Effects of Surface and Interlayer Processing Conditions on Selected Ohmic Contact Metallizations for p-type Silicon Carb
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Effects of Surface and Interlayer Processing Conditions on Selected Ohmic Contact Metallizations for p-type Silicon Carbide L.M. Porter, T. Jang, T. Worren, K.C. Chang, N.A. Papanicolaou1, and J.W. Erickson2 Dept. of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA 15213. 1 Naval Research Laboratory, 7565 Overlook Avenue, Washington, D.C. 20375. 2 Accurel Systems, 350 Potrero Avenue, Sunnyvale, CA 94086. ABSTRACT A comparative study of Pt and Pt/Si contacts to p-type 6H-SiC in terms of various processing conditions and interlayer specifications was performed. Deposition temperature, the thickness of the Si layer, and B-dopant incorporation in the Si were found to significantly affect the specific contact resistivity (SCR) values. In addition, pre-etching of the SiC surface in SF6 + Ar was found to consistently reduce the SCR’s. The lowest average SCR values were 3 x 10-5 Ω cm2 for Pt/Si/SiC contacts deposited on pre-etched SiC surfaces (7.0 x 1018 cm-3 doping concentration) and annealed at 1100 °C for 5 min. Aluminum-titanium contacts also showed dependence on the thicknesses of the Al and Ti layers and on the locations of the layers. Differences in both the SCRs and surface morphology are presented.
INTRODUCTION The fabrication of reproducible ohmic contacts with low contact resistivities to p-type SiC is a critical problem for many devices. The traditional approach consists of annealing an Albased contact (e.g., TiAl) on highly-doped SiC at temperatures between 900 and 1150°C [1-7]. Another approach employs one or more Si layers along with a transition metal, such as Co [8], Pt [9], or Ta [10], to react with the Si and C in the substrate in equal ratios. We have investigated both of these approaches. In the first approach, Pt contacts with and without thin (100 or 500 Å) Si interlayers were deposited and processed under a selected range of conditions and characterized in terms of microstructure, morphology, phase formation and electrical properties. In the second approach, Al/Ti and Ti/Al contacts were compared in terms of morphology and electrical properties. In this study we attempt to answer some important questions regarding factors affecting the characteristics of ohmic contacts. Firstly, does the condition of the SiC surface affect the properties of ohmic contacts, particularly for contacts that have reacted with the SiC substrate during annealing? To answer this question pre-etched and unetched substrates were characterized and compared in terms of the resulting specific contact resistivities. A second set of questions involves the use of a Si interlayer: (1) Does the use of a Si interlayer benefit contact properties for non-carbide formers (Pt in the present case)? (2) What affects do deposition temperature and interlayer thickness affect the properties of the ohmic contacts? Finally, does the incorporation of a p-type dopant in the contact layer reduce the contact resistivity? To answer these questions we fabricated and characterized numerous samples with identical material and
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