Interface chemistry and electric characterisation of nickel metallisation on 6H-SiC

The interface chemistry and the electrical properties of annealed Ni/6H-SiC ohmic contacts have been compared using X-ray photoemission spectroscopy, current-voltage and resistance measurements by a four-point probe method. Substrates of n-type SIC wafers (CREE Res) with N-d = 1 x 10(18) cm(-3) have been used. The XP spectra indicate that carbon is in the graphite state and silicon is bonded predominantly to Ni resulting in NiSi formation which is preceded by decomposition of SiC to silicon and carbon after annealing. One hour annealing leads to a degradation of the contact resistance by a factor of 1.5 as compared with the contacts annealed for 5 min. This seems to be due to an increased graphite precipitation in the subsurface region of the contact layer. Current-voltage characteristics are linear for the contacts annealed above 900 degrees C, while the contact resistance reaches a minimum around 1000 degrees C.