Study of the electrical, thermal and chemical properties of Pd ohmic contacts to p-type 4H-SiC: Dependence on annealing conditions

The electrical and chemical properties of Pd ohmic contacts to p-type 4H-SiC, together with their thermal stability, have been studied in the annealing temperature range 600-700 °C. The ohmic behaviour of as-deposited and annealed contacts has been checked from I-V characteristics and the contact resistivity has been determined by the linear TLM method in order to determine the electrical properties and the thermal stability. An ohmic behaviour was established after annealing at 600 °C, while the lowest contact resistivity 5.5×10-5 Ω.cm2 was obtained at 700 °C. The contact structure, before and after annealing, was investigated using X-ray photoelectron spectroscopy depth analysis. As-deposited Pd films form an abrupt and chemically inert Pd/SiC interface. Annealing causes the formation of palladium silicide. After formation at 600 °C the contact structure consists of unreacted Pd and Pd3Si. During annealing at 700 °C, Pd and SiC react completely and a mixture of Pd3Si, Pd2Si and C in a graphite state is found in the contact layer. The examination of the thermal stability shows that after a 100 h heating at 500 °C, only the contacts annealed at 700 °C did not suffer from a change in resistivity. This can be explained by a more complete reaction between the Pd contact layer and the SiC substrate at this higher annealing temperature.