Materials Science Forum Vol. 711

Abstract: In this article we compare the strain distribution observed in 3C-SiC/Si (100) cantilevers, using the shift of the transverse optical (TO) mode in micro-Raman maps, with the values predicted using a recent analytic theory []. By taking advantage of an under etching of the microstructures during the fabrication processes, that removes a thin layer of highly defective SiC close to the film/substrate interface near the edges of the microstructures, we show that the variation of the experimental measured strain can be ascribed to a non-linearity of the strain field along the 3C-SiC film thickness.

Abstract: The growth of continuous silicon monocrystalline thin films on 3C-SiC epilayers deposited on silicon substrates is presented in this study. Such heterostructures can be beneficial for the fabrication of Micro Electro Mechanical Systems or electronic applications. The elaboration of these heterostructures was carried out using Low Pressure Chemical Vapor Deposition. X-ray Diffraction, Fourier Transformed Infra-Red spectroscopy and Scanning Electron Microscopy have been used to investigate the structural properties of Si epilayers and their dependence on growth conditions. Monocrystalline Si (110) films are obtained on 3CSiC(100)/Si (100) substrates, only when using growth temperatures close to 850°C. The strong influence of the underlying 3C-SiC film on the final structural properties of Si epilayer is evidenced.

Abstract: A top-down fabrication technique for nanometer scale silicon carbide (SiC) pillars has been demonstrated by using inductively coupled SF₆/O₂ plasma etching. At optimal etching conditions, the obtained SiC nanopillars exhibit high anisotropy features (aspect ratio ~ 6.5) with high etch depth (>7 μm). The etch characteristics of SiC nanopillars under these conditions show a high etch rate (550 nm/min) and a high selectivity (over 60 for Ni).

Abstract: Back-gated field effect transistors (FETs) based on 3C-SiC nanowire (NW) were fabricated and the electrical characterization revealed devices with either ohmic or rectifying contacts leading to two different operation modes. The transistors with ohmic-like contacts manifest very weak gating effect and the device switching off is not achievable even for high negative gate voltages due to the high electron concentration along the nanowires. In contrast, the devices with Schottky contact barrier at Source / Drain regions demonstrate a well determined switching off and in general better performance thanks to the modulation of the drain current through the control of Schottky barriers transparency at the source and drain regions. Nevertheless, ohmic contact devices are expected to demonstrate even better performance if the NW material quality as well as the quality of the interface with the gate oxide is substantially improved.

Abstract: β-SiC/SiO₂ core-shell NWs have been synthesized on patterned silicon wafers in a CVD system, using carbon oxide as single precursor and nickel nitrate as catalytic element, in nitrogen or argon atmosphere at 1100°C. The coaxial structure and the crystallinity of the NW core are examined by (scanning) transmission electron microscopy. The patterning of the substrate allows to grow NWs in selected areas only, as imaged by SEM. Cathodoluminescence (CL) panchromatic images of the same areas point out that the light emitted under electron excitation is localized only in the area covered with NWs. The room-temperature CL spectrum has three different components peaked at 2.45 eV, related to the 3C-SiC near-band-edge emission, and at 2.75 and 3.75 eV, that are induced by the triplet and singlet states of oxygen-deficiency centers ODC(II) in silicon dioxide shell.

Abstract: One way to improve the force sensitivity of Atomic Force Microscopy (AFM) cantilevers is to increase their resonance frequency. SiC is an excellent material for that purpose due to its high Young’s modulus and low mass density. This size reduction makes conventional optical motion detection methods inappropriate. Here, we introduce self-sensing, self-excited high frequency AFM cantilevers. The motion detection is based on the measurement of a metallic piezoresistor incorporated in the cantilever. The motion excitation is performed by electrothermal actuation using another metallic circuit. Cantilevers with sizes as low as 4 μm in length, 1.2 μm in width and 0.5 μm in thickness were realized by using different steps of e-beam lithography, deposition of thin gold films to pattern the piezoresistor and the electrothermal actuation electrode. Dry etching SF₆ plasma was used for etching the SiC cantilever and TMAH solution heated to 80°C to release the cantilever. In this case, a thigh control of underetching, which reduces the cantilever resonance frequency was required.

Abstract: A detailed experimental study of the mean and gradient stress, existing in the as-grown cubic silicon carbide epilayers, is presented in this paper. (100) and (111) oriented epiwafers with considerable film thickness variation have been elaborated using a horizontal low pressure chemical vapor deposition reactor. The mean and gradient stress within the 3C-SiC film were estimated from the static mechanical deformation of micromachined clamped-free beams. For both studied orientations, we observe a stress gradient inversion phenomenon that can be explained in terms of creep occurring in 3C-SiC film.

Abstract: Quantitative efficacies of several methods for stacking fault (SF) reduction are evaluated using Monte Carlo (MC) simulation. SF density on a 3C–SiC {001} surface depends on interactions of adjoining SFs: annihilation between counter pairs of SFs and termination by orthogonal SF pairs. However, SFs are not entirely eliminated when growth occurs on undulant-Si and switch back epitaxy (SBE) due to spontaneous SF collimation that suppresses the annihilation probability of counter SFs. The MC simulation also reveals the efficacy of SF reduction method which includes the growth of 3C–SiC on finite area bounded by side walls. One can theoretically reduce the SF density below 100 cm^-1 on 3C–SiC {001} surface. A practical way for eliminating the SF by termination at side walls is demonstrated, and it clearly exhibits that the SF density can be reduced under 120 cm^-1.

Abstract: In this work the band diagrams of different MOS structures based on 3C-SiC substrate were determined. This has been achieved by application of many measurement techniques allowing determination of many electric parameters of the investigated structures. These parameters allowed to construct complete band diagrams which are demonstrated for two modes: for the flat-band state in the semiconductor and for the flat-band state in the dielectric.

Abstract: – 4H-SiC MESFET transistors are very attractive devices for high temperature application and communications. The JFET and MESFET transistors have a promising potential for integrated circuits able to operate at high temperature and harsh radiation environments, due to the superior electrical, mechanical and chemical proprieties of 4H-SiC. Progresses in the manufacturing of high quality SiC substrates open the possibility to new circuit applications.