Physical Characterization of Residual Implant Damage in 4H-SiC Double Implanted Bipolar Technology
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Physical Characterization of Residual Implant Damage in 4H-SiC Double Implanted Bipolar Technology N. G. Wright1, C. M. Johnson1, A. G. O’Neill1, A. Horsfall1, S. Ortolland1, K. Adachi1, G. J. Phelps1, A. P. Knights2, P.G.Coleman3 and C. P. Burrows3 1
Department of Electrical and Electronic Engineering, University of Newcastle, Newcastle upon Tyne, UK, NE1 7RU U.K. Tel. +44 191 222 7345, Fax. +44 191 222 8180 2 School of Electronic Engineering, Information Technology and Mathematics, University of Surrey, Guildford GU2 5XH, United Kingdom. 3 Department of Physics, University of Bath, Claverton Down, Bath, BA2 7AY, United Kingdom. ABSTRACT The effects of post-implant anneal conditions on the level of residual damage resulting from nitrogen and boron implants after different anneal processes are investigated using the Positron Annihilation Spectroscopy (PAS) technique. It is shown that after implantation there is a substantial defect concentration significantly below the range of the implants. However such damage is almost completely recovered after anneal in contrast with the damage close to the implant range point. Such residual damage has a strong effect on the electrical characteristics of double implanted bipolar transistors - principally though reduction in carrier mobility and lifetime. It is shown that the precise implant and anneal conditions play a strong role in the level of such damage and the subsequent electrical performance of bipolar devices. INTRODUCTION SiC is an attractive candidate for manufacturing power switching devices operating at high temperature, high voltage and high current density because of its wide band-gap, high thermal conductivity and high breakdown electric field strength. Although much progress has been made in many areas of device technology, the development of a controlled, normally-off, switching device has been hampered by poor MOSFET performance. This is particularly the case with the 4H polytype, which is preferred for vertical switching devices on account of its higher on-axis mobility. Alternative majority carrier switching device technologies, such as the ACCUFET [1] and SIT, have been proposed but they demand non-trivial processing with very high tolerances to achieve acceptable performance. Bipolar switching devices, such as thyristors, and combinations of devices such as a GTO thyristor-JFET, on the other hand have been demonstrated effectively at high current levels [2]. The humble power bipolar junction transistor (BJT) has, however, received little attention, in spite of the fact it was the backbone of Si technology for many years. Simple bipolar devices have been demonstrated in SiC using multilayer epitaxial wafers [3]. Such devices show reasonable gain (typically ~10) illustrating the potential of bipolar technology in SiC. However the use of multilayer epitaxial wafers raises the cost of the wafers to uncommercial levels. An implanted technology (needing only simple single layer epitaxial wafers) could reduce the wafer cost considerably - offering a relatively e
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