Improved Thermal Stability Observed in Ni-Based Ohmic Contacts to n-Type SiC for High-Temperature Applications

The high-temperature stability of a Pt/TaSi₂/Ni/SiC ohmic contact metallization scheme was characterized using a combination of current–voltage measurements, Auger electron spectroscopy, and transmission electron microscopy imaging and associated analytical techniques. Increasing the thicknesses of the Pt and TaSi₂ layers promoted electrical stability of the contacts, which remained ohmic at 600°C in air for the extent of heat treatment; the specific contact resistance showed only a gradual increase from an initial value of 5.2 × 10⁻⁵ Ω cm². We observed a continuous silicon oxide layer in the thinner contact structures, which failed after 36 h of heating. Meanwhile, thicker contacts with enhanced stability contained a much lower oxygen concentration that was distributed across the contact layers, precluding the formation of an electrically insulating contact structure.