Materials Science Forum Vol. 806

Abstract: The aim of this paper is to review the recent developments conducted by our groups for the achievement of 3C-SiC based heterostructures compatible for MEMS applications. It deals with different aspects, from the influence of the defects generated at the 3C-SiC/Si interface on the mechanical properties to the elaboration of new multilayered structures, required for specific applications like, for example, Atomic Force Microscopy.

Abstract: The following paper explores the development the bulge test technique combined with the micro-Raman analysis and a refined load-deflection model for high quality 3C-SiC squared-membranes. By the minimization of the total elastic energy, starting from the isotropic relation between the stress tensor and the strain tensor, it is possible to calculate the relationship between the maximum deflection and the applied pressure, in both regime of small and large deflection. From the measured breaking pressure through the refined model it is possible to evaluate the breaking strain of the membrane. Furthermore, the relationship between the measured shift of Raman Transverse Optical (TO) phonon modes and the total residual strain (Δa/a) within the epitaxial 3C-SiC layer was found.

Abstract: We describe a procedure for the optimization of a 3C-SiC buffer layer for the deposition of 3C-SiC on (001) Si substrates. A 100 – 150 nm thick SiC buffer was deposited after a standard carbonization at 1125 °C, while increasing the temperature from 1125 °C to 1380 °C. Ramp time influenced the quality and the crystallinity of the buffer layer and the presence of voids at the SiC/Si interface. After the optimization of the buffer, to demonstrate its effectiveness, a high-quality 3C-SiC was grown, with excellent surface morphology, crystallinity and low stress.

Abstract: Micro Raman characterization has been used to determine the stress status of 3C-SiC epilayer grown on pseudomorphic-Si thin layer on Si_1-xGe_x/Si(001). The strain conditions of the Si_1-xGe_x films grown on Si(001) have been determined by the analysis of additional Silicon Raman peaks, which Raman shifts are related to the lattice parameter. Through the analysis of the Raman spectra, the correlation between the Si_1-xGe_x film, the crystal quality and the stress relaxation of the 3C-SiC as a function of the Germanium fraction (x), have been evaluated. The increase of Germanium fraction determines the reduction of the voids density located at the 3C-SiC/Si interface and the relaxation of the stress within the epilayer. Moreover, the 3C-SiC crystal quality, monitored by the Full Width at Half Maximum of the TO Raman mode, remains unchanged for any Germanium fraction values.

Abstract: The aim of this work is to study the effect of Ge introduction during the nucleation step on the SiC growth on 4H-SiC on-axis substrate. After 10 minutes surface pretreatment at 1500°C under C₃H₈ or GeH₄, the grown 3C layer at the same temperature can switch from highly twinned (C₃H₈) to almost twin-free single domain (GeH₄). However, for too low and too high GeH₄ fluxes, the layers display a mixture of polytype. Keeping the best pretreatment but varying the growth temperature degrades the morphology and changes the polytype of the layer. Preliminary electrical results using C-AFM on the 3C-SiC layer are also presented.

Abstract: This work deals with the selective heteroepitaxial growth of silicon carbide on (100) diamond substrates using the Vapour-Liquid-Solid (VLS) transport. The morphology, the structure and doping were determined using various characterization techniques. In order to achieve succesful heteroepitaxy, the diamond surface was silicided by solid-state reaction between a silicon layer and the substrate at 1350 °C. This allowed forming a SiC buffer layer on which p-doped 3C-SiC(100) islands elongated in the <110> directions were obtained after VLS growth. The influence of the experimental parameters on the epitaxial growth is discussed.

Abstract: We report on the synthesis of SiC nanowires (NWs) using iron as catalyst. The NWs were grown on silicon substrate by vapour-liquid-solid (VLS) mechanism with propane and silane as precursors, both 3% diluted in hydrogen, and hydrogen as carrier gas. The growth temperature was 1250°C, to reach the eutectic values of the Si-Fe alloy and to permit the VLS mechanism. The as-grown SiC nanowires were characterized by scanning and transmission electron microscopy. The nanowires are from 30 to 100 nm in diameter and several μm in length, with <111> growth direction.

Abstract: In the present contribution, the trends in voluntary incorporation of aluminum in 4H-SiC homoepitaxial films are investigated. The films were grown on Si-and C-face 4H-SiC 8°off substrates by chemical vapor deposition (CVD) in a horizontal, hot wall CVD reactor. Secondary Ion Mass Spectrometry (SIMS) and capacitance-voltage (C-V) measurements were used to determine the Al incorporation in the samples. The influence of Trimethylaluminum (TMA) flow rate, growth temperature, growth pressure and C/Si ratio on the dopant incorporation was studied.

Abstract: In this work, we focus on heavily aluminum (Al) doped 4H-SiC samples. We compare the effect of the Al concentration and Hall carrier concentration on the Raman spectra in a large frequency range. The Al concentration measured by Secondary Ion Mass Spectrometry ranged from 2×10¹⁶ to 8.4×10¹⁹ cm^-3 while the electrical measurement give a carrier concentration up to 5×10¹⁹ Al×cm^-3. On the Raman spectra, three different frequency domains have been analysed: i) at high frequency where we consider the change in longitudinal optical phonon-plasmon coupled mode; ii°) at low frequency where we consider the continuum of electronic transitions and iii°) finally, considering the Fano interference effect between the continuum of electronic transitions and the Folded Transverse Acoustic phonon modes. This analysis is applied to comment a Raman spectra mapping collected on a 4H-SiC 2 inch wafer.