Interfacial reactions and ohmic contact formation in the Ni/Al–6H SiC system

Abstract

The interface chemistry and the electrical properties of annealed Ni/Al–6H SiC Ohmic contacts are studied by using x-ray photoemission spectroscopy, current–voltage characteristics, and contact resistance measurements employing a four-point method. All depositions and analysis were performed on the Si face of nitrogen doped, n-type (1×1018 cm−3) wafers of 6H SiC (0001). The chemical reactions at the interface are revealed. Al at the SiC interface acts by reducing the SiOx and forming Al2O3. At elevated temperatures, SiC in the presence of Al dissociates with formation of Al4C3 which is a stable compound. At about 1000 °C the Si atoms at the interface bond to Al and Ni either in ternary compounds with different stoichiometry or in NiSi. In the subsurface region carbon is present in the graphite state of ∼5 at. %. The Ohmic behavior of the contact is related to the formation of the NiSi while the weak contact resistivity degradation is due to the low graphite precipitation. The improved temperature stability may also be due to the presence of Al2O3 on the top of the contact structure.