Giuseppe D'Arrigo

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.

Interdigit 4H-SiC Vertical Schottky Diode for Betavoltaic Applications

We demonstrated a 4H-SiC vertical Schottky diode for betavoltaic application using interdigit front metallization. A relevant increase in the betavoltaic short-circuit current with respect to a device with a continuous standard front electrode was achieved with this novel layout allowing to collect also low-energy electrons. In particular, by irradiating the device with a monochromatic electron beam (e-beam) of 17 keV, an internal gain that is 1.4 times higher than in conventional devices was obtained. An open-circuit voltage of ~1 V was obtained for an illumination e-beam current density of 10-8 A/cm2.

Computational analysis of etched profile evolution for the derivation of 2D dopant density maps in silicon

Abstract The numerical simulation of the etched surface evolution is applied to the selective (chemical and electrochemical) etching dopant delineation technique. The analysis of the etched sample section, obtained by means of transmission electron microscopy, is performed using a 3D simulation code based on the level set method for evolving surfaces. The correlation between the etched profile and the total dopant distribution is inferred, assuming that a functional relationship F=F{ρ(r)} occurs between the local dopant density ρ(r) and the local etch rate F(r). The reliability of the etch rate expression, derived by the theory of the charge transport in the solution–semiconductor interface, has been demonstrated by using the direct electrical simulation of the current flow during the etching process. The calibration of the technique consists in the fit of the parameters in the F=F{ρ(r)} relation depending only on the external conditions (bias potential, chemical moisture). The fitting has been performed, using reference profiles, at fixed optimal conditions. The measurement of the 2D dopant density map is based on the cross graphical comparisons, performed automatically by the computational tool, between TEM images of the eroded zone and the simulations of the etched surface, obtained using trial dopant distributions.

Visible Blind 4H-SiC P -N UV Photodiode Obtained by Al Implantation

This paper reports the electrooptical characteristics of ultraviolet light-sensitive 4H-SiC p+-n junction photodiodes obtained by aluminium (Al) ion implantation on low-doped n-type epilayers. A low dark current density (<; 1 nA/cm2 at -100 V) was measured on 1-mm2 area devices up to 90 °C. A peak responsivity of 0.11 A/W at 280 nm corresponding to a quantum efficiency of about 50% and a visible blindness> 103 were demonstrated. The absence of optically active defects and nitrogen donor-aluminum acceptor pair recombination centers was monitored by optical measurements in the visible range.

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.

Raman Stress Characterization of Hetero-Epitaxial 3C-SiC Free Standing Structures

Raman microscopy has been used to study the stress distribution on 3C-SiC/Si(100) micro-machined free standing structures. Linear scans along different structures reveal similar trends of the TO mode Raman Shift. We have found that, independently of the microstructure considered, the Raman frequency decreases close to the undercut. We compare our experimental measurements with FEM simulations finding that, close to the undercut, the stress tensor becomes non-diagonal, modifying the Raman shift to stress relation.

Fully Planar 4H-SiC Avalanche Photodiode With Low Breakdown Voltage

We report on the structure and performance of 4H-SiC p⁺-n APDs fabricated in a fully planar technology. A dark current density lower than 10 nA/cm² at 30-V reverse bias and a breakdown voltage of 88 V were observed. A gain as high as 10⁵ was measured at 94-V reverse bias, confirming the avalanche multiplication working condition. The maximum responsivity value was measured at 270 nm, increasing from 0.06 A/W (QE = 29%) at 0-V bias to 0.10 A/W (QE of about 45%) at 30-V reverse bias.

Residual stress measurement and simulation of 3C-SiC single and poly crystal cantilevers.

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. In this work a comparison between single crystal and poly crystal 3C-SiC micro-machined structures will be presented. The free-standing structures realized (cantilevers and membrane) are also a suitable method for residual field stress investigation in 3C-SiC films. Measurement of the Raman shift indicates that the mono and poly-crystal 3C-SiC structures release the stress in different ways. Finite element analysis was performed to determine the stress field inside the films and provided a good fit to the experimental data. A comprehensive experimental and theoretical study of 3C-SiC MEMS structures has been performed and is presented.

Mechanical Proprieties and Residual Stress Evaluation on Heteroepitaxial 3C-SiC/Si for MEMS Application

SiC is a candidate material for micro- and nano-electromechanical systems (MEMS and NEMS). 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 this work, in order to evaluate the amount of residual stress released from the epi-film, different micro-machined structures were developed. 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) was observed.

Topographic and structural evolution of etched Si samples

Wet chemical and electrochemical etching of doped Si samples is a promising technique with a variety of applications ranging from micro-mechanical manufacturing to profiles delineation in electronic devices. We have developed simulation tools specifically designed to support the optimization phase and the control of these processes. The morphologic evolution of sub-micrometric portions of the material is simulated at atomic level by means of a stochastic approach, in which the single atom detachment probability depends on its coordination status. Etching profile evolution is simulated using a level-set technique for propagating interfaces. The nano-structural features (e.g. surface status) of the etched material are accessible using an atomic level stochastic approach. The simulation results show a general agreement with the experimental finding on etched material characterization, capturing also many peculiar characteristics of the real profiles and nano-structures of the etched material.