Materials Science Forum Vols. 717-720

Abstract: FTIR, Visible and UV Raman scattering, as well as synchrotron radiation X-ray absorption, in combination, have been employed to investigate a series of CVD grown 3C-SiC/Si (100). Significant results on the optical and atomic bonding properties are obtained from these comparative studies.

Abstract: Synchrotron radiation X-ray absorption and UV 325 nm excitation Raman scattering- photoluminescence (PL) have been employed to investigate a series of 4H-SiC wafers, including bulk, epitaxial single or multiple layer structures by chemical vapor deposition. Significant results on the atomic bonding and PL-Raman properties are obtained from these comparative studies.

Abstract: Cubic polytypes of SiC, GaN and AlN were grown on silicon by molecular beam epitaxy. The mechanical properties of the epitaxial layers were investigated by nanoindentation. For 3C-SiC grown on Si(111) and Si(100) a dependence of the mechanical properties on the surface preparation with germanium prior to the carbonization was obtained.

Abstract: Using several characterization techniques (μ-Raman, mechanical profilometer and microstructure deflections) together with a recent stress model[ ] we study the heteroepitaxial growth of cubic silicon carbide on silicon (100). We show that the observed inconsistency between experimental results might be the result of defects generated on the silicon substrate during the carbonization process. In such a situation wafer curvature techniques do not allow the determination of the stress field in the grown films neither quantitatively nor qualitatively.

Abstract: SiC is a candidate material for micro- and nano-electromechanical systems (MEMS and NEMS). In order to understand the impact that the growth rate has on the residual stress of CVD-grown 3C-SiC hetero-epitaxial films on Si substrates, growth experiments were performed and the resulting stress was evaluated. Film growth was performed using a two-step growth process with propane and silane as the C and Si precursors in hydrogen carrier gas. The film thickness was held constant at ~2.5 µm independent of the growth rate so as to allow for direct films comparison as a function of the growth rate. Supported by profilometry, Raman and micro-machined free-standing structures, this study shows that the growth rate is a fundamental parameter for low-defect and low-stress hetero-epitaxial growth process of 3C-SiC on Si substrates. Stress analysis performed by modify Stoney’s equation trough optical curvature measurement, Raman shift analysis and micro-machining of free-standing structures that shows apparent disagreement about the nature of the stress. These odds between the experimental data can be explained assuming a strong stress field located in the substrate and related to defects generated in the silicon during the growth process.

Abstract: In this work, Raman microscopy is used to study the stress distribution on 3C-SiC cantilevers. Also we compare the strain distribution observed on the microstructure, using the shift of the transverse optical (TO) mode in micro-Raman maps, with the values predicted using a recent analytic theory [1]. Along the width of the cantilever is observed a reduction of stress ascribed to the etching processes that removes a thin layer of the interface between the 3C-SiC film and the substrate close to the edge of the microstructure. It is possible to show that this variation can be ascribed to a non-linearity of the strain field along the 3C-SiC film thickness. Also, helped by Finite Element Modelling (FEM), we determined the stress tensor along the cantilever. This result shows that, for a complete stress description of the cantilevers, it is necessary taking into account the role of diagonal and off-diagonal stress tensorial components.

Abstract: In this paper, we report single-crystal 4H-SiC resonant structures fabricated by dopant-selective photoelectrochemical etching. The frequency response of the resonant beams was characterized by a dynamic scanning method using AFM with the beams excited by a piezoelectric actuator under atmosphere pressure and room temperature. The beam with a length of 35 μm shows mechanical resonance at 945 kHz. The Young’s modulus of single-crystal SiC was derived from the measured resonant frequency. Single-crystal 4H-SiC resonators developed in this study fully exploit the excellent electrical, mechanical, and chemical properties of SiC, while dopant-selective photoelectrochemical etching technique significantly simplifies the fabrication process.

Abstract: We report an initial experimental exploration of engineering very thin, suspended amorphous silicon carbide (a-SiC) membranes into vibrating micromechanical devices. We show that micromachined a-SiC thin square membranes can make interesting multiple-mode flexural resonators, with frequency spectra exhibiting many measurable resonant modes over a wide frequency range (100kHz–10MHz) in the low radio frequency (RF) bands. Initial demonstration and preliminary data suggest interesting and rich dynamical, nonlinear, and dissipative properties in these micromechanical resonances. Specifically, for instance, at room temperature (T≈300K) and in moderate vacuum (e.g., ~20mTorr), resonant modes of an a-SiC square membrane (thickness: t≈1.5µm, size: 1mm×1mm) are observed in the ~100kHz–5MHz range, with measured quality factors (Q’s) in the range of ~2,500–9,000.

Abstract: This paper details the development of amorphous hydrogenated silicon carbide (a-SiC:H) films as structural material that is resistant to biofouling. The a-SiC:H films were deposited by PECVD and evaluated for their mechanical and anti-biofouling properties. It was found that the as-deposited films exhibited compressive residual stresses that could be converted to moderate tensile stresses upon a post deposition anneal. The amorphous films exhibited a much lower Young’s modulus but similar burst stress when compared to polycrystalline 3C-SiC films of like thickness. The as-deposited a-SiC:H films were more resistant to biofouling than silicon and silicon dioxide surfaces. Coating the a-SiC:H films with polyethylene glycol (PEG) significantly improved the anti-fouling characteristics for extended periods.

Abstract: The Seebeck coefficient of heavily-nitrogen-doped n-type polycrystalline 3C-SiC (n-SiC) and platinum (Pt) thin films has been measured from room temperature up to 300 °C by using a microfabricated test structure. At room temperature, the absolute Seebeck coefficient of the n-SiC is -10 μV/°C. With ambient temperature increase, the absolute Seebeck coefficient of the n-SiC is found to gradually increase, reaching -20 μV/°C at 300 °C.