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-Si C, together with their thermal stability, have been studied in the annealin g temperature range 600-700 degrees C. The ohmic behaviour of as-deposited and annealed contacts has been checked from I-V characteristics and the con tact resistivity has been determined by the linear TLM method in order to d etermine the electrical properties and the thermal stability. An ohmic beha viour was established after annealing at 600 degrees C, while the lowest co ntact resistivity 5.5 x 10(-5) Omega.cm(2) was obtained at 700 degrees C. T he contact structure, before and after annealing, was investigated using X- ray photoelectron spectroscopy depth analysis. As-deposited Pd films form a n abrupt and chemically inert Pd/SiC interface. Annealing causes the format ion of palladium silicide. After formation at 600 degrees C the contact str ucture consists of unreacted Pd and Pd,Si. During annealing at 700 degrees C, Pd and SiC react completely and a mixture of Pd,Si, Pd,Si and C in a gra phite state is found in the contact layer. The examination of the thermal s tability shows that after a 100 h heating at 500 degrees C, only the contac ts annealed at 700 degrees C did not suffer from a change in resistivity. T his can be explained by a more complete reaction between the Pd contact lay er and the SIC substrate at this higher annealing temperature. (C) 1999 Els evier Science S.A. All rights reserved.