Ohmic Contact Resistance in SiC Diodes with Ti and NiSi P⁺ Contacts

Abstract

Ohmic contacts play a major role in the signal transfer between the semiconductor device and the external circuitry. One of the main technological issues to develop high-performance SiC-based devices is the control of metal/SiC contact properties to fabricate low resistance and high stability SiC Ohmic contacts to p-type SiC. This is mostly due to intrinsic SiC characteristics like large work function, low dopant activation for p-type materials and low hole mobility. These limits are even more emphasized in SiC JBS or MPS diodes, where Schottky and Ohmic contacts on the P doped regions embedded in the active area to improve surge ruggedness are usually formed by using the same metallization process. This naturally results either in a high Schottky barrier height in the Schottky contact with consequent increase of the conduction loss at low currents or in a poorly conductive Ohmic contact, leading to reduced IFSM capability. Therefore, the optimization and control of the process parameters like for example the P+ doping concentration peak underneath the metallization layer and the annealing process temperatures is crucial to obtain a good Ohmic contact and enhance the device´s robustness against surge current.