Carbon-Cap for Ohmic Contacts on Ion-Implanted 4H-SiC

A pyrolyzed photoresist film is commonly used as a protective cap of the surface of ion-implanted 4H-SiC wafers during the postimplantation annealing process with the aim to prevent Si sublimation and step bunching formation. Such a film that is called carbon-cap (C-cap) is always removed after postimplantation annealing and before any other processing step of the SiC wafer. Here, we show that this C-cap is a continuous, hard, black, mirrorlike, and planar thin film that can be patterned by a reactive ion etching O(2)-based plasma for the fabrication of ohmic contact pads on both Al(+)- and P(+)-implanted 4H-SiC. This C-cap material has an electrical resistivity of 1.5 x 10(-3) Omega cm and a good resistance against scratch. Al (1% Si) wires can be ultrasonically bonded on the C-cap pads. Such a bonding and the C-cap adhesion to the implanted 4H-SiC surface are stable for electrical characterizations in vacuum between room temperature and 450 degrees C. The measured specific contact resistance of the C-cap on a 1 x 10(20) cm(-3) P(+)-implanted 4H-SiC is 9 x 10(-5) Omega cm(2) at room temperature. Micro-Raman characterizations show that this C-cap is formed of a nanocrystalline graphitic phase. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3491337] All rights reserved.