Papers by Author: Giovanni Abagnale

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.

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.

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.