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Techniques to fabricate thick multi-layer 4H-SiC epitaxial wafers were studied for very high-voltage p- and n-channel insulated gate bipolar transistors (IGBTs). Multi-layer epitaxial growth, including a thick p- drift layer (~180?μm), was performed on a 4H-SiC n+ substrate to form a p-IGBT structure. For an n-IGBT structure, an inverted growth process was employed, in which a thick n- drift layer (~180?μm) and a thick p++ injector layer (>55?μm) were epitaxially grown. The epitaxial growth conditions were modified to attain a low defect density, a low doping concentration, and a long carrier lifetime in the drift layers. Reduction of the forward voltage drop was attempted by using carrier lifetime enhancement processes, specifically, carbon ion implantation/annealing and thermal oxidation/annealing or hydrogen annealing. Simple PiN diodes were fabricated to demonstrate the effective conductivity modulation in the thick drift layers. The forward voltage drops of the PiN diodes with the p- and n-IGBT structures promise to obtain the extremely low-loss and very high-voltage IGBTs. The change in wafer shape during the processing of the very thick multi-layer 4H-SiC is also discussed. [ABSTRACT FROM AUTHOR]

High-energy (MeV) implantation of Al[sup +] or B[sup +] into 4H-SiC epilayers has been investigated. A 3 µm deep pn junction was formed by multiple-step Al[sup +] or B[sup +] implantation with implantation energies up to 6.2 or 3.4 MeV, respectively. Rutherford backscattering channeling and cross-sectional transmission electron microscopy analyses have revealed residual damages in the implanted layers even after high-temperature annealing at 1600-1800 °C. Nevertheless, high electrical activation ratios over 90% have been achieved for both Al[sup +] - and B[sup +]-implanted layers by annealing at 1800 °C. Mesa pin diodes with a 15-µm-thick i layer formed by MeV implantation have exhibited high breakdown voltages of 2860-3080 V. The reverse characteristics of diodes have been substantially improved by increasing annealing temperature up to 1800 °C. The diode performance is discussed with the results of deep level analyses near the junctions. [ABSTRACT FROM AUTHOR]

3-kV, 600-A, 4H-SiC flat package type pn diodes have been developed and their reverse recovery characteristics have been investigated. In spite of being pn junction diodes, the developed diodes have a short reverse recovery time of 0.153µs at room temperature. These diodes have one-tenth lower recovery loss and one-third lower recovery time than those of a commercialized 2.5-kV Si diode in spite of a high blocking voltage. When this diode is used in a PWM inverter, the carrier frequency at which the on-state loss is equal to the switching loss is 1.45 times the Si diode's frequency at 398 K. By using the developed diode, high-voltage high-frequency inverter operation can be realized. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(1): 10–17, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20557 [ABSTRACT FROM AUTHOR]