Massimo Camarda

Mechanisms of growth and defect properties of epitaxial SiC

In the last ten years, large improvements in the epitaxial silicon carbide processes have been made. The introduction of chloride precursors, the epitaxial growth on large area substrate with low defect density, the improvement of the surface morphology, the understanding of the chemical vapour deposition (CVD) reactions, and epitaxial mechanisms by advanced simulations are just the main results obtained in the homo-epitaxy process of 4H-SiC. After this large stride in the process of SiC epitaxial growth, it is time to collect this knowledge in a review that can be a reference point for the future work in this interesting field. The structure of the review is the following. After an introduction on the evolution and history of the epitaxial growth of 4H-SiC, the main physics parameter of this epitaxial growth process is explained in detail using the traditional Burton-Cabrera-Franck theory and the experimental observations of the surface instability due to the off-axis growths. Then the introduction of ch...

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.

A kinetic Monte Carlo method on super-lattices for the study of the defect formation in the growth of close packed structures

A modified Kinetic Lattice Monte Carlo model has been developed to predict growth rate regimes and defect formation in the case of the homo-epitaxial growth of close packed crystalline structures. The model is an improvement over standard Monte Carlo algorithms, which usually retain fixed atom positions and bond partners indicative of perfect crystal lattices. Indeed, we extend the concepts of Monte Carlo growth simulations on super-lattices containing additional sites (defect sites) with respect to those of the reference material. This extension implies a reconsideration of the energetic mapping, which is extensively presented, and allows to describe a complex phenomenology that is out of accessibility of standard stochastic approaches. Results obtained using the Kawasaki and the Bond-Counting rules for the transition probability of the Monte Carlo event are discussed in details. These results demonstrate how the defect types (local or extended), the formation mechanisms and the defect generation regimes can be characterized using our approach.

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)

Coupled Monte Carlo-Poisson method for the simulation of particle-particle effects in dielectrophoretic devices

Simulations can aid to bridge the gap between the proof-of-concept stage and the engineering of dielectrophoretic devices. We present a simulation method overcoming the limits of fluid-flow based approaches. In our Monte-Carlo-Poisson simulator, the colloidal system is described at the particle resolution. This characteristic allows for taking into account volume forces and particle-particle interactions usually neglected in the continuum approximation. In turn, large number of particles and large systems can be simulated to meet the device design needs. In an experimentally verifiable case study, we discuss the role of the multi-particle interaction in high and moderate density regimes.

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.

Structural and electronic characterization of (2,33) bar-shaped stacking fault in 4H-SiC epitaxial layers

Crystallographic, electronic, and energetic analyses of the (2,33) [or (2,3,3,3) in the standard Zhadanov notation] bar-shaped stacking fault, observed in as-grown 4H-SiC epitaxial layers, are presented. The defect has been identified by means of spatially resolved microphotoluminescence (μ-PL) measurements at different emission wavelengths, focusing on the emission peak at 0.3 eV below the conduction band. Low temperature μ-PL measurements have also been performed. The defect has been identified and characterized using high resolution transmission electron microscopy. Experimental results are correlated and validated by the calculations of the Kohn–Sham electronic band structure and the defect formation energy.

Preferential oxidation of stacking faults in epitaxial off-axis (111) 3C-SiC films

The effect of thermal dry oxidation on an off-axis (111) 3C-SiC film have been studied in order to subsequently realize a metal-oxide-semiconductor structure. A morphological characterization of the SiO2 surface, grown at 1200 °C in an O2 flux, pointed out some defect-related effects as a consequence of the preferential oxidation of stacking faults over the (111) 3C-SiC surface. Scanning electron microscopy and atomic force microscopy confirmed such a hypothesis. Stacking faults are seen as promoters of a local polarity inversion in (111) 3C-SiC, from Si- to C-terminated surface, resulting in a higher oxidation rate as compared to defect-free zones.

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.