Analysis of Al/Ti, Al/Ni multiple and triple layer contacts to p-type 4H-SiC

This paper presents an experimental investigation into different metallisation structures aimed at reducing the contact resistance and morphology of p-type contacts to 4H-SiC. The structures are based on a combination of Al/Ni and Al/Ti layers. The lowest specific contact resistivity obtained was based on a triple layer Al/Ti/Al contact, measured at 5.0 x 10(-6) Omega cm(2). Analogously, for the triple layer contacts comprised of Al/Ni/Al, the lowest specific contact resistivity was measured at 4.9 x 10(-4) Omega cm(2). In all cases it was found that the multiple layer structures remained rectifying even after annealing. A range of physical characterisation techniques were used to investigate these different structures. X-ray diffraction (XRD) scans point to enhanced formation of silicides for triple layer contacts based on Al/Ti (Ti3SiC2) and Al/Ni (NiSi,) when compared to multiple layer contacts. Scanning electron microscope (SEM) and wavelength dispersive analysis (WDA) measurements indicate that a multiple layer metallisation improves the morphology of the contact with respect to the Al spreading, which is known to be problematic during a high temperature anneal. (c) 2007 Elsevier Ltd. All rights reserved