2.5 SiC Contacts and Interconnect

All useful semiconductor electronics require conductive signal paths in and out of each device as well as conductive interconnects to carry signals between devices on the same chip and to external circuit elements that reside off-chip. While SiC itself is theoretically capable of operation under extreme conditions (Section 2.2), such functionality is useless without contacts and interconnects that are also capable of operation under the same conditions. Previously-developed conventional contact and interconnect technologies will likely not be sufficient for reliable operation under such extreme conditions. The durability and reliability of metal-semiconductor contacts and interconnects are one of the main factors limiting the operational high-temperature limits of SiC electronics. Similarly, SiC high-power device contacts and metalizations will have to withstand both high temperature and high current density stress.

The subject of metal-semiconductor contact formation is a very important technical field too broad to be discussed in detail here. More general background discussions on metal-semiconductor contact physics and formation are presented in [37,77]. These references primarily discuss ohmic contacts to conventional narrow-bandgap semiconductors such as silicon and GaAs. Specific overviews of SiC metal-semiconductor contact technology can be found in [78,79,80].

The same basic physics and current transport mechanisms that are present in narrow-bandgap contacts, such as surface states, Fermi-pinning, thermionic emission, and tunneling, also apply to SiC contacts. A natural consequence of the wider bandgap of SiC is the higher effective Schottky barrier height. Analogous with narrow-bandgap ohmic contact physics, the microstructural and chemical state of the SiC-metal interface is crucial to contact electrical properties. Therefore, pre-metal-deposition surface preparation, metal deposition process, choice of metal, and post-deposition annealing can all greatly impact the performance of metal-SiC contacts. Because the chemical nature of the starting SiC surface is strongly dependent on surface polarity, it is not uncommon to obtain significantly different results when the same contact process is applied to the silicon face surface versus the carbon face surface.
T. Ayalew: SiC Semiconductor Devices Technology, Modeling, and Simulation