Papers by Author: Francesco La Via

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Authors: Philipp Schuh, Grazia Litrico, Francesco La Via, Marco Mauceri, Peter J. Wellmann
Abstract: We report on the growth of bulk 3C-SiC by sublimation on epitaxial seeding layers (3C-SiC/Si) from chemical vapor deposition. We have reached a materials thickness of 0.85 mm and an area of 10.5 cm2 which can be enlarged further. The high crystalline quality is characterized by the absence of secondary polytype inclusions and the absence double position grain boundaries.
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Authors: Thomas Kreiliger, Marco Mauceri, Marco Puglisi, Fulvio Mancarella, Francesco La Via, Danilo Crippa, Wlodek Kaplan, Adolf Schöner, Anna Marzegalli, Leo Miglio, Hans von Känel
Abstract: The growth morphology of epitaxial 3C-SiC crystals grown on hexagonal pillars deeply etched into Si (111) substrates is presented. Different growth velocities of side facets let the top crystal facet evolve from hexagonal towards triangular shape during growth. The lateral size and separation between Si pillars determine the onset of fusion between neighboring crystals during growth at a height tailoring of which is crucial to reduce the stacking fault (SF) density of the coalesced surface. Intermediate partial fusion of neighboring crystals is shown as well as a surface of fully coalesced crystals.
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Authors: Andrea Canino, Andrea Severino, Nicolò Piluso, Francesco La Via, Stefania Privitera, Alessandra Alberti
Abstract: 3C-SiC shows encouraging physical properties for the development of low cost high power compatible silicon based technology. The fundamental capability of grown 3C-SiC on silicon substrates leads to the possibility of a full integration of Si based process technologies. This is the driving force for the efforts for development a high quality heteroepitaxial film. The fundamental issue is the reduction of defects and stress due to the lattice mismatch between the 3C-SiC epilayer and the Silicon substrate. In this paper we show a way to reduce macroscopic structural features and to enhance the material quality and the surface quality by simply using a process based on a multilayer (ML) buffer structure with n++ and n doping alternation. This process leads to an evident improvement of both surface roughness, morphology and crystal quality.
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Authors: Ruggero Anzalone, Andrea Severino, Christopher Locke, Davide Rodilosso, Cristina Tringali, Stephen E. Saddow, Francesco La Via, Giuseppe D'Arrigo
Abstract: Silicon Carbide (SiC) is a very promising material for the fabrication of a new category of sensors and devices, to be used in very hostile environments (high temperature, corrosive ambient, presence of radiation, etc.). The fabrication of SiC MEMS-based sensors requires new processes able to realize microstructures on bulk material or on the SiC surface. The hetero-epitaxial growth of 3CSiC on silicon substrates allows one to overcome the traditional limitations of SiC microfabrication. This approach puts together the standard silicon bulk microfabrication methodologies with the robust mechanical properties of 3C-SiC. Using this approach we were able to fabricate SiC cantilevers for a new class of pressure sensor. The geometries studied were selected in order to study the internal residual stress of the SiC film. X-Ray Diffraction polar figure and Bragg- Brentano scan analysis were used to check to crystal structure and the orientations of the film. SEM analysis was performed to analyze the morphology of the released MEMS structures.
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Authors: Giuseppe D'Arrigo, Andrea Severino, G. Milazzo, Corrado Bongiorno, Nicolò Piluso, Giuseppe Abbondanza, Marco Mauceri, Giuseppe Condorelli, Francesco La Via
Abstract: 3C-SiC devices are hampered by the defect density in heteroepitaxial films. Acting on the substrate, it is possible to achieve a better compliance between Si and 3C-SiC. We present here an approach to favorite defect geometrical reduction in both [ ] and [ ] directions by creating Inverted Silicon Pyramids (ISP). A study of 3C-SiC growth on ISP is reported showing benefits in the film quality and a reduction in the linear density of stacking faults. Growth on ISP leads also to a decrease in the 3C-SiC residual stress as well as in the bow of the Si/SiC system.
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Authors: Ruggero Anzalone, Andrea Severino, Giuseppe D'Arrigo, Corrado Bongiorno, Patrick Fiorenza, Gaetano Foti, Giuseppe Condorelli, Marco Mauceri, Giuseppe Abbondanza, Francesco La Via
Abstract: The aim of this work is to improve the heteroepitaxial growth process of 3C-SiC on Si substrates using Trichlorosilane (SiHCl3) as the silicon growth precursor. With this precursor it has been shown that it is possible to simultaneously increase the growth rate of the process and avoid the nucleation of silicon droplets in the gas phase. Growth experiments were conducted on three (3) Si substrate orientations in order to assess the impact of the Si substrate on the resulting 3C-SiC film. X-ray Diffraction (XRD), Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) analysis show the important role of the substrate orientation for the growth process. The different orientation of the substrate modifies the morphology of the 3C-SiC crystalline structure, mostly by changing the density of micro-twins and stacking faults inside the film.
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Authors: Stefania Privitera, Vincenza Brancato, Donatella Spadaro, Ruggero Anzalone, Alessandra Alberti, Francesco La Via
Abstract: The electrical and optical properties of n-doped polycrystalline 3C-SiC films grown on 6 inches Si wafers have been investigated as a function of precursor gases, deposition temperature and C/Si ratio. The Si/SiC interface has been optimized, eliminating the voids formation through a double temperature step process and by introducing a thin not intentionally doped layer. Films with high surface roughness, favourable for light trapping in photovoltaic applications, and with resistivity around 20 mOhm cm have been obtained for C/Si ratio close to 1. Simple solar cells have been also manufactured and proved the functionality of poly 3C-SiC/Si heterojunction solar cell. Increased quantum efficiency in the range 300-500 nm has been observed, compared to amorphous Si, making poly 3C-SiC heterojunction solar cells interesting for high temperature applications or water splitting.
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Authors: Francesco La Via, Fabrizio Roccaforte, Antonino La Magna, Roberta Nipoti, Fulvio Mancarella, Peter J. Wellmann, Danilo Crippa, Marco Mauceri, Peter Ward, Leo Miglio, Marcin Zielinski, Adolf Schöner, Ahmed Nejim, Laura Vivani, Rositza Yakimova, Mikael Syväjärvi, Gregory Grosset, Frank Torregrosa, Michael Jennings, Philip A. Mawby, Ruggero Anzalone, Salvatore Coffa, Hiroyuki Nagasawa
Abstract: The cubic polytype of SiC (3C-SiC) is the only one that can be grown on silicon substrate with the thickness required for targeted applications. Possibility to grow such layers has remained for a long period a real advantage in terms of scalability. Even the relatively narrow band-gap of 3C-SiC (2.3eV), which is often regarded as detrimental in comparison with other polytypes, can in fact be an advantage. However, the crystalline quality of 3C-SiC on silicon has to be improved in order to benefit from the intrinsic 3C-SiC properties. In this project new approaches for the reduction of defects will be used and new compliance substrates that can help to reduce the stress and the defect density at the same time will be explored. Numerical simulations will be applied to optimize growth conditions and reduce stress in the material. The structure of the final devices will be simulated using the appropriated numerical tools where new numerical model will be introduced to take into account the properties of the new material. Thanks to these simulations tools and the new material with low defect density, several devices that can work at high power and with low power consumption will be realized within the project.
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Authors: Nicolo’ Piluso, Massimo Camarda, Ruggero Anzalone, Francesco La Via
Abstract: Recently, a new Micro-Raman technique has been used to detect extended defects in 4H-SiC homoepitaxy. The method is based on the local increase of free carriers in undoped epitaxies (n < 1016 at/cm-3) produced by a high power laser. The Longitudinal optical Raman mode (LO) is coupled with the electronic plasma generated by the laser pumping; such a Raman signal is sensitive to crystallographic defects that lead to trapping (or dispersion) of the free carriers which results in a loss of coupling. The monitoring of the LOPC allows determining the spatial morphology of extended defects. The results show that the detection of defects via the induced-LOPC (i-LOPC) is totally independent from the stacking fault photoluminescence signals that cover a large energy range up to 0,7eV thus allowing for a single-scan simultaneous determination of any kind of stacking fault. Also, the i-LOPC method shows the connection between the carrier concentration and the carrier lifetime for undoped film, obtaining meaningful information related to electrical properties of the film, and demonstrating that this technique is a fast, reliable and powerful method to characterize most of crystallographic defects (extended and point-like defects) in the semiconductor field.
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Authors: Nicolò Piluso, Maria Ausilia di Stefano, Simona Lorenti, Francesco La Via
Abstract: 4H-SiC defects evolution after thermal processes has been evaluated. Different annealing temperatures have been used to decrease the defect density of epitaxial layer (as stacking faults) and recover the damage occurred after ion implantation. The propagation of defects has been detected by Photoluminescence tool and monitored during the thermal processes. The results show that implants do not affect the surface roughness and how a preliminary annealing process, before ion implantation step, can be useful in order to reduce the SFs density. It shown the effect of tuned thermal process. A kind of defect, generated by implant and subsequent annealing, can be removed by an appropriate thermal budget, while others can increase. A fine tuning of thermal process parameters, temperature and timing, is useful to recover the crystallographic quality of the epilayer and increase the yield of the power device.
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