Papers by Author: Stefano Leone

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Authors: Andrea Severino, Corrado Bongiorno, Stefano Leone, Marco Mauceri, Giuseppe Pistone, Giuseppe Condorelli, Giuseppe Abbondanza, F. Portuese, Gaetano Foti, Francesco La Via
Abstract: 3C-SiC/Si heteroepitaxy is hampered by large mismatches in lattice parameters (19.7%) and thermal expansion coefficient (8%) leading to 3C-SiC films containing high defects density. To reduce the presence of defects, a multi-step growth process in a CVD reactor is used. The aim of the work is to study the effect of carbonization on differently oriented Si surfaces, experiencing a 200°C-wide temperature range in a CVD reactor, to improve the crystalline quality. TEM analysis are carried out to evaluate thickness, crystal orientations and defects of carbonized layers with respect to the time-dependence of the process and to the different orientations of the Si substrate. It will be shown that process-related defects are strictly correlated to the substrate orientation either for size, density, occupied area, shape or thickness. Uniform, flat and crystalline thin SiC films are obtained with a low defect density.
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Authors: Francesco La Via, Fabrizio Roccaforte, Salvatore di Franco, Alfonso Ruggiero, L. Neri, Ricardo Reitano, Lucia Calcagno, Gaetano Foti, Marco Mauceri, Stefano Leone, Giuseppe Pistone, Giuseppe Abbondanza, Gian Luca Valente, Danilo Crippa
Abstract: The effects of the Si/H2 ratio on the growth of the epitaxial layer and on the epitaxial defects was studied in detail. A large increase of the growth rate has been observed with the increase of the silicon flux in the CVD reactor. Close to a Si/H2 ratio of 0.05 % silicon nucleation in the gas phase occurs producing a great amount of silicon particles that precipitate on the wafers. The epitaxial layers grown with a Si/H2 ratio of 0.03% show a low defect density and a low leakage current of the Schottky diodes realized on these wafers. For these diodes the DLTS spectra show thepresence of several peaks at 0.14, 0.75, 1.36 and 1.43 eV. For epitaxial layers grown with higher values of the Si/H2 ratio and then with an higher growth rate, the leakage current of the Schottky diodes increases considerably.
429
Authors: Alessandro Veneroni, Fabrizio Omarini, Maurizio Masi, Stefano Leone, Marco Mauceri, Giuseppe Pistone, Giuseppe Abbondanza
Abstract: The present production processes for epitaxial SiC do not allow the matching of productivity with the material quality requested by the microelectronics market. Here, to respond to such a demand, a combined experimental and multi-scale – multi-hierarchy modeling approach was adopted. Models allow to verify a priori the role of process operative parameters on the performance ones for both the final product and of the process itself, like growth rate uniformity, film stoichiometry and dopants incorporation, homogeneous nucleation of particulate, microdefects and film morphology. Specifically, in this work the developing of a lumped deposition mechanism is addressed
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Authors: Francesco La Via, G. Galvagno, A. Firrincieli, Fabrizio Roccaforte, Salvatore di Franco, Alfonso Ruggiero, Milo Barbera, Ricardo Reitano, Paolo Musumeci, Lucia Calcagno, Gaetano Foti, Marco Mauceri, Stefano Leone, Giuseppe Pistone, F. Portuese, Giuseppe Abbondanza, Giovanni Abagnale, Gian Luca Valente, Danilo Crippa
Abstract: The growth rate of 4H-SiC epi layers has been increased by a factor 3 (up to 18μm/h) with respect to the standard process with the introduction of HCl in the deposition chamber. The epitaxial layers grown with the addition of HCl have been characterized by electrical, optical and structural characterization methods. An optimized process without the addition of HCl is reported for comparison. The Schottky diodes, manufactured on the epitaxial layer grown with the addition of HCl at 1600 °C, have electrical characteristics comparable with the standard epitaxial process with the advantage of an epitaxial growth rate three times higher.
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Authors: Maurizio Masi, Alessandro Veneroni, A. Fiorucci, Francesco La Via, Gaetano Foti, Marco Mauceri, Stefano Leone, Giuseppe Pistone, Giuseppe Condorelli, Giuseppe Abbondanza, Gian Luca Valente, Danilo Crippa
Abstract: A simplified deposition model, involving both the description of the deposition and of the film morphology was adopted to quantitatively understand the experimental trends encountered in the epitaxial silicon carbide deposition in an industrial hot wall reactor. The attention was focused on the system involving chlorinated species because its really superior performances with respect the traditional silane/hydrocarbons process. The evolution of the crystalline structure (i.e., from poly to single) and of the surface roughness can be understood by simply comparing two characteristic times, like those inherent the surface diffusion and the matter supply to the surface.
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Authors: Danilo Crippa, Gian Luca Valente, Alfonso Ruggiero, L. Neri, Ricardo Reitano, Lucia Calcagno, Gaetano Foti, Marco Mauceri, Stefano Leone, Giuseppe Pistone, Giuseppe Abbondanza, G. Abbagnale, Alessandro Veneroni, Fabrizio Omarini, L. Zamolo, Maurizio Masi, Fabrizio Roccaforte, G. Giannazzo, Salvatore di Franco, Francesco La Via
Abstract: The results of a new epitaxial process using an industrial 6x2” wafer reactor with the introduction of HCl during the growth have been reported. A complete reduction of silicon nucleation in the gas phase has been observed even for high silicon dilution parameters (Si/H2>0.05) and an increase of the growth rate until about 20 µm/h has been measured. No difference has been observed in terms of defects, doping uniformity (average maximum variation 8%) and thickness uniformity (average maximum variation 1.2 %) with respect to the standard process without HCl.
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Authors: Francesco La Via, G. Galvagno, A. Firrincieli, Fabrizio Roccaforte, Salvatore di Franco, Alfonso Ruggiero, Lucia Calcagno, Gaetano Foti, Marco Mauceri, Stefano Leone, Giuseppe Pistone, Giuseppe Abbondanza, F. Portuese, Giovanni Abagnale, Gian Luca Valente, Danilo Crippa
Abstract: The influence of the epitaxial layer growth parameters on the electrical characteristics of Schottky diodes has been studied in detail. Several diodes were manufactured on different epitaxial layers grown with different Si/H2 ratio and hence with different growth rates. From the electrical characterization a maximum silicon dilution ratio can be fixed at 0.04 %. This limit fixes also a maximum growth rate that can be obtained in the epitaxial growth, with this process, at about 8 μm/h. Several epitaxial layers have been grown, using this dilution ratio, with different temperatures (1550÷1650 °C). At 1600 °C the best compromise between the direct and the reverse characteristics has been found. With this process the yield decreases from 90% for a Schottky diode area of 0.25 mm2 to 61% for the 2 mm2 diodes. Optimizing the deposition process to reduce the defects introduced by the epitaxial process, yield of the order of 80% can be reached on 1 mm2 diodes.
199
Authors: Lucia Calcagno, Gaetano Izzo, Grazia Litrico, G. Galvagno, A. Firrincieli, Salvatore di Franco, Marco Mauceri, Stefano Leone, Giuseppe Pistone, Giuseppe Condorelli, F. Portuese, Giuseppe Abbondanza, Gaetano Foti, Francesco La Via
Abstract: High growth rate of 4H-SiC epitaxial layers can be reached with the introduction of HCl in the deposition chamber. The effect of the Cl/Si ratio on this epitaxial growth process has been studied by optical and electrical measurements. Optical microscopy shows an improvement of the surface morphology and luminescence measurements reveal a decrease of epitaxial layer defects with increasing the Cl/Si ratio in the range 0.05–2.0. The leakage current measured on the diodes realized on these wafers is reduced of an order of magnitude and DLTS measurements show a decrease of the EH6,7 level concentration in the same range of Cl/Si ratio. The value Cl/Si=2.0 allows to grow epitaxial layers with the lowest defect concentration.
137
Authors: Stefano Leone, Marco Mauceri, Giuseppe Pistone, Giuseppe Abbondanza, F. Portuese, Giovanni Abagnale, Gian Luca Valente, Danilo Crippa, Milo Barbera, Ricardo Reitano, Gaetano Foti, Francesco La Via
Abstract: 4H-SiC epitaxial layers have been grown using trichlorosilane (TCS) as the silicon precursor source together with ethylene as the carbon precursor source. A higher C/Si ratio is necessary compared with the silane/ethylene system. This ratio has to be reduced especially at higher Si/H2 ratio because the step-bunching effect occurs. From the comparison with the process that uses silane as the silicon precursor, a 15% higher growth rate has been found using TCS (trichlorosilane) at the same Si/H2 ratio. Furthermore, in the TCS process, the presence of chlorine, that reduces the possibility of silicon droplet formation, allows to use a high Si/H2 ratio and then to reach high growth rates (16 *m/h). The obtained results on the growth rates, the surface roughness and the crystal quality are very promising.
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Authors: Francesco La Via, Stefano Leone, Marco Mauceri, Giuseppe Pistone, Giuseppe Condorelli, Giuseppe Abbondanza, F. Portuese, G. Galvagno, Salvatore di Franco, Lucia Calcagno, Gaetano Foti, Gian Luca Valente, Danilo Crippa
Abstract: The growth rate of 4H-SiC epi layers has been increased by a factor 19 (up to 112 μm/h) with respect to the standard process with the introduction of HCl in the deposition chamber. The epitaxial layers grown with the addition of HCl have been characterized by electrical, optical and structural characterization methods. An optimized process without the addition of HCl is reported for comparison. The Schottky diodes, manufactured on the epitaxial layer grown with the addition of HCl at 1600 °C, have electrical characteristics comparable with the standard epitaxial process with the advantage of an epitaxial growth rate three times higher.
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