interface with blocking by the ductile Cu film. The fracture energy release rate for the delamination of interface was measured as around , affected by SiC deposition condition and testing parameter.

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.

Nonequilibrium Heteroepitaxy of Silicon Carbide on Silicon

A method of silicon carbide (SiC) deposition onto silicon via a nonequilibrium disilicon carbide (Si2C) vapor phase is proposed, theoretically described, and experimentally verified. Estimates obtained using thermochemical calculations show that a sufficiently large number of SiC molecules, which are transported by mobile Si2C species, are obtained using this method on the silicon surface. It is established that homogeneous epitaxial SiC layers can be grown on a Si(111) substrate surface.

In situ Observation of Clusters in Gas Phase during 4H-SiC Epitaxial Growth by Chemical Vapor Deposition Method

We have performed in situ observation of the chemical vapor deposition (CVD) of silicon carbide (SiC), and investigated the relationship between the growth conditions and generation of clusters in the gas phase of the H2–SiH4–C3H8 gas system to realize the high-speed growth of SiC by CVD. It was found that cluster generation can be suppressed by decreasing the partial pressure of the process gases, i.e., increasing the H2 carrier gas flow rate, and decreasing the pressure and process gas flow rate. We concluded that clusters in the gas phase consist of not only Si droplets, but also SiC particles.

Improvement of crystalline silicon surface passivation by hydrogen plasma treatment

A completely dry low-temperature process has been developed to passivate 3.3 Ω cm p-type crystalline silicon surface with excellent results. Particularly, we have investigated the use of a hydrogen plasma treatment, just before hydrogenated amorphous silicon carbide (a-SiCx:H) deposition, without breaking the vacuum. We measured effective lifetime, τeff, through a quasi-steady-state photoconductance technique. Experimental results show that hydrogen plasma treatment improves surface passivation compared to classical HF dip. Seff values lower than 19 cm s−1 were achieved using a hydrogen plasma treatment and an a-SiCx:H film deposited at 300 °C.

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.

Clearance of Deposited Silicon Carbide Whisker from Rat Lungs Inhaled during a 4‐Week Exposure

Pulmonary deposition and the clearance of deposited fiber particles from lungs are key determinant factors in assessing potential carcinogenicity and fibrogenicity. Forty-two Wistar male rats (9 wk old) were exposed to silicon carbide whisker (SiCW) for 6 h/d, 5 d/wk for 4 wk. The mass median aerodynamic diameter was 2.5 microm as detected by an Andersen sampler, and the geometric mean fiber diameter and length determined by a scanning electron microscope were 0.4 and 2.2 microm, respectively. The daily average exposure concentrations were 10.4 0.5 mg/m(3) (214 +/- 31 fibers/ml ) during the exposure period. The rats were sacrificed after 3 d, 2 wk, 1, 2, 3, 6 and 12 months after 4-wk exposure. At the time of sacrifice, the wet lung weights and the deposited SiCW amounts in the lungs were measured by an X ray reference method. The amount of SiCW deposited was 0.60 +/- 0.09 mg 3 d after a 4-wk exposure. The apparent deposition fraction was 4.8 +/- 0.7 (%). During the clearance period, the amount of SiCW deposited in the rat lungs decreased exponentially with the increasing duration of the clearance period. The biological half time in the one-compartment model was determined to be 4.0 months which is similar to the values for glass fiber, potassium titanate whisker and aluminium-silicate ceramic fiber under similar exposure conditions.

Corrosion behaviors of sintered and chemically vapor deposited silicon carbide ceramics in water at 360 °C

Corrosion behaviors of sintered and chemically vapor deposited silicon carbide ceramics in water at 360 °C