Ni, NiSi2 and Si Secondary Ohmic Contacts on SiC with High Thermal Stability

A method for formation of enhanced ohmic contacts on SiC for operation under adverse conditions has been studied. Ni, NiSi2 and Si ohmic contacts were prepared and tested at 300°C on air for hundreds of hours. NiSi2 and Si showed high thermal stability. Moreover, also the so called secondary contacts showed preserved good electrical and structural properties in the thermal test. The secondary ohmic contacts are formed from original ohmic contacts after they are etched off and replaced with new ones. Secondary ohmic contacts originate in a certain surface modification of the SiC substrate created during high temperature annealing of the original contact. All applied contact materials enable formation of quality secondary contacts which is especially noteworthy at NiSi2 and Si. The results bring new SiC device design perspectives with the application of secondary ohmic contacts. For example, the contact is designed so that the primary contact makes as good ohmic behavior as possible with the secondary contact providing further important contact properties as high corrosion resistance, wire-bonding simplicity etc.