Schottky-Ohmic Transition in Nickel Sllicide/SiC System: Is it Really a Solved Problem?

The transition from Schottky to ohmic contact in nickel silicide/SiC system during annealing from 600 to 950 ¬?C was investigated by measuring the electrical proprieties of the contact and by analyzing the microstructure of silicide/SiC interface. The graphite clusters formed by carbon atoms during silicidation are uniformly distributed into the suicide layer after annealing at 600 ¬?C and they agglomerate into a thin layer far from the silicide/SiC interface after annealing at 950 ¬?C. At this temperature an increase of about 0.25 eV of the Schottky barrier height was measured, while Deep Level Transient Spectroscopy evidences an evolution of interfacial defects. The peak related to C-vacancy sited at 0.5 eV from the conduction band has not been observed. This result invalidates the reported literature hypothesis that the formation of ohmic contact after annealing at 950 ¬?C was related to the formation of C vacancies.