Ruggero Anzalone

Effect of the miscut direction in (111) 3C-SiC film growth on off-axis (111)Si

Two miscut directions of (111) Si substrate on 3C-SiC heteroepitaxial growth have been studied with the resulting 3C-SiC stress and defects as a function of miscut axis direction toward [110] and [112] of (111) Si analyzed. We studied this dependency from an experimental point of view, investigating the structural properties of 3C-SiC, and using a kinetic Monte Carlo method on superlattice to confirm our experimental findings with numerical simulations. Residual stress and stacking fault density were halved by growing on a (111) Si substrate off-cut toward the [110] direction. A different surface morphology was revealed between the two inclinations.

Defect Influence on Heteroepitaxial 3C-SiC Young’s Modulus

Heteroepitaxial cubic silicon carbide (3C-SiC) is an extremely promising material for micro- and nano-electromechanical systems due to its large Young’s modulus. Unfortunately, the heteroepitaxy of 3C-SiC on Si substrate is affected by the high mismatch in the lattice parameters and the thermal expansion coefficients between the two dissimilar materials that generate a high number of defects in the material. In this work, through the measurement of natural resonant frequencies and Raman shift analysis, a strong relationship between the mechanical proprieties of the material (Young’s modulus) and the film crystal quality (defect density)

Low Stress Heteroepitaxial 3C-SiC Films Characterized by Microstructure Fabrication and Finite Elements Analysis

Chemical vapor deposition in the low pressure regime of a high quality 3C-SiC film on silicon (100)-oriented substrates was carried out using silane (SiH 4 ), propane (C 3 H 8 ), and hydrogen (H 2 ) as the silicon supply, carbon supply, and gas carrier, respectively. The resulting bow in the freestanding cantilever structures was evaluated by an optical profilometer, and the residual gradient stress (σ 1 ) in the films was calculated to be approximately between 15 and 20 MPa, which is significantly lower than the previously reported 3C-SiC on Si films. Finite element simulations of the stress field in the cantilever have been carried out to separate the uniform contribution (σ 0 ), related to the SiC/Si interface, from the gradient one (σ 1 ), related to the defects present in the SiC epilayer.

High Quality Single Crystal 3C-SiC(111) Films Grown on Si(111)

We have developed a high-quality growth process for 3C-SiC on on-axis (111)Si substrates with the ultimate goal to demonstrate high quality and yield electronic and MEMS devices. A single-side polished 50 mm (111)Si wafer was loaded into a hot-wall SiC CVD reactor for growth. The 3C-SiC process was performed in two stages: carbonization in propane and hydrogen at 1135°C and 400 Torr followed by growth at 1380°C and 100 Torr. X-ray diffraction rocking curve analysis of the 3C-SiC(222) peak indicates a FWHM value of 219 arcsec. This is a very interesting result given that the film thickness was only 2 µm, thus indicating that the grown film is of very high quality compared with published literature values. X-ray polar figure mapping was performed and it was observed that the micro twin content was below the detection limit. Therefore TEM characterization was performed in plan view to allow assessment of the stacking fault density as well as confirmation of the very low micro twin concentration in this film. TEM analysis indicates a low concentration of stacking faults in the range of 104 cm-1.

3C-SiC Film Growth on Si Substrates

The aim of this work is to give an overview on 3C-SiC growth on Si substrates. Starting from the reasons why SiC is considered such an interesting innovative material, with a survey of application already demonstrated, we will present data explaining the most important issues in this hetero-epitaxy system and how the chemical vapor deposition process influences the resulting 3C-SiC film properties. 3C-SiC crystal structure is strongly dependent on the process parameters within the reaction chamber during growth as well as the substrate surface properties. Part of this work is then focused on the main crystallographic defects characterizing the 3CSiC/Si system and on the resulting wafer bow due to the large misfit between the materials. Defects and wafer bow, are a direct consequence of the large stress generated at the interface. The work closes discussing the encouraging improvements in 3C-SiC crystal quality obtained by the introduction of compliant Si substrates.

Theoretical and experimental study of the role of cell-cell dipole interaction in dielectrophoretic devices: application to polynomial electrodes.

BackgroundWe aimed to investigate the effect of cell-cell dipole interactions in the equilibrium distributions in dielectrophoretic devices.MethodsWe used a three dimensional coupled Monte Carlo-Poisson method to theoretically study the final distribution of a system of uncharged polarizable particles suspended in a static liquid medium under the action of an oscillating non-uniform electric field generated by polynomial electrodes. The simulated distributions have been compared with experimental ones observed in the case of MDA-MB-231 cells in the same operating conditions.ResultsThe real and simulated distributions are consistent. In both cases the cells distribution near the electrodes is dominated by cell-cell dipole interactions which generate long chains.ConclusionsThe agreement between real and simulated cells’ distributions demonstrate the method’s reliability. The distribution are dominated by cell-cell dipole interactions even at low density regimes (105 cell/ml). An improved estimate for the density threshold governing the interaction free regime is suggested.

Growth Rate Effect on 3C-SiC Film Residual Stress on (100) Si Substrates

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 XRD analysis, 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. XRD (rocking curve analysis) and Raman spectroscopy show that the crystal quality of the films increases with decreasing growth rate. From curvature measurements, the average residual stress within the layer using the modified Stoney’s equation was calculated. The results show that the films are under compressive stress and the calculated residual stress also increases with growth rate, from -0.78 GPa to -1.11 GPa for 3C-SiC films grown at 2.45 and 4 µm/h, respectively.

Towards Large Area (111)3C-SiC Films Grown on off-oriented (111)Si

The choice of off-axis (111) Si substrates is poorly reported in literature despite of the ability of such an oriented Si substrate in the reduction of stacking faults generation and propagation. The introduction of off-axis surface would be relevant for the suppression of incoherent boundaries. We grew 3C-SiC films on (111) Si substrates with a miscut angle from 3° to 6° along <110> and <11 >. The film quality was proved to be high by X-Ray diffraction (XRD) characterization. Transmission electron microscopy was performed to give an evaluation of the stacking fault density while pole figures were conducted to detect microtwins. Good quality single crystal 3C-SiC films were finally grown on 6 inch off-axis (111)Si substrate. The generated stress on both 2 and 6 inch 3C-SiC wafers has been analyzed and discussed.

Defect Reduction in Epitaxial 3C-SiC on Si(001) and Si(111) by Deep Substrate Patterning

The heteroepitaxial growth of 3C-SiC on Si (001) and Si (111) substrates deeply patterned at a micron scale by low-pressure chemical vapor deposition is shown to lead to space-filling isolated structures resulting from a mechanism of self-limitation of lateral expansion. Stacking fault densities and wafer bowing may be drastically reduced for optimized pattern geometries.

Advanced Stress Analysis by Micro-Structures Realization on High Quality Hetero-Epitaxial 3C-SiC for MEMS Application

SiC is a candidate material for micro- and nano-electromechanical systems (MEMS and NEMS). The fabrication of SiC MEMS-based sensors requires new processes able to realize microstructures on either bulk material or on the SiC surface. The hetero-epitaxial growth of 3C-SiC on silicon substrates allows one to overcome the traditional limitations of SiC micro-fabrication, but the high residual stress created during the film grow limits the development of the material for these applications. In order to evaluate the amount of residual stress released from the epi-film, different micro-machined structures were developed. Finite elements simulations of the micro-machined structures have also been carried out in order to evaluate, in detail, the stress field inside the structures and to test the analytical model used. With finite element modeling a exponential approximation of the stress relationship was studied, yielding a better fit with the experimental data. This study shows that this new approximation of the total residual stress function reduces the disagreement between experimental and simulated data.